Light induced reversible and irreversible mechanical responses in nanotube-polymer composites

It is shown that visible light irradiation of carbon nanotube (CNT) dispersed polymers may yield both reversible and irreversible changes in measured mechanical stress. While light irradiation of PDMS (polydimethylsiloxane)–CNT composite yields a change of stress level at a fixed strain, which reverts to the original value after the incident light is removed, the RET (reactive ethylene terpolymer)–CNT composite exhibits such reversible characteristics as well as an additional irreversible stress-relaxation response when the composite is first irradiated by light. A microscopic model is proposed to explain the mechanism of the dual photomechanical responses of the RET-CNT composites and quantitative predictions are compared with experimental measurements.