4.2.2. Glassy and highly elastic states of polymers
The glassy state is one of the forms of the solid state of amorphous polymers, which is characterized by small elastic deformations with high values of the elastic modulus E≈2.2·10 3 -5·10 3 MPa. These deformations are associated with a slight change in the distances between atoms and bond angles of the main chain.
The highly elastic state is characterized by large reversible deformations (up to 600-800%) and low values of the elastic modulus of the polymer (0.2-2 MPa). Stretching of a polymer during highly elastic deformation is accompanied by the release of energy in the form of heat, while contraction is accompanied by compression. The elastic modulus of a deformable polymer increases with increasing temperature, while the elastic modulus in the glassy state decreases. Highly elastic deformation occurs over time, since it is caused by the movement of segments and, therefore, is a relaxation molecular-kinetic process.
The nature of the elastic force that arises during the deformation of polymers in glassy and highly elastic states is discussed in Section. 2.2.1. In the first case, it is associated with a change in internal energy, in the second - entropy. The molecular mechanism of entropic elasticity associated with the restoration of the most probable sizes of macromolecular coils is discussed in detail in Section. 2.2.
The highly elastic state is most clearly manifested in “cross-linked” rubbers, i.e. rubber In linear polymers, irreversible deformation is superimposed on reversible deformation, i.e. flow. A highly elastic state can be observed in polymers in various temperature ranges - from -100 to 200 °C. The technical use of highly elastic materials is related to their shock-absorbing properties and low elastic modulus.
When exposed to an external periodic force of high frequency, polymers that are in a highly elastic state can transform into an elastic-hard deformation state that is not associated with the “freezing” of the mobility of segments (Table 4.1). This kind of glass transition in force fields at temperatures above the structural glass transition temperature is called mechanical glass transition. The nature of this phenomenon was discussed earlier in section. 2.3.4.
The glass transition of polymers is a relaxation process. It is associated with relaxation, i.e. by moving segments of macromolecules containing 5-20 atoms of the main chain (depending on its flexibility). This process has a pronounced cooperative character.
During glass transition, there is an abrupt change in the heat capacity, the temperature coefficient of volumetric expansion and the coefficient of thermal compressibility, while only a kink is observed in the curves of the specific volume, enthalpy and entropy. At Т Т с the second derivatives of the Gibbs function
change abruptly, which is a sign of a second-order phase transition. Despite this, the glass transition is not a phase transition,
Table 4.1 Glass transition temperature, steric factor (flexibility) σ and Kuhn segment of various classes of polymers
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Kuhn segment, nm | |||
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Flexible chain polymers: | |||
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Polychloroprene | |||
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Polydpmethylsploxane | |||
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Polyesters | |||
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Cis-polyisonren (natural rubber) | |||
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Polybutadiene | |||
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Aliphatic polyamides | |||
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Polymethyl methacrylate | |||
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Paul and methyl acrylic | |||
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Polybutyl acrylate | |||
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Polyvinyl acetate | |||
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Polystyrene | |||
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Polyethylene | |||
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Polypropylene | |||
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Polyacrylonitrile | |||
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Polyvinyl chloride | |||
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Rigid chain polymers: | |||
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Polyarylate of terephthalic acid and phenolphthalein | |||
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Polyamide of terephthalic acid and aniphthalein | |||
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Polyimide dianhydride 3,3",4,4"-tetracarboxyphenyl oxide and aniline fluorene |
since it leads to a nonequilibrium metastable state of the system. This is confirmed by a number of kinetic characteristics:
a monotonous and unlimited decrease in the glass transition temperature with a decrease in the cooling rate and vice versa;
in the opposite direction of the change in heat capacity during glass transition and a second-order phase transition (during glass transition, the heat capacity decreases).
Typically, the glass transition temperature changes by approximately 3 °C when the cooling rate changes by a factor of 10, and only in some cases can it change by 10-15 °C. Bartenev proposed a formula for calculating the glass transition temperature at different rates of temperature change:
where c is the material constant; co - heating rate in °C/s.
Theories of glass transition. The mobility of any kinetic unit is determined by the relaxation time t, which, in accordance with formula (2.93), depends exponentially on the activation energy. It has been shown that with decreasing temperature, the activation energy for the movement of segments increases rapidly, which is associated with a decrease in the free volume of the polymer and an increase in the cooperative relaxation system. During glass transition, the free volume reaches a minimum value and the movement of the segments stops. The free volume of the polymer Vst is determined by the expression:
where V is the total volume, i.e. real volume of the polymer body; V 3 - occupied volume equal to the volume of macromolecules. The free volume is distributed throughout the polymer in the form of micropores, the origin of which is associated with the heterogeneity of the structure.
The change in body volume during heating is characterized by the coefficient
extensions. At T > T c, the change in the volume of the polymer is mainly determined by the change in the free volume; the expansion coefficient for this region is denoted as 1. At T< Т с свободный объем изменяется в существенно меньшей степени (рис. 4.6), изменение объема полимера в этой области происходит по закону, характерному для твердых кристаллических тел с коэффициентом объемного расширения 2 . Величина ∆= 1 - 2 имеет физический смысл коэффициента температурного расширения свободного объема. Она связана с температурой стеклования полимеров эмпирическим уравнением Бойера-Симхи:
In the theory of Gibbs and Di Marzio, the glass transition process of a polymer is considered from the perspective of the thermodynamic state of the system, determined by the number of possible conformations of the macromolecule. It is assumed that possible ways of orienting chain units can be reduced to two extreme cases corresponding to high ε 1 and low ε 2 energy values of the conformers. In relation to the rotational isomer model of the chain, the first can be attributed to ±gauche isomers, the second to trans isomers. At T > T c the polymer is characterized by a large conformational set and significant molar conformational entropy S K . As the temperature decreases, the intensity of the thermal movement of the segments decreases, i.e. flexibility of the chain, therefore, conformations corresponding to large (ε 1) values of internal energy are frozen out, and S K decreases. At a certain temperature T = T 2, the transition of trans conformations to “+” or “-” gauche becomes impossible, and the thermal movement of the segments stops. This means that ∆S K = 0, if we apply the Boltzmann formula to calculate the conformational entropy and assume that the thermodynamic probability is equal to the conformation number.
Since T2 is the temperature at which the excess entropy of a supercooled liquid (in this case an amorphous polymer) compared to a crystal becomes zero, glass transition in the Gibbs-Di Marzio theory is considered a second-order phase transition. Indeed, during glass transition, some formal signs of such a transition are observed - a jump in heat capacity, a sharp change in the coefficient of volumetric expansion, etc. In addition, it was shown that during glass transition, a redistribution of gauche and trans isomers takes place, as proposed according to the Gibbs-Dee theory Marzio. In practice it turned out that T c > T 2 always. Therefore, the authors of the theory assumed that T 2 = T c only at infinitesimal polymer cooling rates, when relaxation phenomena in polymers are reduced to a minimum. But even under this condition, it is incorrect to identify glass transition with a second-order phase transition, because glass transition fixes a metastable state, the entropy of which at any temperature is greater than the entropy of the crystalline state. Thus, it should be considered that there are two independent transitions at T 2 and T c, which correlate with each other. The thermodynamic theory of glass transition was further developed in the works of Adam and Gibbs.
Kinetic theory of glass transition. For polar polymers with strong intermolecular interactions, good results are obtained by the Zhurkov theory, one of the first theories of glass transition. According to this theory, the glass transition of the polymer, i.e. the cessation of thermal movement of segments is due to the formation of a spatial network of weak intermolecular cohesive bonds - dipole, donor-acceptor (including hydrogen).
The energy of intermolecular interaction depends little on temperature, while the energy of thermal motion of units is proportional to kT. As the temperature decreases, the energy of thermal motion decreases and, when it turns out to be insufficient to overcome the forces of intermolecular interaction, a network of intermolecular bonds is formed, i.e. glass transition In this case, for the transition to a glassy state, it is enough to “freeze” the mobility of the Kuhn segments, while the movement of other structural elements - links, lateral substituents - is preserved.
The formation of intermolecular bonds during the transition to a glassy state for a number of polar polymers - polyamides, polyvinyl alcohol, gelatin - has been proven by IR spectroscopy. In accordance with Zhurkov's theory, with increasing polarity of the polymer and, consequently, chain rigidity, the value of the glass transition temperature increases (Fig. 4.7).
Blocking the polar groups of polymers by introducing small additions of low molecular weight compounds leads to a decrease in intermacromolecular interaction and, accordingly, the glass transition temperature. Experimental data confirm this position.
Based on the foregoing, it is obvious that the glass transition temperature will primarily depend on the factors determining the flexibility of the chain and the possibility of conformational transitions. The flexibility of the chain is determined by the nature of the bonds in the main chain, as well as the volume and polarity of the substituents on this chain. It is known, for example, that the introduction of ether bonds into a chain increases its flexibility, and amide groups - decreases it. In accordance with this, in the first case the glass transition temperature decreases, in the second it increases (see Table 4.1). The influence of a substitute most often manifests itself as follows:
so-called bulk non-deformable substituents increase the glass transition temperature, for example, for polystyrene and polyvinylnaphthalene it is 100 °C and 211 °C, respectively;
flexible side groups lower the glass transition temperature, for example, polymethyl acrylate and polybutyl acrylate have a glass transition temperature of 2 ° C and -40 ° C, respectively;
An increase in the polarity of the substituent leads to a decrease in the flexibility of the chain due to the restriction of the freedom of its rotation and, as a consequence, to an increase in the glass transition temperature.
As mentioned above, in the region of low molecular weight values, the latter affects the glass transition temperature of the polymer. This is explained by an increase in the free volume of the polymer containing short chains, since their ends prevent the dense packing of macromolecules. The excess free volume of a low-molecular-weight polymer leads to the fact that conformational transitions of macromolecules can occur at lower temperatures compared to a polymer of higher molecular weight.
In the case of cross-linked polymers, the opposite phenomenon occurs - cross-linking “brings together” the macromolecules, which leads to a decrease in free volume and an increase in the glass transition temperature of the “cross-linked” polymer compared to the linear one.
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The Olenta company sells a huge range of polymer materials. We always have high-quality thermoplastics available, including liquid crystal polymers. Employees working at Olenta have higher specialized education and have an excellent understanding of the peculiarities of polymer manufacturing. With us you can always get advice and any assistance regarding the choice of material and organization of the technological process.
Liquid crystalline polymers have very high rigidity and strength. They do not produce flash when casting. Recommended for precision casting. They have excellent dimensional stability. Characterized by very short cooling times. They are characterized by extremely low joint strength. Here you will find liquid crystal polymer from Toray. The material is produced at a factory in Japan.
Liquid crystal polymer produced by Toray
| Filling | Brand | Description | Application |
| Glass filling | High strength polymer, 35% glass filled | Microelectronics |
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| Short glass | High flow polymer, 35% glass filled | Microelectronics |
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| Short glass and minerals | Super high flow polymer, 30% glass filled | Microelectronics |
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| Antistatic polymer, 50% filling | Microelectronics |
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| Glass and minerals | Low warpage,50% filling | Microelectronics |
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| Minerals | Low warpage,30% filling | Microelectronics |
Features of liquid crystal polymers
Unlike traditional polymer compounds, these materials have a number of distinctive properties. Liquid crystalline polymers are high-molecular compounds that can change their state under the influence of external conditions. Due to flexible molecular bonds, a chain of macromolecules is capable of changing its shape over a wide range and forming a stable and durable crystalline structure.
These polymers retain stable strength properties up to the melting point. They have very high chemical resistance and dielectric properties.
Liquid crystal polymers are widely used in the production of electronic components, microwave-resistant cookware, and medical instruments.
About the company OLENTA
Our company has a number of advantages:
- reasonable prices;
- specialists with extensive experience;
- strict adherence to deadlines and agreements;
- a wide range of structural plastics;
- cooperation with the largest polymer manufacturers.
OLENTA supplies liquid crystal polymers exclusively from trusted manufacturers. This not only serves as a guarantee of impeccable quality, but also minimizes any risks associated with supply disruptions or improper fulfillment of obligations.
We are publishing a transcript of a lecture by a senior researcher at the Department of Macromolecular Compounds of the Faculty of Chemistry of Moscow State University, associate professor, Doctor of Chemical Sciences, laureate of the Presidential Prize of the Russian Federation for young scientists for 2009, Alexey Bobrovsky, given on December 2, 2010 at the Polytechnic Museum as part of the project “Public Lectures Polit. RU".
See also:
Lecture text. Part 1
Good evening! I would like to make a few changes to the regulations: the lecture consists of two parts: first liquid crystals, then liquid crystal polymers, so I would like to suggest asking some questions after the first part. It will be easier.
