Geometrically Templated Dynamic Wrinkling From Suspended Poly(vinyl alcohol) Soap Films

Wrinkling is commonly observed as mechanical instability when a stiff thin film bound on a compliant thick substrate undergoes in‐plane compression exceeding a threshold. Despite significant efforts to create a broad range of surface patterns via wrinkling, little has been studied about a dynamic and transient wrinkling process, where a suspended polymer thin film undergoes liquid‐to‐solid phase transitions. Here, a spontaneous wrinkling process is reported when drying poly(vinyl alcohol) (PVA) soap films suspended on 3D printed wireframes with near‐zero or negative Gaussian curvatures. As water evaporates, a thickness gradient across the sample is developed, leading to non‐uniform drying rates, and a concentration gradient between the inner and outer sides (exposed to air) of the suspended PVA soap film induces a differential osmotic pressure. Together, these effects contribute to an in‐plane compressive stress, leading to the formation of surface wrinkles, whose growth is guided by the geometry of the frame. Importantly, the wrinkles evolve dynamically: the wavelength and number of the wrinkles can be tuned by altering the concentration of the PVA aqueous solutions, the initial mass, the relative humidity of the drying environment; the patterns of the resulting wrinkles can be programmed by the geometry of the wireframe.