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Multiscale Hydrodynamics and Rheology of Dense Suspensions Undergoing Nonlinear Electrokinetics towards Active Rheology Control
Suspension is an important class of complex fluids ubiquitous in many natural processes and industrial applications. The flow properties of these fluids are essentially the direct consequence of micro-hydrodynamics at the particle level and the interplay between the resulting microstructure and the flow. Nonlinear electrokinetic phenomena can be regarded as a promising means to manipulate the rheology and other macroscopic characteristics of suspensions owing to their superior control over particle transport and micro-hydrodynamics. The goal of this dissertation is to conduct theoretical and computational studies to improve our fundamental understanding of the impacts of nonlinear electrokinetics on suspensions under different flow conditions. We start by investigating the collective dynamics, microstructure, and rheology of dense suspensions of conductive particles under an electric field in the absence of flow. This suspension is known to undergo two nonlinear electrokinetics, namely dielectrophoresis and induced-charge electrophoresis. While the effect of the former intimately ties to dipolar interactions of electrorheological fluids, the latter results from an induced quadrupole micro-flow over the particle surface. We find that the predominant effect of induced-charge electrophoresis gives rise to interesting non-trivial behaviors in the concentrated regime in which the suspension dynamics get enhanced and the particle pressure becomes negative. We continue to explore the rheological properties of such suspension in shear flow, where shear-thickening states and intriguing normal stress differences are observed. We further investigate the potential use of the current system as a means for active rheology control. We find that the rheology could be significantly altered by changing the direction or frequency of an electric field. We then study the multiscale nature of the structural formation of a suspension solely undergoing dielectrophoresis or dipolar interactions, where the linkage from the microscopic to mesoscopic to macroscopic responses is identified by linking the particle-level, cluster-level, and stress-level features. Lastly, we redirect our attention toward the regime of finite Reynolds numbers to characterize large-scale and complex hydrodynamics in a constricted flow.
Mechanical engineering|Engineering|Fluid mechanics
Mirfendereski, Siamak, "Multiscale Hydrodynamics and Rheology of Dense Suspensions Undergoing Nonlinear Electrokinetics towards Active Rheology Control" (2022). ETD collection for University of Nebraska-Lincoln. AAI29999334.