Title: Ultralarge Contraction Directed by Light-Driven Unlocking of Prestored Strain Energy in Linear Liquid Crystal Polymer Fibers

Author: Xinlei Pang, Lang Qin, Bo Xu, Quan Liu, Yanlei Yu*

Journal: Adv. Funct. Mater., 2020, 30(32), 2002451

Abstract:

Anisotropic 1D contraction motion of polymeric actuating materials has drawn growing interests in fields ranging from soft robotics to biomimetic muscles. Although light-driven liquid crystal polymers (LCPs) represent promising candidates to realize contraction (< 20%) triggered remotely and spatially, there remain multitudes of challenges to develop an LCP system possessing ultralarge contraction rate. Here, a novel strategy combining shape memory effect and photochemical phase transition is presented to realize light-driven contraction as large as 81% in a newly designed linear liquid crystal copolymer, where the eutectic mesogens of azobenzene and phenyl benzoate self-organize into the smectic B phase.Importantly, this highly ordered structure as the switching segment firmly locks the stress-induced strain energy, which is rapidly released by reversible trans-cis photoisomerization that destroys the lamellar liquid crystal phase,therefore leading to such ultralarge contraction. Fibers serve as light-driven building blocks to achieve precise origami, to mimic the recovery of a “broken”spider web and to screen objects in different sizes, laying new ground for advanced applications of light-driven LCPs from biomimetic robots to human assists.

论文链接：https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202002451

PDF下载：Ultralarge Contraction Directed by Light-Driven Unlocking of Prestored Strain Energy in Linear Liquid Crystal Polymer Fibers.pdf

具有超大收缩形变的线性液晶聚合物纤维如同太上老君的捆仙绳一般，在470 nm蓝光刺激下能够牢牢锁住顽皮的泼猴。

本文报道了一种光化学相转变与形状记忆效应相结合的形变新原理，实现了液晶聚合物纤维高达81%的超大光致收缩形变。产生超大光致收缩形变的原因主要归结于以下几点：（1）将高度有序的近晶B相作为转变单元是实现大收缩率的先决条件，它能在室温下限制主链运动并确保应变能被锁定在纤维中；（2）拉伸结合退火的操作是储存应变能并使液晶基元自组装形成高取向度近晶B相的必要步骤；（3）液晶分子排列在光照下从有序到完全无序的显著变化是释放应变能的关键；（4）光照使得纤维的Tg下降，进一步提高了链段的运动能力，有利于应变能的释放。此外，偶氮苯持续的trans-cis-trans异构化过程会产生一定的自由体积，使链段的运动能力增强。