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The Simplest Complex Fluid? The Remarkable Rheology of Hard-sphere Suspensions
Start Date: 3/27/2014Start Time: 2:00 PM
End Date: 3/27/2014End Time: 3:00 PM

Jeffrey F. Morris
Professor, Chair
Chemical Engineering
City College of the
City University of New York

Member, Levich Institute

2201 G Street NW, Funger Hall 221

Hosted by: Dr. Kausik Sarkar (

Dense suspensions of solid spherical particles in a Newtonian liquid solvent provide a crucial basic model system for development of mixture flow and complex fluid theory. By complex fluid, we mean that there is a dependence of the properties of the fluid upon the shear rate.  In practice, suspensions and slurries appear in coatings, ceramic precursors, mud flows, among numerous examples.    In this work, we see to understand the surprisingly rich rheology, i.e. the stresses, of flowing suspensions under conditions of large particle loading.  Motivations include particle migration phenomena and secondary flows induced by normal stresses as well as the observation of extreme shear rate dependence of the viscosity called “discontinuous shear thickening” (DST).  The phenomenon of DST is known popularly in corn-starch suspensions, on which a person can run if quick enough (solid-like behavior art a high rate of forcing) but will rapidly sink if standing still (liquid behavior at a low rate).  We will consider the underlying microstructure of dense suspensions of Brownian particles (i.e. small enough to be influenced by thermal fluctuations in the solvent), based on our own simulations and theory.  This theory [1] predicts highly anisotropic structure and hydrodynamically-driven normal stresses when the flow dominates Brownian motion, and migration driven by normal stresses is now well-established.     A key feature of the microstructure is that the probability of particles directly adjacent to contact is extremely large (and strongly singular in the limit of maximum packing) so the role of surface friction is expected to play a role in experiments.  We show in recent simulations [2] that a combination of hydrodynamic interactions and surface contact and frictional interactions are able to reproduce well the experimentally observed features of discontinuous shear thickening. 

Professor Morris and his research group are interested in developing a fluid mechanical description appropriate for complex fluids, particularly slurries, suspensions, and colloids.  Applying simulation and experiment, combined with ideas of statistical and continuum mechanics, the research seeks to develop understanding of flow-induced microstructure and the resulting mixture rheology.  Of particular interest are rheologically-induced phenomena unique to mixtures, including bulk particle migration, and the large-scale fluid mechanics of rheologically complex materials. He is author of the text “A Physical Introduction to Suspension Dynamics” with E. Guazzelli.  Professor Morris received his BChE degree from Georgia Tech, and his PhD from Caltech, both in Chemical Engineering.  Before coming to City College since 2005, he spent periods at Halliburton and on the faculty at Georgia Tech.
Cindy Fields Arnold
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