Understanding silicone elastomer curing and adhesion for stronger soft devices

Abstract

Silicone elastomers are widely used in biomedical devices and soft machines because of their compliance, inertness, and biocompatibility. Their sol-gel transition during curing enables mold casting and layer-by-layer manufacturing, allowing the fabrication of fully elastomeric and hybrid soft-rigid devices. However, controlling adhesion at material interfaces remains elusive, especially under diverse temperature conditions. This study introduces a framework that relates adhesion strength to a dimensionless reaction coordinate coupling time and temperature. This reaction coordinate can be used to predict the transition from bulk fracture to adhesive failure, which is crucial to create robust devices with strong interfaces. Using this framework, we fabricated elastomeric robotic actuators and demonstrated 3D printing with direct ink writing. The actuators achieved 50% higher curvature with the same design, and the 3D-printed parts exhibited over 200% improvement in interlayer adhesion. This work serves as a tool for optimizing interfacial adhesion for soft materials across different fabrication approaches.