全息聚合物分散液晶的结构调控与性能

Structure Regulation and Performance of Holographic Polymer Dispersed Liquid Crystals

全息聚合物分散液晶(HPDLCs)是由富聚合物相与富液晶相周期性排列而成的结构有序高分子复合材料.HPDLCs通过单体/液晶复合体系的光聚合诱导相分离而形成,如何调控并定量化描述复合体系的光聚合反应动力学、凝胶化行为和相分离程度,进而获得结构规整、电光性能优异的HPDLCs是关键难题.专论概述了光引发体系、单体结构、纳米无机材料掺杂对HPDLCs结构及性能的影响.光引发阻聚剂通过引发和阻聚的竞争与协同,降低了光聚合反应速率、延迟了凝胶时间,促进形成衍射效率达90%的HPDLCs.超支化单体降低了复合体系黏度和光聚合反应速率,延迟了凝胶时间,促使形成衍射效率达94%、具有一维光子晶体结构的HPDLCs.丙烯酰胺单体优化了相分离结构,将HPDLCs的衍射效率提升至98%.纳米硫化锌掺杂在保持规整结构和高衍射效率的同时,大幅降低了HPDLCs的驱动电压.研究还确定了HPDLCs的相分离程度与凝胶时间的函数关系.构建兼具高衍射效率与低驱动电压的HPDLCs,推进其在彩色3D图像存储等领域的应用仍是重要课题.

Holographic polymer dispersed liquid crystals （HPDLCs） are one type of polymer composites in the form of periodically distributed polymer-rich phase and LCs-rich phase with ordered structure. HPDLCs are typically formed via photopolymerization induced phase separation of monomer/LCs mixtures. Despite of the extensive research on HPDLCs since 1993, it remains challenging to tune and quantitatively describe the photopolymerization kinetics, gelation behaviour, and degree of phase separation, for the aim of achieving HPDLCs with predesigned regular structure and desired electro-optical performance. This review summarizes the influence of the photoinitiating system, monomer structure, and doping of inorganic nanomaterials on the structure and performance of HPDLCs. The deployment of photoinitibitor, which held competitive and synergetic photoinitiation and photoinhibition functions, was found to be able not only to trigger the photopolymerization upon laser light exposure, but also to decrease the photopolymerization rate, to delay the gelation, thus helping the formation of HPDLCs with a high diffraction efficiency of 90%. The first photoinitibitor was composed of 3,3＇-carbonylbis（7-diethylaminocoumarin） （KCD） and a co-initiator N-phenylglycine （NPG）. The photoinitiation and photoinhibition functions were also noted later in a normally used photoinitiating system composed of rose bengal （RB） and N-phenylglycine （NPG）. Hyperbranched monomer was disclosed to be able to decrease the mixture viscosity and the reaction rate, and also to delay the gelation. Consequently, HPDLCs with a diffraction efficiency of 94% and one-dimensional photonic structure were afforded on the basis of the employment of hyperbranched monomer because of the enhanced phase separation. Acrylamide monomer was found to optimize the phase separated structure, offering HPDLCs with a high diffraction efficiency of up to 98%. The doping of mercaptoethanol functionalized nano-ZnS was found to decrease dramatically the driving voltage while maintaining regular structure and high diffraction efficiency of HPDLCs. These ZnS nanoparticles were expected to be localized in the polymer rich-region to increase the conductivity of the region. The numerical relationship between the degree of phase separation of HPDLCs and gelation time of monomer/LCs mixtures is also highlighted. We believe that there remain opportunities to increase simultaneously the diffraction efficiency while decreasing the driving voltage of HPDLCs. Colored 3D holographic image storage and other practical applications of HPDLCs should be further advanced.