Bending, Creasing, and Snapping of Soft, Slender Structures

Abstract

Crosslinked polymers or elastomers are examples of soft, synthetic material that can bend, crease, snap, wrinkle in response to external stimulus like pH, humidity, electric field or swelling. If a droplet of favorable solvent is placed on top of a thin, elastomer beam, it bends drastically to accommodate the excessive swelling stress. Keeping the solvent and its volume constant if we just increase the thickness of the beam, microscopic surface creases appear on the top surface. In this thesis, we experimentally characterize this transition between global bending to surface creasing. Closing of Venus flytrap leaves is a classic example of well known snap-through instability. A knowledge of the timescale of snapping is crucial in designing advanced functional materials. We perform the simplest experiment of poking an soft, elastomer arch at its apex till it snaps. Combining our experiments with analytical model we are able to predict the purely geometric nature of the snapping timescale. We also develop a simple scaling law that captures the dynamics of jumping toy poppers.