纳米二氧化硅增强液晶复合凝胶

Nano-silica enhanced liquid-crystalline composite gels

柔软的微环境是赋予液晶分子对外场快速响应的基本要求之一,但纯液晶材料却无任何力学强度,限制了其进一步应用.本文将粒径为150 nm的二氧化硅引入由向列相液晶4-正戊基-4′-氰基联苯（5CB）和凝胶因子亚苄基山梨醇（DBS）组成的液晶物理凝胶中,通过纳米Si O2与DBS的协同效应来凝胶液晶,大幅度提高了所形成的复合凝胶网络的储能模量.采用差示扫描量热仪（DSC）、偏光显微镜（POM）、场发射扫描电子显微镜（FE-SEM）、流变仪和液晶显示参数测试仪等手段研究了液晶复合凝胶的相转变行为、形貌结构、流变和电光特性.结果表明,固定DBS含量为2.0%（质量分数,下同）时,与未加纳米粒子的液晶凝胶相比,随着纳米Si O2含量的增加,复合凝胶网络由纤维织构转变为类似球晶织构,其储能模量G′呈先增后减的趋势,当Si O2含量为2.0%时达到最大值1.5×10~5Pa,其阈值电压和关闭时间最大增幅不超过1和2倍.当二氧化硅添加量仅为0.5%时,复合凝胶的G′即可达10~5 Pa,提高了1个数量级,其阈值电压和关闭时间也分别只增加了46%和63%.此研究为进一步拓展此类材料在自支撑电光器件等领域的应用提供了新思路.

Soft micro-environment is one of the most important requirements for fast responses of liquid crystals（LCs） to external stimuli; however, the drawback of poor mechanical properties for LCs limits their further applications. In this work, the storage modulus（G′） of the LC physical gels, nematic 4-pentyl-4′-cyanobiphenyl（5CB） and 1,3：2,4-di-O-benzylideneD-sorbitol（DBS）, has been greatly enhanced by the addition of nano-silica into physical gels. The composite gels are formed through the synergistic effects of the nanoparticle and the gelator. The phase transition behaviors, morphologies, dynamic rheological behaviors and electro-optical properties of the composite gels were investigated using differential scanning calorimeter, polarized optical microscope and field emission scanning electron microscope, rheometer and LCD parameter tester, respectively. Compared with the LC physical gel without nano-silica, with the increase of nano-silica content from 0.1wt% to 4.0wt% at a fixed DBS content of 2.0wt%, the network texture of composite gels was changed from nano-fibrillar to spherulite-like. The G′ increased firstly and then decreased with a maximum value of 1.5×105 Pa at the nano-silica content of 2.0wt%. The threshold voltage（Vth） and the off time（toff） increased within 1 time and 2 times, respectively. When the amount of nano-silica was only 0.5wt%, the G′ of the composite gel was improved to 105 Pa, an order of magnitude higher than the gel without nanoparticles. Meanwhile, its Vth and toff only increased 46% and 63%, respectively. This work opens a new window to the applications of LCs with excellent self-supporting ability and fast switch responses.