Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 2 / Section D / 25 / d / i / A

A stable charge-stabilized dispersion has an interaction barrier large compared with $k_{B}T$. In DLVO theory, the total pair potential combines attractive Van der Waals forces with repulsion from overlapping electric double layers. Similar surface charges raise the free energy of overlap; a sufficiently high positive barrier prevents thermally diffusing particles from reaching the deep primary minimum near contact.

Other stabilization mechanisms include steric stabilization by solvated surface chains and combined electrosteric protection by charged chains. Such contributions are additional to the simplest DLVO pair potential. Increasing salt shortens the Debye length, so double-layer repulsion becomes shorter-ranged and the protective barrier can decrease.