Conductivity, permittivity, and characteristic time of colloidal suspensions in weak electrolyte solutions

The analytical theory of the thin double-layer concentration polarization i n dilute suspensions of colloidal particles, generalized by the authors to the case of weak electrolyte solutions [C. Grosse and V. N. Shilov, J. Coll oid Interface Sci. 211, 160 (1999)], was used to determine the conductivity dispersion amplitude, the dielectric increment, and the characteristic tim e of the low-frequency dielectric dispersion (LFDD). It is shown that at co nstant ionic strength, the conductivity dispersion amplitude always diminis hes for weak electrolytes. This is due to the increment in the zero-frequen cy dipolar coefficient, which occurs because the field-induced ion concentr ation change around the particle is lowered. On the contrary, while the die lectric increment and the characteristic time of the LFDD usually decrease, they can actually increase when the diffusion coefficient of co-ions is la rger than that of counterions. The origin of this behavior is in the appear ance of volume charge distributions outside the double layer which do not v anish for weak electrolytes in the low-frequency limit. (C) 2000 Academic P ress.