Skačej Gregor, Querciagrossa Lara, Zannoni Claudio
Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia.
Dipartimento di Chimica Industriale "Toso Montanari", Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy.
ACS Appl Polym Mater. 2023 Jul 26;5(8):5805-5815. doi: 10.1021/acsapm.3c00361. eCollection 2023 Aug 11.
We investigate main-chain liquid crystal elastomers (LCEs) formed by photoresponsive azobenzene units with different populations of and conformers (from fully to fully ). We study their macroscopic properties as well as their molecular organization using extensive Monte Carlo simulations of a simple coarse-grained model where the and conformers are represented by soft-core biaxial Gay-Berne particles with size and interaction energy parameters obtained by fitting a bare bone azobenzene moiety represented at atomistic level. We find that increasing the fraction of conformers, as could be obtained by near-UV irradiation, shifts the nematic-isotropic transition to a lower temperature, consistently with experiment, while generating internal stress in a clamped sample. An analysis of pair distributions shows that the immediate surroundings of a bent molecule are slightly less dense and more orientationally disordered in comparison with that of a conformer. Comparing nematic and smectic LCEs, actuation in the smectic phase proved less effective, disrupting the smectic layers to some extent but preserving orientational order of the azobenzene moieties.
我们研究了由具有不同顺反异构体比例（从全反式到全顺式）的光响应偶氮苯单元形成的主链液晶弹性体（LCE）。我们使用一个简单的粗粒化模型进行了广泛的蒙特卡罗模拟，研究了它们的宏观性质以及分子组织，其中顺反异构体由软核双轴Gay-Berne粒子表示，其尺寸和相互作用能参数通过拟合原子水平表示的裸骨偶氮苯部分获得。我们发现，如通过近紫外照射可实现的那样，增加顺式异构体的比例会使向列相-各向同性转变温度降低，这与实验结果一致，同时在夹紧的样品中产生内应力。对成对分布的分析表明，与反式异构体相比，弯曲的顺式分子的紧邻环境密度略低且取向无序程度更高。比较向列相和近晶相LCE，近晶相中的驱动效果较差，在一定程度上破坏了近晶层，但保留了偶氮苯部分的取向有序性。