I would like to say that the main task that I set for myself in preparing for this lecture is not so much to load you with an abundance of information about liquid crystals and their use, but to somehow interest you in liquid crystals, to give you some initial concepts: what they are and show how beautiful and interesting they are, not from a utilitarian point of view (where they can be used), but from the point of view of science and art (how beautiful they are in themselves). Plan of my report.
First of all, I will tell you when and how the liquid crystalline state was discovered, what makes liquid crystals unique compared to other objects, and in the second part of my report I will talk about liquid crystalline polymers and why they are interesting and wonderful.
Everyone knows that in most substances the molecules form a crystalline state, the molecules form a three-dimensional crystal lattice, ordered in three dimensions, and when heated to a certain temperature, a phase transition is observed from a three-dimensional ordered state to a disordered liquid state, and with further heating - to a gaseous state . It turned out that there are some intermediate phases that have the aggregate state of a liquid, but, nevertheless, have some order: not three-dimensional, but two-dimensional or some other degenerate order. I will now explain what is at stake.
The first report of an unusual state of matter - the liquid crystalline state of matter, although this term did not exist at that time - took place in 1888. According to some other data, such an unusual state of the substance was recorded in 1850, but it is generally accepted that in 1888 Friedrich Reinitzer, an Austrian scientist, examined the substance cholesteryl benzoate - a derivative of cholesterol - and discovered that when heated to 145°, the crystalline phase (white powder) turns into a strange cloudy liquid, and upon further heating to 179°, a transition into an ordinary transparent liquid is observed. He tried to purify this substance, since he was not sure that he had pure cholesteryl benzoate, but nevertheless these two phase transitions were reproduced. He sent a sample of this substance to his friend physicist Otto von Lehmann. Lehman studied ordinary crystals, including plastic crystals, which are soft to the touch and different from ordinary hard crystals. The main method of study was polarization optical microscopy - a microscope in which light passes through a polarizer, passes through a substance, and then through an analyzer - through a thin layer of substance. When crystals of a certain substance are placed between the polarizer and the analyzer, you can see textures - characteristic images for different crystalline substances - and thus study the optical properties of the crystals. It turned out that Otto von Lehmann helped him understand what was the reason for the intermediate state, the delusion. Otto von Lehmann was seriously convinced that all the properties of crystalline substances, crystals, depend solely on the shape of the molecules, that is, it does not matter how they are located in this crystal, the shape of the molecules is important. And in the case of liquid crystals, he was right - the shape of the molecules determines the ability to form a liquid crystalline phase (mainly the shape of the molecules). Here I would like to talk about the main historical stages in the study of liquid crystals, the most important in my opinion.
In 1888, Reinitzer wrote that there are crystals whose softness is such that they can be called liquid, then Lehmann wrote an article about flowing crystals, in fact, he coined the term liquid crystals. An important historical episode: in the 20-30s, the Soviet physicist Fredericks studied the influence of various magnetic and electric fields on the optical properties of liquid crystals, and he discovered an important thing: the orientation of molecules in liquid crystals very easily changes under the influence of external fields, and these fields very weak and changes very quickly. Since the late 60s, a boom in the study of liquid crystal systems and liquid crystal phases began, and it is associated with the fact that they learned to use them. First, for information display systems in ordinary electronic digital watches, then in calculators, and with the advent of computer technology, it became clear that liquid crystals can be actively used for the manufacture of displays. Naturally, such a technological leap has stimulated the study of liquid crystals from the point of view of fundamental science, but I would like to point out how large the time gap is between scientific discoveries related to liquid crystals. In fact, people were interested in them out of curiosity, there was no utilitarian interest, no one knew how to use them, and, moreover, in those years (20-30s) the theory of relativity was much more interesting. By the way, Fredericks was the popularizer of the theory of relativity in the Soviet Union, then he was repressed and died in the camps. In fact, 80 years passed after the discovery of liquid crystals until they learned to use them. I often give this example when talking about the peculiarities of science financing.
I would like to dwell on the main types of liquid crystalline phase. How does the mesophase, namely the liquid crystalline phase, work?
Typically, the liquid crystalline phase is formed by molecules that have a rod- or disk-shaped shape, that is, they have shape anisometry, primarily rods or disks. You can imagine a good experiment that is easy to set up: if you randomly pour sticks into a box and shake it, then as a result of this shaking you will notice that the sticks themselves are stacked in parallel, which is how the simplest nematic phase is arranged. There is orientational order along a certain direction, but the center of mass of the molecules is disordered. There are much more complex phases, for example, of the smectic type, when the center of mass is in planes, that is, such layered phases. The cholesteric phase is very interesting: its local order is the same as that of the nematic one, there is an orientational order, but at a distance of hundreds of nanometers a helical structure with a certain direction of twist is formed, and the appearance of this phase is due to the fact that the molecules are chiral, that is, it is necessary to molecular chirality (I will explain what this is later) in order to form such a helical twist. This phase also has interesting properties, like the nematic one, and can also find some application. The phases I talked about are the simplest ones. There are so-called blue phases.
I will dwell on them a little when I talk about polymers, this is a little related to my work. Here these lines indicate the direction of orientation of the molecules, and the main structural element of such phases is such cylinders in which the orientation of the long axes of the molecules cleverly changes, that is, in the center of this cylinder the orientation is along the axis of the cylinder, and as it moves away to the periphery, a rotation is observed. These phases are very interesting from the point of view of structure, very beautiful in a polarizing microscope, and it is important to note that in the case of low molecular weight liquid crystals these phases exist in some tenths of a degree, at best a 2-3° temperature range, and in the case of polymers I managed to capture these interesting structures, and I will tell you about it later. A little chemistry. What do the structures of liquid crystal molecules look like?
Usually there is an aromatic moiety of 2-3 benzene rings, sometimes there may be two aromatic rings linked directly, there may be a linking moiety. It is important that this fragment is elongated, that is, its length is greater than its width, and that it is quite rigid, and rotation around a long axis is possible, but during this rotation the shape remains elongated. This is very important for the liquid crystal phase to form. The presence of flexible tails in the molecule is important - these are various alkyl tails, and the presence of various polar substituents is important. This is important for the application, and it creates dipole moments and the ability to reorient in external fields, that is, this molecule is composed of two main parts: a mesogenic fragment with some substituent (polar or non-polar) and a flexible tail that can bend. Why is it needed? It acts as an internal plasticizer, because if you take rigid molecules, they will crystallize - they will form a three-dimensional crystal without any mesophases, without liquid crystalline phases, and the flexible tail often helps that an intermediate phase is formed between the crystal and an ordinary isotropic liquid. Another type of molecules are disk-shaped molecules. Here is the general structure of such disks, which can also form mesaphases, but they have a completely different structure than phases based on elongated molecules. I would like to emphasize to you how beautiful liquid crystals are under a polarizing microscope.
Polarization microscopy is the first method for studying liquid crystals, that is, from the picture that is observed by a researcher in a polarizing microscope of crossed polarizers, one can judge what kind of mesophase, what type of liquid crystalline phase is formed. This is the characteristic picture for the nematic phase, the molecules of which form only an orientational order. This is what the smectic phase looks like. To give you an idea of the scale of all this, that is, it is much larger than the molecular scale: the width of the picture is hundreds of microns, that is, it is a macroscopic picture, much larger than the wavelength of visible light. And by analyzing such pictures, one can judge what kind of structure there is. Naturally, there are more accurate methods for determining the structure and some structural features of these mesophases - methods such as X-ray diffraction analysis, various types of spectroscopy - this allows us to understand how and why the molecules are packed in one way or another.
Another type of picture is a concentrated solution of short DNA fragments (aqueous solution) - such a picture was obtained at the University of Colorado. Generally speaking, the importance and features of the formation of liquid crystalline phases in biological objects is a topic for a separate large discussion, and I am not an expert in this, but I can say that many polymers of a biological nature can produce a liquid crystalline phase, but this is usually a lyotropic liquid crystalline phase, that is It is important that a solvent, such as water, is present in order for this liquid crystalline phase to form. These are the pictures I received.
This is what the cholesteric mesophase looks like - one of the typical pictures. I would like to show how beautiful phase transitions look: when the temperature changes, we can observe a phase transition.
When the temperature changes, a change in refraction is observed, so the colors change, we approach the transition - and a transition to an isotropic melt is observed, that is, everything has darkened, a dark picture is visible in the crossed polarizers.
In another case, it’s a little more complicated: at first a dark picture is visible, but nature is deceiving us, the molecules are simply oriented so that they look like an isotropic melt, but there was a liquid crystalline phase. Here is the transition to another liquid crystalline phase - upon cooling, more ordered changes in orientation. The red color is associated with a helical structure with a certain pitch of the helix, and the pitch of the helix changes, the helix twists, so there is a change in colors. Various disclinations are visible, that is, the spiral is twisting, and now at some point crystallization of this sample will be observed, all this will turn blue. I show this by the fact that one of my personal motives for studying, for example, liquid crystals is their beauty, I look at them with pleasure through a microscope, I have the happiness of doing this every day, and the aesthetic interest is supported by scientific interest. Now there will be crystallization, everything happens in real time. I don’t have any bells and whistles, it’s an ordinary soap dish mounted on a microscope, so the quality is appropriate. Here the spherulites of this compound grow. This compound was synthesized for us by chemists in the Czech Republic. (We also synthesize LCD compounds ourselves.) A little needs to be said about why they are widely used.
Each of us carries with us a small amount of liquid crystals, because all mobile phone monitors are based on liquid crystals, not to mention computer monitors, displays, television monitors, and serious competition from plasma monitors and LED monitors in general - then, as far as I know (I'm not an expert in this), no. Liquid crystals are stable and do not require much voltage to switch the picture - this is very important. An important combination is observed in liquid crystals, the so-called anisotropy of properties, that is, the dissimilarity of properties in different directions in the medium, their low viscosity, in other words, fluidity, it is possible to create some kind of optical device that would switch and react with a characteristic switching time milliseconds or even microseconds is when the eye does not notice the speed of this change, which is why the existence of LCDs and television displays is possible, and very high sensitivity to external fields. These effects were discovered before Fredericks, but were studied by him, and the orientation transition that I will talk about now is called the Fredericks transition. How does a simple digital watch dial work, and why are liquid crystals so widely used?
The device looks like this: there is a layer of liquid crystal; the sticks represent the direction of orientation in the liquid crystal molecule, of course they are not to scale, they are much smaller than the rest of the design elements, there are two polarizers, they are crossed in such a way that if there were no liquid crystal layer, light would not pass through them. There are glass substrates on which a thin conductive layer is applied so that an electric field can be applied; There is also such a tricky layer that orients the liquid crystal molecules in a certain way, and the orientation is set in such a way that on the top substrate the molecules are oriented in one direction, and on the other substrate - in the perpendicular direction, that is, a twist orientation of the liquid crystal molecules is organized, so the light , when it falls on a polarizer, it is polarized - it enters a liquid crystalline medium, and the plane of its polarization rotates following the orientation of the liquid crystal molecule - these are the properties of liquid crystal molecules. And, accordingly, due to the fact that it rotates 90° in plane polarization, light passes through this geometry calmly, and if an electric field is applied, the molecules line up along the electric field, and therefore polarized light does not change its polarization and cannot pass through another polarizer. This is how a dark image appears. In reality, a mirror is used on a wristwatch and segments can be made that allow one to visualize some image. This is the simplest scheme, of course, liquid crystal monitors are much more complex structures, multi-layered, the layers are usually very thin - from tens of nanometers to microns - but the principle is basically the same, and this transition is when the orientation of the molecules changes along the electric or magnetic field ( monitors use an electric field because it is easier) is called the Fredericks transition (effect) and is actively used in all such devices. The first prototype is a nematic display in the dial.
And this is a picture illustrating how small an electric field it takes to reorient a liquid crystal molecule. In fact, this is a galvanic cell made up of two potatoes as an electrolyte, that is, a very small voltage in the region of 1V is needed for such a reorientation, which is why these substances have received such widespread use. Another application, and we are talking about cholesteric liquid crystals, which I will talk about in more detail, is due to the fact that they are able to change color depending on temperature.
This is due to the different pitch of the spiral, and it is possible to visualize, for example, the temperature distribution. I have finished with low molecular weight liquid crystals and am ready to listen to your questions on them before moving on to polymer liquid crystals.
Discussion of the lecture. Part 1
Tatyana Sukhanova, Institute of Bioorganic Chemistry: Answer the question of an amateur: in what range does the color of liquid crystals change, and how does this depend on their structure?
