The Extreme Mechanics of Balloons: From Interfacial Films to Inflated Membranes and Back*

Deformable sheets are ubiquitous in nature and industry across a vast range of scales, from graphene to metal foil to the earth’s crust. Thin sheets are also central to advanced applications including flexible electronics and deployable satellites or emergency shelters. Despite their ubiquity, there are still significant fundamental challenges in predicting how a thin elastic sheet will deform under confinement, from the selection of a macroscopic deformed shape all the way down to the fine details of the microstructural features. I will discuss a suite of experiments using interfacial films and inflated membranes to address problems spanning this entire range. First, I will describe how an ultrathin polymer film wrapped around a liquid droplet adopts highly nonsymmetric shapes as the droplet size is decreased, and how this overall shape selection may be understood using a simple model wherein the exposed liquid surface area is minimized [1]. This geometric model reveals a fundamental connection between interfacial films and mylar balloons. Inspired by this connection, we are conducting experiments using inflated membranes to discover how smooth sinusoidal wrinkles transition into sharp “crumples”, a striking behavior that was originally observed on interfacial polymer films in a spherical geometry [2]. We have now isolated these buckled structures on interfacial films in hyperbolic and cylindrical geometries, suggesting that such crumples are a generic building block for confined sheets.
[1] Paulsen, Démery, et al., Nat. Mater. 14 (2015); Paulsen, arXiv 1804.07425 (2018)
[2] King, Schroll, Davidovitch, and Menon, PNAS 109 (2012)