Light-Triggered Shape-Reconfiguration of Programmable and Stretchable Electronics with Enhanced Mechanical and Actuation Performance

초록

For shape-tunable miniaturized soft electronics, smart materials with material intelligence are necessary to achieve tailorable actuation under external stimuli. The molecular machine (e.g. azobenzene) embedded liquid crystalline polymer networks (azo-LCN) can be a promising candidate toward the platform of shape-reconfigurable electronics. However, azo-LCNs are electrically insulating and there are trade-off relationships between stiffness and deformability. To overcome these limitations, we introduced newly designed patterning process of reduced graphene oxide (rGO) onto azo-LCN. The evaporative self-assembly of GO solution and reduction was applied for preparing the rGO patterned glass cell which was used as a site of photopolymerization. The rGO patterned azo-LCN (azo-LCN/rGO) demonstrates enhancement of both mechanical and electrical properties without sacrificing the shape programmability of the azo-LCN. The storage modulus of the azo-LCN/rGO increased by a factor of 5 (E=6.4 GPa) yet with larger photo- and thermal responsivity in comparison with the neat azo-LCN. Also, the electrical conductivity of the azo-LCN/rGO was recorded to be 380 S cm^-1. In the actuation performance point of view, the in-plane bending angle of azo-LCN/rGO was drastically enhanced for both forward and backward bending under broadband UV exposure than that of the neat azo-LCN. The higher bending performance of azo-LCN/rGO than neat azo-LCN was driven by coefficient of thermal expansion (CTE) mismatch between azo-LCN and rGO layers in conjunction with photoisomerization of azobenzene. The azo-LCN/rGO also demonstrated multi-stimuli responsive actuation under near infrared (NIR), focused sunlight and direct heating by portable lighter. Finally, we integrated the azo-LCN with concept of ‘kirigami’ for enhanced degree of freedom about shape reconfigurability. The kirigami-engineered azo-LCN/rGO demonstrated the dual-stimuli responsive 3D shape-morphing by passive-type mechanica