Diffusion, plasticity, and excess entropy in complex colloidal fluids*

Excess entropy is the difference between the “true” system entropy and that of an equivalent ideal gas. Rosenfeld first observed that the diffusivity and viscosity of simple liquids scale exponentially with excess entropy. This intriguing discovery had motivated numerous studies of excess entropy scaling in a wide variety of materials spanning different particle type, size, density, interaction, temperature, and even shear rate, most of which are computer simulation work. In this talk, I will discuss our recent experiments utilizing excess entropy concept to understand the dynamics of complex fluids. In the first experiment, we investigate the structure and dynamics in dense colloidal fluids with tunable short-range attractions. From particle trajectory data we measure the two-body excess entropy and the long-time diffusion coefficients from samples with different packing fractions and attraction strengths. These results are found to follow Rosenfeld’s excess entropy scaling that is independent of sample packing fraction and attraction strength. In the second experiment, we study plastically deformed colloidal solids. We directly imaged the dynamics and micro-structure induced by plastic shear flow in a series of amorphous solids under oscillatory shear. Data reveal novel scaling relationships between plastic flow, viscous response, and excess entropy. These findings extend the application of excess entropy concept from equilibrium to nonequilibrium systems.