Effect of specific rotation of chiral dopant and polymerization temperature on reflectance properties of polymer stabilized cholesteric liquid crystal cells

A series of polymer stabilized cholesteric liquid crystal (PSCLC) cells were prepared by photo‐polymerization of a cholesteric liquid crystal (Ch‐LC) mixture containing a nonreactive LC, a nematic diacrylate and a novel cholesteryl monomer. The influence of the specific rotation and concentration of the chiral dopants, and the polymerization temperature on reflection properties was investigated. The results demonstrate that the reflection band was broadened after polymerization for all the systems both left‐handed S811 and right‐handed R1011 as the chiral dopant, which is speculated to be a result of an inhomogeneous consumption of the chiral monomer within the system. Additionally, the polymer temperature plays an integral role in the observed reflection spectra, and at optimum polymerization temperature the broadband reflection effect becomes much more pronounced. Scanning electron microscopy (SEM) was used to examine the role of microscopic changes of the polymer network induced by polymerization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1562–1570, 2008     

The role of crosslinking and polarity in the dark relaxation of azobenzene-based,polymer-stabilised cholesteric liquid crystals

Prior examinations have reported that polymer stabilisation of azobenzene-based cholesteric liquid crystal (CLC) mixtures can reduce the time necessary for complete colour restoration in the dark from three days to as few as five minutes. This work extends upon these prior examinations by exploring and elucidating the role of crosslinker concentration and monomer polarity on the colour restoration of a representative CLC mixture composed of a high HTP bis(azo) binapthanyl chiral dopant (QL76) mixed into the cyanobiphenyl nematic liquid crystal host MDA-00-1444. The impact of these variables was unexpectedly convoluted. In all the formulations examined here, polymer stabilisation dramatically reduces the time for complete colour restoration of the starting reflection notch. In mixtures based on nonpolar liquid crystal monomers, increasing the crosslinker concentration reduces the time necessary for complete colour restoration. However, the dependence on crosslinker concentration reverses in mixtures composed from polar liquid crystal monomers in which increasing the crosslinker concentration serves to increase the time necessary for complete colour restoration.     

Electrically controllable smart window with greyscale based on polymer-stabilised cholesteric texture films

The study reports a novel liquid crystal (LC) film that can be applied on the transmissive substrates or stuck on existing casement window to upgrade the shield. The shadow area and transmittance can be adjusted according to the condition of the outer sunshine. The window is energy saving for which maintains the transmittance after a once-off operation of pulse amplitude modulation (PAM) electric driving. Such a film can be applied in smart curtain, display frame edge and other transmissive electro-optical devices.     

Characteristics of wide-band reflection of polymer-stabilised cholesteric liquid crystal cell prepared from an unsticking technique

An unsticking technique was applied for the fabrication of a polymer-stabilised cholesteric liquid crystal (PSCLC) cell. The template of polymer matrix in the planarly aligned cholesteric liquid crystal (Ch-LC) was perfectly preserved by lifting off the hydrophilic antisticking substrate. The desired PSCLC cell could then be obtained by injecting a third Ch-LC sample between two designed templates of PSCLC layer. By adjusting the pitch distribution in the two stacking templates, a reflectivity of nearly 50% incident light could be yielded and the bandwidth of the reflection spectrum could be controlled accurately in the PSCLC cell. Thus, a method to modulate the wide-band reflection of 50% visible light flux range was offered.     

Preparation and phase behavior of side‐chain cholesteric liquid‐crystalline elastomers

A series of new side‐chain cholesteric elastomers derived from cholesteryl 4‐(10‐undecylen‐1‐yloxy)‐4′‐ethoxybenzoate and phenyl 4,4′‐bis(10‐undecylen‐1‐yloxybenzoyloxy‐p‐ethoxybenzoate) was synthesized. The chemical structures of the monomers were confirmed by elemental analyses, Fourier transform infrared, and ¹H NMR and ¹³C NMR spectra. The mesomorphic properties of elastomers were investigated with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the content of the crosslinking unit on the phase behavior of the elastomers was examined. Monomer M₁ showed a cholesteric phase, and M₂ displayed smectic and nematic phases. The elastomers containing <15 mol % of the crosslinking units revealed reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3315–3323, 2005     

