Toughening of hydrogel adhering interface based on soft/hard heterogeneous structures

Emerging technologies like hydrogel based stretchable devices call for new interfacial toughening strategies for the achievement of reliable hydrogel adhering interface. Here, we propose a soft/hard composite design to enhance the average peel force for stretchable hydrogel adhesion. We fabricate a hydrogel/elastomer composite with alternate structures where the hydrogel acts as the soft component and the elastomer acts as the hard component. The elastomer is embedded in the hydrogel, with a thin hydrogel layer coated on its surfaces to work as the interfacial hydrogel layers for adhesion. When two pieces of the adhering composites are separated in a 180°peeling test, the peeling front will get stuck when it extends from a soft phase to an adjacent hard phase. The interfacial hydrogel layers between the entire symmetric elastomer units near the peeling front are stretched and the elastomer bends steadily until a sudden debonding occurs, which releases the stored energy and improves the overall adhesion properties. We adjust the structural parameters and obtain an average peak peel force of 330 N/m, which is almost 5 times the peel force of 70 N/m required to peel homogeneous hydrogels. We establish a beam model to study the peeling behaviors of the hydrogel/elastomer composite in the 180°peeling test. The numerical results agree with the experimental results quantitatively. We also show that the peeling performance of the hydrogel/elastomer composite can be tuned by controlling the patterning of the composite structures.