Liquid Crystal Alignment Behavior Research Articles

Vertical Alignment of Liquid Crystal on Sustainable 2,4-Di-tert-butylphenoxymethyl-Substituted Polystyrene Films.

We synthesized sustainable 2,4-di-tert-butylphenoxymethyl-substituted polystyrenes (PDtBP#, # = 88, 68, 35, and 19, where # is molar percent contents of 2,4-di-tert-butylphenoxymethyl moiety), using post-polymerization modification reactions in order to study their liquid crystal (LC) alignment behaviors. In general, LC cells fabricated using polymer film with higher molar content of 2,4-di-tert-butylphenoxymethyl side groups showed vertical LC alignment behavior. LC alignment behavior in LC cell was related to the surface energy of the polymer alignment layer. For example, when the total surface energy value of the polymer layer was smaller than about 29.4 mJ/m2, vertical alignment behaviors were observed, generated by the nonpolar 2,4-di-tert-butylphenoxymethyl moiety with long and bulky carbon groups. Orientation stability was observed at 200 °C in the LC cells fabricated using PDtBP88 as the LC alignment layer. Therefore, as a natural compound modified polymer, PDtBP# can be used as a candidate LC alignment layer for environmentally friendly applications.

Effect of Position and Structure of the Terminal Moieties in the Side Group on the Liquid Crystal Alignment Behavior of Polystyrene Derivatives.

We synthesized a series of polystyrene derivatives containing various side groups, such as the 4-(tert-butyl)-phenoxymethyl, 3-(tert-butyl)-phenoxymethyl, 2-(tert-butyl)-phenoxymethyl, 4-cumyl-phenoxymethyl, and 4-trityl-phenoxymethyl groups, through a polymer modification reaction to examine the liquid crystal (LC) alignment of these derivatives. In general, the vertical LC alignment on polymer films can be affected by the position and structure of the terminal moiety of the polymer side group. For example, the LC cells fabricated with 4-(tert-butyl)-phenoxymethyl-substituted polystyrene having a tert-butyl moiety as a para-type attachment to the phenoxy groups of the polystyrene derivatives exhibited vertical LC alignment, whereas the LC cells prepared from 3-(tert-butyl)- and 2-(tert-butyl)-phenoxymethyl-substituted polystyrene films exhibited planar LC alignment. In addition, the LC cells fabricated from 4-cumyl- and 4-trityl-phenoxymethyl-substituted polystyrene films with additional phenyl rings in the side groups exhibited planar LC alignment, in contrast to the LC alignment of the (tert-butyl)-phenoxymethyl-substituted polystyrene series. The vertical LC orientation was well correlated with the surface energy of these polymer films. For example, vertical LC orientation, which mainly originates due to the nonpolar tertiary carbon moiety having bulky groups, was observed when the surface energy of the polymer was lower than 36.6 mJ/m2.

Alignment Layer of Liquid Crystal Using Plant-Based Isoeugenol-Substituted Polystyrene.

We synthesized a series of renewable and plant-based isoeugenol-substituted polystyrenes (PIEU#, # = 100, 80, 60, 40, and 20, where # is the molar percent content of isoeugenol moiety), using polymer modification reactions to study their liquid crystal (LC) alignment behavior. In general, the LC cells fabricated using polymer film with a higher molar content of isoeugenol side groups showed vertical LC alignment behavior. This alignment behavior was well related to the surface energy value of the polymer layer. For example, vertical alignments were observed when the polar surface energy value of the polymer was smaller than approximately 3.59 mJ/m2, generated by the nonpolar isoeugenol moiety with long and bulky carbon groups. Good alignment stability at 100 °C and under ultraviolet (UV) irradiation of 15 J/cm2 was observed for the LC cells fabricated using PIEU100 as a LC alignment layer. Therefore, renewable isoeugenol-based materials can be used to produce an eco-friendly vertical LC alignment system.

A novel thermoresponsive membrane as potential material for tissue engineering

ABSTRACT In this study, a thermoresponsive cholesteric liquid crystal (TCLC) was successfully fabricated from a binary mixture of cholesteryl nonanoate (CN) and cholesteryl oleyl carbonate (COC) at different ratios. Furthermore, blends of TCLC and polyurethane (PU) with different weight ratios were prepared by spin coating. Moreover, the mesomorphic temperature ranges of TCLC and TCLC/PU membranes were discussed, and their physicochemical properties were systematically studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) equipped with a heating stage. In addition, the interaction of cells with the TCLC/PU membranes was studied and correlated with the liquid crystal alignment behaviors on the blend films. The results revealed that the different weight ratios of CN and COC determined the liquid crystal properties of the membranes and that the presence of TCLC was essential for metabolizing MC3T3-E1 cells. The biophysical expression of cells on biocompatible blend membranes suggested that TCLC/PU membranes could be a new class of biologically relevant materials.