Alexey Bobrovsky: We are talking about cholesteric liquid crystals. Here the color changes depending on the pitch of the cholesteric helix. There are cholesterics that selectively reflect light in the UV region, respectively, the invisible region, and there are cholesterics that selectively reflect light due to this periodicity in the infrared region, that is, we are talking about microns, tens of microns, and in the case of color pictures, which I showed in polarizing optical microscopy, it is more difficult there, and the color is due to the fact that polarized light, the plane of polarization in a liquid crystal rotates differently, and this depends on the wavelength. There is a complex color gamut, and the entire visible range is closed, that is, you can contrive to get a variety of colors.
Boris Dolgin: Can you tell us a little more about life?
Alexey Bobrovsky: About life? Specifically about the role of liquid crystals in biology?
Boris Dolgin: Yes.
Alexey Bobrovsky: Unfortunately, this is not my topic at all. I'll give you a link to the book at the end. First of all, when they talk about the connection of liquid crystals in biology, they talk about how they can be used in medicine - there are a lot of different options. In lipid cell membranes, the liquid-crystalline state takes place at reasonable biological temperatures.
Boris Dolgin: And this is not an artifact at all, and this is additional research.
Alexey Bobrovsky: Yes. It seems to me that the role of the liquid crystal state is still not really known, and sometimes there is evidence that DNA in a cell can exist in a liquid crystal state, but this is a topic for future research. This is not my field of science. I am more interested in liquid crystal synthetic polymers, which I will continue to talk about.
Boris Dolgin: Are LCD polymers completely artificial?
Alexey Bobrovsky: Yes, mostly everything is artificial. The coloration, for example, of some beetles and butterflies is due to such natural not liquid crystals, but a frozen liquid crystalline state due to chitinous biological polymers. So the evolution was distributed, that the coloring is not due to pigments, but due to the cunning structure of polymers.
Mikhail Potanin: I have a question about the magnetic sensitivity of liquid crystals. How sensitive are they to the Earth's magnetic fields? Is it possible to make compasses with them?
Alexey Bobrovsky: No you can not. Unfortunately, this is what happened. What determines the sensitivity of liquid crystals? There is the concept of diamagnetic susceptibility and permittivity, and in the case of an electric field, everything is much more convenient and better, that is, it is enough to really apply 1 V to such a liquid crystal cell - and everything will be reoriented, and in the case of a magnetic field, we are talking about teslas - such field strengths incomparably higher than the strength of the Earth's magnetic field,
Lev Moskovkin: I may have a completely amateurish question. The lecture is absolutely charming, the aesthetic satisfaction is great, but the presentation itself is smaller. The pictures you showed resemble the core - they are also aesthetically active - and the Jabotinsky reaction, although your pictures are not cyclical. Thank you.
Alexey Bobrovsky: I'm not ready to answer this question. This needs to be looked at in the literature. In polymers and liquid crystals there is a theory of "scaling" (scaling), that is, self-similarity. I find it difficult to answer this question; I am not competent in this topic.
Natalia: Now Nobel Prizes are being awarded to Russian scientists. In your opinion, Fredericks, if he had remained alive, could have received this award? In general, did any of the scientists who dealt with this topic receive the Nobel Prize?
Alexey Bobrovsky: I think, of course, Fredericks would be the first candidate. He died in a camp during the war. If he lived until 1968-1970, then he would have been the first candidate for the Nobel Prize - this is quite obvious. Still a great physicist, but was not awarded (we are talking about our scientists), - Tsvetkov - the founder of the school of physicists in St. Petersburg, unfortunately, it fell apart to one degree or another. He did not specifically consider the question of who received the Nobel Prize for liquid crystals, did not study it, but, in my opinion, only Paul de Genne received the Nobel Prize for polymers and liquid crystals.
Boris Dolgin: Is the fashion for studying liquid crystals gone forever?
Alexey Bobrovsky: Yes, of course, there is no hype anymore, because a lot is already clear with the simplest mesophase (nematic liquid crystal phase), and it is clear that it is the most optimal for use. There is still some interest in more complex phases, because one can get some advantages over the well-studied one, but the number of publications on the liquid crystal state is declining.
Boris Dolgin: That is, you do not see any qualitative leaps in understanding, no zones where there would be a global mystery.
Alexey Bobrovsky: I think it’s better not to make predictions, because anything can happen. Science does not always develop consistently. Sometimes there are strange jumps, so I do not undertake to make any predictions.
Konstantin Ivanovich: I would like to know how safe they are for human life.
Alexey Bobrovsky: People who make LCD displays undergo safety tests. If you drink a liter of liquid crystal, you will probably feel bad, but since milligrams are used, then there is no serious danger. This is much safer than broken, leaking mercury from a thermometer. This is completely incomparable in harm. Research is now emerging on the recycling of liquid crystals. I've heard one report where this issue is being taken seriously, that there's already a lot of scrap and how it can be reclaimed, but the environmental issues are minimal. They are safe.
Boris Dolgin: There was a very interesting thing at the end. If you imagine a used LCD monitor and so on. What will happen to him next, what is happening? How is it disposed of - or not disposed of, or somehow decomposed, or remains?
Alexey Bobrovsky: I think that liquid crystal molecules are the first thing that will decompose under the action of external influences.
Boris Dolgin: So there is no particular specificity here?
Alexey Bobrovsky: Of course not. I think the problems there with recycling plastics and polymers are much more complicated.
Oleg: Please tell me what determines the temperature range of liquid crystalline phases? As you know, all modern displays operate over a very wide temperature range. How was this achieved, and by what properties and structure of matter are they determined?
Alexey Bobrovsky: Great question. Indeed, ordinary compounds, most of the organic compounds that are synthesized individually, have such temperatures as I showed, cholesteryl benzoate melts at 140°, then isotropic decomposition 170°. There are individual substances that have a low melting point, around room temperature, and transform into an ordinary isotropic liquid around 50°, but in order to realize such a wide temperature range, down to sub-zero temperatures, mixtures had to be made. Conventional mixed compositions of different substances, when mixed, their melting point is greatly reduced. Such a trick. Usually these are homologous series, what is used in displays is a biphenyl derivative, where there is no X and a nitrile substituent, and tails of different lengths are taken as alkyl tails, and a mixture of 5-7 components makes it possible to lower the melting point below 0°, while leaving the temperature of clearing, that is, the transition of the liquid crystalline into the isotropic phase, above 60° - this is such a trick.
Lecture text. Part 2
First of all, I would like to say what polymers are.
Polymers are compounds that are obtained by repeated repetition, that is, chemical bonding of identical units - in the simplest case, identical ones, as in the case of polyethylene, these are CH 2 units connected to each other in a single chain. Of course, there are more complex molecules, even DNA molecules, whose structure is not repeated and is organized in a very complex way.
The main types of polymer topology: the simplest molecules are linear chain molecules, there are branched, comb-shaped polymers. Comb-shaped polymers have played an important role in the preparation of liquid crystalline polymers. Star-shaped, ring-linked polycatenanes are a variety of molecular shapes. When research into the liquid crystalline state was in full swing, when liquid crystals were being studied, an idea arose: is it possible to combine the unique optical properties of liquid crystals with the good mechanical properties of polymers - the ability to form coatings, films, and some products? And what came to mind in 1974 (there was the first publication) - in the late 60s - early 70s they began to propose different approaches to the production of liquid crystalline polymers.
One approach is to attach rod-shaped, stick-shaped molecules to a linear macromolecule, but it turned out that such polymers do not form a liquid crystalline phase - they are ordinary fragile glasses, which when heated begin to decompose and do not give anything. Then, in parallel, in two laboratories (I will talk about this in more detail later), an approach was proposed for attaching such rod-shaped molecules to the main polymer chain through flexible spacers - or decouples, in Russian. And then the following turns out: there is a slight autonomy between the main polymer chain, it proceeds largely independently, and the behavior of rod-shaped molecules, that is, the main polymer chain does not interfere with the formation of the rod-shaped fragments of the liquid crystalline phase.
This approach turned out to be very fruitful, and in parallel, in two laboratories - in the laboratory of Nikolai Alfredovich Plate in the Soviet Union and in the Ringsdorf laboratory - such an approach was independently proposed, and I am happy to work now in the laboratory of Valery Petrovich Shibaev at the Faculty of Chemistry of Moscow State University, that is, I work in the laboratory where all this was invented. Naturally, there were disputes about priorities, but this is all unimportant.
Main types of liquid crystal polymers. I will not talk about such main chains or the main groups of the main polymer chain (this is one type of such polymers), I will mainly talk about comb-shaped liquid crystalline polymers, in which the rod-shaped fragments are connected to the main chain through a flexible aliphatic decoupler.
An important advantage of the approach to creating liquid crystalline polymers from the point of view of synthesis and combination of different properties is the possibility of obtaining homopolymers. That is, you take a monomer that is capable of forming a chain molecule, for example, due to a double bond, schematically depicted here, and you can get a homopolymer, that is, a polymer whose molecules consist of identical rod-shaped fragments, or you can make copolymers by combining two different fragments - they can both form a mesophase, or they can combine non-mesogenic fragments with mesogenic fragments, and it turns out that we have the ability to chemically force dissimilar components to be in the same polymer system. In other words, if we tried to mix such a monomer with such a monomer without chemical binding, they would give two separate phases, and by chemically binding them, we force them to be in the same system, and then I will show why this is good.
An important advantage and difference between polymer liquid crystals and low-molecular liquid crystals is the possibility of forming a glassy state. If you look at the temperature scale: we have an isotropic phase at high temperatures, when the temperature decreases, a liquid crystalline phase is formed (under these conditions the polymer looks like a very viscous liquid), and when cooled, a transition to a glassy state is observed. This temperature is usually close to or slightly above room temperature, but this depends on the chemical structure. Thus, unlike low molecular weight compounds, which are either liquid or go into a crystalline state, the structure changes. In the case of polymers, this structure turns out to be frozen in a glassy state, which can persist for decades, and this is important from the point of view of application, for example, for recording the storage of information, we can change the structure and orientation of the molecule, fragments of the molecule and freeze them at room temperature. This is an important difference and advantage of polymers from low molecular weight compounds. What else are polymers good for?
This video demonstrates a liquid crystal elastomer, that is, it feels like a rubber band that contracts when heated and expands when cooled. This work is taken from the Internet. This is not my work, here is an accelerated image, that is, in reality, unfortunately, this transition is observed within tens of minutes. Why is this happening? What is a liquid crystal elastomer, which has a fairly low glass transition temperature, that is, it is in an elastic state at room temperature, but the macromolecules are cross-linked, and if we synthesize a film in the liquid crystalline phase, then the polymer chain slightly repeats the orientation of the mesogenic groups, and if we If we heat it, the mesogenic groups go into a disordered state and, accordingly, transfer the main polymer chains into a disordered state, and the anisometry of macromolecular coils changes. This leads to the fact that upon heating, during the transition from the mesophase to the isotropic phase, a change in the geometric dimensions of the sample is observed due to a change in the shape of the polymer coils. In the case of low molecular weight liquid crystals, this cannot be observed. Two groups in Germany - Finkelman, Zentel - and other groups worked a lot on these things. The same can be observed under the influence of light.
There are a lot of works on photochromic polymers that contain an azobenzene fragment - two benzene rings connected to each other by an NN double bond. What happens when such molecular fragments are exposed to light? The so-called trans-cis isomerization is observed, and the rod-shaped fragment, when irradiated with light, transforms into a beveled curved cis form, a bent fragment. This also leads to the fact that the order in the system decreases greatly, and just as we saw earlier during heating, also during irradiation there is a reduction in the geometric dimensions, a change in the shape of the film, in this case we observed a reduction.
Various kinds of bending deformations can be realized during irradiation, that is, when irradiated with UV light, such bending of the film can be realized. When exposed to visible light, reverse cis-trans isomerization is observed, and this film expands. All sorts of options are possible - this may depend on the polarization of the incident light. I'm talking about this because this is now a fairly popular area of research into liquid crystalline polymers. They even manage to make some devices based on this, but so far, unfortunately, the transition times are quite long, that is, the speed is low, and therefore it is impossible to talk about any specific use, but, nevertheless, these are such artificially created muscles, which act, work when temperature changes or when exposed to light of different wavelengths. Now I would like to talk a little about my work directly.