近红外电致变色胆甾相液晶高分子的设计、合成及旋光开关性质

通过单体4′-甲氧基苯基-4-烯丙氧基苯甲酸酯(M1)、(S)-(-)-N-(5-己烯基)-6-(4′-(2-甲基丁氧基)苯基)-蒽醌-2,3-二羧酸酰亚胺(M2)与聚甲基氢硅氧烷间的硅氢加成反应,制得了3个新的具有近红外电致变色性质的侧链型液晶共聚物(PC5A10,PC5A20CB,PC5A30CB),并对其液晶性,电化学,光谱电化学和旋光开关性质进行了表征.当M2单体的含量为10mol%,20mol%时,共聚物可形成胆甾相液晶,而当其含量为30mol%时,所能形成的液晶相为近晶A相.3个共聚物的循环伏安曲线均出现了两对可逆的氧化还原峰,分别对应于蒽醌酰亚胺基团得电子而形成自由基阴离子和二价阴离子.中性态时,共聚物在420nm处有较强吸收,而当被还原为自由基阴离子后,在近红外区域840nm出现了新的强烈的吸收.以聚合物为阴极电致变色层,普鲁士蓝为离子储存层的全固态电致变色器件在800nm有较好的光学调制性.此外,本文还就该器件的电化学调控手性光开关性质进行了初步研究.     

Synthesis and characterization of chiral liquid‐crystalline polyesters containing sugar‐based diols via melt polymerization

Liquid‐crystalline (LC) polyesters based on hexanediol or butanediol, dimethyl 4,4′‐biphenyldicarboxylate, and a sugar‐based diol, isosorbide or isomanide, were prepared with conventional melt polymerization. ¹H NMR spectroscopy confirmed that 50 mol % of the charged sugar diol was successfully incorporated into various copolyesters. Modest molecular weights were obtained, although they were typically lower than those of polyester analogues that did not contain sugar‐based diols. Thermogravimetric analysis demonstrated that the incorporation of isosorbide or isomanide units did not reduce the thermal stability in a nitrogen atmosphere. Melting points that ranged from 190 to 270 °C were achieved as a function of the copolyester composition. The lined focal conic fan textures, typical indications of a chiral smectic C LC phase, were observed upon the shearing of the LC melt under polarized light microscopy. Atomic force microscopy revealed that the twisted molecular orientation in the chiral LC phase induced periodically soft lamellar structures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2512–2520, 2003     

Time‐dependent deformation of structurally chiral polymer networks in stabilized cholesteric liquid crystals

Polymerization of crosslinkable liquid crystal monomers in chiral liquid crystalline media stabilizes the phase and enables distinct electro‐optic properties relative to small‐molecule analogs. Particularly interesting are cases where the polymerization forms a crosslinked polymer network that maintains a “structural” chirality. Recent reports have employed this methodology to realize a diverse set of electro‐optic responses in polymer stabilized cholesteric liquid crystals (PSCLCs) including reflection bandwidth broadening, reflection wavelength tuning, and dynamic scattering modes. It has been proposed that the mechanism at the root of these electro‐optic responses is an ion‐mediated, electromechanical deformation of the stabilizing and structurally chiral polymer network. In an effort to better understand the nature of these deformations, here we have characterized the electro‐optic response of PSCLCs with different polymer concentrations and crosslink densities. The dynamic response of PSCLCs to electric fields exhibits a time‐dependent behavior reminiscent of the creep of polymeric materials to mechanical deformations. The electro‐optic response can be described as the superposition of two contributions: the fast deformation of a relatively soft component of the polymer network (1–2 s) and the slower (10–20 s) deformation of a harder component. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1087–1093     

New cholesteric liquid‐crystal epoxy resins derived from 6‐hydroxy‐2‐naphthoic acid

Liquid‐crystalline epoxy resins were synthesized from 6‐hydroxy‐2‐naphthoic acid, which was used as a mesogenic component, with phenylhydroquinone or isosorbide and via a further reaction with (6‐bromo‐1‐hexyl)glycidylether, which was used as a flexible spacer. In this way, phenylhydroquinone‐bis‐6‐[6‐(glycidyloxy)hexyloxy]2‐naphthoate (Gly A) and isosorbide‐bis‐6‐[6‐(glycidyloxy)hexyloxy]2‐naphthoate (Gly B) were obtained. Nematic elastomers were obtained by the crosslinking of Gly A with 2,4‐diaminotoluene (DAT) and 1,10‐decanedicarboxylic acid (SA). The liquid‐crystalline behavior was investigated with differential scanning calorimetry, polarizing light microscopy, and X‐ray diffractometry. Cholesteric mesophases were produced by the blending of different ratios of Gly A and Gly B, and these blends were then crosslinked with SA to produce nematic mesophases. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2847–2858, 2001     

Surface anchoring energy of cholesteric liquid crystals

ABSTRACT

In this paper, we propose a suitable surface energy expression for cholesteric liquid crystals. We show that there exists a symmetry allowed term for chiral nematics that doesn’t appear in the traditional Rapini-Papoular surface energy form. We discuss some consequences of this new surface anchoring term.     

