Donnan equilibrium and the osmotic pressure of charged colloidal lattices

TL;DR

This paper models the osmotic pressure in charged colloidal lattices considering Donnan equilibrium, using density functional theory, and compares theoretical predictions with experimental data for various colloidal systems.

Contribution

It introduces a theoretical framework for calculating osmotic pressure in colloidal crystals considering charge effects and validates it against experimental measurements.

Findings

The model accurately predicts osmotic pressure across different salt concentrations.

Theoretical results agree with experimental data for polystyrene colloidal lattices.

Charge and size of colloids significantly influence osmotic pressure predictions.

Abstract

We consider a system composed of a monodisperse charge-stabilized colloidal suspension in the presence of monovalent salt, separated from the pure electrolyte by a semipermeable membrane, which allows the crossing of solvent, counterions, and salt particles, but prevents the passage of polyions. The colloidal suspension, that is in a crystalline phase, is considered using a spherical Wigner-Seitz cell. After the Donnan equilibrium is achieved, there will be a difference in pressure between the two sides of the membrane. Using the functional density theory, we obtained the expression for the osmotic pressure as a function of the concentration of added salt, the colloidal volume fraction, and the size and charge of the colloidal particles. The results are compared with the experimental measurements for ordered polystyrene lattices of two different particle sizes over a range of ionic strengths and colloidal volume fractions.