Explicit interrelationship between Donnan and surface potentials and explicit quantification of capacitance of charged soft interfaces with pH-dependent charge density

We derive, hitherto unknown, explicit analytical relationships between Donnan (ψD) and surface (ψ0) potentials of a charged soft interface, represented by a charged polyelectrolyte layer sandwiched between a rigid surface and an electrolyte solution, and use this interrelationship for computing the double layer capacitance of the soft interface.