Dielectric Studies on Emulsion of Water in Hydrophobic Colloidal Silica-Oil Gel. II

  • KANEKO HIDEO
    Pharmaceutical Formulation Research Center, Research Institute, Daiichi Seiyaku Co., Ltd.
  • HIROTA SADAO
    Pharmaceutical Formulation Research Center, Research Institute, Daiichi Seiyaku Co., Ltd.

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Abstract

Dielectric relaxation due to the interfacial polarization of emulsions of water in a hydrophobic colloidal silica-oil gel without any surfactant (denoted as W/ (S・O) emulsion, hereinafter) was investigated over a wide range of volume fraction of the dispersed aqueous phase having various electric conductivity values at frequencies ranging from 10 kHz to 3 MHz. The observed values of the limiting electric conductivities at high frequencies, k_h, of W/ (S・O) emulsion (ε_<p3'>=78.32,k_<p3'>=20.09×10^<-6>〓/cm) are compared with the values predicted by Wagner's theory [K.W. Wagner, Arch. Elektrotech. (Berlin), 2,371 (1914)]. The observed values for the case of finely dispersed particles were a little larger than the theoretical values. The values of limiting electric conductivities at low frequencies, k_l, could not be obtained because they were too small to be determined by the present apparatus. The observed values of the relaxation frequency, f_0,of the W/ (S・O) emulsion showed a good agreement with Wagner's theoretical curve regardless of the dispersed particle size. In W/ (S・O) emulsions containing two kinds of dispersed particles having different electric conductivities, the parameter, α, for the distribution of relaxation frequencies as determined from complex plane plots (Cole-Cole plots) became larger than zero, even though the particles were homogeneously dispersed. From the present and previous studies [H. Kaneko and S. Hirota, Chem. Pharm. Bull., 31,5,1445 (1983)], it is considered that new dielectrics are formed by particle aggregation, and the new dielectrics produce a dielectric anomaly at the interface layer of the aggregated particles.

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