What is the purpose of my work, our laboratory. I have already talked about the advantages of copolymerization, the possibility of combining completely dissimilar fragments in one polymer material, and the main task, the main approach to creating such different multifunctional liquid crystalline polymers is the copolymerization of a wide variety of functional monomers, which can be mesogenic, that is, responsible for the formation of liquid crystalline polymers. phases, chiral (I will talk about chirality later), photochromic, that is, they are capable of changing under the influence of light, electroactive, which carry a large dipole moment and can be reoriented under the influence of a field, various kinds of functional groups that can, for example, interact with metal ions, and material variations are possible. And this is such a hypothetical comb-shaped macromolecule drawn here, but in reality we get double or ternary copolymers that contain different combinations of fragments, and, accordingly, we can change the optical and other properties of these materials using different influences, for example, light and an electric field. One such example is the combination of chirality and photochromism.
I have already spoken about the cholesteric mesophase - the fact is that a helical molecular structure is formed with a certain helix pitch, and such systems have selective reflection of light due to such periodicity. This is a schematic diagram of a film section: a certain helix pitch, and the fact is that selective reflection is linearly related to the helix pitch - proportional to the helix pitch, that is, by changing the helix pitch in one way or another, we can change the color of the film, the wavelength of the selective reflection. What causes such a structure with a certain degree of twist? In order for such a structure to form, chiral fragments must be introduced into the nematic phase.
Molecular chirality is the property of molecules to be incompatible with their mirror image. The simplest chiral fragment we have in front of us is our two palms. They are roughly mirror images of each other and are in no way comparable. Molecular chirality introduces into a nematic system the ability to twist and form a helix. It must be said that there is still no clear, well-explaining theory of spiral twisting, but, nevertheless, it is observed.
There is an important parameter, I will not dwell on it, - this is the twisting force, and it turned out that the twisting force - the ability of chiral fragments to form a helical structure - strongly depends on the geometry of the chiral fragments.
We have obtained chiral-photochromic copolymers that contain a mesogenic fragment (shown as a blue stick) - it is responsible for the formation of a nematic liquid crystalline phase. Copolymers with chiral-photochromic fragments have been obtained, which, on the one hand, contain a chiral molecule (group), and on the other hand, a fragment that is capable of photoisomerization, that is, changing geometry under the influence of light, and by irradiating such molecules, we induce trans -cis-isomerization, we change the structure of the chiral photochromic fragment and - as a result - its ability to induce the efficiency of inducing the cholesteric helix, that is, in this way we can, for example, unwind the cholesteric helix under the influence of light, we can do this reversibly or irreversibly. What does an experiment look like, what can we implement?
We have a section of a cholesteric film of a cholesteric polymer. We can irradiate it using a mask and locally induce isomerization; during isomerization, the structure of the chiral fragments changes, their twisting ability decreases, and locally unwinding of the helix is observed, and since unwinding of the helix is observed, we can change the wavelength of the selective reflection of color, that is, the color films.
The samples that were obtained in our laboratory are polymer samples irradiated through a mask. We can record various kinds of images on such films. This may be of applied interest, but I would like to point out that the main focus of our work is to study the influence of the structure of such systems on molecular design, on the synthesis of such polymers, and on the properties of such systems. In addition, we have learned not only to control light, the wavelength of selective reflection, but also to control electricity. For example, we can record some kind of color image, and then, by applying an electric field, somehow change it. Due to the versatility of such materials. Such transitions - unwinding-twisting of the helix - can be reversible.
It depends on the specific chemical structure. For example, we can cause the wavelength of selective reflection (in fact, coloring) to depend on the number of recording-erasing cycles, that is, when irradiated with ultraviolet light, we unwind the spiral, and the film turns from green to red, and then we can heat it at a temperature of 60° and induce reverse twist. This way you can implement many loops. In conclusion, I would like to return a little to the aesthetic aspect of liquid crystals and liquid crystal polymers.
I showed and talked a little about the blue phase - a complex, very interesting structure, they are still being studied, nanoparticles are introduced there and they see what changes there, and in low molecular weight liquid crystals this phase exists in some fractions of degrees (2°-3 °, but no more), they are very unstable. It is enough to push the sample a little - and this beautiful texture, an example of it is shown here, is destroyed, and in polymers in 1994-1995, by heating for a long time, firing films at certain temperatures, I was able to see such beautiful textures of cholesteric blue phases, and I managed without Any tricks (without using liquid nitrogen) just cool these films and observe these textures. More recently, I found these samples. 15 years have passed - and these textures have remained absolutely unchanged, that is, the cunning structure of the blue phases, like some ancient insects in amber, has remained fixed for more than 10 years.
This, of course, is convenient from the point of view of research. We can put this in an atomic force microscope and study sections of such films - it’s convenient and beautiful. That's all for me. I would like to refer to the literature.
The first book by Sonin Anatoly Stepanovich, I read it more than 20 years ago, 1980, from the publishing house “Centaur and Nature”, then, while still a schoolchild, I became interested in liquid crystals, and it so happened that Anatoly Stepanovich Sonin was a reviewer of my thesis. A more modern publication is the article by my scientific supervisor Valery Petrovich Shibaev “Liquid crystals in the chemistry of life.” There is a huge amount of English-language literature; If you have interest and desire, you can find a lot of things yourself. For example, Dirking's book Liquid Crystal Textures. I recently found a book that focuses on the use of liquid crystals in biomedicine, that is, if someone is interested in this particular aspect, I recommend it. There is an e-mail for communication, I will always be happy to answer your questions and maybe send you some articles if there is such interest. Thank you for your attention.
Discussion of the lecture. Part 2
Alexey Bobrovsky: It was necessary to show some specific chemistry. This is my omission. No, this is a multi-stage organic synthesis. Some simple substances are taken, in flasks it resembles a chemical kitchen, molecules during such reactions are combined into more complex substances, they are isolated at almost every stage, they are somehow analyzed, the agreement of the structure that we want to obtain is established with those spectral data that instruments give us so that we can be sure that this is the substance we need. This is a rather complex sequential synthesis. Of course, liquid crystalline polymers require even more labor-intensive synthesis to obtain. It looks like orange powders are made from various white powders. A liquid crystalline polymer looks like a rubber band, or it is a solid sintered substance, but if you heat it up and make a thin film (this is possible when heated), then this strange substance gives beautiful pictures in a microscope.
Boris Dolgin: I have a question, maybe from a different area, in fact, maybe first Lev, then me, so as not to distract from the factual part.
Lev Moskovkin: You really fascinated me with today’s lecture, for me this is the discovery of something new. The questions are simple: how big is the muscle strength? What does it work on? And out of ignorance, what is texture, how does it differ from structure? After your lecture, it seems to me that everything that is structured in life, all thanks to liquid crystals, is also largely regulated by light and a weak impulse. Thank you very much.
Alexey Bobrovsky: Of course, it cannot be said that everything is regulated by liquid crystals; this, of course, is not the case. There are different forms of self-organization of matter, and the liquid crystalline state is only one of these forms of self-organization. How strong are polymer muscles? I don’t know the quantitative characteristics compared to existing iron-based devices, roughly speaking, of course, they are not so strong, but I want to say that modern body armor, for example, contain the Kivlar material - a fiber that has a liquid crystalline structure main chain type, a polymer with mesogenic groups in the main chain. In the process of obtaining this fiber, macromolecules are stretched along the direction of drawing and very high strength is provided, this allows the making of strong fibers for body armor, actuators, or muscles, in the development stage, but the forces can be achieved there very weak. The difference between texture and structure. Texture is a concept that is used by people who are involved in carpets, design of things, some visual things, artistic design, that is, it is primarily a look. It’s lucky that the texture of liquid crystals, that is, a characteristic picture, helps a lot in determining the structure of a liquid crystal, but these are, in fact, different concepts.
Oleg Gromov, : You said that there are polymer liquid crystal structures that have a photochromic effect and electrical and magnetic sensitivity. The question is this. It is also known in mineralogy that Chukhrov described liquid crystalline formations of inorganic composition in the 50s, and it is known that inorganic polymers exist; therefore, the question is: do inorganic liquid crystalline polymers exist, and if so, is it possible for them to perform these functions? and how are they implemented in this case?
Alexey Bobrovsky: The answer is more likely no than yes. Organic chemistry, the property of carbon to form a variety of different compounds, has made it possible to carry out a colossal design of various kinds of low-molecular liquid crystals, polymer compounds, and, in general, that’s why we can talk about some kind of diversity. These are hundreds of thousands of low molecular weight polymer substances that can form a liquid crystalline phase. In the case of inorganic ones, I don’t know about polymers, the only thing that comes to mind is some suspensions of vanadium oxide, which also seem to be polymers, and their structures are usually not precisely established, and this is at the research stage. This has turned out to be a little out of the mainstream of science, where everyone is working on the design of organic conventional liquid crystals, and there can actually be formations of lyotropic liquid crystal phases, when the phase is induced not by a change in temperature, but primarily by the presence of a solvent, that is, these are usually nanocrystals necessarily elongated, which due to the solvent can form an orientational order. Specially prepared vanadium oxide gives this. I may not know other examples. I know that there are several such examples, but to say that this is a polymer is not entirely correct.
Oleg Gromov, Institute of Biochemistry and Analytical Chemistry of the Russian Academy of Sciences: How then should we consider the liquid crystalline formations discovered by Chukhrov and others in the 50s?
Alexey Bobrovsky: I am not aware, unfortunately, this area is far from me. As far as I know, it seems to me that it is certainly impossible to talk specifically about the liquid crystalline state, because the word “liquid,” to be honest, is not applicable to polymers that are in a glassy state. It is incorrect to say that this is a liquid crystalline phase; it is correct to say “frozen liquid crystalline phase”. Probably, similarity, degenerate order, when there is no three-dimensional order, but there is a two-dimensional order, is probably a general phenomenon, and if you look, you can find many places. If you send links to such works to my e-mail, I will be very grateful.
Boris Dolgin: It’s very good when we manage to become another platform where scientists of different specialties can maintain contact.
Alexey Bobrovsky: It's great
Voice from the audience: Another amateurish question. You said that photochromic liquid crystal polymers have a relatively low response rate to changes in the environment. What is their approximate speed?
Alexey Bobrovsky: We are talking about response within minutes. In the case of strong light exposure of very thin films, people achieve a second response, but so far this is all slow. There is such a problem. There are effects that are related to something else (I didn’t talk about this): we have a polymer film, and there are photochromic fragments in it, and we can be exposed to polarized light of sufficient intensity, and this light can cause rotational diffusion, that is, the rotation of these molecules perpendicular to the plane of polarization - there is such an effect, it was initially discovered a long time ago, now it is also being studied, and I am also doing this. With a sufficiently high light intensity, effects can be observed within milliseconds, but usually this is not associated with a change in the geometry of the film, it is internally, first of all, the optical properties change.
Alexey Bobrovsky: There was an attempt to make material for recording information, and there were such developments, but, as far as I know, such materials cannot compete with existing magnetic recording and other inorganic materials, so somehow interest died out in this direction, but this does not mean that it will not resume again.
Boris Dolgin: The emergence of, say, new requirements due to something.
Alexey Bobrovsky: The utilitarian side of the matter doesn’t interest me too much.
Boris Dolgin: My question is partly related to it, but not about how it can be used, it is a bit organizationally utilitarian. In the area in which you work at your department and so on, as we said, you have joint projects, orders from some business structures, and so on. How is interaction generally structured in this area: the actual research scientist, relatively speaking, an inventor/engineer or inventor, and then an engineer, maybe different subjects, then, relatively speaking, some kind of entrepreneur who understands what to do with it, maybe, but this is unlikely, an investor who is ready to give money to an entrepreneur so that he can implement this, as they say now, innovative project? How is this chain structured in your environment to the extent that you somehow came into contact with it?
Alexey Bobrovsky: There is no such chain yet, and whether there will be one is unknown. In principle, the ideal form of funding is the same as conventional basic science. If we take the Russian Foundation for Basic Research and all that as a basis, which has been discussed many times, because personally I would not want to do something so applied, an order.
Boris Dolgin: That’s why I’m talking about different subjects and in no case am I saying that a scientist must be an engineer, an entrepreneur, and so on. I’m talking about different subjects, about how interaction can be set up, how interaction may already be working.
Alexey Bobrovsky: We have various offers from outside, but these are mainly companies from Taiwan, Korea, and Asia, for various types of work related to the use of liquid crystal polymers for various display applications. We had a joint project with Philips, Merck and others, but this is within the framework of a joint project - we are doing part of some research work, and such an intellectual output or output in the form of polymer samples either has a continuation or does not, but most often ends with an exchange of opinions, some kind of scientific development, but this has not yet reached any application. Seriously - it’s impossible to say.
Boris Dolgin: You are given an order for some kind of research, the development of some option, some idea.
