Strong and Programmable Dry Adhesion through Graded Modulus Design

Strength of soft adhesives is limited by interfacial stress concentrations at corners and edges, which hinder the full utilization of their load-bearing capability. Here, we propose a new class of scalable, compliant graded modulus adhesives (GMAs) that improve strengths by one-order-of-magnitude, extend size limitation of soft adhesives by three-orders-of-magnitude, enable adaption to various surface morphologies, and provide on-demand detachment. We fabricate the GMAs by differential photopolymerization via light attenuation, generating continuous modulus gradient of two-orders-of-magnitude over a 1 mm thick sample, and resulting in glassy and rubbery phase on opposing surfaces. The GMAs effectively homogenize the interfacial stresses over the entire contact surface, eliminate stress concentrations at corners and edges, and enable adhesion at theoretical limit. Upon heating to 80 ℃, the modulus gradient is diminished, leading to drastically lower adhesion strength and easy detachment. These advantages establish GMAs as new adhesive design paradigm for developing next-generation soft adhesives.