Specimen Thickness Dependency of Energy Release Rate of a Gelatin Hydrogel and Glass Substrate Interface

Soft solids, such as rubbers, elastomers, and gels, are the important polymeric materials. A better understanding of their interfacial properties such as friction and adhesion is critical for variety of technological applications. Motivated by the experimental observation that interfacial properties can be modified even without changing the content of a soft solid, the effect of specimen thickness on the energy release rate (G) of a soft gelatin hydrogel is investigated in direct shear test. Slide-hold-slide (SHS) experiments have shown that shear strength decreases, while corresponding crack length increases, with increase in thickness of gel specimens. However, G at static, dynamic and residual strengths increase with specimen thickness. At the end, these observations are explained in light of mixed mode I/II fracture and shear rate effects at the sliding interface.