[SY-H1] Symposium H-1

[SY-H1] Investigation of photo-mechanical behavior of azobenzene-based polymer: A coarse-grained molecular dynamics study

^○Junghwan Moon¹, Byungjo Kim¹, Joonmyung Choi², Maenghyo Cho^1,3 (1.Divison of Multiscale Mechanical Design, School of Mechanical and Aerospace Engineering, Seoul National University, Korea, 2.Mechatronics R&D center, SAMSUNG ELECTRONICS CO., LTD, Korea, 3.Institute of Advanced Machines and Design, Seoul National University, Korea)

Photo-active deformable structures have drawn great attention because they can exhibit complex 3D deformations without any electronic circuit. Among the photo-responsive polymers (PRPs), liquid crystalline polymers (LCPs) doped with photochromic azobenzene molecules have diverse applications for soft micro-mechanical actuators because of a reversible photo-isomerization under ultraviolet (UV)/visible light illumination. The micro-scale photo-mechanical behavior of the polymer network can be greatly represented using conventional molecular dynamics (MD) simulations. However, MD simulation cannot be applied to examine the meso-scale phenomena occurred in the photo-deformable structure because too much degrees of freedom (DOFs) are required for full-atomistic description. To overcome this limitation, we propose a multi-scale/multi-physics computational framework based on a coarse-grained (CG) molecular dynamics simulation, which combines molecular switching induced by the photo-isomerization, and overall shape change of the polymer network. The structure-based iterative Boltzmann inversion (IBI) method was utilized to systematically represent the photo-chemical reaction-induced change of the polymeric structure, and effectively expand time- and length-scales of the atomistic simulations. As a result, we could observe the transition between three different liquid crystalline phases (smectic A - nematic - isotropic) under light irradiation, which cannot be reproduced using the all-atom MD simulations. Also, we investigated a unique photo-deformation of the smectic LCP network and its effect on the mechanical properties. We expect the proposed multiscale modeling and simulations to be a guideline for mechanically designing the photo-responsive smart materials.