Poly(ethylene-co-vinyl acetate)/graphene shape-memory actuator with a cyclic thermal/light dual-sensitive capacity

Abstract Although increasing efforts have been made to design shape-memory devices, the development of actuators with dual-sensitive capacities and cyclic actuations is still faced with many challenges. In this work, a kind of shape-memory composite (cEVA/G) based on poly(ethylene-co-vinyl acetate) and graphene was prepared. The cyclic actuation is enabled by the cEVA matrix, which possesses an excellent two-way shape-memory effect (2W-SME) featuring crystallization-induced elongation (CIE) and melting-induced contraction (MIC). Moreover, this composite has a suitable crystallization temperature (Tc) greater than 40 °C, which allows effective CIE during cooling to room temperature wherein the proposed actuator maintains its normal state. In addition, the incorporated graphene provides a near-infrared (NIR)-response, and thus the actuator exhibits a thermal/light dual-sensitive capacity. The theoretical aspects of 2W-SME were systematically investigated by varying the temperature ranges and heating/cooling rates, and the results indicate that CIE and MIC are sufficiently effective even under the most severe conditions. More importantly, a shape-memory cEVA/G specimen and an indicating circuit, which uses a lamp as an alarm, was assembled to form a conceptual actuator for sensing applications. This actuator can effectively raise an alarm (i.e., the lamp is turned on) when responding to direct heating and NIR irradiation, which reveals its thermal/light dual-sensitive capacity. After removing heating resources, the alarm is disengaged (i.e., the lamp is turned off) because of the automatic elongation of the shape-memory component during natural cooling to room temperature. Moreover, the performance of the proposed actuator in successive cycles of either direct heating or NIR irradiation further demonstrates the excellent cyclic dual-sensitive capacity of the proposed actuator.