Determination of the intrinsic acid-base dissociation constant and site density of ionizable surface groups by capillary rise measurements

Abstract

A theoretical description is presented for the equilibrium capillary height (heq) of a solution between parallel, flat, solid surfaces which contain ionizable groups. The heq is related to the change in gravitational potential energy, the intrinsic wettability of the un-ionzied surface, and the free energy of formation of the ionizable surface in aqueous solution. The theoretical approach takes into account both the electrostatic free energy of charging the surface and the change in the free energy associated with the acid-base reactions of the surface sites. It is shown that the dependence of heq on pH depends on the number of ionizable surface sites per unit area, the intrinsic acid - base..