Experimental Investigation of Spontaneous Buckling-Driven Delamination of Thin Films on Soft Spherical Substrate

Abstract This study develops a new experimental system to investigate surface buckling patterns that emerge due to the biaxial compression of elastomeric bilayer spherical shell. The sample used in this study is a thick PDMS (polydimethylsiloxane) substrate and a thin PDMS film. In order to induce biaxial strain to the surface of PDMS substrate, air pressured device like bulge test is first developed. This system enables a flat PDMS plate to isotropically expand and become a hemisphere due to air pressure. In other words, the surface of PDMS substrate is stretched and subjected to biaxial loading. Subsequently, a thin PDMS film is covered on the hemisphere substrate. By releasing the air pressure, the pre-stretch in the substrate is released gradually and the outer film is subjected to biaxial compression. During the biaxial compression, various film buckling patterns are observed. It is found that the surface buckling patterns are wrinkle formation that is associated with film delamination. This formation pattern is dependent on the surface strain distribution, i.e. radial strain and circumferential strain. In order to control the pattern of buckling-delamination, we systematically changed the material parameters, such as the film thickness, Young’s modulus, interfacial fracture toughness, etc. Our experiment is capable in reproducing various wrinkle patterns with film delamination on an elastomeric bilayer spherical shell.