Water-Driven Film Wrinkling with Tunable Modes for Frictional and Optical Applications

Wrinkle patterns are ubiquitous in natural and artificial systems, such as biological surfaces, layered structures, and film materials. They have great application prospects in the fields of flexible electronics, elastic optics, energy devices, bionic structures, and surface engineering. Although various wrinkle patterns including labyrinths, herringbones, stripes, and hierarchical structures have been extensively reported, precisely controlling wrinkles in real time and in the desired region is still a great challenge. Here we report on water-driven wrinkling with tunable modes in metal films sputter-deposited on poly(vinyl alcohol) (PVA) substrates. Two techniques, high humidity and water droplets, significantly reduce the modulus of PVA, enabling the controllable formation of wrinkles. The growth and evolution behaviors, morphological characteristics, film thickness dependence, and formation mechanisms of these wrinkles are thoroughly investigated. The frictions are significantly anisotropic for striped wrinkles but are nearly isotropic for herringbone wrinkles. The water drop-driven orthogonal wrinkles exhibit unique light diffraction patterns, demonstrating a strong correlation between functional performances and wrinkle features. This work enhances our understanding of wrinkle patterns triggered by water conditions and provides an efficient technique to fabricate wrinkles with tunable modes and desired arrays for practical applications.