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Schematic representation of macromolecules of different rigidity: (a) flexible chains; (b) rigid-rod LC polymers; (c) main-chain LC polymers with mesogenic groups; (d) side-chain LC polymers with mesogenic groups (comb-shaped LC polymers).
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... is well known that flexibility (or rigidity) of polymer chain is determined by a Kuhn segment length, l. Flexible polymers are characterized by the l values in the range 15-50 A ̊ (Figure 4(a)), whereas l values for rigid-chain macromolecules lie in the range 100-1000 A ̊ or even higher (Figure 4(b)). ...
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... is well known that flexibility (or rigidity) of polymer chain is determined by a Kuhn segment length, l. Flexible polymers are characterized by the l values in the range 15-50 A ̊ (Figure 4(a)), whereas l values for rigid-chain macromolecules lie in the range 100-1000 A ̊ or even higher (Figure 4(b)). ...
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... examples of such compounds are a-helical polypeptides, macromolecules of DNA, aromatic polyamides, a number of cellulose ethers, and some polyisocyanates. Macromolecules of such polymers can be approximated in the form of long rods (Figure 4(b)). ...
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... LC polymers belong to a relatively new class of LC compounds. More than three decades have already passed since the appearance of the first publications devoted to the synthesis and study of thermotropic LC polymers containing mesogenic groups in both main chains (main-chain LC polymers) (Figure 4(c)) and side branches (side-chain polymers) or comb- shaped LC polymers (Figure 4(d)). A great number of studies devoted exclusively to LC polymers, including dozens of mono- graphs, thematic collections of articles, encyclopedias, and review papers, have been published. ...
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... LC polymers belong to a relatively new class of LC compounds. More than three decades have already passed since the appearance of the first publications devoted to the synthesis and study of thermotropic LC polymers containing mesogenic groups in both main chains (main-chain LC polymers) (Figure 4(c)) and side branches (side-chain polymers) or comb- shaped LC polymers (Figure 4(d)). A great number of studies devoted exclusively to LC polymers, including dozens of mono- graphs, thematic collections of articles, encyclopedias, and review papers, have been published. ...
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... Further development of such studies resulted in the self-reinforced plastics based on LC polymers with main-chain mesogenic groups and laid a foundation for the use of comb-shaped LC polymers as new photoactive materials for optics, optoelectronics, photonics, holography, display technology, telecommunications systems, and other no-less important areas of modern engi- neering. 9,[16][17][18][19][20][35][36][37][38] Note that the LC polymers of the first type (Figures 4(b) and 4(c)) are usually classified as 'construction materials,' while the LC polymers of the second type are usually called 'functional materials' (Figure 4(d)). ...
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... Further development of such studies resulted in the self-reinforced plastics based on LC polymers with main-chain mesogenic groups and laid a foundation for the use of comb-shaped LC polymers as new photoactive materials for optics, optoelectronics, photonics, holography, display technology, telecommunications systems, and other no-less important areas of modern engi- neering. 9,[16][17][18][19][20][35][36][37][38] Note that the LC polymers of the first type (Figures 4(b) and 4(c)) are usually classified as 'construction materials,' while the LC polymers of the second type are usually called 'functional materials' (Figure 4(d)). ...
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... polymer systems differ in that the stability of the LC phase is influenced by the addition of a low-molecular-mass solvent. An important consequence of solvent addition is that LC phase can be obtained with rigid-rod polymers (Figure 4(b)) which would not otherwise show the mesophase at temperatures below that of thermal decomposition. In other words, lyotropic LC phase formation is a route to melting point reduction of rigid polymers. ...
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... specific structure of such macromolecules, characterized by both mobility of the side chains and their ordering ability, allowed one to use these polymers as self-organizing systems and convenient polymeric matrices for the creation of LC polymers that were called 'comb-shaped LC polymers.' Long aliphatic spacers chemically linked to mesogenic group (Figure 4(d)) provide sufficient autonomy to side branches for the formation of diverse types of LC phases. The first attempts to obtain LC polymers via the synthesis of polymer with mesogenic groups directly linked to the backbone (without spacer) failed 1-3 because of noticeable steric hindrances and conformation restrictions imposed by main chains on the packing of side mesogenic groups. ...
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... although LC polymers contain rather flexible main chains, they can form all three main types of LC structures (Section 2), namely the nematic structure, characterized only by the orientational order (Figure 14(a)); the smectic structure accompanied by development of the layered structure (Figures 14(a) and 14(b)); and finally, the so-called cholesteric helical structure, which appears when chiral moieties in the form of monomer units (red fragments in Figure 14(c)) exist in the macromolecules. ...
