title: Contact instability of thin elastic films on patterned substrates.
abstract: The free surface of a soft elastic film becomes unstable and forms an isotropic labyrinth pattern when a rigid flat plate is brought into adhesive contact with the film. These patterns have a characteristic wavelength, lambda approximately 3H, where H is the film thickness. We show that these random structures can be ordered, modulated, and aligned by depositing the elastic film (cross-linked polydimethylsiloxane) on a patterned substrate and by bringing the free surface of the film in increasing adhesive contact with a flat stamp. Interestingly, the influence of the substrate "bleeds" through the film to its free surface. It becomes possible to generate complex two-dimensional ordered structures such as an array of femtoliter beakers even by using a simple one-dimensional stripe patterned substrate when the instability wavelength, lambda approximately 3H, nearly matches the substrate pattern periodicity. The free surface morphology is modulated in situ by merely varying the stamp-surface separation distance. The free surface structures originating from the elastic contact instability can also be made permanent by the UV-ozone induced oxidation and stiffening.
authors: Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208 016, India.
authors: Rabibrata
authors: R
authors: Mukherjee
authors: Ravindra C
authors: RC
authors: Pangule
authors: Ashutosh
authors: A
authors: Sharma
authors: Indrani
authors: I
authors: Banerjee