Textures and disclinations in the cholesteric liquid‐crystalline phase of a cyanoethyl chitosan solution

Disclinations in the fingerprint‐like cholesteric texture of a natural polymer derivative, cyanoethyl chitosan, were observed and studied by both polarizing optical microscopy and scanning electron microscopy. In the latter technique, permanganic etching was developed for this cholesteric texture to increase the contrast. A special mechanism for cholesteric phase etching is suggested and discussed. Some χ, λ, and τ disclinations and domain walls were observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 980–986, 2000     

New polymer synthesis. LXXXIII. Synthesis of chiral and cholesteric polyesters from silylated “sugar diols”

A series of polycondensation was conducted with the purpose to optimize the reaction conditions for the polycondensation of silylated 2,3-isopropylidene D -threitol with a dicarboxylic acid dichloride. Polycondensation in o-dichlorobenzene or 1-chloronaphthalene at 180–230°C were found to be most satisfactory. Trifluoroacetic acid/H₂O allow an easy cleavage of the isopropylidene group without hydrolysis of the polyester. Ten cholesteric copolyesters were prepared by polycondensation of mixtures of silylated methylhydroquinone and isosorbide, isomannide, or 2,3-isopropylidene threitol with the dichloride of 1,10-bis(4′-carboxyphenoxy)decane. All these copolyesters form a broad cholesteric phase above 200°C. The copolyesters containing 5 or 10 mol % of a sugar diol display a blue Grandjean texture. © 1996 John Wiley & Sons, Inc.     

Short wavelength light reflecting films from side‐chain liquid crystal homopolymers with chiral spacers

A series of acrylate monomers with alkoxy tails of varying lengths are synthesised and polymerised. The butoxy analogue had a stable enantiotropic cholesteric liquid crystalline phase which formed a grandjean texture when prepared as a thin film between glass slides. The polymer was mixed with a low molar mass nematic liquid crystal in various proportions and the pitch of the chiral nematic phases were determined using a cano‐wedge cell technique. The polymer prepared from (S)‐2‐(4‐butoxyphenyl‐4′‐benzoyloxy)‐1‐methyl ethyl acrylate had a pitch length of 113 nm which indicates that the polymer film could be employed in optical devices requiring selective reflection of light with short wavelengths in the region of 170 nm. Copyright © 2001 John Wiley & Sons, Ltd.     

Surface characterization of polymer‐stabilized colloidal metal catalysts

A new method for measuring hydrogen chemisorption on polymer‐stabilized metal colloids, in conjunction with variable coverage infrared spectroscopy of adsorbed CO, is applied to analyse the surface of Pt/polyvinylpyrrolidone colloids. The results correlate well with the measured activity of Pt/PVP as a hydrogenation catalyst.     

Helix‐sense‐selective copolymerization of triphenylmethyl methacrylate with chiral 2‐isopropenyl‐4‐phenyl‐2‐oxazoline

The asymmetric induction leading to a one‐handed helix was investigated in the anionic and radical copolymerization of triphenylmethyl methacrylate (TrMA) and (S)‐2‐isopropenyl‐4‐phenyl‐2‐oxazoline ((S)‐IPO), and highly isotactic copolymers with a reasonable optical activity were obtained. In the anionic copolymerization, the optical activity of the obtained copolymers depended on the polarity of solvents, and a highly optically active copolymer was produced in the copolymerization in toluene. The chiral oxazoline monomer functioned not only as a comonomer but also as a chiral ligand to endow the polymer with large negative optical rotation in the copolymerization with TrMA. The copolymers with small positive optical rotation were obtained in THF, indicating that IPO unit may work only as the chiral monomer that dictates the helical sense via copolymerization with TrMA. The isotacticity of the obtained copolymers depended on the contents of TrMA units in the copolymers, but was almost independent of the solvent for copolymerization. In the radical copolymerization, the obtained copolymers exhibited small optical activities. It seemed that the chiral monomer cannot induce one‐handed helical structure of TrMA sequences even if the sequences probably have a high isotacticity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 441–447     

Chiral recognition in molecular and macromolecular pairs of (S)‐ and (R)‐1‐cyano‐2‐methylpropyl‐4′‐ {[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐ carboxylate enantiomers

