甲壳素类液晶高分子的研究 Ⅰ侧基长度对羧酰化甲壳素的液晶性的影响

四种羧酰化甲壳素即乙酰化、丙酰化、丁酰化和己酰化甲壳素在二氯乙酸溶液中均呈现胆甾型溶致液晶相．临界浓度随侧基长度增加而略有增加,衍生物的临界浓度明显都比原甲壳素高许多,这些规律都可以用链刚性的变化来解释．四种羧酰化甲壳素在剪切时均能形成条带织构,而且能形成条带织构的最低浓度有明显差别,随侧基长度增加而提高,进一步表明侧基较长,液晶性减少．     

甲壳素类液晶高分子的研究Ⅱ-侧基长度和取代度对羧酰化壳聚糖的液晶性的影响

五种羧酰化壳聚糖即乙酰化、丙酰化、丁酰化、己酰化和庚酰化壳聚糖在二氯乙酸溶液中均呈现胆甾型溶致液晶相．临界浓度随侧基长度的增加而增加,但取代度（ 从０－２１ 变化到０－９４） 对临界浓度没有影响．在两相共存浓度区内,均呈现典型的滴状织构．从两相共存到完全液晶相的转变浓度也随侧基长度的增加而增加．     

Synthesis and Characterization of a Novel Liquid Crystalline Chitin — Quaternary Ammonium Chitosan Salt

N-Butyl chitosan(NBCS) derivatives were prepared by introducing butyl groups into the amine groups of chitosan via Schiff base intermediates. The quaternization of NBCS was carried out by using ethyl iodide to produce water-soluble cationic polyelectrolytes. The degree of the substitution of the products was measured by means of the electron spectroscopy for a successful chemical analysis. The quaternary ammonium chitosan salt(QACS) was proved to be a novel cholesteric liquid crystalline chitin, by means of the polarized optical microscopy and the circular dichroism spectropolarimetry. The critical mass fraction of the QACS/formic acid solution forming a lyotropic liquid crystal phase was 50%, which was almost the same as that of the NBCS/formic acid solution, but much hiuher than that of the chitosan in the same solvent.     

PREPARATION AND PROPERTIES OF ETHYL-CYANOETHYL CELLULOSE/POLYACRYLIC ACID COMPOSITE FILMS WITH REFLECTION COLORS*

Ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid (AA) becomes a cholesteric liquid crystalline solution withvivid colors when the (E-CE)C concentration is 42 wt%～52 wt%. (E-CE)C/polyacrylic acid (PAA) composites withcholesteric structure were prepared by polymerzing AA in (E-CE)C/AA liquid crystalline solutions. The layers of orderedpolymer chains in the cholesteric phase were inclined during polymerization and the degree of the inclination depended onthe polymerization temperature and the concentration of the solution before polymerization. The cholesteric structure in thecomposites could not be changed when temperature was lower than 100℃. Cross-linking of the PAA in compositesimproved their water-resistance. The cholesteric order of the composites without cross-linking was destroyed when theywhere immersed in water. The color derived from the selective reflection of the cholesteric phase of the cross-linkedcomposites turned from blue to red after the composites absorbed water. The color of the composites could be returned to theoriginal one when the absorbed water was removed from the swollen composites.     

Visible Light and Temperature Regulated Reflection Colors in Self-supporting Cholesteric Liquid Crystal Physical Gels

