Enhancing the hermeticity of liquid-vapor phase change soft actuators via sandwich-like liquid metal seals

Soft actuators based on phase change materials (PCMs) hold great potential for advancing soft robotics through their high energy density and flexibility in design. However, vapor leakage in such actuators undermines their long-term functionality and durability. In this study, we developed a liquid-vapor phase change soft actuator with enhanced hermeticity. We evaluated four sealing strategies using (1) untreated silicone, (2) silicone with hydrophobic surface, (3) silicone/liquid metal (LM) mixture, and (4) sandwich-like silicone-LM-silicone structure, respectively. Among these, the LM sandwich structure exhibited the best hermetic performance, reducing ethanol leakage by approximately two-thirds compared to untreated silicone. The actuator sealed by LM sandwich maintained its flexibility and exhibited improved bending performance, sustaining a large bending angle over extended cycles. The proposed actuators were incorporated into a soft gripper, demonstrating stable and prolonged gripping functionality. These findings offer a promising strategy for developing durable and reliable soft actuators for real-world robotic applications.