Electrophoretic mobility of colloidal particles in weak electrolyte solutions

The analytical theory of the thin double layer concentration polarization i n suspensions of colloidal particles is generalized to the case of weak ele ctrolyte solutions, i.e,, when the dissociation-recombination equilibrium a nd rate constants have both finite values. It is shown that under the actio n of a static applied field, regions near the particle appear where there i s departure from the dissociation-recombination equilibrium. The resulting ion and ion-pair sources have a strong bearing on their flows, leading to a change of the electrolyte concentration gradients around the particle. Thi s phenomenon also modifies the value of the particle electrophoretic mobili ty, which is dependent on the concentration polarization. At constant ionic strength, the theoretical maximum of the electrophoretic mobility versus z eta potential curve can substantially surpass in weak electrolyte solutions the corresponding value attained in strong electrolytes. (C) 1999 Academic Press.