Controlled Wrinkling Patterns in Periodic Thickness-Gradient Films on Polydimethylsiloxane Substrates

Abstract

Surface wrinkles in homogeneous and heterogeneous film-substrate systems have received intense attention in both science and engineering. Understanding the wrinkling phenomena of heterogeneous systems with continuously variable features is still a challenge. In this work, we propose an unconventional strategy to prepare periodic thickness-gradient metal films on polydimethylsiloxane (PDMS) substrates by masking of copper grids which are weaved by orthometric copper wires. It is found that a periodic thickness-gradient film spontaneously forms during the sputtering process because of the specific structures of the copper grids. Surface wrinkles are strongly modulated by the copper grid structures and are position-dependent within a period. A phase diagram has been established to correlate the wrinkle morphology with the mesh size and film thickness. The film surfaces at mesh centers are evolved from labyrinth wrinkling to herringbone wrinkling and then to stripe wrinkling and finally to wrinkling-free state when the mesh size decreases and/or the film thickness increases. The morphological characteristics, evolutional behaviors, and underlying mechanisms of such wrinkling are discussed in detail based on the stress theory and numerical simulation.

Harnessing Heterogeneous Wrinkles in Metal/Polydimethylsiloxane Film System by Combination of Mechanical Loading and Heat Treatment

“…[ 6,7 ] Introduction of film impurity can induce local strain anisotropy and guide wrinkle orientation, achieving highly ordered wrinkle arrays. [ 8,9 ] The wavelength of wrinkles depends on the film thickness [ 10 ] and the modulus ratio of film to substrate. [ 11 ] It can range from submicron to macroscale (kilometers in tectonic plates for instance).…”

Mechanically Switchable Wetting Petal Effect in Self-Patterned Nanocolumnar Films on Poly(dimethylsiloxane)

“…Particularly, in elastomeric surfaces of PDMS, self-generated wrinkling processes are known to induce reversible wetting, although the phenomenon is hardly controllable due to the randomness in the generation of surface structures [24] and the dependence of water adhesion on the hysteresis contact angle [25]. Nonetheless, the fabrication of mechanically switchable wetting devices relying on anisotropically structured PDMS has been attempted with different success using complex processes such as ink transfer printing [26] and 3D printing [27], laser [28][29][30], bending by magnetic induction [31], wave-like nanofibers on pre-stretched substrates [32,33], incorporation of templates [34,35], nanostructures [36,37], metallic [38][39][40] and oxide [12,41] coatings, the selective surface functionalization through plasma treatments [42] or the deposition of superhydrophobic layers [24,43,44]. In general, these procedures lack robustness and require relatively sophisticated engineering steps to ensure straightforward functionality and full reversibility upon actuation.…”

Buckling Behaviors at the Interface of Liquid–Solid Systems

“…[8][9][10][11][12][13][14] Meanwhile, the wrinkles pattern always are inevitable when the metal films are deposited on soft elastic or liquid substrates because of the residual compression between the metal films and the substrates. [15][16][17][18][19][20][21][22][23] The evolutionary rules of buckling structures are fundamental laws of the universe, whose detection in bilayer films are essential for understanding the structures of organisms and the morphology of planets. [24,25] Generally, wrinkles are first type of buckling structures in bilayer films, which can be stimulated by a minor compressive strain.…”