Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2020 / Paper 1 / Section A(iii) / 5 / iv / Solution

Use steric stabilization: attach or strongly adsorb a dense layer of polymer chains or compatible ligands, with tails well solvated by the nonpolar liquid. Overlap of these layers costs osmotic and conformational free energy and prevents particle cores reaching the strongly attractive contact region. The anchoring groups must bind the particle while the exposed chains prefer the solvent; sufficient coverage and a good solvent are essential. Nonpolar media do not make charging impossible, but electrostatic stabilization there requires an appropriate ion-generation and charge-stabilization mechanism, rather than assuming aqueous dissociation behaviour.