Vertical Liquid Crystal Alignment of Comb-Like Alkyl Hydroxybenzoate-Substituted Polystyrene

We investigated the liquid crystal (LC) alignment behaviors of butyl hydroxybenzoate-substituted polystyrene (PBHB#; # = 20, 40, 60, 80, and 100, where # indicates the molar fraction of butyl hydroxybenzoate in the side chain), methyl hydroxybenzoate-substituted polystyrene (PMHB100), and ethyl hydroxybenzoate-substituted polystyrene (PEHB100). Generally, LC cells made employing polymer films having longer alkyl groups in the side chain show vertical LC alignment. For instance, a LC cell fabricated with the PMHB100 film showed random planar LC alignment, while the LC cells made from the PEHB100 and PBHB100 films exhibited vertical LC alignment. Moreover, LC cells prepared from a polymer film having a higher molar content of butyl hydroxybenzoate in the side chain exhibited vertical LC alignment. The observed vertical LC alignment behaviors are closely related to the surface energy of these polymer films. For instance, vertical LC alignment was observed when the surface energy of the polymer film was less than ~43.86 mJ/m2, which could result from the nonpolar alkyl groups of the alkyl hydroxybenzoate moiety. The LC cell prepared from PBHB100 as the LC alignment layer showed good electro-optical characteristics such as voltage holding ratio, residual DC voltage, and alignment stability at 200 °C.

LC alignment behaviors on polystyrene blend alignment films

ABSTRACTWe prepared blend alignment film based on 4-ethylphenoxymethyl-substituted polystyrene (P4EP) and polystyrene (PS) for liquid crystal (LC) alignment. Stable and uniform LC cells having pretilt angles adjustable from 90o to 0o were obtained from these polystyrene blend films having weight contents of P4EP and PS of 1 and 100 weight %, respectively. The LC alignment behavior was well correlated with the wettability of the polymer films. These polystyrene blends having good solubility in many organic solvents and their films having low process temperature can be candidates for LC alignment layer in the flexible display. This study contributes to the latest efforts to develop new alignment layers for pretilt angle control.

Isomeric effects on liquid crystal alignment behaviors of polystyrene derivatives

ABSTRACTWe synthesized a series of 4-ethylphenoxymethyl (P4EP) and 3-ethylphenoxymethyl (P3EP) and 2-ethylphenoxymethyl-substituted polystyrenes (P2EP), using polymer analogous reactions, in order to study the isomeric effect of the ethylphenoxymethyl side groups on the liquid crystal (LC) alignment properties. The LC cells fabricated with the unrubbed P4EP, P3EP, and P2EP films exhibited uniform vertical, partial vertical, and random planar LC alignment. A high pretilt angle of about 90° was observed from the LC cell prepared from the rubbed film of P4EP at number of rubbing of 1. On the contrary, the LC cells prepared from the rubbed films of P3EP and P2EP showed pretilt angles of approximately 30° and 0° at number of rubbing of 1, respectively. Therefore, the position of ethyl group attached to phenyl group in the side chain was found to LC alignment behavior of the polystyrene derivatives. The LC alignment behavior was well correlated with the wettability of the polymer films. These polystyrene derivatives having good solubility in many organic solvents and their films having low process temperature can be candidates for LC alignment layer in the flexible display. This study contributes to the latest efforts to develop new alignment layers for pretilt angle control.

Vertical alignment of liquid crystal on tocopherol-substituted polystyrene films

ABSTRACTWe synthesised a series of vitamin-based and renewable tocopherol-substituted polystyrene (PTOC#, # = 20, 40, 60, 80 and 100), where # is the molar content of tocopherol moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a higher molar content of tocopherol side group showed vertical LC alignment behaviour. The vertical alignment (VA) behaviour was well correlated with the surface energy value of these polymer films. For example, VA was observed when the surface energy values of the polymer were smaller than about 35.22 mJ/m2 generated by the nonpolar tocopherol moiety having long and bulky carbon groups. Good electro-optical characteristics, such as voltage holding ratio and residual DC voltage, and aligning stabilities at 200°C and ultraviolet irradiation of 10 J/cm2 were observed for the LC cells fabricated using PTOC100 as a LC alignment layer. Therefore, it was first found that the renewable tocopherol-based materials can produce an eco-friendly vertical LC alignment system.

Liquid Crystal Elastomer Actuators from Anisotropic Porous Polymer Template.

