Growth of biomimetic films – influences of polymer topography and phase structure

Abstract

The current work explains the influence of the polymer substrate on the topography formation of nano-wrinkled thin titanium films. Similar to the biomimetic antetype of human skin, this wrinkling phenomenon increases the elastic deformability of hard materials under tensile loading by flattening the wrinkled waves before high tensile stresses occur. Low energetic plasma deposition in direct current magnetron sputtering leads to smoother films with equiaxed domed wrinkle topography without a distinct preferred orientation on polymers (polyethylene terephthalate, polycarbonate, thermoplastic polyurethane). These domes are at least one order of magnitude larger than the commonly found topography on stiff silicon and correlates to the size of crystalline spherulites and segments in the applied semi- and pseudo-crystalline polymers. High energetic plasma deposition in pulsed laser deposition results in denser films with stretching of wrinkles. Higher intrinsic stresses require for relaxation deformation of deeper regions of the polymer below the surface. Because the width of these sinusoidal wrinkles is quite similar to sputtered films and the preferred stretching orientation correlates to the main direction of the polymer chains, the change in the wrinkle shape can only be explained by stress relaxation due to mechanical anisotropy by extrusion-based manufacturing.