Alexey Bobrovsky: In general, yes, this happens, but I don’t like this form of work (my personal feeling). Whatever came into my head, I do it to the best of my ability, and not because someone said: “Make such and such a film with such properties.” I'm not interested.
Boris Dolgin: Imagine a person who is interested in this. How could he, he, who is interested in refining your general scientific ideas that you received from your altruistic, strictly scientific interest, how could he interact with you in a way that would be truly interesting to both of you? What is this organizational chart?
Alexey Bobrovsky: I find it difficult to answer.
Boris Dolgin: General seminars? What could this be? There are no such attempts - some engineers?..
Alexey Bobrovsky: Within the framework of a joint project, everything can be realized. Some kind of interaction is quite possible, but I probably didn’t quite understand the question, what’s the problem?
Boris Dolgin: So far the problem is the lack of interaction between different types of structures. It puts pressure on you as a scientist, or it puts pressure on you to do things that you might not want to do. This is the problem.
Alexey Bobrovsky: This is a problem of colossal underfunding
Boris Dolgin: Imagine that there will be additional funding, but this will not eliminate the need for technical development. How can you move from you to technology in a way that satisfies you?
Alexey Bobrovsky: The fact is that modern science is quite open, and what I do, I publish - and the sooner the better.
Boris Dolgin: So you are ready to share the results, hoping that those who have taste can take advantage of it?
Alexey Bobrovsky: If someone reads my article and has some idea, I will be only grateful. If concrete developments come out of this publication, there will be patents, money, for God’s sake. In this form, I would be happy, but, unfortunately, in reality it turns out that everything exists in parallel, there is no such way out. The history of science shows that there is often a delay in specific application after some fundamental discovery - large or small.
Boris Dolgin: Or after some request arises.
Alexey Bobrovsky: Or so.
Lev Moskovkin: I have a slightly provocative question. The topic that Boris raised is very important. Is there any influence of a certain fashion here (this was heard at one of the lectures on sociology)? You said that working with liquid crystals is not fashionable now. This does not mean that since they are not engaged in them, then they are not needed, maybe this interest will return, and most importantly...
Boris Dolgin: That is, Lev returns us to the question of the mechanisms of fashion in science as in a certain scientific community.
Lev Moskovkin: In fact, Tchaikovsky also spoke about this; fashion there is extremely strong in all sciences. Second question: I know well how authorities in science were chosen who knew how to generalize. You can publish your materials as much as you like, I personally never come across them, for me this is a whole layer that I simply did not know. Summarize in such a way as to understand the value of this for understanding the same life, for understanding what else we can do. Thank you.
Boris Dolgin: I didn’t understand the second question, but let’s deal with the first one for now - about fashion in science. What is the mechanism why this is not fashionable now, is there any danger in this?
Alexey Bobrovsky: I don’t see any danger. It is clear that issues related to financing are important, but, nevertheless, it seems to me that in many ways science now rests on specific people who have specific personal interests, interest in this or that issue. It is clear that conditions dictate some restrictions, however, the activity of specific people leads to the fact that a certain area develops, as everything develops. Despite the fact that much is said about the fact that science has become collective. Indeed, now there are large projects, sometimes quite successful, but, nevertheless, the role of the individual in the history of science is enormous even now. Personal likes and interests play a significant role. It is clear that, as in the case of liquid crystals, such a development in electronics served as a great impetus for the development of liquid crystal research, when they realized that liquid crystals could be used and make money from it, naturally, a lot of money went into research. It is clear that such a connection...
Boris Dolgin: Feedback from business and science.
Alexey Bobrovsky: ...this is one of the features of modern science, when an order comes from people who earn money and produce a product - and then the research is funded, and, accordingly, there is a shift in emphasis from what is interesting to what is profitable. This has its pros and cons, but that's how it is. Indeed, now interest in liquid crystals has gradually dried up, because everything that could be extracted is already being produced, and everything remains to be improved. I don’t know, I’ve never seriously thought about it, nevertheless, there are various kinds of display applications, in optoelectronics, applications of liquid crystals (people are working on this), as sensors, to the point that work is underway on the possibility of using liquid crystals as a biological sensor molecules. So, in general, I think that interest simply will not dry up, in addition, a large wave of research is associated with the fact that money began to be given for nano. In principle, despite the fact that it is such a popular fashion to insert nanoparticles into liquid crystals, there is a large number of works, but among them there are good interesting works related to this topic, that is, what happens to nanoobjects when they enter a liquid crystalline medium what effects appear. I think that development is possible in terms of obtaining all sorts of different complex devices, which is associated with the emergence of metamaterials that have very interesting optical properties - these are unusual structures that are made in various ways in combination with liquid crystals, the emergence of new optical effects and new applications is possible . I am currently reviewing articles in the journal Liquid Crystals, and their level is falling, and the number of good articles is decreasing, but this does not mean that everything is bad, and the science of liquid crystals will not die, because it is a very interesting object. The drop in interest doesn't look like a disaster to me.
Boris Dolgin: Here we quietly move on to the second question asked to us by Leo. If some fundamentally new theory is born on the basis of the existing one, promising something plus for liquid crystals, apparently, interest will immediately increase.
Alexey Bobrovsky: It is possible that this will happen.
Boris Dolgin: As far as I understand the question, this is what we are talking about: there are intrascientific texts that gradually change something in understanding, there are innovative texts that change radically, but at the same time a kind of interface between specialists and society, perhaps consisting of the same scientists , but from other areas, there are some generalizing works that explain to us, as if soldering these pieces into some kind of general picture. As I understand it, Lev spoke to us about this, asking how it is chosen, and who writes these generalizing works?
Alexey Bobrovsky: There is such a concept - scientific journalism, which is not very developed in our country, but it exists all over the world, and I can imagine how well it is developed there, and, nevertheless, it also exists here. The current public lecture also indicates this
Boris Dolgin: It cannot be said that someone is deliberately closing the scope of work.
Alexey Bobrovsky: No, no one is hiding anything, on the contrary, all normal scientists are trying their best to show the world what they have done: as quickly as possible and as accessible as possible to the best of their abilities. It is clear that someone can tell a good story, and someone can tell a bad story, but that’s what science journalists are for, who can serve as a transmitter of information from scientists to society.
Boris Dolgin: Even in Soviet times, popular science literature existed, and there was also a special genre - scientific fiction, partly the collections “Paths into the Unknown” in the early 60s, books in the “Eureka” series, one of the first post-war pioneers was Daniil Danin , who wrote mainly about physics. Another question is that there are still scientists who write some kind of generalizing works, popularizing something for someone, but it’s unlikely that anyone chooses who will write and who to read or not to read. The aforementioned Tchaikovsky writes something, someone likes it.
Alexey Bobrovsky: The problem, I think, is the following. The fact is that in our country there are now catastrophically few normal scientists, and the state of science itself is worse than ever. If we talk about liquid crystals and liquid crystal polymers, then these are isolated laboratories that are already dying. It is clear that in the 90s there was some kind of collapse and nightmare, but, in general, we can say that there is no science about liquid crystals in Russia. I mean - the scientific community, it turns out that I more often communicate with people who work abroad, read articles and all that, but there are practically no articles coming from us. The problem is that we do not have science, and not that there are no generalizing works in this science. You can generalize what is happening in the West - this is also wonderful, but there is no basis, no important link, there are no scientists.
Lev Moskovkin: I'll clarify, although in principle everything is correct. The fact is that we are always revolving around the topic of the last lecture. The competition in science between scientists is so strong that I am absolutely flattered to have seen it with my own eyes, and I agree that every scientist strives to show the world his achievements. This is available only to someone who is a recognized authority, like Timofeev-Resovsky. This was done in Soviet times - it is known how - and here there is an effect, an example that may explain a lot - the effect of the green notebook, which was published who knows where, and no one can remember what this ordinary conference was called, because no a journal now accredited by the Higher Attestation Commission, an academic journal, would not accept such novelty in principle, but it gave birth to a new science, it turned into the science of genetics, into the understanding of life, and this, in general, is now already known. This was in Soviet times with support from above - Timofeev-Resovsky was supported at the plenum of the CPSU Central Committee from the competition of his colleagues, otherwise he would have been eaten.
Boris Dolgin: A situation where the state finished off a significant part of science: without support from other bases of the state it was impossible to escape.
Lev Moskovkin: There is an avalanche of data in genetics that there is no one to generalize, because no one trusts anyone and no one recognizes the authority of others.
Boris Dolgin: Why?! We had geneticists speak, who were listened to by other geneticists, and they discussed with pleasure.
Alexey Bobrovsky: I don’t know what happens in genetics, but in the science that I do, the situation is absolutely the opposite. People who get a new interesting result immediately try to publish it as quickly as possible.
Boris Dolgin: At least from the interests of competition - to stake out a place.
Alexey Bobrovsky: Yes. It is clear that they may not write down some details of the methods and so on, but usually, if you write an e-mail and ask how you did it there, it’s just very interesting, it all opens up completely - and...
Boris Dolgin: According to your observations, science is becoming more open.
Alexey Bobrovsky: At least I live in the era of open science, and that's good.
Boris Dolgin: Thank you. When molecular biologists spoke to us, they usually referred us to quite open databases and so on, and recommended that we contact them.
Alexey Bobrovsky: In physics there is the same thing, there is an archive where people can post a raw (controversial) version of an article even before going through a review, but here there is rather a struggle for the speed of publication, the faster those have priority. I don't see any closure. It is clear that this has nothing to do with the closed military and others, I am talking about science.
Boris Dolgin: Thank you. More questions?
Voice from the audience: I don't have a question, but a suggestion, an idea. I think this theme of crystallization pictures has great potential for teaching science to children and young people in schools. Maybe it makes sense to create one electronic lesson, designed for 45 minutes, and distribute it to secondary schools? Now there are electronic boards, which many do not use; schools have been ordered to have them. I think it would be nice to show these pictures to children for 45 minutes, and then, at the end, explain how it’s all done. It seems to me that it would be interesting to propose such a topic, somehow finance it.
Alexey Bobrovsky: I'm ready to help if anything happens. Provide, write what you need.
Boris Dolgin: Amazing. This is how generalizations are formed, this is how it is ordered. Fine. Thanks a lot. Any other creative questions? Maybe someone was missed, we don’t see, in my opinion, we basically discussed it.
Boris Dolgin: There are scientists, there is no science.
Boris Dolgin: That is, is it a necessary or necessary and sufficient condition?
Alexey Bobrovsky: Yes, the damage is irreversible, time has been lost, this is completely obvious, and, of course, it sounds: “How is it that there is no science in Russia?! How come? This cannot be, there is science, there are scientists, there are articles.” First of all, on a level level, I read scientific journals every day. It is very rare to come across articles by Russian authors, made in Russia, on liquid crystals or polymers. This is because either nothing happens, or everything happens at such a low level that people are not able to publish it in a normal scientific journal; naturally, no one knows them. This is an absolutely terrible situation.
Alexey Bobrovsky: More and more.
Boris Dolgin: That is, the problem is not with the authors, the problem is with science.
Alexey Bobrovsky: Yes, that is, there is, of course, no perfect, well-functioning structure or at least somehow working under the name “Science” in Russia. Fortunately, there is an openness of laboratories that work more or less at a normal level and are involved in the general scientific process of international science - this is the development of communication capabilities via the Internet, in other ways, the openness of borders allows you not to feel separated from the global scientific process, but what is happening within the country so, naturally, there is not enough money, and if you increase funding, it is unlikely to change anything, because in parallel with increasing funding, it is necessary to be able to examine those people to whom this money is given. You can give money, someone will steal it, spend it on who knows what, but the situation will not change in any way.
Boris Dolgin: Strictly speaking, we have a chicken and egg problem. On the one hand, we will not create science without funding, on the other hand, with funding, but without the scientific community, which will provide a market for expertise and ensure normal reputations, we will not be able to give this money in a way that will help science.
Alexey Bobrovsky: In other words, it is necessary to attract international expertise and assessment from strong scientists, regardless of their country of location. Naturally, it is necessary to switch to English the certification cases related to the defense of candidate and doctoral theses; At least abstracts must be in English. This is absolutely obvious, and there will be some movement in this direction, maybe it will somehow change for the better, and so - if you give everyone money... naturally, strong scientists who will get more money - they, of course, will work more efficiently , but most of the money will disappear to no one knows where. This is my opinion.
Boris Dolgin: Please tell me, you are a young scientist, but you are already a doctor of science, and young people come to you in a different sense, students, younger scientists. Are there those who are coming for you?
Alexey Bobrovsky: I work at the University, and willy-nilly, sometimes I want it, sometimes I don’t want it, I supervise coursework, diploma and postgraduate work.
