Friday, November 30, 2012
Swelling Structures that Bend, Buckle, Twist and Snap their way to Functionality
Douglas P. Holmes, Assistant Professor, Department of Engineering Science & Mechanics, Virginia Tech
Soft mechanical structures, such as biological tissues and gels, exhibit motion, instabilities, and large morphological changes when subjected to external stimuli. Swelling a dry gel with a favorable solvent is a robust approach for inducing these structural changes. Small volumes of fluid that interact favorably with a material can cause dramatic and geometrically nonlinear deformations including beam bending, plate buckling, and surface wrinkling. This talk will address an overarching question regarding swelling-induced deformations: will the structural change occur globally, or will it be confined to the material's surface? We introduce a materials and geometry defined transition point that describes a fluid-structure's characteristic "elastoswellability" length scale. By locally swelling unconstrained slender beams and plates with solvents of varying solubility, we identify a transition between local surface wrinkling and global structural bending. We explore these global structural deformations by examining how thin elastic plates undergo rapid bending, buckling, and snapping instabilities after non-homogenous exposure to a favorable solvent that swells the network. An unconstrained beam bends along its length, a constrained beam exhibits snap-buckling instabilities, and a circular disc bends and buckles with multiple curvatures. Finally, we demonstrate how these fundamental, swelling-induced deformations can be scaled down and incorporated into rapid, responsive advanced materials.