Tough, Flexible, Strong: Characterization of Soft-Soft Silicone Interfaces for Soft Robotics.

The soft robotics field is moving toward increasingly complex and integrated systems, which will contain interfaces between soft components and other soft, compliant, and/or rigid components. Although many soft interfaces leverage adhesion, soft robot designers currently have limited information for selecting appropriate materials and fabrication techniques. Through experimental testing, this article characterizes how the substrate material and bonding process influence the performance of soft-soft silicone i.e., polydimethylsiloxane-based interfaces, provides a framework for approaching this analysis, and contextualizes the data to provide initial insights into material selection for soft-soft interfaces by showing how the data could be used to guide design decisions. Specifically, this article characterizes five addition-curing silicone rubbers and five bonding processes, and it defines performance using quantitative metrics relating to desirable qualitative behaviors: toughness (adhesive fracture energy), flexibility (maximum localized strain during peeling), and strength (ratio of initial-to-average force and magnitude of initial peak peel force). Together, the substrate material and bonding method jointly determine the failure behavior of soft-soft silicone interfaces, influencing both the achievable performance (toughness, strength, flexibility) and characteristic failure modes (adhesive, cohesive, mixed-mode). Understanding characteristic failure modes can inform design strategies to mitigate interfacial failure, enabling higher-capability soft robots with improved operating loads and component lifetimes.