Electrical properties of aqueous dispersions of polymer microspheres

Abstract

The dielectric constants and conductivities at 10 to 10 5 Hz of aqueous dispersions of monodisperse polymer microspheres of sizes 2.0, 1.1, 0.45, and 0.09 μm were measured at various particle weight fractions φ w and aqueous NaCl concentrations. The specific dielectric increments (ϵ —ω ∞) φ w were independent of φ w and depended strongly on the particle radius a and on κa, where κ is the Debye inverse length in the aqueous medium. Although the ζ potential should be an important variable, the dependence of (ϵ — ϵ ∞) φ w on the ζ potential was unclear, because ζ varied with κ. A distribution of characteristic relaxation times or frequencies corresponds to a given size. This distribution becomes narrower and closer to monodisperse the larger the value of κ a. The central characteristic frequency ν 0 is proportional to ( a + κ 1) −n where n = 1.50 ± 0.12. This value differs slightly from the predicted value of 2. These results are important for developing the dielectric relaxation method for estimating size distributions and possibly surface charges in concentrated aqueous colloidal dispersions.