Roger T. Bonnecaze

The University of Texas at Austin

Chemical Engineer

Fellow, Elected 2018

Prof. Roger Bonnecaze has made major contributions to the rheology of suspensions in three areas: (1) microstructure and rheology of soft particle glasses; (2) microstructure and rheology of electrorheological fluids; and (3) experimental measurements of the microstructure of suspensions in pressure-driven flow. He has also made significant contributions to particle transport and rheology for petroleum engineering applications and the microrheology and metastatic potential of cancer cells.

The microstructure and rheology of soft particle glasses

Soft particle glasses (SPGs) are very concentrated suspensions of deformable or soft particles. Examples of soft particles include emulsions, vesicles, microgels, polymer-coated particles, core-shell micelles, and star-polymers. The particles can range in size from tens of nanometers to a few microns. The elasticity of the particles can arise from surface-tension, osmotic or steric forces. SPGs exhibit a yield stress and are shear thinning under continuous deformation. These suspensions are used as rheological modifiers and viscosifiers.

Roger and his students have developed an accurate particle-dynamics simulation tool to predict the rheology of soft particle glasses (SPGs) and the underlying microstructure that gives rise to these properties. From these results, general models have been created to predict the rheological properties of SPGs as function of the size, concentration and mechanical properties of the particles and the rheology of the suspending fluid. Using these tools, SPGs can be designed to have desired properties. Also, SPGs can now be fully characterized with limited rheological data. Their work has shown theoretically that despite the differences in size and sources of elasticity, SPGs exhibit a universal rheology. Roger and his long-time experimental collaborator and friend, Dr. Michel Cloitre from the ESPCI ParisTech, have won two Journal of Rheology Publication Awards along with their co-authors for their work on SPGs.

Microstructure and rheology of electrorheological fluids

In his PhD, Roger developed a simulation of electrorheological fluids that accurately accounted for the viscous and electrostatic interactions among the particles in the suspension. From his simulations he discovered how the chains of particles repeatedly strain, break and reform to store and dissipate electrostatic energy which results in their yield stress and shear thinning behavior.

Experimental measurements of the microstructure of suspensions in pressure-driven flow

Roger and his students used electrical impedance and magnetic resonance tomography to probe the microstructure of mono- and bidisperse suspensions in steady and oscillatory pressure-driven flow. They were the first to measure and map the anomalous shear migration of low-Reynolds number particles to the wall and periodic axial variation of particle concentration in oscillating flows depending on the amplitude of the oscillations.

Other contributions to rheology

Roger has made contributions to the microstructure and rheology of particles for petroleum engineering applications in particle transport in porous media and fracturing. He also has used microrheology to understand the correlation between softness of different types of cancer cells and their migration, metastatic potential and tumor growth.