Unique aspects of a shape memory polymer as the substrate for surface wrinkling.

Typical bilayer wrinkle systems employ soft elastomers as the substrates. In contrast, shape memory polymers have recently emerged as attractive alternatives. Besides the shape fixing capability, shape memory polymers distinguish from elastomers in that they are rigid at room temperature, but experience significant modulus drop upon heating. We hereby report unique aspects of shape memory polymers as the wrinkle substrate utilizing a metallic thin film as the top layer. The feasibility to create both reversible and irreversible wrinkles (and diffraction colors) on a single substrate is demonstrated. Experimental conditions are identified to create crack free wrinkles and the impact of various experimental parameters on the wrinkle wavelength and amplitude is investigated. The results suggest that the wrinkle mechanics deviate notably from the existing theories established with elastomers as the wrinkle substrates. Thus, a new theory will need to be developed in the future, taking into account of unique thermomechanical properties of the shape memory substrate and possible plastic deformation of the thin film.