Event

Meaningful advances in energy generation, utilization, or storage require exquisite control and optimization of the transport properties of materials far-from-thermal-equilibrium.  Whether concerned with ion-transport through a battery, or molecule extraction through porous rock, or transporting granular matter, a central issue is that of designing materials and flow geometries that give use spatiotemporal control of the mobility of interacting particles.  However, at present, we cannot efficiently predict the behavior of these many-body systems by theoretical or computational means over timescales relevant to practical applications, chiefly due to the breakdown of assumptions of detailed-balance and ergodicity in the time-evolution. Progress requires the development of experimental systems simple enough to characterize microscopically, yet sufficiently far from thermal equilibrium to allow observation of time-evolution of bulk properties, study of hierarchical energy redistribution structures, and testing of theoretical concepts.

I will present results from two far-from-equilibrium experimental systems that meet these criteria, both composed of spherical particles driven by a laminar fluid. First, a quasi-two-dimensional hard-sphere Brownian suspensions of submicron particles confined in a microfluidic device, driven such that the distance to thermal-equilibrium is tunable. We drive the formation of a spatially confined rigid pack and study its response to external perturbations. By theoretically describing the interparticle interactions as a series-expansion of interparticle clusters, we quantify the many-body contribution to measurements of the bulk modulus. Second, a three-dimensional hard-sphere granular suspension of millimeter particles confined in an annular chamber. We drive the packs with a laminar flow and record dynamics by laser scanned particle tracking. We find that the dynamics of grains are not well-described by “hydrodynamic” equations. We experimentally study how this breakdown occurs and study its effects on the effective friction, the energy dissipation rate, as a function of depth into the material.  

I will briefly discuss the design of future experiments combining these techniques and enabling the simultaneous study of independent instances of far-from-equilibrium experiments with access to both microscopic and bulk measurements. With these techniques, we can study not only driven diffusive particle systems, but also driven rough interfaces, depinning transitions, and other dynamical phase transitions, suggesting great promise to identify and classify a broad set of non-equilibrium universality classes. By doing so, this research may open the possibility to move from passive observers of phase transitions to active designers of the phase diagram and material properties.