John de Bruyn, Professor

My research in condensed matter focuses on several key areas, including granular flows, non-Newtonian fluids, and the physics of biological systems. A brief overview of my research into each of these areas is provided below. I do lots of other things, too! For more information on some of the projects we are working on right now, please use the menu on the left.

Granular materials (like sand, for example) can behave like solids, fluids, or gases, depending on the situation. If you pour sand from a jar, it flows like a fluid, but if you stand on a pile of sand, it supports your weight like a solid would. I am interested in the analogy between granular flows and conventional fluids. To what extent does a continuum description of granular material (analogous to the Navier-Stokes equations used in fluid dynamics) describe granular flows? When do the peculiar properties of granular fluids start to matter? I do experiments on granular flows, using high-speed video and other visualization methods, to investigate these questions.

Much of our research into non-Newtonian fluids is focused on materials with a yield stress, so-called viscoplastic fluids. Yield-stress fluids are very common: examples include hair gel, mustard, shaving foam, mud, and paint. They are typically suspensions of colloidal particles in a solvent (often water). They behave as soft solids when subjected to a small shear stress, but flow like a viscous fluid when the applied stress is large enough. This interesting flow behavior is a result of small-scale structure within the fluid, resulting from, for example, interactions between the suspended particles. We are interested in studying both the bulk properties and the small scale structure of yield-stress fluids, and ultimately in understanding the link between the small and large scale physics. I also study the rheology and microstructure of a variety of other polymer materials, including polymer-nanoparticle composites.

I collaborate with colleagues on research that involves the use of physics-based ideas and techniques to study problems of interest in the life and medical science. At present we are using light scattering to investigate the effects of various proteins on the precipitation of bone minerals, and studying the forces exerted by certain cells when they adhere to a substrate.

1. S. Amirnia, J. R. de Bruyn, M. A. Bergougnou, and A. Margaritis, Continuous rise velocity of air bubbles in non-Newtonian biopolymer solutions, Chem. Eng. Sci.94, 60 (2013).
2. J. R. de Bruyn, Modeling the microrheology of inhomogeneous media, J. Non-Newt. Fluid Mech., 193, 21 (2013).
3. S. J. de Vet and J. R. de Bruyn, The collapse of a cylindrical cavity in a granular medium, Granular Matter 14, 661 (2012).
4. J. R. de Bruyn, M. Goiko, D. Bator, R. Dauphinee, M. Mozaffari, Y. Liao, R. L. Flemming, M. S. Bramble, G. K. Hunter, and H. A. Goldberg, Dynamic light scattering study of inhibition of nucleation and growth of hydroxyapatite crystals by osteopontin, PLoS One 8, e56764 (2013).

• Best Talk, VPF-2009
• APS Outstanding Referee, 2008
• Best Paper on Condensed Matter Physics, Canadian Journal of Physics, 2004
• Memorial University Dean of Science Distinguished Scholar Medal, 2004
• MUN President's Award for Outstanding Research, 1996
• NSERC University Research Fellowship, 1989-98
• NSERC Postdoctoral Fellowship, 1987-89

• CAP Professional Affairs Committee, 2012-present.
• Director of Full Members, CAP, 2011-present.
• Session co-chair/co-organizer, Canadian Association of Physicists Congress, May 2013.
• Scientific Organizing Committee, Colloids and complex fluids: Challenges and opportunities, Paris, October 2012.
• Session co-chair/co-organizer, Society of Rheology Conference, Oct. 2009.