A composite material with room temperature shape processability and optical repair

A photoresponsive shape memory composite material with room temperature programmability is reported in this paper. The material is composed of poly(styrene-b-ethylene-co-butadiene-b-styrene) (SEBS: a thermoplastic elastomer), paraffin wax (PW: a mixture of short hydrocarbon chains with a melting point around 60 degrees C) and gold nanoparticles (AuNPs). On one hand, the SEBS/PW system is room temperature programmable, meaning that the temporary shape can be processed by directly deforming the material into a desired shape at room temperature. Particularly interesting is that the fixed deformation is not limited to elongation or compression, but includes other types of deformation like twisting and bending. This attribute makes three-dimensional shape processing doable under ambient conditions without heating or cooling. The results of wide-angle X-ray diffraction measurements on elongated SEBS/PW samples suggest that the stretching-induced orientation and reorganization of PW crystals could form a solid skeleton to sustain the elastic extension of the rubbery EB chains, resulting in the apparent plastic deformation. On the other hand, by loading a small amount of AuNPs (0.18 wt%) in the composite material, the shape recovery, which occurs upon melting of PW crystals, becomes controllable using visible light based on the photothermal effect arising from the surface plasmon resonance of AuNPs. Thanks to the ability of remote activation and spatiotemporal control, a potential application of photoresponsive shape memory materials with room temperature programmability is demonstrated using SEBS/PW/AuNP: damage inflicted on an object or a product in the form of mechanical deformation or shape distortion can be conveniently and effectively repaired using a visible light laser (532 nm) at room temperature.