Boris Dolgin: Are there future scientists among them?
Alexey Bobrovsky: Has already. There are quite successfully working people whom I have supervised, for example, who are postdocs or heads of scientific groups; naturally, we are talking only about abroad. Those whom I led and they remained in Russia, they do not work in science, because they need to feed their family and live normally.
Boris Dolgin: Thank you, that is, finances.
Alexey Bobrovsky: Naturally, financing and salaries do not stand up to criticism.
Boris Dolgin: This is still private...
Alexey Bobrovsky: There is no secret in this. The rate of a senior researcher with a candidate's minimum at the University is fifteen thousand rubles a month. Everything else depends on the activity of the scientist: if he is able to have international grants, projects, then he gets more, but he can count on fifteen thousand rubles a month.
Boris Dolgin: What about a doctorate?
Alexey Bobrovsky: They haven’t set me yet, I still don’t know exactly how much they will give, plus four thousand more will be added.
Boris Dolgin: The grants mentioned are quite an important thing. Only today we have published news sent by an interesting researcher, but when the question of funding was asked, she spoke, in particular, about the importance of this area, and again, not to mention our publications, Minister Fursenko says that scientific supervisors should grants to finance their graduate students and thus financially motivate them.
Alexey Bobrovsky: No, this is how it usually happens in a good scientific group, if a person, like Valery Petrovich Shibaev, head of the laboratory in which I work, has a well-deserved name in the scientific world, there is an opportunity for grants, projects. More often than not, I don’t find myself at a “naked” rate of fifteen thousand, there are always some projects, but not everyone can, this is not a general rule, which is why everyone leaves.
Boris Dolgin: That is, the leader must have a sufficiently high international authority and, moreover, be in the stream.
Alexey Bobrovsky: Yes, most often. I think I was lucky in many ways. The element of joining a strong scientific group worked in a positive way.
Boris Dolgin: Here we see the feedback of the good old science, that this most powerful scientific group arose, due to which you were able to realize your trajectory. Yes, this is very interesting, thank you. I have the last word.
Voice from the audience: I don’t pretend to have the last word. I would like to note that what you are talking about is absolutely understandable, and do not take it as a sport. I want to note that in Alexey Savvateev’s lecture it was said that there is no science at all in America. His point of view is just as convincingly argued as yours. On the other hand, in Russia science developed especially rapidly when science did not pay at all, but was actively stolen, and such things happened.
Boris Dolgin: Are we talking about the end of the 19th - beginning of the 20th centuries?
Boris Dolgin: In Germany?
Boris Dolgin: And when his scientific research more actively developed...
Voice from the audience: In Russia, not him, but in Russia in general, science developed most effectively when they did not pay. There is such a phenomenon. I can justify this, this is not a point of view, Boris, this is a fact. I also want to tell you quite responsibly - this is no longer a fact, but a conclusion - that your hopes that international expertise and the English language will help you are in vain, because, working in the Duma, I see fierce competition for rights and lobbying in The Duma of unilateral copyright laws towards America. They all attribute a huge percentage of intellectual property, they are not at all interested in ensuring that our weapons are not copied there, they do it themselves.
Boris Dolgin: I see, the problem...
Alexey Bobrovsky: Weapons and science are parallel things.
Voice from the audience: The last example: the fact is that when Zhenya Ananyev, he and I studied together at the Faculty of Biology, discovered mobile elements in the Drosophila genome, recognition came only after publication in the journal “Chromosomes”, but Khisin’s authority broke through this publication, because the review was like this: “in your dark Russia they don’t know how to replicate DNA.” Thank you.
Boris Dolgin: Ideas about the level of scientific research in a particular country in the absence of a rigid, clear system for reviewing articles, when general ideas are used, is a problem.
Alexey Bobrovsky: Regarding the English language, everything is very simple - it is an international scientific language. Any scientist involved in science, for example in Germany, a German publishes almost all of his articles in English. By the way, many dissertations are defended in English in Germany, not to mention Denmark and Holland, if only because there are many foreigners there. Science is international. Historically, the language of science is English.
Boris Dolgin: It just happened recently that the language of science used to be German.
Alexey Bobrovsky: Relatively recently, but, nevertheless, now it is so, so the transition to English was obvious, at least at the level of abstracts and certification things, so that normal Western scientists could read these abstracts, give feedback, evaluate, in order to get out of our swamp, otherwise it will all completely sink into the unknown and what will remain is a complete profanation. It’s already happening in many ways, but we must somehow try to get out of this swamp.
Boris Dolgin: Open the windows to prevent odors.
Alexey Bobrovsky: At least start ventilating.
Boris Dolgin: Fine. Thank you. This is an optimistic recipe. In fact, your trajectory inspires optimism, despite all the pessimism.
Alexey Bobrovsky: We again deviated from the fact that the main idea of the lecture is to demonstrate to you how beautiful and interesting liquid crystals are. I hope that everything I have said will arouse some interest. Now you can find a lot of information about liquid crystals, this is the first thing. And secondly, regardless of any conditions, scientists will always exist, nothing can stop scientific progress, this also inspires optimism, and history shows that there are always people who move science forward, for whom science is above all.
In the cycles “Public lectures “Polit.ru” and “Public lectures “Polit.ua”” the following speakers were performed:
- Leonard Polishchuk. Why did large animals go extinct in the late Pleistocene? Answer from the perspective of macroecology
- Miroslav Marinovich. Spiritual training of the Gulag
- Kirill Eskov. Evolution and autocatalysis
- Mikhail Sokolov. How scientific productivity is managed. Experience from Great Britain, Germany, Russia, USA and France
- Oleg Ustenko. The story of an unfinished crisis
- Grigory Sapov. Capitalist manifesto. The life and fate of L. von Mises's book "Human Activity"
- Alexander Irvanets. So that's what you are, uncle writer!
- Vladimir Katanaev. Modern approaches to the development of drugs against cancer
- Vakhtang Kipiani. Periodical samizdat in Ukraine. 1965-1991
- Vitaly Naishul. The adoption of culture by the church
- Nikolai Kaverin. Influenza pandemics in human history
- Alexander Filonenko. Theology at the University: a comeback?
- Alexey Kondrashev. Human evolutionary biology and health
- Sergei Gradirovsky. Modern demographic challenges
- Alexander Kislov. Climate in the past, present and future
- Alexander Auzan, Alexander Paskhaver. Economics: social restrictions or social reserves
- Konstantin Popadin. Love and harmful mutations or why does a peacock need a long tail?
- Andrey Ostalsky. Challenges and threats to freedom of speech in the modern world
- Leonid Ponomarev. How much energy does a person need?
- Georges Nivat. Translating the dark: ways of communication between cultures
- Vladimir Gelman. Subnational authoritarianism in modern Russia
- Vyacheslav Likhachev. Fear and Loathing in Ukraine
- Evgeny Gontmakher. Modernization of Russia: position of INSOR
- Donald Boudreau. Antimonopoly policy in the service of private interests
- Sergey Enikolopov. Psychology of violence
- Vladimir Kulik. Language policy of Ukraine: actions of the authorities, opinions of citizens
- Mikhail Blinkin. Transport in a city convenient for life
- Alexey Lidov, Gleb Ivakin. Sacred space of ancient Kyiv
- Alexey Savvateev. Where is economics going (and leading us)?
- Andrey Portnov. Historian. Citizen. State. Nation building experience
- Pavel Plechov. Volcanoes and volcanology
- Natalia Vysotskaya. Contemporary US literature in the context of cultural pluralism
- Discussion with Alexander Auzan. What is modernization in Russian?
- Andrey Portnov. Exercises with history in Ukrainian: results and prospects
- Alexey Lidov. Icon and iconic in sacred space
- Efim Rachevsky. School as a social elevator
- Alexandra Gnatyuk. Architects of Polish-Ukrainian mutual understanding of the interwar period (1918-1939)
- Vladimir Zakharov. Extreme waves in nature and in the laboratory
- Sergey Neklyudov. Literature as tradition
- Yakov Gilinsky. On the other side of the ban: the view of a criminologist
- Daniil Alexandrov. Middle strata in transit post-Soviet societies
- Tatiana Nefedova, Alexander Nikulin. Rural Russia: spatial compression and social polarization
- Alexander Zinchenko. Buttons from Kharkov. Everything we don’t remember about Ukrainian Katyn
- Alexander Markov. Evolutionary roots of good and evil: bacteria, ants, humans
- Mikhail Favorov. Vaccines, vaccination and their role in public health
- Vasily Zagnitko. Volcanic and tectonic activity of the Earth: causes, consequences, prospects
- Konstantin Sonin. Economics of the financial crisis. Two years later
- Konstantin Sigov. Who is looking for the truth? "European Dictionary of Philosophies"?
- Mykola Ryabchuk. Ukrainian post-communist transformation
- Mikhail Gelfand. Bioinformatics: molecular biology between the test tube and the computer
- Konstantin Severinov. Heredity in bacteria: from Lamarck to Darwin and back
- Mikhail Chernysh, Elena Danilova. People in Shanghai and St. Petersburg: an era of great change
- Maria Yudkevich. Where you were born is where you come in handy: university personnel policy
- Nikolay Andreev. Mathematical studies - a new form of tradition
- Dmitry Bak. "Modern" Russian literature: change of canon
- Sergey Popov. Hypotheses in astrophysics: why is dark matter better than UFOs?
- Vadim Skuratovsky. Kiev literary environment of the 60s - 70s of the last century
- Vladimir Dvorkin. Strategic weapons of Russia and America: problems of reduction
- Alexey Lidov. Byzantine myth and European identity
- Natalya Yakovenko. The concept of a new textbook of Ukrainian history
- Andrey Lankov. Modernization in East Asia, 1945-2010.
- Sergey Sluch. Why did Stalin need a non-aggression pact with Hitler?
- Guzel Ulumbekova. Lessons from Russian healthcare reforms
- Andrey Ryabov. Intermediate results and some features of post-Soviet transformations
- Vladimir Chetvernin. Modern legal theory of libertarianism
- Nikolai Dronin. Global climate change and the Kyoto Protocol: results of the decade
- Yuri Pivovarov. Historical roots of Russian political culture
- Yuri Pivovarov. The evolution of Russian political culture
- Pavel Pechenkin. Documentary Film as a Humanitarian Technology
- Vadim Radaev. Revolution in trade: impact on life and consumption
- Alec Epstein. Why doesn't someone else's pain hurt? Memory and oblivion in Israel and Russia
- Tatiana Chernigovskaya. How do we think? Multilingualism and brain cybernetics
- Sergey Aleksashenko. Year of crisis: what happened? what is done? what to expect?
- Vladimir Pastukhov. The force of mutual repulsion: Russia and Ukraine - two versions of the same transformation
- Alexander Yuryev. Psychology of human capital in Russia
- Andrey Zorin. Humanities education in three national educational systems
- Vladimir Plungyan. Why modern linguistics should be corpus linguistics
- Nikita Petrov. The criminal nature of the Stalinist regime: legal grounds
- Andrey Zubov. Eastern European and post-Soviet paths to a return to pluralistic statehood
- Victor Vakhshtain. The End of Sociology: Perspectives for the Sociology of Science
- Evgeniy Onishchenko. Competitive support for science: how it happens in Russia
- Nikolai Petrov. Russian political mechanics and crisis
- Alexander Auzan. The Social Contract: A View from 2009
- Sergey Guriev. How the crisis will change the world economy and economic science
- Alexander Aseev. Academic towns as centers of science, education and innovation in modern Russia
Ministry of Education and Science of the Russian Federation
Kazan (Volga region) Federal University
Chemical Institute named after. A. M. Butlerova
Department of Inorganic Chemistry
Abstract on the topic:
« Liquid crystal polymers"
Work completed
student of group 714
Khikmatova G.Z.
I checked the work
Ignatieva K.A
Kazan-2012.
Introduction…………………………………………………………………………………..3
1. Liquid crystals………………………………………………………......
1.1.History of discovery…………...……………………………………….……...4
1.2. Types of crystalline phase………………...…………………….……....7
1.3.Methods for studying liquid crystals………..………………….…………....11
2. Liquid crystal polymers……..…………………………………….13
2.1.Principles of molecular design of LC polymers............14
2.2. Main types of liquid crystal polymers……………….18
2.3.Structure and features of the properties of LC polymers..………………….….20
2.4.Areas of application….……………………………………………………..
2.4.1. Electric field control - the path to obtaining thin-film optical materials………………...………………………21
2.4.2.Cholesteric LC polymers - spectrozonal filters and circular polarizers…………………………………………………….23
2.4.3.LC polymers as controlled optically active media for recording information……………………………………………………….………………..24
2.4.4.Super-high-strength fibers and self-reinforced plastics………………………………………………………………………………….25
Used literature…………………………………………………….…28
Application.
