基于动态C-N键的可重塑形液晶弹性体的制备及光致弯曲形变特性研究

Fabrication of re-shapeable liquid crystalline elastomers with dynamic C-N bonds and investigation of their reversible photoresponsive bending behaviors

在加热和光辐照等外界刺激下,液晶弹性体(LCEs)可自发改变尺寸和形状,但是基于传统共价交联的LCEs是一类热固性材料,难以实现重塑形加工或制作复杂三维(3D)柔性致动器.本工作中,我们制备了通过硫醇-烯基点击反应在侧基同时引入苯甲酸对甲氧基苯酯(PB)和偶氮苯(Azo)液晶基元的聚硅氧烷侧链液晶聚合物,再基于炔基-叠氮点击反应形成的三氮唑与烷基溴之间在加热至较高温度时高效的交叉烷基化反应形成的C-N动态共价键,实现交联网络的重排再生并固定经单轴拉伸诱导产生的液晶基元宏观取向,制得可重塑形的单畴液晶弹性体LCE-M薄膜.具有光致顺反异构化转变特性的Azo基元的引入赋予LCE-M薄膜在紫外-可见光辐照下向光弯曲-伸展回复的可逆形变特点.液晶弹性体材料取向与驱动方式的分离,使该单畴液晶弹性体LCE-M薄膜在室温下经光辐照可反复多次稳定地驱动,有望用于制备较快速光响应的可重塑形柔性驱动器.

Liquid crystalline elastomers(LCEs) spontaneously change their dimensions and shapes in response to external stimuli, such as heat or light irradiation;however, LCEs based on conventional covalent crosslinks are thermosetting materials and thus unable to remold or fabricate into complex three-dimensional(3 D) soft actuators. In this work, we prepared polysiloxane side-chain liquid crystalline polymers with both p-methoxyphenyl benzoate(PB)and azobenzene(Azo) mesogens introduced as side groups through thiol-ene click reaction. Then a monodomain liquid crystalline elastomer LCE-M film was fabricated by fixing the macroscopic alignment of mesogens induced by uniaxial stretching upon heating to a higher temperature through C-N dynamic covalent bonds via highly efficient transalkylation between alkyl bromide and triazole from azide-alkyne click reaction to achieve rearrangement and regeneration of the crosslinked networks. The introduction of Azo mesogen with trans-cis isomerization characteristics endowed the LCE-M thin films with reversible photoresponsive deformation properties of bending-stretching recovery upon alternate irradiation of UV and visible light. With the separation of alignment method and driving mode of such liquid crystalline elastomer material, the monodomain liquid crystalline elastomer LCE-M thin films can be repeatedly and stably driven by light irradiation at room temperature, which is expected to be employed for the fabrication of reshapeable flexible LCE actuators with faster photo response.