Abstract
Dielectric relaxation due to the interfacial polarization of emulsions of water in a hydrophobic colloidal silica-oil gel (W/(S·O) emulsion, below) was investigated over a wide range of volume fraction of dispersed phase at frequencies ranging from 10kHz to 3MHz. W/(S·O) emulsions without surfactant showed a dielectric relaxation, and the limiting dielectric constants at high and low frequencies were both shown to satisfy the equations given by Wagner's theory1, 2) up to a water volume fraction as high as 0.65. In W/(S·O) emulsions without surfactant, absence of any aggregation of water particles was ascertained by microscopic observation, while aggregation was observed in W/(S·O) emulsions with nonionic surfactant. In emulsions with aggregation, the limiting dielectric constant at low frequencies deviated from both Wagner's and Hanai's theoretical curves, though the limiting dielectric constant at high frequencies was consistent with Hanai's theoretical curve. The dielectric anomaly, i.e. the deviation from the theoretical values at low frequencies, may be related to the particle aggregation of w/o emulsions, and it may be possible to make a quantitative evaluation of the colloid-chemical stability of w/o emulsions in terms of particle aggregation.
