Design and Analysis of Photo-responsive polymers: scale bridging between CG MD and shell FE
Maenghyo Cho , Seoul National University
Crosslinked liquid crystalline polymer (CLCP) containing the photochromic azobenzene molecules exhibits novel mechanical deformations triggered by the UV and visible light illuminations. Owing to the virtues of wireless and remote control, these photo-responsive polymers (PRPs) have been utilized as the photo-actuated mechanical devices. In order to efficiently design and predict the photo-mechanical deformations through the computational model, development of the multiscale and multiphysics analysis is essentially required. Therefore, we propose a scale-bridging simulation framework via using coarse-grained molecular dynamics (CG MD) and two-dimensional shell finite element (FE) simulations. The macromolecular response of the PRPs are captured by using the CG MD simulations. The photo-isomerization from the trans- to cis-azobenznes are described by the mesoscale photo-switching potential, which is derived in order to reflect the conversion of molecular shape and corresponding collapse of the LC symmetry. As a result, the light-induced phase transition (smectic A (Sm A) – nematic (N) – isotropic (I)) and mechanical responses are successfully reproduced, which cannot be achieved by using the conventional all-atom MD (AA MD) simulations due to its huge computational costs. The light-induced effects on the PRPs are classified by two parts: (i) macromolecular shape change and (ii) photo-softening effect on mechanical properties. Accordingly, the shape parameter and elastic moduli (shear and layer moduli) of the polymer network are expressed as a function of the morphology change generated by the photo-chemical reactions. These mesoscale parameters are integrated with opto-mechaincal coupled constitutive equation, which is based on the neo-classical elastic free energy. Then, the FE shell formulation is carried out with considering the geometric nonlinearity generated by rotation of the azobenzene molecules. We demonstrated not only simple photo-bending deformations but also exotic 3D deformations with the aid of the blueprinted patterns using the developed scale-bridging technique. Furthermore, this study reveals that the PRPs with different initial phases and micro-morphologies can be deformed into diverse topographies, and its shape can be controlled in terms of the external light conditions. It is expected that the proposed scale-bridging framework can expand the capability of multiscale computational mechanics in the field of photo-responsive soft actuators and robots.
Maenghyo Cho , Seoul National University
Crosslinked liquid crystalline polymer (CLCP) containing the photochromic azobenzene molecules exhibits novel mechanical deformations triggered by the UV and visible light illuminations. Owing to the virtues of wireless and remote control, these photo-responsive polymers (PRPs) have been utilized as the photo-actuated mechanical devices. In order to efficiently design and predict the photo-mechanical deformations through the computational model, development of the multiscale and multiphysics analysis is essentially required. Therefore, we propose a scale-bridging simulation framework via using coarse-grained molecular dynamics (CG MD) and two-dimensional shell finite element (FE) simulations. The macromolecular response of the PRPs are captured by using the CG MD simulations. The photo-isomerization from the trans- to cis-azobenznes are described by the mesoscale photo-switching potential, which is derived in order to reflect the conversion of molecular shape and corresponding collapse of the LC symmetry. As a result, the light-induced phase transition (smectic A (Sm A) – nematic (N) – isotropic (I)) and mechanical responses are successfully reproduced, which cannot be achieved by using the conventional all-atom MD (AA MD) simulations due to its huge computational costs. The light-induced effects on the PRPs are classified by two parts: (i) macromolecular shape change and (ii) photo-softening effect on mechanical properties. Accordingly, the shape parameter and elastic moduli (shear and layer moduli) of the polymer network are expressed as a function of the morphology change generated by the photo-chemical reactions. These mesoscale parameters are integrated with opto-mechaincal coupled constitutive equation, which is based on the neo-classical elastic free energy. Then, the FE shell formulation is carried out with considering the geometric nonlinearity generated by rotation of the azobenzene molecules. We demonstrated not only simple photo-bending deformations but also exotic 3D deformations with the aid of the blueprinted patterns using the developed scale-bridging technique. Furthermore, this study reveals that the PRPs with different initial phases and micro-morphologies can be deformed into diverse topographies, and its shape can be controlled in terms of the external light conditions. It is expected that the proposed scale-bridging framework can expand the capability of multiscale computational mechanics in the field of photo-responsive soft actuators and robots.
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