Introduction.
The 80s in polymer science were marked by the birth and rapid development of a new field - the chemistry and physics of liquid crystalline polymers. This area, which united synthetic chemists, theoretical physicists, classical physical chemists, polymer scientists and technologists, has grown into an intensively developed new direction, which very quickly brought practical success in the creation of high-strength chemical fibers, and today attracts the attention of opticians and microelectronics specialists. But the main thing is not even this, but the fact that the liquid crystalline state in polymers and polymer systems, as it turned out, is not only extremely common - many hundreds of polymer liquid crystals have been described today - but also represents a stable equilibrium phase state of polymer bodies.
There is even some paradox in this. In 1988, the centenary was celebrated since the Austrian botanist F. Reinitzer described the first liquid crystalline substance, cholesteryl benzoate. In the 30s of the last century, the physics of low-molecular organic liquid crystals was developed, and in the 60s, millions of devices based on these crystals were already operating in the world. However, in the 60s and 70s, most polymer scientists could not imagine, for example, the existence of thermotropic liquid crystalline polymers of the cholesteric type, and in general such systems seemed to be exotic representatives of atypical macromolecular objects. And in fact, in recent years there has been a kind of “explosion” of information, and today no one is surprised by lyotropic and thermotropic liquid crystalline polymers, synthesized by the dozens every month.
In this work, I wanted to talk about when and how the liquid crystalline state was discovered, what is unique about liquid crystals compared to other objects, about liquid crystalline polymers and why they are interesting and wonderful.
Liquid crystals.
Most substances can exist in only three states of aggregation: solid, liquid and gaseous. By changing the temperature of a substance, it can be transferred sequentially from one state to another. Usually, the structure of solids was considered, which included crystals and amorphous bodies. A distinctive feature of crystals is the existence in them of long-range order and anisotropy of properties (except for crystals with a center of symmetry). In amorphous solids there is only short-range order and, as a consequence, they are isotropic. Short-range order also exists in a liquid, but the liquid has a very low viscosity, that is, it has fluidity.
In addition to the listed three states of matter, there is a fourth, called liquid crystal. It is intermediate between solid and liquid and is also called mesomorphic state. In this state there can be a very large number of organic substances with complex rod-shaped or disk-shaped molecules. In this case they are called liquid crystals or mesophase.
In this state, the substance has many features of a crystal, in particular, it is characterized by anisotropy of mechanical, electrical, magnetic and optical properties, and at the same time they have the properties of a liquid. Like liquids, they are fluid and take the shape of the container in which they are placed.
Based on their general properties, LCs can be divided into two large groups. Liquid crystals that form when temperature changes are called thermotropic. Liquid crystals that appear in solutions when their concentration changes are called lyotropic.
1.1. Liquid crystals were discovered in 1888. Austrian professor of botany F. Reinitzer while studying the new substance he synthesized, cholesteryl benzoate, which is an ester of cholesterol and benzoic acid.
He discovered that when heated to 145°, the crystalline phase (white powder) turns into a strange cloudy liquid, and when further heated to 179°, a transition is observed into an ordinary transparent liquid. He tried to purify this substance, since he was not sure that he had pure cholesteryl benzoate, but nevertheless these two phase transitions were reproduced. He sent a sample of this substance to his friend physicist Otto von Lehmann. Lehman studied ordinary crystals, including plastic crystals, which are soft to the touch and different from ordinary hard crystals. The main method of study was polarization optical microscopy - a microscope in which light passes through a polarizer, passes through a substance, and then through an analyzer - through a thin layer of substance. When crystals of a certain substance are placed between the polarizer and the analyzer, you can see textures - characteristic images for different crystalline substances - and thus study the optical properties of the crystals. It turned out that Otto von Lehmann helped him understand what was the reason for the intermediate state, the delusion. Otto von Lehmann was seriously convinced that all the properties of crystalline substances, crystals, depend solely on the shape of the molecules, that is, it does not matter how they are located in this crystal, the shape of the molecules is important. And in the case of liquid crystals, he was right - the shape of the molecules determines the ability to form a liquid crystalline phase (mainly the shape of the molecules). In 1888, Reinitzer wrote that there are crystals whose softness is such that they can be called liquid, then Lehmann wrote an article about flowing crystals, in fact, he coined the term liquid crystals. It was found that liquid crystals are very numerous and play an important role in biological processes. They are, for example, part of the brain, muscle tissue, nerves, and membranes. The term “liquid crystals”, based on the joint use of two, in a certain sense, opposite words – “liquid” and “crystalline”, has taken root well, although the term “mesophase”, introduced by the French physicist J. Friedel thirty years after the discovery of F. Reinitzer, derived from the Greek word "mesos" (intermediate), is apparently more correct. These substances represent an intermediate phase between crystalline and liquid; they arise during the melting of the solid phase and exist in a certain temperature range until, upon further heating, they turn into an ordinary liquid. An important historical episode: in the 20-30s, the Soviet physicist Fredericks studied the influence of various magnetic and electric fields on the optical properties of liquid crystals, and he discovered an important thing: the orientation of molecules in liquid crystals very easily changes under the influence of external fields, and these fields very weak and changes very quickly. Since the late 60s, a boom in the study of liquid crystal systems and liquid crystal phases began, and it is associated with the fact that they learned to use them. First, for information display systems in ordinary electronic digital watches, then in calculators, and with the advent of computer technology, it became clear that liquid crystals can be actively used for the manufacture of displays. Naturally, such a technological leap stimulated the study of liquid crystals from the point of view of fundamental science, but it should be noted how large a time gap there is between scientific discoveries related to liquid crystals. In fact, people were interested in them out of curiosity, there was no utilitarian interest, no one knew how to use them, and, moreover, in those years (20-30s) the theory of relativity was much more interesting. By the way, Fredericks was the popularizer of the theory of relativity in the Soviet Union, then he was repressed and died in the camps. In fact, 80 years passed after the discovery of liquid crystals until they learned to use them.
1.2. In the process of studying liquid crystals, the physical reasons for the fourth state of matter became clear. The main one is the non-spherical shape of molecules. The molecules in these substances are elongated in one direction or disk-shaped. Such molecules are located either along a certain line or in a selected plane. Three main types of crystalline phase are known: nematic(from the Greek word “nema” - thread), smectic(from the Greek word “smegma” - soap), cholesteric.
In nematic liquid crystals, the centers of mass of the molecules are located and move chaotically, as in a liquid, and the axes of the molecules are parallel. Thus, long-range order exists only with respect to the orientation of the molecules. In fact, nematic molecules perform not only translational movements, but also orientational vibrations. Therefore, there is no strict parallelism of the molecule, but there is a predominant average orientation (Fig. 7.19). The amplitude of orientation vibrations depends on temperature. As the temperature increases, greater deviations from parallelism in orientation occur, and at the point of phase transition the orientation of the molecules becomes chaotic. In this case, the liquid crystal turns into an ordinary liquid.
Of greatest interest for practical applications are substances that exist in the nematic mesophase at room temperature. At present, by preparing mixtures of various substances, nematics are obtained in the range from -20 to +80 degrees and even in a wider temperature range.
To characterize the orientational order in liquid crystals, two parameters are usually introduced: director and degree orientation order, also called the order parameter. The director is a unit vector I, the direction of which coincides with the direction of the average orientation of the long axes of the molecules. In nematic liquid crystals, the director coincides with the direction of the optical axis. The vector I phenomenologically characterizes the long-range order in the arrangement of molecules. It only determines the direction of orientation of the molecules, but does not provide any information about how perfect the ordering of the mesophase is. The measure of long-range orientational order is order parameter S, defined as follows:S=1/2(3 ² θ -1) (*), where θ – the angle between the axis of an individual molecule and the director of the liquid crystal. Averaging in (*) is carried out over the entire ensemble of molecules. The value S=1 corresponds to complete orientational order, i.e., an ideal liquid crystal, while S=0 means complete orientational disorder and corresponds to a nematic that has passed into an isotropic liquid.
Cholesteric liquid crystals They get their name from cholesterol because in most cases they are cholesterol esters. At the same time, in addition to cholesterol esters, a number of other substances also form the cholesteric mesophase. The molecules of all compounds that form a cholesteric contain an asymmetric carbon atom linked by four covalent bonds to different atoms or groups of atoms. Such molecules cannot be combined with themselves by simple superposition, just like the left and right hands. They're called chiral molecules (from the ancient Hebrew “heir” - hand).
Consisting of chiral molecules, cholesteric liquid crystals are similar in structure to nematics, but have a fundamental difference. It lies in the fact that, unlike a nematic, the uniform orientation of molecules in a cholesteric is energetically unfavorable. Chiral cholesteric molecules can be arranged parallel to each other in a thin monolayer, but in the adjacent layer the molecules must be rotated by a certain angle. The energy of such a state will be less than with a uniform orientation. In each subsequent layer, director I, lying in the plane of the layer, is again rotated through a small angle. Thus, a helical ordering of molecules is created in a cholesteric liquid crystal (Fig. 7.20). These spirals can be either left or right. The angle α between vectors I of neighboring layers is usually hundredths of a full revolution, i.e. α≈1®. In this case, the pitch of the cholesteric helix R is several thousand angstroms and is comparable to the wavelength of light in the visible part of the spectrum. Nematic liquid crystals can be considered as a special case of cholesteric liquid crystals with an infinitely large spiral pitch (P→∞). The helical ordering of molecules can be destroyed by an electric or magnetic field applied perpendicular to the axis of the helix.
Smectic liquid crystals are more ordered than nematic and cholesteric ones. They are like two-dimensional crystals. In addition to the orientational ordering of molecules, similar to the ordering in nematics, there is a partial ordering of the centers of mass of molecules. In this case, the director of each layer no longer lies in the plane of the layer, as in cholesterics, but forms a certain angle with it.
Depending on the nature of the ordering of molecules in the layers, smectic liquid crystals are divided into two groups: smectics with non-structural And smectics with structural layers.
IN smectic liquid crystals with nonstructural layers the centers of mass of molecules in the layers are located randomly, as in a liquid. Molecules can move quite freely along the layer, but their centers of mass are on the same plane. These planes, called smectic, are located at the same distance from each other, approximately equal to the length of the molecule. In Fig. 7.21 a shows the arrangement of molecules in such a smectic. For the smectic liquid crystal shown in the figure, the director I and the normal n to the plane coincide in direction. In other words, the long axes of the molecules are perpendicular to the smectic layers. Such liquid crystals are called smectics A. In fig. Figure 7.21b shows a smectic with non-structural layers, in which the director is not directed along the normal to the layer, but forms a certain angle with it. Liquid crystals with this arrangement of molecules are called smectics C. In a number of smectic liquid crystals there is a more complex ordering than in smectics A and C. An example is smectic F, the details of the ordering in which have not yet been fully studied.
IN smectics with structural layers we are already dealing with three-dimensional statistical ordering. Here, the centers of mass of molecules also lie in smectic layers, but form a two-dimensional lattice. However, unlike crystalline substances, the layers can freely slide relative to each other (as in other smectics!). Because of this free sliding of layers, all smectics have a soap-like feel to the touch. Hence their name (the Greek word “smegma” means soap). In a number of smectics, there is an ordering of the centers of mass of molecules the same as in smectics B, but the angle between director I and the normal n to the layers is non-zero. In this case, a pseudohexagonal monoclinic ordering is formed. Such smectics are called H smectics. There are also D smectics, which are close to a cubic structure with a body-centered lattice. Among the newly synthesized liquid crystals, there are those that cannot be classified as nematics, cholesterics and smectics. They are usually called exotic mesophases. These include, for example, the so-called disc-shaped liquid crystals, or discotics, which are being intensively studied.
1.3. Polarization microscopy is the first method for studying liquid crystals, that is, from the picture that is observed by a researcher in a polarizing microscope of crossed polarizers, one can judge what kind of mesophase, what type of liquid crystalline phase is formed. This is the characteristic picture for the nematic phase, the molecules of which form only an orientational order. This is what the smectic phase looks like. To give you an idea of the scale of all this, that is, it is much larger than the molecular scale: the width of the picture is hundreds of microns, that is, it is a macroscopic picture, much larger than the wavelength of visible light. And by analyzing such pictures, one can judge what kind of structure there is. Naturally, there are more accurate methods for determining the structure and some structural features of these mesophases - methods such as X-ray diffraction analysis, various types of spectroscopy - this allows us to understand how and why the molecules are packed in one way or another.
