Monday, April 06, 20153:00 PM - 4:00 PMCNLS Conference Room (TA-3, Bldg 1690)|
Mechanics of soft spheres
Craig MaloneyCarnegie Mellon University
Many complex fluids such as emulsions or micro-gel suspensions become rigid at sufficiently large particle volume fraction. These systems can be essentially athermal, where the macroscopic elasticity results from persistent deformation at the particle contacts rather than Brownian fluctuations. We will discuss simple particle-scale models of these systems and present results on both the elastic response of static packings and rheology under steady shear. For the case of the elastic response, we show that the system obeys continuum linear isotropic elasticity, but only beyond a lengthscale which diverges in the limit of zero confining pressure. We identify two distinct lengths for the longitudinal and transverse component of the response function. For the case of the rheology, we show that simple drag laws that mimic the full hydrodynamics give rise to the same rheology, a Herschel-Bulkley form with a strain rate exponent of 1/2, as more sophisticated models and argue that this exponent results from the correlated plastic rearrangements that occur during flow.
Host: Turab Lookman