Controlling self-assembly behaviors of liquid crystals is a fundamental issue for designing them as intelligent actuators. Here, anisotropic porous polyvinylidene fluoride film is utilized as a template to induce homogeneous alignment of liquid crystals. The mechanism of liquid crystal alignment induced by anisotropic porous polyvinylidene fluoride film is illustrated based on the relationship between the alignment behavior of liquid crystals and surface microstructure of anisotropic polyvinylidene fluoride film. Liquid crystal elastomer actuators with fast responsiveness, large strain change, and reversible actuation behaviors are achieved by the photopolymerization of liquid crystal monomer in liquid crystal cells coated with anisotropic porous films.

Liquid crystal alignment behaviors on capsaicin substituted polystyrene films

The liquid crystal (LC) alignment behavior on plant-based capsaicin substituted polystyrene film was investigated. This can give the basic idea for the design of eco-friendly LC alignment layer based on renewable resource containing polymer film.

Liquid Crystal Alignment Behavior on Rubbed Films of Cellulose Acetate

ABSTRACTThe liquid crystal (LC) alignment behaviors of LC cells fabricated with cellulose acetate films were investigated. These polymer films exhibited good optical transparency in the visible light region (400–700 nm). For example, transmittance value (92%) of the cellulose acetate film onto glass substrate at 550 nm is better that (89%) of the polyimide (PI) film, the most commonly used LC alignment layers. These LC cells fabricated with the rubbed cellulose acetate films showed the homogeneous planar LC alignment with parallel direction with respect to the rubbing direction. The electro-optical characteristics of the LC cells made from the cellulose acetate films such as response time were as good as those fabricated from rubbed PI films.

Polystyrene Blend Alignment Layers for High Pretilt Angle Control

ABSTRACTWe prepared blend alignment layer based on 4-ethylphenoxymethyl-substituted polystyrene (P4EP) and polystyrene containing 7-hydroxycoumarin (P7COU) for liquid crystal (LC) alignment. Stable and uniform vertical LC cells having pretilt angles adjustable from 90° to 81.2° were obtained from these polystyrene films having molar contents of P4EP and P7COU in the ranges of 100–70 and 0–30 mol%, respectively. The LC alignment behavior was well correlated with the wettability of the polymer films. These polystyrene blends having good solubility in many organic solvents and their films having low process (curing) temperature can be candidates for LC alignment layer in the flexible display. This study contributes to the latest efforts to develop new alignment layers for pretilt angle control.

Liquid Crystal Alignment Behaviors on Comb-Like Fluorinated Polystyrene Films

ABSTRACTWe synthesized a series of fluorinated polystyrene (PCMSF#, # = 50, 80, and 100), where # is the molar content of 1H,1H,2H,2H-perfluorodecanethiolate moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a higher molar content of fluorinated side group showed vertical LC alignment behavior with a pretilt angle of about 90°. The vertical alignment behavior was well correlated with the surface energy value and fluorine atomic percent of these polymer films. For example, vertical alignment was observed when the surface energy values of the polymer were smaller than about 8.77 mJ/m2 generated by the nonpolar and long fluorocarbon groups. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), and aligning stabilities at 250°C were observed for the LC cells fabricated using PCMSF100 as a LC alignment layer.

Photoalignment Behavior on Polystyrene Films Containing Coumarin Moieties

We synthesized a series of polystyrene derivatives containing coumarin side groups, poly(6-(4-vinylbenzyloxy)coumarin)(P6COU#), where # is the molar content of 6-hydroxycoumarin using polymer modification reaction, in order to study the effect of the 6-hydroxycoumarin side groups on the liquid crystal (LC) alignment properties. The LC alignment behavior of these polymers was investigated using photoalignment method. The LC cells made from photoirradiated P6COU# films exhibited homogeneous planar LC alignment with a pretilt angle of approximately 0°. We found that LC aligning ability of the LC cells made from photoirradiated P6COU# films was affected by the molar content of 6-hydroxycoumarin side groups. For example, the azimuthal anchoring energy of a P6COU80 compared to P6COU25 is about 1 × 10−5 J/m2 and 5 × 10−7 J/m2, respectively. The electro-optical characteristics of the LC cells fabricated with P6COU80 films such as voltage holding ratio and residual DC voltage, threshold voltage, driving voltage, and response time were as good as those fabricated from rubbed polyimide films, the most commonly used LC alignment layers.

Liquid crystal alignment behavior and OTFT performance of poly(3-hexylthiophene) blends with comb-like poly(oxyethylene)

Alignment characteristics of nematic liquid crystal (LC) on the surface of conjugated semi-conducting polymer blends with a comb-like polymer were studied. Conoscopic polarized optical microscope images show vertical alignment of LC on the blend films regardless of blend ratio. The LC alignment behavior on the blended film surface can be explained by a preponderance of comb-like polymers at the film surface. The mobility values of organic thin film transistors (OTFT) prepared with the blend film as an active layer are found to be similar to those with a pure conjugated semi-conducting polymer film. This result suggests a novel route for effectively reducing the amount of active semi-conducting polymer without significant deterioration of charge carrier mobility in an OTFT device. Since the LC alignment can be controlled on the surface of channel layer of OTFT by employing the polymer blend as the semi-conducting layer, the LC alignment and OTFT performance with the blend composition can be investigated simultaneously.