(S)‐1‐Cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐ 4‐carboxylate [ (S)‐11 ] and (R)‐1‐cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐carboxylate [( R)‐11 ] enantiomers, both greater than 99% enantiomeric excess, and their corresponding homopolymers, poly[ (S)‐11 ] and poly[ (R)‐11 ], with well‐defined molecular weights and narrow molecular weight distributions were synthesized and characterized. The mesomorphic behaviors of (S)‐11 and poly[ (S)‐11 ] are identical to those of (R)‐11 and poly[ (R)‐11 ], respectively. Both (S)‐11 and (R)‐11 exhibit enantiotropic S_A, S, and S_X (unidentified smectic) phases. The corresponding homopolymers exhibit S_A and S phases. The homopolymers with a degree of polymerization (DP) less than 6 also show a crystalline phase, whereas those with a DP greater than 10 exhibit a second S_X phase. Phase diagrams were investigated for four different pairs of enantiomers, (S)‐11 /( R)‐11 , (S)‐11 /poly[ (R)‐11 ], and poly[ (S)‐11 ]/poly[ (R)‐11 ], with similar and dissimilar molecular weights. In all cases, the structural units derived from the enantiomeric components are miscible and, therefore, isomorphic in the S_A and S phases over the entire range of enantiomeric composition. Chiral molecular recognition was observed in the S_A and S_X phases of the monomers but not in the S_A phase of the polymers. In addition, a very unusual chiral molecular recognition effect was detected in the S phase of the monomers below their crystallization temperature and in the S phase of the polymers below their glass‐transition temperature. In the S phase of the monomers above the melting temperature and of the polymers above the glass‐transition temperature, nonideal solution behavior was observed. However, in the S_A phase the monomer–polymer and polymer–polymer mixtures behave as an ideal solution. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3631–3655, 2000     

Effects of crosslinking agent,cure temperature,and UV flux on the electro‐optical properties of polymer‐dispersed liquid crystal cells

We present results for the effects of a crosslinking agent, cure temperature, and UV flux on the electro‐optical properties of polymer‐dispersed liquid crystal (PDLC) cells. These cells were fabricated using a mixture of a liquid crystal (E8) and an acrylic monomer (CN135). The maximum in the first derivative of the transmission vs. applied, sinusoidal voltage (inflection voltage, V_inf), varies systematically with PDLC formulation and cure‐process conditions. For PDLC cells fabricated with a crosslinking agent (SR295), V_inf increases with increasing the concentration of SR295. However, for cells fabricated without the use of a crosslinking agent, V_inf decreases with increasing the UV flux and decreasing temperature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 404–410, 2004     

Mesomorphism,polymerization, and chirality induction in α‐cyanostilbene‐functionalized diacetylene‐assembled films: Photo‐triggered Z/E isomerization

Engineering of molecular stacking arrangement via environmental stimuli is of particular interest in stimuli‐responsive self‐assembling architectures. A novel dual photo‐functionalized diacetylene ((Z)‐CNBE‐DA) molecule was synthesized, in which photo‐responsive cyanostilbene moieties exhibited interesting Z‐E isomerization upon UV light irradiation and could be utilized to modulate mesomorphism, molecular stacking arrangement and resulting polymerization behavior. Rod‐like (Z)‐CNBE‐DA could self‐assemble into well‐defined lamellar structures and the helical polydiacetylene (PDA) chains could be formed upon irradiation with circularly polarized ultraviolet light (CPUL). However, the bent‐shaped (E)‐CNBE‐DA molecules only self‐assembled into irregular loose packing, inhibiting the formation of ordered helical PDA chains upon CPUL irradiation. In this work, we established the links between chemical structures, molecular packing engineering and photophysical properties, which would be of great fundamental value for the rational design of smart soft materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2458–2466     

Flat optics with cholesteric and blue phase liquid crystals

ABSTRACT

The cholesteric (Ch) phase is an ancient liquid crystal (LC) phase, with its roots dating back to the days of Friedrich Reinitzer. It is most well known for its ability to selectively reflect circularly polarised light with the same rotation handedness as the helical structure, and have found applications in polarising and display devices. Most studies to date utilising the reflective properties of ChLCs, however, have treated ChLCs as simple dielectric mirrors in which light follows the law of reflection. We have recently shown that through controlling the phase of the Ch helix, it is possible to control the phase of reflected light. Because the phase can be controlled over 0–2π, the reflected wavefront from a planar device can be designed to possess non-specular properties, such as deflection and lensing. In this paper, we aim to provide a comprehensive understanding of the phenomenon by presenting theoretical and experimental results on the dependence of the reflected light phase on the helix phase, and the effect of chiral handedness on the phenomenon. Also, we show that wavefront manipulation based on the same concept can be achieved in Ch blue phases (BPs), which are chiral LCs with three-dimensional periodicity.     

Crystallographic report: [N,N′‐Bis‐(6‐methylpyrid‐2‐ylium)‐(1R,2R)‐1,2‐diaminocyclohexane] bis‐[(p‐cymene)‐ trichlororuthenate(II)]

The chiral compound (H₂cydiampy)[RuCl₃(p‐cymene)]₂ has been obtained in high yield by treating [RuCl₂(p‐cymene)]₂ with an excess of hydrochloric acid in the presence of one equivalent of N,N′‐bis‐(6‐methylpyrid‐2‐yl)‐(1R,2R)‐1,2‐diaminocyclohexane (cydiampy). It crystallizes in the chiral tetragonal space group P4₃2₁2, with half of the atoms of the dication related to the other half by a crystallographic C₂ axis that also makes equivalent the two anionic metal moieties. Copyright © 2005 John Wiley & Sons, Ltd.