CNC基手性向列液晶衍生材料制备及应用研究进展

纤维素纳米晶(cellulose nanocrystal,CNC)由于其独特的手性向列液晶相结构,已经引起众多科学研究领域的广泛关注,尤其是其在生物液晶材料的应用已成为当前的研究热点。本文综述了近年来国内外对CNC及其手性向列衍生材料的研究进展。首先介绍了CNC手性向列液晶相的形成和调控;其次归纳了CNC基手性向列衍生材料的制备方法,如硫酸水解结合蒸发诱导自组装法、手性模板结合溶胶凝胶法以及溶液共混法;最后阐述了CNC基手性向列液晶结构组装材料在光学材料、功能高分子树脂膜材料、医学材料等领域的应用,并对其在今后的发展应用前景进行了展望。     

液晶高分子材料的新功能:微管执行器及其光控微量液体运动

微量液体的精确操控在生物医药、液体传输等领域具有广泛的应用价值.目前,基于光诱导的毛细作用力操控液体的方法引起了人们极大的兴趣,因为这类方法在操控过程中无需特殊的光学装置和复杂的微组装过程.但是目前报道的方法只适用于少数特定的液体,并且驱动距离短、运动速度慢、局限于直线运动.最近,俞燕蕾等设计了一种新型结构的侧链液晶高分子材料,以此制备了液晶高分子微管执行器,可以通过不对称光致形变诱导毛细作用力,实现了光控各种类型液体按照设计的速度和方向运动,有望在可控微流体传输、微反应系统、微机械系统、芯片实验室等领域展现出巨大的应用价值.     

三维自组装蓝相液晶光子晶体

蓝相液晶由于其独特的三维自组装结构、可见光波段的选择性光反射性能和软物质特性,被认为是最具发展潜力的可调三维光子晶体材料之一,在下一代超快响应显示、反射型显示、可调激光器和光通信等领域具有广阔的应用前景。本文综述了近年来蓝相液晶自组装结构的研究进展,包括蓝相的多级自组装三维微纳结构及子相相变行为的最新研究,通过基板表面取向处理或纳米图案化诱导、电场诱导、热处理诱导等方法控制蓝相自组装行为和三维周期性晶体结构的研究现状,以及蓝相光子晶体材料在可调谐激光器、可调光栅等光学器件领域的应用研究,最后对该领域的目前存在的挑战和未来发展方向进行了展望。     

盘状液晶材料的研究进展

盘状液晶分子容易形成柱状堆积的超分子组装体, 由于分子在液晶态具有一定的流动性, 使得组装体具有良好的结构缺陷自修复功能. 因此具有特定芳香共轭结构的盘状液晶分子可以呈现较高的导电特性, 能够有效传输电荷, 具有制备光电器件的潜在应用价值. 本文主要介绍以苯环、苯并菲、六苯并蔻、苝和肽菁为中心核的盘状液晶材料, 其分子结构的化学修饰对液晶性能的影响, 液晶材料在有机发光二极管(OLED)、有机场效应晶体管(OFET)和太阳能电池器件中的应用, 以及盘状液晶材料相关的动力学研究进展.     

侧基含纳米构筑单元的甲壳型液晶高分子的多层次自组装

甲壳型液晶高分子可以呈现超分子柱或片层的链构象,因此可以作为超分子液晶基元形成多种液晶相态,如六方柱状相、柱状向列相、六方柱状向列相、近晶相等.将纳米构筑单元,如一维的二联苯、二维的苯并菲、三维的多面体低聚倍半硅氧烷(POSS)等,引入到甲壳型液晶高分子中,所得聚合物可以自组装形成在亚十纳米和近纳米尺度的多级有序结构.这些结构具有尺寸可控及单分散的优点,可望在有机光电、纳米多孔膜以及纳米光刻等领域有着广阔的应用前景.本文主要介绍了将二联苯、偶氮苯、棒状多苯结构、苯并菲和POSS基元引入到甲壳型液晶高分子中制备多级组装结构的相关工作.     