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... although LC polymers contain rather flexible main chains, they can form all three main types of LC structures (Section 2), namely the nematic structure, characterized only by the orientational order (Figure 14(a)); the smectic structure accompanied by development of the layered structure (Figures 14(a) and 14(b)); and finally, the so-called cholesteric helical structure, which appears when chiral moieties in the form of monomer units (red fragments in Figure 14(c)) exist in the macromolecules. ...
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... although LC polymers contain rather flexible main chains, they can form all three main types of LC structures (Section 2), namely the nematic structure, characterized only by the orientational order (Figure 14(a)); the smectic structure accompanied by development of the layered structure (Figures 14(a) and 14(b)); and finally, the so-called cholesteric helical structure, which appears when chiral moieties in the form of monomer units (red fragments in Figure 14(c)) exist in the macromolecules. ...
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... Authors of this work developed a new universal method that uses the photopatterning of LC polymer, which is accurately translated into a controlled, intricately wrinkled metal surface. Remarkably, the patterns have an oscillation in amplitude of the wrinkles (Figure 24). ...
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... of polymerizable liquid crystals is followed by photopolymerization and sputter coating of a gold layer, which induces compressive stress in the system. Heating the material above glass transition temperature releases stress through wrinkling; the wrinkles form perpendicular to the alignment director of the LC polymer network due to the lower elastic modulus in that direction ( Figure 24). Many applications for wrinkled surfaces have been described: preparation of superhydro-phobic surfaces, actuators, fabrication of patterned electrodes, optical focusing, etc. ...
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... PDLCs are prepared from mixtures of low-molecular-mass nematic liquid crystals which in the form of microdroplets (0.5-1 mm) are dispersed in polymer films, such as poly(vinyl alcohol), poly(vinyl acetate), and acrylic copolymers. Such compounds are usually used as sandwich cells, or polymer compositions with liquid crystals (or mixtures of reactive monomers with liquid crystals followed by their polymerizations) which are placed between conducting glasses or polymer films (Figure 40). An important feature of such cells is the proper selection of refractive indices of a matrix (polymer) (n p ) and a mixture of liquid crystals (n o ) so that the initial nontransparent mixture becomes optically transparent under application of an electric field. ...
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... of the smart PDLC windows are used today in the form of the self-adhesive laminate films for interior and exterior settings for privacy control (e.g., conference rooms, intensive-care-areas, bathroom/shower doors) as a temporary projection screen. One example of using the smart switchable interior panels is shown in Figure 41. ...
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... current use, laminating the liquid crystal mixture between two embossed plastic sheets is widely exploited. The cholesteric polymer films obtained by all these methods are widely Figure 41 The interior smart panels before (off) and after switching on. ...
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... for temperature-sensing applications. Figure 42 shows thermograph of a human hand. The red colour corresponds to about 30 1C, the blue color -32-331C. ...
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... Figure 43 shows how the CdSe/ZnS QDs containing trioctylphosphine oxide as 'edging' may be modified via interactions with mesogenic compounds and the terminal sulfhydryl groups. 20,138 Schematic representation of a model proposed for the organization of the mesogen-containing 'hybridic nanoparticles' within the LC polymers is shown in Figure 44. ...
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A look at the liquid crystal nematic scalar and tensorial order parameters as well as nematic director orientation in two and three dimension.
In the 1960s Jerry Ericksen made major contributions to the construction of the continuum theory of nematic liquid crystals. This paper gives a brief summary of his work and the consequent giant impact on the field.
Citations
... The concept of spacers was proposed, for the first time, in studies by Plate, Shibaev, and Freidzon in the middle of the 1970s. 1,[48][49][50] As early as 1976, Soviet scientists received a patent for the method of synthesizing cholesterol-containing combshaped LC polymers. 49 In 1977, Shibaev and Plate published their comprehensive review on thermotropic LC polymers, 1 in which they presented a detailed justification of the spacer concept, describing various principles of the preparation of LC comb-shaped polymers, and analyzed unsuccessful attempts of the synthesis of such systems. ...
... In this texture, the direction of the director is parallel to the plane of the layer, while the direction of the helix axis Z is perpendicular to this plate. This supramolecular helical structure is characterized by selective light reflection (SLR), which (see eqn [1]) reflects incident light as a common diffraction grating. The region of SLR usually lies in the range 300-10 5 nm (depending on the chemical nature and composition of LC copolymers) covering thus the UV-, visible-, and IR-spectral regions. ...
