Shear-induced diffusion (SID) is a phenomenon which occurs in suspensions undergoing shear when effectively diffusive motions of the particles, due to the hydrodynamic interactions between them, are much greater than Brownian diffusion. Most of the literature on SID over the past 20 years has focused on suspensions of noncolloidal spheres, whereas experimental measurements has been mainly performed in circular Couette flow. We instead exploited the recent developments of microfluidic technologies to investigate the lateral diffusion in dilute suspensions of micron-sized nonspherical particles. In particular, we used an H-sensor, a well-established device typically adopted to make diagnostic determinations of analyte concentrations or diffusion-based extraction, to measure the transverse migration of Montmorillonite clay disk-shaped particles in very long (up to 50 cm) but thin channels (typical height of about 10 microns). Such a microfluidic setup presents several advantages, as, for instance, the possibility to achieve very high and controlled shear rates and avoiding unwanted convection effects, which allow us to obtain quantitative and reproducible results over a wide range of shear rates and concentrations.

The results we obtained show a remarkably large shear-induced diffusivity, about two orders of magnitude higher than experimental data and theoretical calculations for spherical particles with the same equivalent radius and particle concentration. Moreover, our data for SID scale linearly with the shear rate over a large range (from 50 to 5000 s-1) and, at very low concentration, show a simple proportionality to the volume fraction, which means irreversible interactions, plus a higher-order dependence on the square of particle concentration. Additional experiments are presently ongoing to better clarify these results.