Modeling ion correlations in electrical double layers and its applications to inhomogeneous charged polymers

Modeling ion correlations in inhomogeneous charged systems with spatially varying ionic strength or dielectric permittivity remains a great challenge. We developed a modified Gaussian renormalized fluctuation theory to systematically include ion correlations in the description of electrical double layers. Particularly, the ion correlation is decomposed into a short-range contribution associated with the local electrostatic environment and a long-range contribution accounting for the spatially varying ionic strength and dielectric permittivity. The theory successfully explained long-standing puzzles such as charge inversion, like-charge attraction, opposite-charge repulsion and interfacial tension of charged fluids. Furthermore, we incorporate our theoretical model for ion correlations into the self-consistent field theory for polymers. Applied to polyelectrolyte brushes, the theory predicts that ion correlations induce non- monotonic change of the brush height: collapse followed by reexpansion. Strong ion correlations can trigger microphase separation, either in the lateral direction as pinned micelles or in the normal direction as oscillatory layers. We also predict that the interactions between two opposing PE brushes show hysteretic feature in the presence of multivalent ions: repulsive in the compression branch and adhesive in the separation branch. Our theoretical predictions are in quantitative agreement with the experimental results reported by Tirrell group. Based on the theory, we develop a computational platform to study a variety of conformation and self-assembly behaviors of biomacromolecules, including protein aggregation, salt effect on the liquid-liquid phase separation of proteins, protein-ATP binding and neurofilament-derived protein brushes.