Interfacially Driven Plastic Deformation of Soft Solids

Capillary forces acting on the surface of a solid result in elastic deformation on the scale of the elastocapillary length. While these elastic deformations may be negligible in stiff materials, they can dominate the behavior of soft solids, including rubbers, hydrogels, and biological tissues. In the extreme case, capillary forces may exceed the material’s yield stress, resulting in plastic deformation near the contact line. Although this plastocapillary effect has been theorized, experimental exploration into this phenomenon have remained limited. Understanding the role of interfacial forces on the deformation of soft surfaces is necessary as new methods for manufacturing soft materials with low moduli and yield stresses are developed. Here, we investigate interfacial instabilities of 3D printed microbeams, using jammed granular microgels swollen in aqueous and organic solvents as both sacrificial support materials and as printed inks. By leveraging the highly tunable material properties of these microgel systems and the structural control offered by 3D printing, we systematically explore a range of yield stresses and beam widths to understand how plastocapillary effects can drive mechanical instabilities and material failure in soft solids.