Electrokinetics of concentrated suspensions of spheroidal hematite nanoparticles

The effect of the volume fraction of solids on the concentration polarization around spheroidal particles has been recently investigated using data on the low frequency dielectric dispersion (LFDD) of suspensions [Rica et al., Soft Matter, 2011, 7, 3286]. In this work, we extend our previous experimental analysis including new measurements at different surface charge together with dynamic electrophoretic mobility determinations. This joint study allows us to detect two a relaxations, due to the two characteristic dimensions of our rod-like particles, in addition to the Maxwell-Wagner-O'Konski relaxation and the inertial effects on the electrophoretic mobility. Available theoretical models for the polarization of a single rod are extended to consider particle-particle interactions, this leading to the estimation of the zeta potential and the characteristic size and geometry of the particles. The most significant result of the LFDD experiments is the different trend of low and high frequency relaxations with volume fraction. Calculation of the concentration polarization maps around the spheroidal particle suggests that such different trends can be explained by the different extent of the polarization clouds along both semiaxes.