A statistical field theory of salt solutions of 'hairy' dielectric particles

TL;DR

This paper develops a field-theoretical model for dilute salt solutions containing 'hairy' dielectric colloid particles, analyzing electrostatic free energy and potential behavior, including crossover phenomena and limiting regimes.

Contribution

It introduces a novel statistical field theory for colloid particles with peripheral charges, extending understanding of electrostatic interactions in complex salt solutions.

Findings

Derived an expression for electrostatic free energy in dilute salt solutions.

Identified a crossover from monotonic to oscillatory electrostatic potential behavior.

Provided analytical relations for free energy in high salt and large charge cloud regimes.

Abstract

In this paper, we formulate a field-theoretical model of dilute salt solutions of electrically neutral spherical colloid particles. Each colloid particle consists of a 'central' charge that is situated at the center and compensating peripheral charges (grafted to it) that are fixed or fluctuating relative to the central charge. In the framework of the random phase approximation, we obtain a general expression for electrostatic free energy of solution and analyze it for different limiting cases. In the limit of infinite number of peripheral charges, when they can be modelled as a continual charged cloud, we obtain an asymptotic behavior of the electrostatic potential of a point-like test charge in a salt colloid solution at long distances, demonstrating the crossover from its monotonic decrease to damped oscillations with a certain wavelength. We show that the obtained crossover is determined by certain Fisher-Widom line. For the same limiting case, we obtain an analytical expression for the electrostatic free energy of a salt-free solution. In the case of nonzero salt concentration, we obtain analytical relations for the electrostatic free energy in two limiting regimes. Namely, when the ionic concentration is much higher than the colloid concentration and the effective size of charge cloud is much bigger than the screening lengths that are attributed to the salt ions and the central charges of colloid particles. The proposed theory could be useful for theoretical description of the phase behavior of salt solutions of metal-organic complexes and polymeric stars.