Contact Information

John R. de Bruyn
Physics & Astronomy 230
(519) 661-2111 x86430
debruyn [at] uwo [dot] ca
FAX: (519) 661-2033

Non-Newtonian Fluids - Current Interests

  1. Rheology of yield stress materials: We measure the behavior of yield-stress fluids in response to an applied stress or strain, to characterize the materials and to learn about how their bulk properties depend on things like composition, temperature, and time. We can use rheological measurements to study the storage and dissipation of energy in these fluids, and this in turn gives us some clues as to the processes that take place on the microscopic scale.

  2. Viscoplastic Flows: The flow of viscoplastic materials is important in areas ranging from the development of cosmetics, to bioreactors, to the study of lava flows and avalanches. Because of the existence of a yield stress, viscoplastic flows are quite different from flows in Newtonian fluids like water. We are doing experiments using several flow visualization techniques to understand the flow of yield-stress materials in a variety of situations: drainage from the bottom a cylinder, flow around a sphere, flow down an inclined plane. We are also studying the motion of bubbles through yield-stress fluids.

  3. Microrheology of yield-stress fluids: We study the viscoelastic properties of structured fluids on micro-meter length scales using the techniques of microrheology. We track the diffusive motion of small suspended fluorescent particles using a fluorescence microscope. We also do dynamic light scattering, which involves determination of the motion of small tracer particles from fluctuations in the intensity of laser light scattered by the particles. In both cases, the data allows us to extract the microscopic viscous and elastic moduli and infer information about the micron-scale structure of the material.

  4. Rheology of polymeric materials: We study the structure, properties and rheological behaviour of a range of polymer fluids. We have looked at associative polymers, in which the polymer molecules interact via to form a network structure. We are also interested in composites made up of polymer molecules and nanometer-sized particles such as carbon nanotubes or clay particles. We used light scattering, rheometry, microrheology, and other techniques to study these interesting and complex materials.

  5. Materials for biomedical phantoms: It is often important to use materials which mimic the propertied of human tissue in the testing of medical devices. Wtih Blaine Chronik , I am investigating the properties of polymer-based materials to be used as phantoms for the testing of devices for magnetic resonance imaging.

  6. Onset of yield stress: Typically yield stress develops in a material as the concentration of the suspended particle is increased. In some cases yield stress develops over time as the suspended particles aggregate. We are interested in the transition from the fluid state, with no yield stress, to the solid, which has a yield stress. This is a gelation transition in the case of clay suspensions, but can take other forms in other materials. We have been studying this transition in a variety of different materials using both microscopic techniques and bulk rheological methods.

  7. Rayleigh-Benard convection in complex fluids: A thin layer of fluid heated from below will develop flow in a pattern of convective rolls or cells when the temperature difference across the layer becomes sufficiently large. In small fluid samples, the flow pattern is very simple, but in large samples it can be extremely complex. We have studied convection in Newtonian fluids and are now planning to look at flow patterns that develop in complex fluids, including yield-stress fluids and viscoelastic materials.