Moon Junghwan, Chung Hayoung, Cho Maenghyo
Institute of Advanced Machines and Design, Seoul National University, Seoul, Republic of Korea.
School of Mechanical, Aerospace, and Nuclear Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea.
Phys Rev E. 2021 Jan;103(1-1):012703. doi: 10.1103/PhysRevE.103.012703.
The azobenzene-containing crosslinked liquid crystalline polymer is a potential candidate for a stimuli-responsive soft robot, as it provides contactless actuation without the implementation of any separate component. For facilitating practical applications of this novel material, complicated and predefined motions have been realized by tailoring the chemical structure of the polymer network. However, conventional multiscale mechanical analysis, which utilizes the all-atom molecular dynamics to represent a microscopic model, is unsuitable for handling diverse material design parameters due to excessive computational costs. Hence, a multiscale optomechanical simulation framework, which combines the coarse-grained molecular dynamics (CG MD) and the finite-element (FE) method, is developed in this study. The CG MD simulation satisfactorily reproduces the light-induced phase transition and photosoftening effect on the mechanical properties. In particular, using the mesoscale analysis, the presented methodology can treat diverse morphology parameters (liquid crystal phase, spacer length, and crosslinking density) to observe the associated photodeformations. The photostrain and elastic modulus profiles in terms of photoisomerization ratio are implemented into the continuum-scale governing equation, which is based on the neoclassical elasticity theory. To efficiently reflect the light-induced large rotations of liquid crystal mesogens and the corresponding geometric nonlinearity, a corotational formulation is employed in the FE shell model. We examine the mesostructural-morphology-dependent photobending deformations of the nematic and smectic photoresponsive polymers (PRPs). In addition, the mesoscopic-texture-mediated unique 3D deformations are investigated by modeling the topological defects. This study offers insight into the engineering of PRP materials for designing the mechanical motions of smart actuators.
含偶氮苯的交联液晶聚合物是刺激响应型软机器人的潜在候选材料，因为它无需任何单独组件即可实现非接触式驱动。为了促进这种新型材料的实际应用，通过调整聚合物网络的化学结构实现了复杂且预定义的运动。然而，传统的多尺度力学分析利用全原子分子动力学来表示微观模型，由于计算成本过高，不适用于处理各种材料设计参数。因此，本研究开发了一种结合粗粒度分子动力学（CG MD）和有限元（FE）方法的多尺度光机械模拟框架。CG MD模拟令人满意地再现了光诱导相变以及对机械性能的光软化效应。特别是，使用中尺度分析，所提出的方法可以处理各种形态参数（液晶相、间隔长度和交联密度）以观察相关的光致变形。基于新古典弹性理论，将光异构化率方面的光应变和弹性模量分布纳入连续介质尺度控制方程。为了有效反映光诱导的液晶分子大旋转以及相应的几何非线性，在有限元壳模型中采用了共旋公式。我们研究了向列相和近晶相光响应聚合物（PRP）的介观结构 - 形态依赖性光弯曲变形。此外，通过对拓扑缺陷进行建模研究了介观纹理介导的独特三维变形。本研究为设计智能致动器的机械运动的PRP材料工程提供了见解。
