Adhesion-induced instability patterns in thin confined elastic film

Adhesion-induced instability has been observed at the interface of a flexible plate and a thin elastic film bonded to a rigid substrate. The surface of the confined film develops undulations almost instantaneously, and instability patterns appear in the form of fingers or bubbles at the interface. The characteristic wavelengths of these instabilities remain independent of all material and geometrical properties of the system except the thickness of the film. These observations contrast sharply with the Saffman-Taylortype phenomenon in which the length scale of the instability patterns depends on the viscous and surface tension forces in addition to the thickness of the liquid film. The analogy between the phenomenon reported here and the Rayleigh-Kelvin instability with curved liquid menisci is more pronounced, as, in both cases, surface force triggers the instability while not determining its wavelength. The instability also throws light on cavitation phenomena in confined adhesive layers.