Stress Formation and Relaxation in colloidal Dispersions: Transient, Nonlinear Microrheology

点击翻译按钮获取中文摘要

PI: Zia, RoseannaProposal Number: 1605836The goal of the proposed research is to investigate colloidal dispersions when forces and stresses acting on them change. Both theoretical analysis and a class of computations known as Accelerated Stokesian Dynamics simulations will be used to accomplish this goal. The work could have an impact on the chemical and food industry, where control of material properties and of complex fluids, like colloids, is important.The goal of the proposed research is to develop predictive theory and computational models for the temporal formation and relaxation of viscosity and stress in colloidal dispersions via the framework of active microrheology, with a focus on connections to particle microstructure as it evolves in time. Most non-equilibrium microrheological work to date has focused on steady-state flow behavior, yielding insight into steady-state non-Newtonian behaviors, relating them to flow-strength induced changes in the relative contributions of hydrodynamic, Brownian, and interparticle forces. However, understanding of how such relative contributions evolve in time-during flow startup and cessation-lags behind. Such understanding is key to resolving important questions such as the origins of stress "overshoots" during flow startup, and whether structural evolution and rheological evolution reach steady state simultaneously. The results of the proposed research are of fundamental scientific interest and will impact applications as diverse as intracellular flow, drilling fluids, and impact-resistant materials. The PI hypothesizes that the relative contributions of hydrodynamic, interparticle, and Brownian forces to the stress and viscosity in colloidal dispersions are not instantaneously formed upon flow startup, and thus that the climb to steady state rheology may lead or lag formation of steady state structure. The proposed work will combine theoretical and computational rheological studies. Theoretical studies will center on formulation and solution of time-dependent Smoluchowski equations, which will then be utilized to compute suspension viscosity and stress as it evolves in time, for any range of interparticle repulsion (i.e., strength of hydrodynamic interactions), particle size ratio, and attractive potentials. The educational plan will improve the participation of underrepresented students via mentored learning utilizing guided, hands-on experiments. The PI will develop fluid mechanics modules for classrooms and outreach at Cornell University, rheology conferences, and quarterly "Science Days" at National Academy Foundation high schools for underrepresented minority students.