Mutual effect of charge- and number-density correlations in ionic liquids and concentrated electrolytes

TL;DR

This study investigates the interplay of charge and number density correlations in ionic liquids and concentrated electrolytes using mesoscopic Gaussian approximation, highlighting the need for beyond-Gaussian theories to explain experimental decay behaviors.

Contribution

It incorporates fluctuation contributions into correlation function analysis and derives conditions for decay types, advancing understanding of ionic system correlations beyond previous models.

Findings

Fluctuation contributions do not significantly alter correlation lengths.

Necessary conditions for decay types are derived but not satisfied at Gaussian level.

Extension beyond Gaussian approximation is required for accurate decay behavior predictions.

Abstract

Correlation functions in concentrated ionic systems are studied within the mesoscopic theory at the level of the Gaussian approximation. The previously neglected fluctuation contribution to the inverse charge-charge correlation function is taken into account to verify the accuracy of the previous results. We calculate the correlation lengths and the amplitudes and show that the fluctuation contribution does not lead to significant changes of the results. We also derive necessary conditions for the presence of both, the oscillatory and the monotonic decays of the charge-charge correlations that must be satisfied by the noncoulombic contributions to the inverse charge-charge correlation function. At the level of the Gaussian approximation, these conditions are not satisfied. Extension of the theory beyond the Gaussian approximation is necessary to verify whether the asymptotic decay of the charge-charge correlations is monotonous or oscillatory, as suggested by the surface force apparatus or by the SAXS experiments, respectively.