Reversibly texturing active surfaces with spatial and temporal control

Abstract

Textured surfaces, formed through wrinkling and folding, are observed abundantly in nature. We are especially motivated by the unique capabilities of some species of cuttlefish that camouflage themselves by rapidly switching from smooth to textured skin by expressing protuberances called papillae. Inspired by this, we developed a shape memory alloy–elastomer composite as a platform for reversible surface texture. A shape memory alloy wire embedded in an elastomer is forced to shrink due to Ohmic heating. This shrinkage is used to drive the reversible buckling of a thin stiff film attached to the elastomer surface. The platform is scalable, produces wrinkling patterns in the flip of a switch, operates at voltages under 10 V, and can be operated reversibly over multiple cycles. The amplitude and kinetics of the surface wrinkling are experimentally characterized. The wrinkle patterns appear and disappear in timescales ranging from tens of seconds to as little as a second depending on the voltage actuating the shape memory alloy wire. Finally, this platform can create reversible wrinkle patterns in a spatially reconfigurable fashion, that is, the location of the texture changes can be varied in real time. A two-dimensional shear lag model is developed to establish the important design parameters governing the formation of wrinkles.