On the macroion virial contribution to the osmotic pressure in charge-stabilized colloidal suspensions

TL;DR

This paper investigates the virial contributions to the osmotic pressure in charge-stabilized colloidal suspensions, highlighting the importance of surface effects and micro-ionic forces for accurate modeling, especially in salt-free systems.

Contribution

It clarifies the role of surface effects and wall-induced forces in the virial contributions, improving the understanding of the equation of state in colloidal suspensions.

Findings

Neglecting surface effects leads to paradoxical results.

Wall-induced forces resolve the naive model's issues.

Micro-ionic contributions dominate in salt-free systems.

Abstract

Our interest goes to the different virial contributions to the equation of state of charged colloidal suspensions. Neglect of surface effects in the computation of the colloidal virial term leads to spurious and paradoxical results. This pitfall is one of the several facets of the danger of a naive implementation of the so called One Component Model, where the micro-ionic degrees of freedom are integrated out to only keep in the description the mesoscopic (colloidal) degrees of freedom. On the other hand, due incorporation of wall induced forces dissolves the paradox brought forth in the naive approach, provides a consistent description, and confirms that for salt-free systems, the colloidal contribution to the pressure is dominated by the micro-ionic one. Much emphasis is put on the no salt case but the situation with added electrolyte is also discussed.