Liquid metal fillers enabled remote actuating and localizing reversible wrinkles on polymeric bilayer

Abstract

Surface wrinkling enabled by interfacial instability is a facile and straightforward way to manipulate the physical properties of surfaces. Wrinkles are typically formed on mechanically heterogeneous bilayers by compressive stress arising from mismatch in the thermal expansion of individual layers upon thermal treatment. The ability of polymeric bilayers to store and release strain can enable reversible actuation of surface topography. Although this principle has been demonstrated previously, it is appealing to remotely actuate and localize the reversible wrinkles because it can be applied for fabricating soft robotics and manipulating physical properties of surfaces by forming hierarchical topographies. Here, we demonstrate topographically reversible wrinkles on polymeric bilayer, i.e., poly(dimethyl siloxane) (PDMS) and polyacrylonitrile (PAN) layer used as a soft substrate and a stiff top layer respectively. The reversible actuating of the surface wrinkles using the polymeric bilayer has been demonstrated previously by utilizing carbon fillers dispersed elastic substrates, but here we utilized the liquid metal (LM) fillers to remotely and locally actuate the surface topography. The PDMS substrates with LM fillers dispersed can enhance thermal conductivity resulting in remote actuating wrinkles by exposing it to IR. The microchannel of PDMS filled with LM wire can locally and reversibly actuate hierarchical topographies by applying electrical current through the LM wire. This approach to reversible wrinkling may find use in fabricating functional surfaces with tunable wettability, optical properties, and adhesion.