(271g) Shear Induced Diffusivity of Spherical and Non-Spherical Particles

Shear induced diffusion can be utilized for enhancing transport in suspensions. In order to establish criteria as to what kind of particle leads to larger transport enhancement, the shear induced diffusivity due to two particle interactions of spherical and non-spherical particles is studied both experimentally and numerically. Experimentally, the shear induced diffusivity is obtained by measuring the width of the interface between dyed and non-dyed suspensions flowing adjacently in a microfluidic channel using Leveque scaling. Numerical calculations of the shear induced diffusivity of spheres, rods, ?bucky balls? and branched particles are performed by integrating the mean square displacement upon collision of two particles over all possible collisions. Particle trajectories are calculated using rigid body dynamics along with the Stokesian Dynamics method, and a source of irreversibility between the two particles. For spheres the irreversibilities considered are: surface roughness, repulsive force and electrostatic interaction; for the non spherical particles the diffusivity is calculated in the purely hydrodynamic case and also with a repulsive force between beads belonging two different particles. A broad range of parameters describing the irreversibility is studied. The diffusivity is compared to an approximate upper bound. It is found that spheres are much more sensitive to the irreversibility when compared to the other particles. At small repulsion, when the range of the repulsive force r_c is 10^-6 the particle radius, the shape of the particle has a large impact on the shear induced diffusivity, and therefore particles with broken symmetry have diffusivities that are up to five orders of magnitude larger than the ones of spheres. At high repulsion, r_c = 10^-1, the effect on the particle shape on the diffusivity is not as strong and all particles have diffusivities with the same order of magnitude.