Electrostatic double layer forces in the case of extreme charge regulation.

We analyze the interaction forces between charged surfaces across aqueous solutions under the conditions of extreme charge regulation. Under such conditions, interactions may be weaker than those given by the constant potential (CP) boundary conditions. Thermodynamically, even vanishing electrostatic interactions are conceivable. Within the constant regulation approximation, the known results can be extended to this sub-CP regime by adopting regulation parameters outside of the common range. A mean-field lattice model of an adsorbed layer shows that such conditions are most likely found near critical points within the adsorbed layer.