The article deals with the liquid crystalline (LC) polymers which belong to interdisciplinary science attracting the attention of wide range of researchers in the fields of polymer and material science, solid and soft matter physics, as well as nanotechnology and the electronics industry. In the short historical overview the main features of low-molecular-mass liquid crystals embracing their constitution molecular and supramolecular structures of these unique compounds are considered. A concept of the synthesis of main-chain and side-chain (comb-shaped) LC polymers containing the mesogenic groups and flexible spacers is discussed. The main attention focus on the design, synthesis, and study of photo-, electro- and thermo-optical properties of photochromic and chiral comb-shaped LC polymers, LC composites, LC block-copolymers forming nematic, smectic, and cholesteric mesophases. The last part of the review briefly covers some ionogenic and ionophoric LC polymers, LC dendrimers and LC elastomers, as well as polymer-dispersed liquid crystals, LC networks and fluorescent LC composites based on polyethylene. Particular emphasis are placed on the creation of new promising materials for colour data recording, holographic gratings, ‘command’ coatings, photo-responsive actuators, and sensors.
... The recent direction of research and development of LCPs is towards the molecular design of main chain LCPs in order to fulfill either functional characteristics or lower material costs. Although many approaches, such as tailoring the molecular structure with swivel structures, kinks, flexible bonds and lateral groups, have been extensively employed [7][8][9][10][11][12][13][14][15][16], studies on the relationship between liquid crystalline heterogeneity and the chain rigidity, persistence ratio and chemical structure, by means of both experiments and computational simulation, are very limited. ...
... The introduction of aliphatic spacers linking mesogenic groups has been one of many well received study subjects. The uses of aliphatic monomers has dramatically reduced T m and improved chain flexibility [8][9][10][11][12][13][14][15][16]. Common aliphatic moieties employed are alkyl and alkoxy units, -(CH 2 ) n -and -(OCH 2 CH 2 ) n -, with different flexible spacer lengths [11,[17][18][19][20][21]. ...
We have introduced a series of perfluoroalkyl dicarboxylic acids with different lengths of fluorinated aliphatic segments into the 2,6-acetoxynaphthoic acid (ANA) and acetoxy acetanilide (AAA) systems; and their effects on the evolution of liquid crystal texture and liquid crystallinity have been investigated. The perfluoroalkyl dicarboxylic acids are tetrafluorosuccinic acid (TFSA, n=2), hexafluoroglutaric acid (HFGA, n=3), perfluorosuberic acid (PFSUA, n=6) and perfluorosebacic acid (PFSEA, n=8). Computational results based on the ‘RIS’ Metropolis Monte Carlo method indicate that the ANA/AAA/perfluoroalkyl system may form thermotropic liquid crystalline polymers (LCPs) because the calculated persistence ratios are greater than 6.42. Computational results also predict that the systems containing even-numbered perfluoroalkyl acids have greater persistence length and molar stiffness than that containing odd-numbered acids. Experiments were carried out using the in situ thin film polymerization technique under a polarizing optical microscope. We observed that systems containing short aliphatic units (n=2, 3) tend to remain in the LC phase, while systems containing a long aliphatic spacer (n=8) tend to crystallize during the late stage of the polycondensation reaction. The liquid crystal domain formed in the early stage has a disclination strength S of +1. Ternary phase diagrams were plotted to show the relationship among monomer structure, composition, anisotropic and crystalline phases. FTIR results confirm the formation of LCPs.
... Only the presence of spacers between mesogenic groups and the main polymeric chain results in formation of liquid crystal mesophases. 31 It is also necessary to take into account the influence of the siloxane present in a spacer. The unique flexibility of the group -(CH 3 ) 2 Si-O-Si(CH 3 ) 2 -is known from the literature. ...
A systematic study of the influence of generation number on the phase behavior of LC dendrimers is presented. For this purpose, phase behaviors and structures of first to fifth generations of liquid crystalline (LC) carbosilane dendrimers with 8, 16, 32, 64, and 128 terminal cyanobiphenyl groups were investigated. Investigation of thermal behavior of the LC dendrimers by means of polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction experiments reveals smectic-type mesophases over a wide temperature region. It is shown that with increasing generation number the isotropization temperature increases whereas the enthalpy of this phase transition decreases. The strongest influence of spherical molecular architecture on the phase behavior of the LC dendrimers appears at high generations. In the case of LC dendrimer of the fifth generation, it leads to the formation of two levels of a structural organization. This dendrimer forms different supramolecular nanostructures of columnar type in addition to smectic-like arrangement of mesogenic groups. Possible structures of all mesophases formed are discussed.
