Dielectric Studies of Emulsions of Polyol in Hydrophobic Colloidal Silica-Oil Gel

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The dielectric relaxation due to the interfacial polarization of emulsions of either polyol or aqueous solutions of polyol in a hydrophobic colloidal silica-oil gel (P/(S·O) emulsions) was investigated over a wide range of volume fractions of the dispersed phase at frequencies ranging from 10 kHz to 3MHz. P/(S·O) emulsions without surfactant showed dielectric relaxation, and the limiting dielectric constants at high and low frequencies, ε_h, ε_l, limiting dielectric conductivity at high frequency, K_h, and relaxation frequency, f_o, were shown to satisfy the equations given by Wagner's theory⁴⁾ up to a dispersed phase fraction as high as 0.6. In P/(S·O) emulsions without surfactant, the absence of any particle aggregation was ascertained by microscopic observation. When the polyol was diglycerin, several dispersed phases with different dielectric constants were obtained at different mixing ratios of water and diglycerin. It was found that the values of ε_l changed markedly on the addition of surfactant, increasing as the dielectric constant of the dispersed phase, ε_p, became larger. In P/(S·O) emulsions with surfactant, particle aggregation was found by microscopic observation. The f_o values of P/(S·O) emulsions with particle aggregation were smaller than in those without particle aggregation, in spite of the increase in electric conductivity of the dispersed phase brought about by the addition of a surfactant. It should be noted that the magnitude of the dielectric anomaly¹⁾ varies with the magnitude of ε_p even if the added amount of surfactant is the same.