Pressure of correlated layer-charge and counterion fluctuations in charged thin films

We predict the fluctuation contribution to the interaction between two surfaces with both mobile layer charges and delocalized counterions. The correlation (coupling) between the layer-charge fluctuations and the counterion fluctuations (around a piecewise homogeneous mean-field density profile) is taken into account in the Gaussian approximation. We find that this correlation significantly increases the magnitude of the interlayer fluctuation attraction. The counterion fluctuation pressure is calculated as a function of the intersurface distance and we show how the large and small distance limits correspond to three-dimensional (3D) and 2D fluctuations, respectively. In addition, we predict the charge density-density correlation functions. Experimental implications of the model are discussed.