Finding the effective structure parameters for suspensions of nano-sized insulating particles from low-frequency impedance measurements

Abstract

Based on the method of compact groups of inhomogeneities, we formulate new mixing rules for suspensions of charged insulating particles. They express the quasistatic conductivity and permittivity of a suspension in terms of the effective geometric and dielectric parameters of the particles, electric double layers (EDLs), and suspending liquid. Also, we present our low-frequency impedance measurements of the conductivity and permittivity of Al2O3-isopropyl alcohol nanofluids as functions of Al2O3-particle volume concentration. Our rules give good fits for most of these data and allow us to estimate, among other things, the effective thickness, conductivity, and permittivity of the EDLs. The experimentally-recovered values agree well with elementary theoretical estimates suggesting the charging of the particles through preferential adsorption of contaminant ions. The possible effects of other mechanisms on the effective conductivity and permittivity of suspensions are also discussed.