Speaker

Prof. Jeff Morris 
CUNY City College of New York
Levich Institute and Department of Chemical Engineering

Abstract

A “dense suspension” is a flowable material composed of a liquid very highly loaded with solid particles. In dense suspensions, the particle concentration closely approaches the jamming fraction, at which the material is able to withstand load without flow, forming a fragile porous solid.  Examples of these materials are cements and coatings, a number of foodstuff pastes, and mud (as suggested by the title). These materials are thus quite important practically, but I will try to show that they also serve as a basic model for nonequilibrium statistical mechanics.

The rheology of these materials involves a range of quite complicated behaviors: these include development of a yield stress, strong shear thinning and thickening, and shear-induced jamming. As background, an overview of the behaviors observed experimentally in dense suspensions, and advancements made in understanding the behavior based on inclusion of frictional interactions, will be presented.  This will emphasize our own work in study the flow of these materials by discrete-particle simulation.  From these simulations, the contact networks that arise and their relationship to the bulk properties will be described, with statistical mechanical approaches based on describing the fluctuations of particle motion (translational and rotational) and their spatial correlations applied to describe, insofar as we currently understand, the behavior associated with two phenomena.  One of these is discontinuous shear thickening, an abrupt change from one stress to a larger value as shear rate is increased, and the second is the shear jamming event itself.

Biosketch

Jeff Morris is Director of the Levich Institute (since 2015) and Professor of Chemical Engineering at CUNY City College of New York (CCNY). He received his bachelor’s degree at Georgia Tech (1989), and his MS (1991) and Ph.D. (1995) at Caltech, all in Chemical Engineering. He has worked industrially for Shell Research Amsterdam (1994-1995) and Halliburton Energy Services (2002-2004). Morris develops constitutive and bulk fluid mechanical descriptions appropriate for complex fluids. The focus has been on suspensions, from submicron colloids to sand slurries. Unifying features of these materials are the influence of hydrodynamic interactions and the flow-induced microstructure on rheology and bulk flow, as well as particle migration phenomena. Morris has recently focused on instabilities due to inertia in flows of suspensions, on frictional interactions of particles in viscous liquids, toward understanding shear thickening, and has interest in molecular aspects of solid-solid contact in liquids.
Morris was elected Fellow of the American Physical Society (APS) in 2013 and of the Society of Rheology (SOR) in 2019. He is the recipient of the 2017 AICHE/Shell Thomas Baron Award for Fluid-Particle Systems, the 2019 Stanley Corrsin Award of the APS, the 2022 Weissenberg Award of the European Society of Rheology, and the 2023 Bingham Medal of the SOR.

He is currently the President of the SOR (2026-2027). He served as the Secretary-Treasurer of APS Division of Fluid Dynamics (2018-2021), and since 2016 has served as an Associate Editor of the Journal of Fluid Mechanics. He authored the text A Physical Introduction to Suspension Dynamics, with Elisabeth Guazzelli. For the years 2023-2026, he has been named one of the inaugural “Fellow-Ambassadors” by the French CNRS.