Title: Between a droplet and a soft place: The extreme mechanics of thin sheets
Speaker: Dr. Joseph Paulson
Institute: Syracuse University
Description: When unrolling plasticwrap, handling a large flimsy poster, or watching a fluttering flag, we becomeaware of the multitude of deformations that are available to thin materials.These scenarios suffer from geometric nonlinearities that make their analysisnotoriously difficult. Here I present a general approach that circumvents thesedifficulties for highly flexible films attached to liquid surfaces. First, Iwill show how an initially-flat polymer film wraps itself around a waterdroplet whose volume is gradually decreased. The resulting conformations arehighly non-axisymmetric and are patterned with small-scale wrinkles, folds, andcrumples. Remarkably, the essence of the wrapping process can be understoodwithout describing any of these complicated small-scale features. Inparticular, a thin sheet spontaneously minimizes the area of the exposed watersurface. I will then show how this general geometric principleapplies to the indentation of a floating polymer film, where it explains themechanical stiffening and softening of the normal force that we observe in ourexperiments and simulations.