Photoalignment behaviour on polystyrene films containing chalcone moieties

A series of polystyrene derivatives containing chalcone (one of the biological compounds) side groups, poly(4-(4-vinylbenzyloxy)chalcone) (PCHAL#), where # is the molar content of chalcone using polymer modification reactions, were prepared in order to study the effect of the chalcone side groups on the liquid crystal (LC) alignment properties. The LC alignment behaviour of the polymer was investigated using photoalignment method. The LC cells made from photoirradiated PCHAL# films exhibited homogeneous planar LC alignment with an extremely low pretilt angle of approximately 0°. We found that LC aligning ability of the LC cells made from photoirradiated PCHAL# films was affected by the molar content of chalcone side groups. For example, the azimuthal anchoring energy of a PCHAL100 (9 × 10−6 J/m2) was found to be much larger than that of PCHAL18 (5 × 10−7 J/m2). In addition the electro-optical characteristics of the LC cells fabricated with PCHAL100 films such as threshold voltage, driving voltage, and response time were as good as those fabricated from rubbed polyimide films, the most commonly used LC alignment layers.

Homeotropic Alignment Properties of Liquid Crystal and Photocurable Monomer System via UV Irradiation

We investigated the homeotropic (or vertical) liquid crystal (LC) alignment properties in a LC and photocurable monomer mixture system through UV irradiation. Different homeotropic LC alignment behaviors were observed depending on the type of photocurable monomers and UV irradiation time. The LC alignment behavior showed a good correlation with the wettability of the alignment films due to surface morphology on the alignment layer surfaces by photopolymerization-induced phase separation. The electro-optical characteristics of the LC cells fabricated with these polymer films were as good as or even better than those fabricated from rubbed polyimide (PI) films, the most commonly used LC alignment layers.

Liquid crystal alignment behaviours on poly(methyl methacrylate) having polyhedral oligomeric silsesquioxane groups

A series of poly(methyl methacrylate) derivatives containing polyhedral oligomeric silsesquioxane (POSS) groups (MCP#) were synthesised via free radical polymerisation (FRP) using methacryl isobutyl POSS (MA-POSS) and methyl methacrylate as monomers to investigate liquid crystal (LC) alignment property of these polymer films. The LC cells made from the films of the polymers having 100 mol% of MA-POSS units (MCP100) showed vertical LC alignment having a pretilt angle of about 90°. The vertical LC alignment behaviour on the MCP100 film was ascribed to the very hydrophobic MCP100 surface having the surface energy value smaller than about 23 mJ/m2 generated by the nonpolar bulky POSS group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using MCP100 as a LC alignment layer.

Liquid crystal alignment behavior on sulfonated poly(arylene ether sulfone) films

A series of sulfonated poly(arylene ether sulfone) (PAES#, # is the feed monomer ratio of 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone) derivatives were synthesized to investigate the liquid crystal (LC) alignment property of these polymer films.

Liquid Crystal Alignment Behaviors of Polystyrene Derivatives Containing Coumarin Moieties

We synthesized a series of polystyrene derivatives containing coumarin side groups, poly(7-(4-vinylbenzyloxy)coumarin) (P7COU#) and poly(7-(4-vinylbenzyloxy)4-phenylcoumarin) (P7COU4P#), where # is the molar content of 7-hydroxycoumarin and 7-hydroxy-4-phenyl coumarin, respectively, using polymer analogous reaction, in order to study the effect of the 7-hydroxycoumarin and 7-hydroxy-4-phenyl coumarin side groups on the liquid crystal (LC) alignment properties. The LC alignment behavior of these two series was investigated by photoalignment or rubbing alignment. The LC cells made from photoirradiated P7COU# and P7COU4P# films showed homogeneous planar LC alignment. We found that LC aligning ability of the LC cells made from rubbed P7COU# and P7COU4P# films were affected by the structure and molar content of coumarin side groups. For example, anchoring energy of the LC cell fabricated with rubbed P7COU82 (7 × 10−5 J/m2) and P7COU4P81 (7 × 10−7 J/m2) film was increased drastically and slightly compared to polystyrene (10−7−10−8 J/m2), respectively. Particularly, anchoring energy of the LC cell made from rubbed P7COU# having more than 51 mol % of the 7-hydroxycoumarin as a side groups is comparable to that of the conventional polyimide in the LCD industry.