Environmental dynamic wrinkling in crack-free PDMS bilayers

Wrinkling of polydimethylsiloxane (PDMS) has unlocked a myriad of technological applications, from tuneable surface wetting to photonic response. Surface undulations with prescribed wavelength and amplitude are excited by the compression of bilayers comprising a stiff, thin skin, supported by a softer, compliant substrate, such as PDMS. Plasma oxidation is widely used to generate such thin (≈10 nm) glassy skins. While spontaneous wrinkling can occur even in the absence of an external mechanical trigger, for instance due to thermal cycling and associated bilayer expansion-contraction, we have shown that exposure to water vapor is, in effect, the lead responsible for surface wrinkling, due to the swelling the oxidized skin layer. This environmental susceptibility accounts for the apparent ‘temperamental’ and ‘irreproducible’ nature of the process, and can be precisely modelled using a simple sorption-swelling-wrinkling framework. The responsive nature of the skin thus also provides a route to environmental sensing, for instance with a structural colour response. Finally, since intrinsic crack formation restricts last-area patterning via wrinkling, we demonstrate a facile suppression strategy by a combination of a high heat transfer coefficient (HTC) of the support and low PDMS thickness, which retains the overall functionality of the responsive skins.