Surface reconstruction of chiral glassy oligomers under the action of volatile organic compounds (VOCs)

The response of chiral polymers to volatile organic compounds (VOCs) was studied by atomic force microscopy. It was found that under the influence of toluene vapour, the focal conic domains on the surface of chiral polymer undergo remarkable reconstruction that is at least partially reversible. This opens new ways for building VOC sensors and using surface reconstruction in creating new surface patterns for nanotechnology.     

Polarization plane's weak rotation amplifiers and polarization azimuth stabilizers

A simple and effective method to measure an electromagnetic wave polarization plane's weak rotations in various media is proposed. The specific features of the polarization plane's rotation amplification for the light reflection and transmission through the absorbing and amplifying isotropic layers are calculated. The amplification effects on an anisotropic and cholesteric liquid crystal (CLC) layers are also considered. In conclusion the question of probable choice of the amplifier's noise/signal ratio is discussed.     

Director distribution in field-induced undulated structures of cholesteric liquid crystals

Structures with a periodic in-plane liquid crystal director field modulation induced by an electric field are studied in cholesteric liquid crystals (CLCs). A phenomenon of the electric-field-induced instability in a planarly aligned cholesteric cell is used to create these undulated structures. The initial field-off state is planarly aligned with the cholesteric helix axis oriented perpendicular to the cell substrates. The interaction of the CLC with an electric field results in modulation of the refractive index, which is visualised as stripe domains oriented either along or perpendicular to the rubbing direction at cell alignment surfaces. The threshold electric field for the undulation appearance and a period of stripes are measured experimentally for three Grandjean zones (ratio d/p ~ 0.5, 1.0, and 1.5, where d is a cell thickness and p is the natural cholesteric pitch). For the zone with d/p ~ 1.0 using numerical simulations, we describe in detail the director distribution at an applied electric field. It is found that the in-plane undulated structure is characterised by a conical director rotation on moving along the alignment direction. The conical axis is tilted with respect to the alignment axis. The sign of the tilt angle depends on the handedness of CLC.     

丁酸壳聚糖液晶的织构研究

用偏光显微镜研究了一种新的液晶高分子－丁酸壳聚糖液晶的织构。丁酸壳聚糖能溶于十多种溶剂中形成胆甾型液晶相。指纹状织构是主要织构，此外还观察到鲜偏振场织构、滴状织构、平面织构和条带织构等，与纤维素衍生物的液晶态结构很相似。     

甲壳素类液晶高分子的研究Ⅶ.N,O-苄基壳聚糖的胆甾螺旋行为

N ,O-苄基壳聚糖在浓溶液中形成胆甾液晶相 .用圆偏光二向色性谱 (CD)研究了这一聚合物的螺旋行为 ,主要包括螺距和螺旋方向 .浓度越高 ,螺距P越大 ,意味着胆甾相的扭转力随浓度增加而减弱 .CD谱图上观测到两类吸收 ,即在 5 70nm附近较宽但较强的吸收和 330nm附近较尖但较弱的吸收 .前者归属于胆甾相层片的超分子螺旋构象 ,而后者可以归属于分子链的螺旋构象 .改变浓度或溶剂性质时这两个层次的构象都会发生符号的变化 .提高浓度 (固定二氧六环为溶剂 )时两种螺旋结构先后发生反转 .以氯仿为溶剂 (固定浓度为 6 5 % )时两种螺旋结构均为左旋 (正Cotton效应 ) ,但二氧六环和四氢呋喃为溶剂时均变为右旋 (负Cotton效应 ) .溶剂的影响可能与溶剂和高分子间形成氢键的能力有关     

胆甾型侧链液晶共聚物的研究

合成并表征了两个胆甾型液晶烯类单位以及它们分别与辛烯－１，二氧化硫进行自由基共聚合得到的一系列不同组成的胆甾型侧链液晶三元共聚砜。研究结果表明：该共聚砜的两个液晶热转变温度均随其中辛烯－１单体单元组份含量的增加而降低。     

KINETICSOF TRANSITION FROM ISOTROPIC TO CHOLESTERIC PHASE FOR A THERMOTROPIC CELLULOSE DERIVATIVE

The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetatefrom isotropic phase to cholesteric mesophase has been studied by means of depolariz-ing transmittance method. Avrami type analysis of the data gives an exponent n close to1, which suggests the nucleation followed by rod-like growth. It means that the kineticbehavior of phase transition from isotropic to cholesteric mesophase is very similar to thatof the mesophase formation from isotropic to nematic mesophase.     

Optical properties and photonic density of states in one-dimensional and three-dimensional liquid-crystalline photonic crystals

ABSTRACT

Complex optical investigations were performed in one-dimensional (cholesteric) and three-dimensional (Blue Phase II) liquid-crystalline photonic crystals. Spectra of optical transmission and luminescence in the range of the photonic stop band contain information about the local anisotropy, characteristics of the photonic stop band, photonic density of states. We determine the photonic density of states in one-dimensional and three-dimensional liquid-crystalline photonic crystals employing measurements of polarised luminescence. The width of the photonic band gap, density of states and the optical characteristics related to the density of states essentially change with temperature in one-dimensional cholesteric photonic crystal. Drastic transformation of the density of states was found at the transition from one-dimensional to three-dimensional (Blue Phase II) photonic crystal. The results of our investigations demonstrate the possibility to employ the applied method for various types of photonic structures.     

侧链胆甾液晶聚合物及弹性体的液晶性能研究

把胆甾液晶单体 4 烯丙氧基苯甲酸胆甾醇酯 (Mch)分别和向列液晶单体 4 烯丙氧基苯甲酰氧基 4′ 甲氧基苯 (Mn) ,向列液晶交联剂 2 叔丁基对苯二酚双 [4 (6 丙烯酰氧基己氧基 )苯甲酸酯 ](Mnc)接枝到聚硅氧烷链上 ,得到系列侧链液晶聚合物Pn 系列和液晶弹性体Pe 系列 .通过热分析、偏光显微分析和X 射线分析等手段分别研究了向列液晶单体和向列液晶交联剂对含同一胆甾液晶基元聚合物的影响 .结果表明 ,向列液晶单体的摩尔百分比在 80 %以下 ,液晶聚合物Pn 系列为胆甾型液晶 ,在研究的范围内 ,液晶弹性体Pe 系列也为胆甾型液晶 ,Pn 系列和Pe 系列都具有较宽的液晶相范围 ,热分解温度均在 2 80℃以上 .     

Elucidating the fine details of cholesteric liquid crystal shell reflection patterns

ABSTRACT

Clusters of planar-aligned short-pitch cholesteric liquid crystal spheres generate dynamic colourful patterns due to multiple selective reflections from the radially oriented cholesteric helices in neighbour shells at varying distances. These photonic communication patterns were widely investigated for the cases of both droplets and shells, demonstrating not only intriguing optical phenomena but also potential for applications as new optical elements for photonics, sensing or security pattern generation. However, the optics of these clusters is truly complex and until now only the strongest and most fundamental reflections have been analysed and explained. In this report, we elucidate the origin of a number of more subtle reflections and we explain the extension in space of various spots as well as their internal colour variations.