智能响应蓝相液晶光子晶体

具有刺激响应性的智能驱动材料已成为材料科学领域的研究热点之一。液晶的超分子自组装结构与其刺激响应特性使其在新型智能功能材料的开发应用上具有天然优势。蓝相液晶由于其独特的三维超分子自组装结构、软物质特性以及可见光波段的选择性光反射,被认为是最具潜力的智能光子晶体材料之一。在温度、光照、电场、湿度等外场刺激作用下,蓝相超分子自组装结构的晶体学参数或相态非常容易发生变化,造成光子带隙的改变进而呈现出反射颜色的变化。因此,蓝相的外场响应性能及在智能材料上的应用引起了研究者的广泛关注。本文综述了智能响应蓝相液晶光子晶体外场响应性能方面的前沿动态,对蓝相液晶光子晶体的光、磁、电、力、湿度响应等方面取得的系列重要的研究成果进行了总结,并对该领域目前存在的挑战以及未来发展趋势做出展望。     

具有不同柱状结构的苯并菲盘状液晶化合物的合成及自组装

合成了3种含有不同长度烷基链的苯并菲盘状液晶化合物; 通过1H NMR 和 MALDI-TOF MS对其结构进行了表征; 利用差示扫描量热法(DSC)、热台偏光显微镜(POM)和小角X射线散射实验(SAXS)对3种液晶化合物的自组装行为进行了研究. 结果表明, 烷基链的长度对苯并菲盘状液晶化合物自组装结构的影响显著. 柔性链为辛基的苯并菲盘状液晶化合物自组装成六方柱状液晶相; 柔性链为十二烷基的化合物自组装成倾斜柱状液晶相; 而柔性链为十六烷基的化合物则未形成液晶相.     

苯并菲类液晶高分子合成及应用北大核心CSCD

苯并菲液晶材料能够自组装成柱状相,被广泛应用在光电材料方面、功能分子膜、信息储存等方面。苯并菲衍生物合成方法简单,并且具有非常良好的光电性质,引起了研究者的广泛关注。苯并菲液晶高分子可以分为不同的类型,其合成方法也不相同。本文在简单介绍苯并菲液晶高分子合成方法的同时,对苯并菲液晶高分子的应用也做简要的概括。     

胆甾相液晶螺旋方向的光调控

光响应胆甾相液晶是一类在光刺激下通过改变液晶分子排列调控光学特性的智能“软”光子晶体材料,其分子自组装形成周期性螺旋结构,选择性地反射与自身螺旋方向相同的圆偏振光。近年来,利用光刺激诱导胆甾相液晶在左手螺旋和右手螺旋之间发生螺旋翻转的研究引起了广泛关注。胆甾相液晶的螺旋翻转能够改变反射光的圆偏振特性,有望拓展光子晶体材料在可调节滤光器、防伪与加密技术、圆偏振激光器、三维显示等领域的潜在应用。本综述重点关注光响应胆甾相液晶螺旋翻转的研究进展;总结了调控胆甾相液晶螺旋方向的两种主要策略：(1)直接引入螺旋性可逆转变的光响应手性分子开关,(2)利用光响应手性分子开关和与之螺旋性相反的手性掺杂剂之间的手性竞争;分析了分子空间构型转变对调控螺旋翻转程度的影响;并讨论了不同材料体系面临的挑战以及未来的发展方向。     

光致形变液晶高分子

交联液晶高分子兼具液晶的各向异性和高分子网络的弹性,并且具有优异的分子协同作用.在交联液晶高分子中引入光响应基团,例如偶氮苯后,即可赋予其光致形变性能,利用分子协同作用可以将光化学反应引起的分子结构变化放大为宏观形变,从而将光能直接转化成机械能.通过合理的分子结构和取向设计可以使液晶高分子产生诸如伸缩、弯曲、扭曲、振动等多种形式的光致形变,并用于各类光控柔性执行器件的构筑,在人工肌肉、微型机器人、微量液体操控等领域呈现出独特的优势和广阔的应用前景.本文总结和评述了光致形变液晶高分子的研究,包括材料结构对光致形变性能的影响、新型可加工光致形变材料的研究、利用可见光和近红外光触发形变的策略,以及光致形变液晶高分子微执行器在微量液体操控中的应用,最后展望了该领域的发展方向.     

