Colloidal suspensions – where micro-size or nano-size particles are suspended in a fluid – exhibit various equilibrium structures ranging from face-centered and cubic-centered crystals to binary ionic crystals, and even kagome lattices. When driven out-of-equilibrium by shear, even more diverse colloidal structures can be accessed. These structures lead to unique flow behaviors of suspensions.
Fascinating rheological properties like shear thickening/thinning and anisotropic viscosity arise from underlying structure in complex fluids. We develop and use techniques to simultaneously analyze emergent, large-scale properties and image particle-level positions and stresses in such suspensions.
In thermal equilibrium, particles suspended in a fluid randomly move about due to kicks from the fluid molecules, in what is known as Brownian motion or diffusion. Shear a fluid, however, and the particles' diffusion will be greatly enhanced. Why? Diffusion spreads some of the particles to regions of the fluid with different velocities. As the fluid then carries different particles with different speeds, the particles spread out faster, effectively increasing the diffusion. This mechanism, dubbed Taylor dispersion after its discoverer G. I.