The cholesteric mesophase looks like this - one of the typical pictures.
When the temperature changes, a change in refraction is observed, so the colors change, we approach the transition - and a transition to an isotropic melt is observed, that is, everything has darkened, a dark picture is visible in the crossed polarizers.
liquid crystal polymers.
Liquid crystalline (LC) polymers are high-molecular compounds capable of transforming into the LC state under certain conditions (temperature, pressure, concentration in solution). The LC state of polymers is an equilibrium phase state, occupying an intermediate position between the amorphous and crystalline states, therefore it is also often called mesomorphic or mesophase (from the Greek mesos - intermediate). Characteristic features of the mesophase are the presence of orientational order in the arrangement of macromolecules (or their fragments) and anisotropy of physical properties in the absence of external influences. It is very important to emphasize that the LC phase is formed spontaneously, while the orientational order in the polymer can be easily induced by simply stretching the sample due to the high anisodiametry (asymmetry) of the macromolecules.
If polymers pass into the LC state or mesophase as a result of thermal action (heating or cooling), they are called thermotropic LC polymers; if the LC phase is formed when polymers are dissolved in certain solvents, they are called lyotropic LC polymers.
The first scientists who predicted the possibility of polymers forming a mesophase were V.A. Kargin and P.Flory.
Lecture 4/1
Subject. Physical states of polymers. Crystalline, amorphous and liquid crystalline polymers.
Distinguish aggregate and phase polymer states.
Polymers exist in two states of aggregation: hard And liquid The third state of aggregation - gaseous - does not exist for polymers due to the very high forces of intermolecular interaction caused by the large sizes of macromolecules.
IN hard In their state of aggregation, polymers are characterized by a high packing density of molecules, the presence of a certain shape and volume in bodies, and the ability to preserve them. The solid state is realized if the energy of intermolecular interaction exceeds the energy of thermal motion of molecules.
IN liquid in the state of aggregation, a high packing density of macromolecules is maintained. It is characterized by a certain volume, a certain shape. However, in this state the polymer has little resistance to maintaining this shape. That's why
the polymer takes the shape of the vessel.
They exist in two states of aggregation thermoplastic polymers that can melt. These include many linear and branched polymers - polyethylene, polypropylene, polyamides, polytetrafluoroethylene, etc.
Mesh polymers, as well as linear and branched polymers, which acquire a network structure when heated, exist only in solid state.
Depending on the degree of orderliness in the arrangement of macromolecules, polymers can be found in three phase states: crystalline, liquid crystal And amorphous.
Crystalline the condition is characterized long-range order in the arrangement of particles , i.e., on the order of hundreds and thousands of times greater than the size of the particles themselves.
liquid crystal state intermediate between crystalline and amorphous.
Amorphous the phase state is characterized short-range order in disposition particles , i.e., the order observed at distances comparable to the particle sizes.
Crystalline state of polymers
The crystalline state of polymers is characterized by the fact that the units of macromolecules form structures with three-dimensional long-range order. The size of these structures does not exceed several microns; they are usually called crystallites . Unlike low-molecular substances, polymers never completely crystallize; along with crystallites, amorphous regions (with a disordered structure) are preserved in them. Therefore, polymers in the crystalline state are called amorphous-crystalline or partially crystalline. The volumetric content of crystalline regions in a sample is called degree of crystallinity . It is quantified by various structure-sensitive methods. The most common of them are: density measurement, X-ray diffraction method, IR spectroscopy, NMR. For most polymers, the degree of crystallinity ranges from 20 to 80%, depending on the structure of macromolecules and crystallization conditions.
The morphology of crystallites and the type of their aggregation are determined crystallization method . So, during slow crystallization from dilute solutions in low-molecular solvents (concentration ~ 0.01%), crystallites are single, regularly faceted plates ( lamellas ), which are formed by folding the macromolecule “on itself” (Fig. 1).
Fig.1. Scheme of the structure of a lamellar crystal of folded macromolecules
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The thickness of the lamellae is usually 10-15 nm and is determined by the length of the fold, and their length and width can vary within wide limits. In this case, the axis of the macromolecule turns out to be perpendicular to the plane of the plate, and loops are formed on the surface of the plate (Fig. 2). Due to the presence of regions in which loops of folding macromolecules are collected, there is no complete crystalline order. The degree of crystallinity even for individual polymer single crystals is always less than 100% (for polyethylene, for example, 80-90%). The morphology of polymer single crystals reflects the symmetry of their crystal lattices, and the thickness strongly depends on the crystallization temperature and can vary several times.
Rice. 2. Folds of macromolecules in polyethylene crystallites svarka-info/com
The degenerate form of lamellar crystals are fibrillar crystals (fibrils), which are characterized by a large length-to-thickness ratio (Fig. 3). They develop under conditions that favor the preferential growth of one of the faces, for example, a high rate of solvent evaporation. The thickness of the fibrils is usually 10 -20 nm, and the length reaches many microns.
Rice. 3. b - microfibril; c - fibril. Scanning electronogram.. www. ntmdt. ru
Crystal plates represent the simplest form of crystallization from solution. An increase in the rate of crystallization or an increase in the concentration of the solution leads to the appearance of more complex structures: spiral formations of “twins” (two plates connected along a crystallographic plane), as well as various dendritic forms, including a large number of plates, helical terraces, “twins” and others. With further increase in concentration, spherulites . Spherulites are also formed during the crystallization of polymers from melts. This is the most common and common form of crystalline formations in polymers.
IN spherulites the lamellas diverge radially from common centers (Fig. 4). Electron microscopy studies show that the fibril of spherulites is composed of many lamellas stacked on top of each other and twisted around the radius of the spherulite. Spherulites with a diameter from several microns to several cm are observed. Three-dimensional spherulites appear in block samples, and two-dimensional, flat ones appear in thin films. It is assumed that in the crystallites of block samples, part of the macromolecule has a folded conformation, and the other part passes from crystallite to crystallite, connecting them with each other. These “passing” chains and folding regions form the amorphous part of the spherulites.
Rice. 4. Ring spherulites of polyethylene sebacate
The same polymer, depending on crystallization conditions, can form spherulites various types ( radial, annular ) (Fig. 5). At low degrees of supercooling, ring-type spherulites are usually formed; at high degrees, radial spherulites are formed. For example, polypropylene spherulites have different optical properties and even different melting points depending on the crystalline modification in which the polymer crystallizes. In turn, polypropylene spherulites with a monoclinic cell can be either positive or negative. A spherulite is called positive if its birefringence is greater than zero. If it is less than zero, then the spherulite is negative.
Fig.5. Types of spherulites: a - radial, b - annular.
Crystallization of the melt at a temperature close to the melting point (supercooling no more than 1˚C) occurs very slowly and leads to the formation of the most perfect crystal structures built from straightened chains. The mechanism of crystallization with straightened chains is rarely realized in practice. To do this, simultaneously with cooling the melt, it is necessary to apply large stresses.
Most polymers crystallize in the form of spherulites. However, in some cases, only groups of lamellar crystals are found in a block polymer. Structural formations intermediate between single crystals and spherulites were also found. Often these structures are faceted and large - up to tens of microns. It has not yet been clarified whether there is a certain number of intermediate structures or whether various morphological forms continuously transform into one another.
Amorphous state of polymers
Amorphous polymers do not have a crystalline structure. This state of polymers is characterized by:
· lack of three-dimensional long-range order in the arrangement of macromolecules,
· short-range order in the arrangement of units or segments of macromolecules, quickly disappearing as they move away from each other.
Polymer molecules seem to form “swarms”, the lifetime of which is very long due to the enormous viscosity of polymers and the large size of the molecules. Therefore, in some cases such swarms remain practically unchanged. IN amorphous are also in good condition polymer solutions And polymer jellies .
Amorphous polymers are single-phase and built from chain molecules collected in packs. Packs are structural elements and are capable of moving relative to neighboring elements. Some amorphous polymers can be constructed from globule Globules consist of one or many macromolecules rolled into spherical particles (Fig. 6). The possibility of folding macromolecules into a ball is determined by their high flexibility and the predominance of intramolecular interaction forces over intermolecular interaction forces.
Fig.6. The globular form of hemoglobin containing four molecules of the iron complex
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Amorphous polymers, depending on temperature, can be in three states that differ in the nature of thermal motion: glassy, highly elastic And viscous. The stage in which the polymer is located is determined by the change in its structure and the adhesion forces between the macromolecules of linear polymers.
At low temperatures amorphous polymers are in glassy condition. The molecular segments do not have mobility, and the polymer behaves like an ordinary solid in an amorphous state. In this state the material fragile . The transition from a highly elastic state to a glassy state with decreasing temperature is called vitrification , and the temperature of such a transition is glass transition temperature .
Highly elastic a condition characterized by the ability of a polymer to easily stretch and shrink, occurs at high enough temperatures when the energy of thermal motion becomes sufficient to cause movement of segments of the molecule, but not yet sufficient to set the molecule as a whole in motion. In a highly elastic state, polymers, under relatively small mechanical stresses, have very large elastic deformation . For example, rubbers can stretch almost 10 times.
IN viscous state, not only segments, but also the entire macromolecule can move. Polymers acquire the ability to flow, but, unlike ordinary liquids, their flow is always accompanied by the development of highly elastic deformation. The material in this state, under the influence of small forces, exhibits irreversible plastic deformation , which can be used for its technological processing.
With a linear structure of macromolecules, polymers in the amorphous state are elastic-viscous bodies, and when a strong spatial structure is formed, they are viscoelastic bodies.
Any external influence that affects the mobility of particles in amorphous bodies (changes in temperature, pressure) affects the physical properties (dielectric characteristics of the material, gas permeability).
Liquid crystalline state of polymers
Liquid crystals are unusual substances. They combine the properties inherent in liquids and solids, as reflected in the name. From liquids they took fluidity, that is, the ability to take the shape of the vessel into which they are poured. From solid crystalline bodies - anisotropy properties . The latter is explained by the structure of liquid crystals - the molecules in them are arranged not chaotically, but in an orderly manner. However, not as strict as in solid crystals
Not all compounds pass into the liquid crystalline state, but only those whose molecules have a significant anisometry (shape of sticks or disks). Depending on the packaging of molecules, they are distinguished three types of structures liquid crystals - smectic , nematic And cholesteric .
Smectics, perhaps closest to ordinary crystals. The molecules in them are packed in layers, and their centers of mass are fixed (Fig. 7). IN nematics On the contrary, the centers of mass of the molecules are located chaotically, but the axes of their molecules, usually rod-shaped, are parallel to each other (Fig. 8). In this case they are said to be characterized by orientational order.
The most complex structure of the third type of liquid crystals is cholesteric. For the formation of cholesterics, so-called chiral molecules are required, that is, incompatible with their mirror image.
Rice. 7. Schematic representation of a liquid crystal in the smectic phase
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Fig.9. Schematic illustration of cholesteric liquid crystal
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Other functional groups can be introduced into such a polymer chain, for example, photochromic light controlled groups, or electroactive groups oriented under the influence of an electric field.
Liquid crystals themselves are viscous liquids only within a narrow temperature range. Therefore, they have their special properties only in this temperature range. Liquid-crystalline polymers, unlike liquid crystals, retain both the structure and properties of the liquid-crystalline phase when cooled. That is, it is possible to fix a sensitive liquid crystal structure in a solid without losing, for example, its unique optical properties.
Cholesterics easily react to temperature. Some change color very quickly with a very small temperature change - you can create original ones from them. thermal imagers , or temperature indicators. For example, by irradiating the surface of such a material with a laser, one can study the distribution of the intensity density of its beam. Cholesteric polymer coatings can be used to test aircraft in a wind tunnel, as the temperature distribution will clearly indicate which places are more turbulent and which are laminar air flow around the aircraft.
One of the most interesting examples of the use of polymeric cholesterics is the preparation light-controlled films . If a monomer with a photochromic group is introduced into the polymer chain, the shape of which changes when it is exposed to light with a certain wavelength, then the helix pitch in the cholesteric structure can be changed. In other words, by irradiating a material with light, you can change its color. This property of the resulting material can be used to record and store color information, in holography And display technology .
However, the helix pitch can be changed not only by the action of light and temperature changes (as in thermal imagers), but also by the action of electric and magnetic fields. To do this, it is necessary to introduce electroactive or magnetically active groups. The impact of an electric or magnetic field leads to the orientation of the molecules of the liquid crystal and to distortion, and then to the complete unwinding of the cholesteric helix.
The study of liquid crystal polymers, which are much younger than low molecular weight liquid crystals, will open up many more unexplored aspects of their physicochemical behavior.
