Spontaneous formation of hierarchical wrinkles in Cr films deposited on silicone oil drops with constrained edges

We report on the spontaneous formation of hierarchical wrinkling patterns in Cr films deposited on silicone oil drops with constrained edges. The appearance of the wrinkling patterns is strongly dependent on the film thickness and the size of the silicone oil drop. Because the Cr film at the drop edge is constrained due to the strong adhesion between the film and the glass surface, the wrinkle wavelength merely depends on the distance starting from the drop edge. When the distance increases, the wavelength increases quickly first, and then it slows down gradually in compliance with a simple power law. The evolution of the wrinkle amplitude is similar to that of the wavelength, but it is also closely related to the film thickness and the oil drop size. Based on the fact that the silicone oil is polymerized to form an elastic layer during deposition, the formation and evolution of the hierarchical wrinkling patterns have been analyzed in detail.