... All of these questions are very important in connection with the possibility for creating LC materials with desirable as well as locallyregulated optical properties which could be easily and reversibly (or This article predominently deals with PLCs bearing mesogenic side groups chemically linked to the backbone via spacers (so called combshaped PLCs) [2 -41. These polymers have attracted increased interest due to their possible applications as electro-and photo-optical regulated media [3,4,8,11,13-1. 51. The LC nature of these compounds, due to the side mesogenic groups existence forming the mesophase, permits one to use external fields for their orientation and for controlling their structure in the LC state. ...
Effects of electric fields on monomer liquid crystals (MLCs) and polymer liquid crystals (PLCs) are analyzed, dealing separately with nematic and cholesteric PLCs. Electro-hydrodynamic instabilities affect the behavior of these systems. Thermooptical recording depends on the magnitude of the thermooptical effects. Information recording can be alternatively performed on the basis of photoorientation and the photoinduced birefringence. Capabilities and limitations of these techniques are pointed out.
... In recent years a number of books (1)(2)(3)(4)(5) and reviews (6)(7)(8)(9)(10)(11)(12)(13) have appeared in scientific literature related to thermotropic LCPs. ...
An attempt has been made to simulate a novel continuous ultrasonic process for devulcanising of ground rubber tyres. The model is based on a mechanism of rubber network breakup caused by cavitation, which is created by high intensity ultrasonic waves in the presence of pressure and heat. Theoretical results are obtained for the development of pressure, velocity, shear rate, and temperature during devulcanisation together with gel fraction and crosslink density of devulcanised rubber. Comparison of predicted and experimental data on gel fraction, crosslink density, and pressure indicates that the model describes experimental observation qualitatively only. Deficiencies of the present modelling are emphasised and some possible methods of improving the model are described, particularly with regard to the flow mechanism of ground rubber tyres in the die.
... This chapter deals with liquid-crystalline (LC) and amorphous polymers containing anisometric side chains chemically linked to the backbone via spacers. Such polymers, which are very often called comb-shaped polymers, have attracted much attention during the last few years as electro-and photo-optical regulated media [7][8][9][10][11][12][13][14][15][16][17][18][19]. ...
... Moreover, even more complex LC polymers containing meso genic groups in the main chains and in the side branches have been obtained as well as polymers consisting of macromolecules with alternating laterally bound rod-like and disk-like groups. The detailed consideration of molecular architecture and the concrete chemical formulas of such polymers are given in the literature [10,25,26]. The possibility, in principle, of synthesizing macromolecules consisting of any combination of mesogenic and nonmesogenic fragments opens up the richest possibility for the molecular construction of new polymeric LC compounds. ...
... 10. Comparison of some characteristics of low-molar-mass cholesteric (Chol) and smectic LC materials[89] as well as LC polymer, used for thermooptical recording[11,18] ...
Liquid crystalline polymers have been widely used in recent decades. Their application varies from electronic displays, via switches, sensors, waveguides, optical devices, and many more. Their exceptional abilities lie often in the possibility of arranging them alongside the lines of a magnetic or electric field. The chapter depicts some commercially successful liquid crystalline polymers, as well as developing scientific research concerning rigid and elastic liquid crystalline polymer networks, with emphasis put on the epoxy variant of those materials with the large amount of their possible applications. Thermal analysis is the crucial set of methods used in the characterization of liquid crystalline polymers, with the differential scanning calorimetry (DSC) as a leading tool enabling the study of the cure kinetics and the observation of the mesophase formation, the determination of the properties of synthesized polymer precursors, polymers themselves, and the influence of fillers on the composite matrix. Some more advanced methods, like temperature‐modulated differential scanning calorimetry (TMDSC), are also presented and discussed as a very useful additional possibility of unravelling some overlapping processes, which are impossible to clearly detect with the use of the original differential scanning calorimetry.
Leading international experts survey the recent significant theoretical and experimental developments in the synthesis, physico-chemical study and potential applications of electroresponsive and photooptical active polymers. Attention is focused on materials for information technique, optical data storage, optoelectronics and holography. Written by authors from the academic and industry, the book is intended for polymer scientists, engineers and technologists in polymer science. Interdisciplinary in nature it will be also of interest to students, researchers and practitioners in polymer science, photochemistry, materials science, optics and liquid crystals.
