Dielectric relaxation of suspensions of nanoscale particles surrounded by a thick electric double layer

Dielectric relaxations of suspensions of nanoscale silica particles surrounded by a thick electric double layer are investigated to examine the effect of the concentration of particles. It is found that at low concentrations, the low-frequency dispersion gradually merges with the high-frequency one to become a broad dispersion. The relaxation mechanisms are discussed by using the observed relaxation time. The low-frequency dispersion is caused by the electric double layer polarization while the high-frequency dispersion results from the interfacial polarization. The inner characteristics of the dispersed particles and the dispersing media are obtained from a two-step analytical method developed by the authors [K. He and K. Zhao, Langmuir 21, 11878 (2005)]. With the results of the analysis, Hill's standard electrokinetic model is employed to interpret the merging of the low- and high-frequency dispersions. The discrepancy between the experimentally observed χa and that derived from the model estimation is preliminarily explained by the overlap of an electric double layer.