Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 155, Issue 13, Pages -Publisher
AIP Publishing
DOI: 10.1063/5.0058676
Keywords
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Funding
- Office of Naval Research, Director of Research Early Career Award [N000141812105]
- U.S. Department of Defense (DOD) [N000141812105] Funding Source: U.S. Department of Defense (DOD)
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The non-Newtonian rheology of an attractive colloidal suspension was studied, finding that interactions between attractions and hydrodynamics lead to pronounced flow-induced negative osmotic pressure.
Equilibrium phase instability of colloids is robustly predicted by the Vliegenthart-Lekkerkerker (VL) critical value of the second virial efficient, but no such general criterion has been established for suspensions undergoing flow. A transition from positive to negative osmotic pressure is one mechanical hallmark of a change in phase stability in suspensions and provides a natural extension of the equilibrium osmotic pressure encoded in the second virial coefficient. Here, we propose to study the non-Newtonian rheology of an attractive colloidal suspension using the active microrheology framework as a model for focusing on the pair trajectories that underlie flow stability. We formulate and solve a Smoluchowski relation to understand the interplay between attractions, hydrodynamics, Brownian motion, and flow on particle microstructure in a semi-dilute suspension and utilize the results to study the viscosity and particle-phase osmotic pressure. We find that an interplay between attractions and hydrodynamics leads to dramatic changes in the nonequilibrium microstructure, which produces a two-stage flow-thinning of viscosity and leads to pronounced flow-induced negative osmotic pressure. We summarize these findings with an osmotic pressure heat map that predicts where hydrodynamic enhancement of attractive bonds encourages flow-induced aggregation or phase separation. We identify a critical isobar-a flow-induced critical pressure consistent with phase instability and a nonequilibrium extension of the VL criterion.
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