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Biggins_2017_2

Surface-tension driven deformations in soft solids


Molecules at a condensed phase’s surface have fewer neighbors than those in the bulk, so all materials suffer an energy proportional to their exposed area, known as surface tension. The resulting tendency to reduce area is familiar in fluids, explaining why droplets are round, taps drip, and pond skaters do not drown. We are less familiar with solids distorting to minimize their surface area, and with good reason: in conventional stiff solids the elastic energy of the such deformations always outweighs the surface energy gains. However, soft solids, such as elastomers, gels, can be distorted by their surface energy, taking on dramatically different shapes. These effects are particularly large in the small soft systems that abound in biology, and emerge from a fundamental and ubiquitous trade off between elasticity and surface tension. In this project we will build a finite element code that combines surface tension and large deformation elasticity, to predict and understand the distorted shapes that emerge from this trade off, and apply it to soft fibers, sheets, balloons, ellipsoids and platonic solids. We will then use this code to study how solid-surface tension modifies classic JKR adhesion/contact theory between a rigid sphere and a soft solid substrate.