Spatial inhomogeneities in ionic liquids, charged proteins and charge stabilized colloids from collective variables theory

TL;DR

This study investigates how size and charge asymmetries influence spatial inhomogeneities in ionic systems using an advanced collective variables theory, revealing significant modifications in phase behavior across various charged particle systems.

Contribution

The paper extends previous collective variables theory by incorporating a non-local hard-sphere approximation and Coulomb regularization, providing more accurate phase diagrams for ionic and colloidal systems.

Findings

Large quantitative changes in phase diagrams due to model modifications

Identification of dominant fluctuations along the λ-lines

Analysis applicable to electrolytes, ionic liquids, proteins, and colloids

Abstract

Effects of size and charge asymmetry between oppositely charged ions or particles on spatial inhomogeneities are studied for a large range of charge and size ratios. We perform a stability analysis of the primitive model (PM) of ionic systems with respect to periodic ordering using the collective variables based theory. We extend previous studies [A. Ciach et al., Phys. Rev.E \textbf{75}, 051505 (2007)] in several ways. First, we employ a non-local approximation for the reference hard-sphere fluid which leads to the Percus-Yevick pair direct correlation functions for the uniform case. Second, we use the Weeks-Chandler-Anderson regularization scheme for the Coulomb potential inside the hard core. We determine the relevant order parameter connected with the periodic ordering and analyze the character of the dominant fluctuations along the $\lambda$-lines. We show that the above-mentioned modifications produce large quantitative and partly qualitative changes in the phase diagrams obtained previously. We discuss possible scenarios of the periodic ordering for the whole range of size- and charge ratios of the two ionic species, covering electrolytes, ionic liquids, charged globular proteins or nanoparticles in aqueous solutions and charge-stabilized colloids.