自支撑向列相液晶物理凝胶的设计及其电控光散射行为

Liquid-crystalline physical gels (LCPGs) are a new class of stimuli-responsive thermoreversible soft solid materials based on the non-covalent self-assembly of fibrous networks of low molecular mass organic gelators in liquid crystals. This kind of material has potential broad applications on large-scale, ultrathin and flexible displays, information storages, advanced anti-counterfeits, and so on. However, the non-covalent fibrous networks in LCPGs are not solid or hard enough, leading to low thermal, shear and voltage resistance, which is lack of self-supporting ability. In this proposal, self-supporting LCPGs with high modulus and low driving voltage are prepared by a series of sorbitol derivatives with different numbers of methyl groups on the benzyl rings, i.e. DBS, MDBS and DMDBS, as gelators and nematic liquid crystals including 5CB and P0616A. The effects of gelators, isotropic-nematic transition temperatures of liquid crystals, preparation conditions including gelation process and magnetic field strength up to 16 Tesla on the microstructures and macroscopic performances of LCPGs, such as electro-optical properties, and phase transition and rheological behaviors, will be investigated for light-scattering display materials with high modulus and low driving voltage. Three gelation processes used herein are isothermal process, continuous decreasing temperature process, as well as the process with nucleation at low temperature & growth at high temperature. The formation mechanism of gelation process and the quantitative relationship between light-scattering properties and fractal dimension of the fibrous networks of LCPGs will be emphasized. The study can provide theoretical and practical aspects for the design and preparation of such materials.

液晶物理凝胶（LCPG）作为一类新颖的刺激-响应、热可逆软固体材料，在大面积、超薄、柔性的光散射型电光显示、信息存储和高端防伪等领域应用前景广阔，但其模量往往不高，导致耐电压性低和抗剪切力的性能差，难以满足自支撑要求。本申请项目拟以有机小分子山梨醇类衍生物为凝胶因子，与向列相液晶形成LCPG。通过选取不同烷基取代基数目的凝胶因子（DBS、MDBS和DMDBS）和不同相转变温度的液晶（5CB和P0616A）、改变制备条件（如等温、连续降温、低温成核-高温增长三种凝胶化过程和0~16T的稳态磁场）等手段调控界面作用和微结构，制备出兼有高模量和低驱动电压的LCPG，实现其自支撑能力。结合相转变及流变行为、电光特性等宏观性能与微观结构分析，阐明高模量凝胶纤维网络的形成机理及其对液晶电控光散射特性的影响规律，建立电光特性与分形维数的定量关系，为此类材料的设计、制备及其应用提供理论和实验依据。

作为一类新颖的刺激‐响应、热可逆软固体材料，液晶物理凝胶（LCPG）的刚度往往不足，导致其耐电压性低和抗剪切能力差，难以满足自支撑要求；同时，低驱动电压和快速响应也是光电器件的必备要求。针对这两个难点，本项目以有机小分子山梨醇类衍生物为凝胶因子，与向列相液晶构筑形成兼具自支撑能力和优良电光特性的LCPG。通过选取不同烷基取代基数目的凝胶因子（DBS、MDBS和DMDBS）和不同相转变温度的液晶（5CB和P0616A）、改变制备条件（如降温、液晶盒内表面取向或稳态强磁场取向）、添加氧化硅纳米粒子等手段， 对LCPG的微结构和界面作用进行调控，系统研究了各体系的凝胶化行为及相图。着重研究了各凝胶体系的微结构、电光特性和流变特性，制备出兼有高模量和低驱动电压的LCPG，实现了LCPG的自支撑行为，即储能模量达到10kPa以上。首先，建立了制备具有稳定光散射性能的LCPG的有效方法，通过调节凝胶因子的化学结构，成功制备了具有高模量和低驱动电压的液晶物理凝胶，并揭示同系物凝胶因子分子结构、含量及其相行为和微结构之间的相互关系。其次，利用Gompertz方程阐述了凝胶储能模量与凝胶因子含量之间的标度关系，为构筑自支撑凝胶提供了理论依据，阐明了高模量凝胶纤维网络的形成机理及其对液晶电控光散射特性的影响规律。再次，在液晶态下，建立了在TN盒表面取向和强磁场作用下制备有序排列LCPG的有效方法，体系的有序网络有利于实现快速响应和低驱动电压双重效果，阐明了电光特性与有序结构之间的关系。最后，建立了一种通过外加无机纳米粒子进一步提升液晶复合凝胶自支撑能力的方法，该方法还能保持凝胶体系的快速响应和低驱动电压行为。本项目的实施，为此类软固体材料的设计、制备及其在大面积、超薄、柔性的光散射型电光显示、信息存储和高端防伪等领域的应用提供了理论基础和实验依据。

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