In this paper the dynamic aspects of colloid particle interaction during Brownian coagulation are considered. The disequilibration of double layers is due to incomplete relaxation of the adsorbed charge at the particle surface. Surface diffusion is investigated as a rate-determining process of the adsorption charge relaxation. Influence of the relaxation process on the interaction between two spherical particles is studied for small surface potentials. We paid particular attention to the transition between the charge regulation (the complete equilibrium) interaction and the constant surface charge (the total disequilibration) regime. The criterion is derived, which shows when the standard DLVO potential corresponding to the constant surface charge interaction, or to the charge regulation regime, is applicable. Also, calculations in the transition region between these two regimes have been carried out, and a rather simple approximate expression for the pair interaction potential is derived. Consequences of the dynamic approach for the colloid stability problem are discussed.