No abstract

Materials with complex curvature and micro-structured surface topography allow scientists to replicate surfaces observed in nature. Initiated chemical vapor deposition is used to grow polymer films on substrates of various 3D shapes which exhibit wrinkling during film growth, termed self-wrinkling. Self-wrinkling avoids separate film growth and compression steps and moreclosely mimics processes observed in nature. The self-wrinkling process is elucidated on flat elastic substrates, revealing control over the amount of compressive stress by changing deposition conditions. Next, a study of films grown on liquid substrates with interface profiles that either resemble cylinders or contain repeating concave cones, saddles, and bowls affirms the principle that the wrinkle roundness increases with interface curvature. The selection of high versus low stress generating conditions allows for the choice of the wrinkle pattern to be directed by either the stress concentration at boundaries or the substrate curvature. Experiments confirm the observation from simulations by other authors that on the inside of a torus, the lowest energy ridge wrinkle state is oriented around the major axis. The ability to control the character of wrinkle patterns via changes to the local and global substrate shape provides a route to generate materials with contrived surface topography.