Activated transport, tunable fragility and thermal jamming in microgel suspensions

Microgels composed of crosslinked polymers are deformable objects of controllable softness that exhibit glassy dynamics that is a highly variable function of suspension volume fraction and single particle modulus. We have developed a microscopic theory for this class of polymer colloids that relates interparticle repulsive forces, structure, elasticity and relaxation. A kinetic arrest diagram is determined in the reduced temperature versus volume fraction plane; no activated dynamics regime is predicted below a critical microgel stiffness or above a critical temperature. As the microgel becomes softer the dynamical slowing down with growing volume fraction increasingly resembles a strong glass former. At fixed concentration, an increase of particle stiffness results in a broad range of dynamic fragilities which partition into two qualitatively different categories. A soft jamming crossover is predicted beyond which local packing order is reduced and the elastic modulus follows a gas-like concentration dependence. Comparison of the theoretical results with recent mechanical and relaxation experiments has been performed.