Photo-responsive cholesteric liquid crystals (CLCs) have attracted much attention in recent years due to their wide applications in filters,tunable optical lasers,dynamic display devices,etc.However,UV light is usually used as the external stimulus source,which is not environment-friendly enough.On the other hand,the mechanical properties of CLCs are not strong enough for these practical applications.Therefore,it still remains a challenge to endow the CLCs with visible light response and high mechanical properties at the same time.Herein,an axially chiral tetra-fluorinated binaphthyl azobenzene gelator (S-4F-AG) is synthesized.Upon 550 and 450 nm light irradiations,S-4F-AG exhibits excellent photo-switchable behaviors.Notably,the maximum content of cis-isomer and its half-life are as high as 35％ and 89 h in acetonitrile,respectively.A self-supporting CLC physical gel with a storage modulus around 104 Pa can be obtained when 3wt％ S-4F-AG and 12wt％binaphthyl azobenzene derivative (dopant 2) are co-doped into a nematic LC host P0616A.This CLC physical gel exhibits a temperature-driven blue,green,and red reflection colors reversibly.Importantly,such three primary RGB colors can also be realized by adjusting the exposure time of 550 nm green light.This work lays a solid foundation for the applications ranging from information storage to high-tech anticounterfeit.     

Light-rewritable geometric phase and reflectance modulations enabled by pattern-aligned photoresponsive liquid crystal superstructures

ABSTRACT

We propose a universal method of fabricating and operating a multifunctional diffractive optical element (DOE) with light-rewritable geometric phase and reflectance modulations enabled by pattern-aligned photoresponsive liquid crystal superstructures via manipulating the photoalignment layers as well as the phototunable helical pitch of the cholesteric liquid crystal (CLC) under different light stimuli, i.e. ultraviolet and visible (green) lights. The diffractive behaviour of the fabricated CLC DOE is simultaneously governed by the geometric phase induced by the pattern-aligned CLC and the reflectance (amplitude) modulation attributed to the helical pitch manipulation, endowing the proposed DOE with versatile practical light-controllable characteristics and outstanding performance.     

Enhancement of the optical absorption in cholesteric liquid crystals due to photonic effects: an experimental study

An anomalous strong optical absorption was measured in a cholesteric liquid crystal (CLC) at both edges of its photonic band gap. The experiment was carried out by studying the luminescence generated by the CLC sample doped with a small amount of fluorescent dye. The material was excited with monochromatic light at different angles of incidence and polarisations. Clear peaks were found in the luminescence response at angles for which the pumping wavelength coincides with the positions of the gap edges. The effect is especially noticeable for excitation under circularly polarised light of the same handedness as that of the CLC helix, and it is the highest at the long-wavelength edge. The modification of the absorption is originated by the helicoidal (photonic) structure of the material, which drastically influences the propagation of electromagnetic waves at certain frequencies and polarisations. The results were analysed numerically using an extension of the Berreman method that incorporates absorption effects. Good agreement with the experiment was found.     

Localised optical states in a structure formed by two oppositely handed cholesteric liquid crystal layers and a metal

A new model for observing localised optical states in a structure containing a cholesteric liquid crystal is proposed. The dependence of the mode frequency on the angle between directors at the interface of oppositely handed cholesterics is established. The effect of the metal layer thickness on localisation of light at the localised state frequency is studied. Polarisation features of the transmission spectrum are investigated. The possibility of experimental implementation of the proposed structure is discussed.     

乙烯基二联苯单体的螺旋选择性自由基聚合

为了深入理解乙烯基二联苯单体自由基聚合过程中的手性传递,进行了手性单体(+)-2-[(S)-异丁氧羰基-5-(4′-己氧基苯基)苯乙烯、非手性单体2-丁氧羰基-5-(4′-己氧基苯基)苯乙烯的均聚反应及它们二者的共聚反应,探讨了聚合温度和溶剂性质对手性单体均聚物旋光活性、手性单体含量对共聚物旋光活性以及聚合反应溶剂的超分子手性对共聚物旋光活性的影响.研究发现,降低聚合温度、采用液晶性反应介质有利于得到旋光度大的聚合物;少量手性单体的引入即可诱导共聚物形成某一方向占优的螺旋构象,比旋光度随手性单体的含量增加呈线性增长;在胆甾相液晶中制备的非手性单体聚合物不具有光学活性.这些结果表明,该类乙烯基二联苯聚合物具有动态螺旋构象,其光学活性主要依赖于主链的立构规整度和侧基不对称原子的手性.     

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.