Jeffrey F. Morris

City College of CUNY

Chemical Engineer

Fellow, Elected 2019

Jeff Morris is recognized for his research contributions elucidating the microscopic mechanistic basis for the rheological properties of multi-phase mixtures and their influence on macroscopic flow phenomena.

These contributions include the development of understanding of nonequilibrium microstructure in Stokes flow of Brownian colloidal suspensions, which has been explored through both the Stokesian Dynamics simulation technique and developed into a Smoluchowski equation theory for concentrated suspensions under shear or in active microrheology.

A major theme of the research of Morris and collaborators has been to establish fundamentally based but computationally tractable constitutive modeling to allow bulk flow analysis of concentrated suspensions. This effort has focused on exposing the coupling of mass and momentum conservation through the relation of phase migration to rheological properties, and the approach has been applied not only to the original motivation of shear-induced migration in noncolloidal suspensions, but also to migration in Brownian colloidal dispersions and pattern formation in flow of electrorheological fluids. A key element of this flow modeling is the development of theory and experimental measurement of the particle pressure, or nonequilibrium osmotic pressure.

The behavior of suspensions in the very concentrated or “dense” limit, approaching the maximum solid packing fraction, has been explored by simulation methods to expose the minimal ingredients to reproduce experimentally observed “discontinuous shear thickening.” A change of mechanism from dominance by hydrodynamic lubrication to contact friction has provided a rational basis for both shear thickening and shear jamming.

While the research noted above has considered the overdamped, or Stokes flow, limit, investigation to expose the influence of particle-scale inertia on rheology and mixture flows has made significant progress. This has shown how finite Reynolds number at the particle scale is related to the stress system in the suspension, as well as its role in particle migration, and to bulk flow phenomena such as particle-laden flow past bluff bodies and inertial instability of suspensions in Taylor-Couette flow.

The majority of the work in the group has been directed toward fundamental suspension flow properties. However, the Morris group demonstrated various methods to experimentally determine rheological properties caused by clathrate hydrate formation in emulsions, a crucial problem in petroleum pipelining. This work has shown the coupling of the thermodynamic state of the material to the rheological properties, and has opened the way to explaining the bulk behavior in terms of interfacial properties and hydrate crystal aggregation.

Morris, in collaboration with Élisabeth Guazzelli has published a book A Physical Introduction to Suspension Dynamics to provide an accessible entry for researchers new to the field.