Electrostatic correlation forces between surfaces with surface specific ionic interactions

Abstract

We have studied some consequences of a generalized theory of electrostatic interactions between two macroscopic surfaces immersed in a dilute electrolyte. The ionic interactions close to the two bounding surfaces were supposed to be specifically affected by the presence of the surfaces, leading to a surface contribution to the total free energy density of the system. A functional integral (sine-Gordon) representation of the grand canonical partition function was derived and evaluated in the saddle-point approximation, leading to the repulsive mean-field and an attractive first-order correlation correction to the interaction free energy. The magnitude of the correlation term was investigated in detail and general conditions on the form of the surface-specific free energy density were derived that would lead to an anomalously large exponentially decaying attractive interactions. We present some arguments in favor of the view that this anomalous long-range attraction could well represent a case for the electrostatic nature of the recently measured long-range ‘‘hydrophobic’’ attraction.