Conductivity, Permittivity, and Characteristic Time of Colloidal Suspensions in Weak Electrolyte Solutions.

The analytical theory of the thin double-layer concentration polarization in dilute suspensions of colloidal particles, generalized by the authors to the case of weak electrolyte solutions [C. Grosse and V. N. Shilov, J. Colloid Interface Sci. 211, 160 (1999)], was used to determine the conductivity dispersion amplitude, the dielectric increment, and the characteristic time of the low-frequency dielectric dispersion (LFDD). It is shown that at constant ionic strength, the conductivity dispersion amplitude always diminishes for weak electrolytes. This is due to the increment in the zero-frequency dipolar coefficient, which occurs because the field-induced ion concentration change around the particle is lowered. On the contrary, while the dielectric increment and the characteristic time of the LFDD usually decrease, they can actually increase when the diffusion coefficient of co-ions is larger than that of counterions. The origin of this behavior is in the appearance of volume charge distributions outside the double layer, which do not vanish for weak electrolytes in the low-frequency limit. Copyright 2000 Academic Press.