Abstract: Surface patterns that can reconfigure under external stimuli are important for tailoring diverse properties such as surface adhesion, optical transmittance, and wettability. Wrinkling a stiff skin layer on a softer pre-strained substrate is a promising strategy to create responsive structures without using complex lithographic processes. Most efforts to fabricate wrinkles used skin layers of metals or silica, but tunability in functional response of the patterned surface is limited because (1) the skin/substrate system cannot readily access nanoscale features and (2) cracks form at random locations in the skin layer and hinder precise tuning of properties.
In this talk, I will present wrinkling systems based on plasma-mediated polymer skin layers that address these challenges. Soft fluoropolymer layers deposited on elastomer substrates via a CHF3 plasma treatment achieves more than a tenfold increase in the amount of pre-strain that could be relieved without cracking compared to conventional hard skins. Because the plasma process allows for nanometer-scale tunability in skin thickness, the resulting wrinkle wavelength can be controlled both in nano- and micrometer regimes. Furthermore, the wrinkle orientation can be switched under stretching without cracks or delamination and hence switching of directional properties such as anisotropic water spreading is possible. I will then discuss opportunities for soft skin materials to create multiscale textures in two-dimensional nanomaterials, demonstrating graphene as a representative example. I will conclude by introducing an ongoing effort to design hierarchical structures to develop functional surfaces with superhydrophobicity and antibacterial fouling properties.
Bio: Dongjoon Rhee is a Ph.D. candidate in materials science and engineering at Northwestern University.