Liquid vaporization actuated soft structures with active cooling and heat loss control

Abstract Soft robotic systems that are inspired by nature utilize soft materials to perform various tasks in diverse environments. One promising method to control their movement is by utilizing liquid vaporization. In most cases, liquid with high vapor pressure is injected into hollow cavities inside the elastomer. Heating the system vaporizes the liquid, and the structure is inflated by the generated gas. However, there is a significant time lag between powering the system and structural actuation due to the slow increase in temperature that is exacerbated by heat loss. Simply using materials with low thermal conductivity can improve actuation, but the reduced heat loss concurrently increases cooling time during the reversing process. Furthermore, underwater actuation through vaporization remains a challenge, since heat loss becomes even more significant. To address these issues, this study aims to develop a system that can actively control heat loss to enhance both actuation and cooling while performing consistently even in extreme environments. First, double-walled structures were fabricated with silicone elastomer to drastically lower thermal conductivity. Next, a thermoelectric device was installed on the bottom layer to heat and cool the sealed liquid by reversing current flow. The low thermal conductivity of the double-walled structure enhanced actuation performance, while actively cooling the system with the thermoelectric device accelerated the reversing process. Structures with single- and double-layered walls were tested underwater to validate their performance. Finite element models verified the effects of wall designs on heat transfer and structural mechanics. Demonstration of enhanced reversible actuation of the system was performed using a soft anemone-like structure operated underwater.