Deformability and response

Complex soft solids like emulsions (e.g. mayonnaise), foams (e.g. cappuccino froth) and tissues (e.g. your epidermis) are composed of inherently deformable objects like droplets, bubbles or cells, yet how deformability affects collective behavior is poorly understood. In our recent paper, we studied the effect of single-particle deformability on global vibrational and mechanical response near jamming. We found that stiff, weakly deformable particles reach a rigid-particle limit, but increasing deformability leads to anomalous normal mode spectra and shear moduli.

Shown here are examples of normal modes found in jammed packings of highly deformable particles. These packings contain a few “quartic modes” which are higher-order and much floppier than standard, quadratic modes. Floppy quartic modes can be either extended (black, left) or localized (black, right), while the quadratic modes (red and blue) vary in extent, but predominantly change particle shape.