  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.
