Swelling-induced deformations: A materials-defined transition from macroscale to microscale deformations

Swelling-induced deformations are common in many biological and industrial environments, and the shapes and patterns that emerge can vary across many length scales. Here we present an experimental study of a transition between macroscopic structural bending and microscopic surface creasing in elastomeric beams swollen non-homogeneously with favorable solvents. We show that this transition is dictated by the materials and geometry of the system, and we develop a simple scaling model based on competition between bending and swelling energies that predicts if a given solvent droplet would deform a polymeric structure macroscopically or microscopically. We demonstrate how proper tuning of materials and geometry can generate instabilities at multiple length scales in a single structure.