Attempts to quantitatively describe the CR mechanism date back to the early 70's, with the pioneering work of Ninham and Parsegian (NP) . The NP theory is based on the Poisson-Boltzmann (PB) mean-field description of electrostatic interactions, with the adsorption of protons from solution controlled by the bulk acid dissociation constant . NP theory does not account for the interfacial effects, as its formulation relies on the bulk equilibrium constant . However, the equilibrium dissociation constants of acid can be quite different, depending if the residue is free in the bulk or bound to the surface . Furthermore, it also ignores the electrostatic discrete surface charge effects , which have been shown to play a very important role for CR . The more recent theoretical models are based on the chemical equilibrium between free hydronium ions and acid functional groups regularly arranged on a 2D substrate, following the reaction HA ----H + + A -, corresponding to protonation/deprotonation of surface sites. The equilibrium number of deprotonated sites determines the surface charge, which depends on the electrostatic potential, solution pH , and intrinsic pK a of surface groups. The titration curves can be obtained by varying the amount of acid/base added to the system.