The effect of voltage controlled orientation order of liquid crystals in non-acrylic polymer dispersed liquid crystals films

The nematic liquid crystals (LCs) are randomly dispersed material with random orientation order in polymer dispersed liquid crystal (PDLC) films. The LCs change their orientation from random to vertical as electric field is applied. This transformation of orientation order of nematic liquid crystals in the PDLC films is controlled by many factors operating simultaneously. For instance, some factors like the internal forces of attractions among the neighboring LC molecules, anchoring with polymeric matrix, ITO glass boundaries, and chemical structures of the materials are less studied. The learning of extent of vertical orientation of liquid crystal droplets in an electric field is essential to attain optimum electro optical properties of PDLCs. In this finding, bipolar and radial LCs droplets with random orientation have been observed in non-acrylic polymeric media. It is learned that with small increase of contents of external material, the extent of vertical orientation has been varied intensely. The extent of vertical orientation of LCs molecules increases as the contents of external non-acrylic polymeric material decreased. For this study, the orientations of LCs with respect to material type/contents, external applied force, and restoration of electric filed as hysteresis have been studied in details.     

Liquid crystals for display applications

Active Matrix (AM) LCDs and STN LCDs are the leading display technologies for portable applications such as notebook computers. Recently, new LCD device configurations and new LCD operation modes have been introduced. The existing technologies and the new LCD operation modes require improved liquid crystal materials. The history of liquid crystals for display applications and recent progress in new liquid crystal structures is presented.     

Genetically Engineered Supercharged Polypeptide Fluids: Fast and Persistent Self‐Ordering Induced by Touch

Mechanically induced disorder–order transitions have been studied in fluid surfactant solutions or polymer thermotropic liquid crystals. However, isothermally induced ordered phases do not persist after cessation of shear, which limits their technological applicability. Moreover, no such stimuli‐responsive materials involving biomacromolecules have been reported although biopolymer liquids are gaining a lot of attention. A biological fluid system is introduced in which anionic polypeptides are complexed with cationic surfactants. The resulting fluids exhibited very sensitive isotropic–nematic transition triggered by shear. The formed liquid crystal was preserved after cessation of mechanical stimulus. Self‐ordering behavior of the material was achieved through water flow and finger pressing. The latter mechanical induction resulted in the formation of complex pattern that can be read out by birefringence, allowing the recording of fingerprint information.     

Self-organization of disc-like molecules: chemical aspects

The hierarchical self-assembly of disc-shaped molecules leads to the formation of discotic liquid crystals. These materials are of fundamental importance not only as models for the study of energy and charge migration in self-organized systems but also as functional materials for device applications such as, one-dimensional conductors, photoconductors, light emitting diodes, photovoltaic solar cells, field-effect transistors and gas sensors. The negative birefringence films formed by polymerized nematic discotic liquid crystals have been commercialized as compensation foils to enlarge the viewing angle of commonly used twisted nematic liquid crystal displays. To date the number of discotic liquid crystals derived from more than 50 different cores comes to about 3000. This critical review describes, after an in-depth introduction, recent advances in basic design principles and synthetic approaches towards the preparation of most frequently encountered discotic liquid crystals.     

Remarkable effect of pre‐organization on the self assembly in chiral liquid crystals

In this article, liquid crystal phases possessing a helical molecular assembly, including frustrated three dimensional (3D) structures, are overviewed. Then, the chirality‐originated superstructures in liquid crystals studied by the author are reviewed. The importance of the concept of “pre‐organization” is highlighted, thus, molecular design producing a strong chiral effect has been proposed. Dichiral twin materials have been prepared systematically based on this concept, and correlation between molecular architectures and resulting frustrated liquid crustal phases, such as smectic blue, cubic, tetragonal smectic Q, and sponge phases, has been investigated. An electrically induced anisotropic birefringent structure in the chiral isotropic phase and a photoinduced 3D‐3D phase transition in the smectic Q phase are introduced as possible application on the basis of the frustrated chiral 3D structured liquid crystal phases. A new type of chiral effect inducing the structural anisotropy in the 3D cubic structure of soft material is also described. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 340–355; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200900029     

