Rapidly Reversible Organic Crystalline Switch for Conversion of Heat into Mechanical Energy

Solid state thermosalience—a sudden exertion of an expansive or contractive physical force following a temperature change in a solid state compound—is rare, few are reversible systems, and most of these are limited to a dozen or so cycles before the crystal degrades or they reverse slowly over the course of many minutes or even hours. In this work, we show a fully reversible actuator that is stable at room temperature for multiple years and is capable of actuation for more than two hundred cycles at near ambient temperature. Specifically, the crystals shrink to 90% of its original length instantaneously upon heating beyond 45 °C and expands back to its original length upon cooling below 35 °C. This temperature regime is important because it occurs around physiologically important temperatures. Furthermore, the phase transition occurs instantaneously, with little obvious hysteresis, allowing us to create real-time actuating thermal fuses that cycle between on and off rapidly.