室温光致形变主链型交联液晶高分子纤维执行器

Photodeformable Main-chain Crosslinked Liquid Crystal Polymer Fiber Actuators at Room Temperature

将分别含有偶氮苯和苯甲酸苯酯的2种液晶单体与伯胺进行迈克尔加成反应,得到分子量可控的主链型液晶低聚物.利用先熔融提拉、后自由基聚合的方法将低聚物制备成交联液晶高分子纤维.液晶单体与伯胺之间的扩链反应有效地降低了高分子网络的交联密度,进而降低纤维的玻璃化转变温度.同时,这种先拉伸、再聚合的方式将纤维的取向与交联过程分开,保证了纤维中的液晶基元沿拉伸方向呈规整排列.因此,取向后的交联液晶高分子纤维可在室温下实现可逆光致弯曲形变,其最大弯曲角度接近60°,且弯曲方向可以通过改变光照方向进行调控.这种形变幅度大、方向可控的主链型交联液晶高分子纤维有望推动光响应柔性执行器等领域的发展.

Photodeformable crosslinked liquid crystal polymer fiber actuators have potential applications in soft robots and other fields.However,due to the limitations of processing methods,it is still a great challenge to fabricate fiber actuators that can undergo large and direction-controllable light-induced bending at room temperature.Here,the main-chain liquid crystal oligomer with controllable molecular weight is synthesized by the Michael addition reaction between primary amines and liquid crystal monomers containing azobenzene or phenyl benzoate mesogens,respectively.On the basis,the cross-linked liquid crystal polymer fiber is obtained through dip-drawing the melt oligomer followed by the radical polymerization.The chain extension reaction between the primary amine and liquid crystal monomers effectively decreases the crosslinking density of the polymer network,thus lowering the glass transition temperature.Meanwhile,the alignment and crosslinking processes are decoupled by the strategy that the oligomer is stretched first and then the polymerization is implemented,which ensures that mesogens in the fiber are aligned along the stretching direction.Accordingly,the aligned fiber exhibits reversible light-induced bending at room temperature,whose maximum bending angle is close to 60°,and furthermore the bending direction can be adjusted by the light irradiation direction.The main-chain crosslinked liquid crystal polymer fiber with large and direction-controllable deformation has great potential in the field of soft robots.In addition,the method of processing oligomers and then polymerizing actuators is expected to be combined with the template method and 3D printing to fabricate actuators with complex shapes,promoting the development of photoresponsive flexible actuators and other fields.