Effect of liquid oils on the properties of multiple emulsions containing liquid crystals

Recently, many cosmetic researchers have been focused on multiple emulsions due to better performance. Limited application of multiple emulsions has been attributed to their instability, which can be resolved by the presence of liquid crystals. Multiple emulsions containing liquid crystals are affected by various formulation parameters, such as liquid oils. In this paper, the influence of liquid oils on the formation mechanism was studied. Besides, stability, small-angle x-ray scattering (SAXS) spectra analysis, and rheological analysis of the emulsions were investigated as well. The results showed that when the gap of the polarity between inner oils and external liquid oils is greater, the multiple structures were more easily formed. Multiple emulsions containing liquid crystals were superior in stability to multiple emulsions prepared in the same way with liquid oils that did not form liquid crystals. SAXS indicated that the liquid crystal orientation was lamellar. Rheological analysis indicated that the different structure emulsions showed shear-thinning behavior. The presence of liquid crystal decreased the viscosity and resulted in pseudoplastic enhancement. Both the storage modulus (G′) and the loss modulus (G″) of multiple emulsions were slightly higher than those of O/W-type emulsions, implying the existence of multiple structures.     

Thermally Twistable,Photobendable, Elastically Deformable,and Self‐Healable Soft Crystals

The first example of a smart crystalline material, the 2:1 cocrystal of probenecid and 4,4′‐azopyridine, which responds reversibly to multiple external stimuli (heat, UV light, and mechanical pressure) by twisting, bending, and elastic deformation without fracture is reported. This material is also able to self‐heal on heating and cooling, thereby overcoming the main setbacks of molecular crystals for future applications as crystal actuators. The photo‐ and thermomechanical effects and self‐healing capabilities of the material are rooted in reversible trans–cis isomerization of the azopyridine unit and crystal‐to‐crystal phase transition. Fairly isotropic intermolecular interactions and interlocked crisscrossed molecular packing secure high elasticity of the crystals.     

Star-shaped supramolecular ionic liquid crystals based on pyridinium salts

Series of novel star-shaped liquid crystals containing [1,1?-biphenyl]-4,4?-diyl diisonicotinate mesogens with various counterions (Br^?, B-SO₃^?,C-SO₃^?,H₂PO₄^?, BF₄^?) have been synthesized and characterized, which display a nematic phase. The molecular structures of the liquid crystals, thereof consisting of rod-like mesogens linked together by different long alkyl spacers to a small disc-like core of central benzene-1,3,5-triyl triisonicotinate, have been fully characterized by ¹H NMR. Their thermal and supramolecular organization behaviours have been studied by combining polarized optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. These investigations showed that the mesophase temperature range increased with increasing alkyl chain length and the clearing point decreased with increase of anion size. These star-shaped liquid crystals have a long and ordered molecular structure, the electron delocalization of the π-π stacking conjugation effect and the electrostatic attraction of ionic make them have good ferroelectric properties and ionic conductivity properties. The interest in preparing ionic liquid crystal with a nematic phase lies in the technological applications as it is well known that the nematic phase has the highest fluidity of all liquid crystalline phases and hence the possibility to align it by applying an external electric/magnetic field, commonly used in electro-optical devices.     

Thermally Twistable,Photobendable, Elastically Deformable,and Self‐Healable Soft Crystals

The first example of a smart crystalline material, the 2:1 cocrystal of probenecid and 4,4′‐azopyridine, which responds reversibly to multiple external stimuli (heat, UV light, and mechanical pressure) by twisting, bending, and elastic deformation without fracture is reported. This material is also able to self‐heal on heating and cooling, thereby overcoming the main setbacks of molecular crystals for future applications as crystal actuators. The photo‐ and thermomechanical effects and self‐healing capabilities of the material are rooted in reversible trans–cis isomerization of the azopyridine unit and crystal‐to‐crystal phase transition. Fairly isotropic intermolecular interactions and interlocked crisscrossed molecular packing secure high elasticity of the crystals.