An Optical Actuator Based on Gold-Nanoparticle-Containing Temperature-Memory Semicrystalline Polymers.

Photoresponsive actuators based on semicrystalline poly(ethylene-co-vinyl acetate) (EVA) loaded with small amounts of gold nanoparticles (AuNPs) are described. Upon absorption of light (532 nm), the heat released by the AuNPs raises the temperature in the irradiated region to Tlight to melt crystallites with lower melting temperatures (Tm <Tlight ), resulting in a contraction force on the sample sustained by the crystalline skeleton domains with Tm >Tlight  . Once the light is turned off, the recrystallization of oriented chains in the actuation domains upon cooling gives rise to an expansion force. We show that the photoinduced contraction force, Tlight  , and the speed for reaching Tlight can readily be adjusted, which makes EVA/AuNP a robust, fast optical actuation system tunable in both speed and magnitude. The material design can easily be extended to other temperature-memory semicrystalline polymers in combination with various light-absorbing and heat-generating additives.