Equilibrium swelling of colloidal polymeric particles with water-insoluble organic solvents

The Morton–Kaizerman–Altier (MKA) equation fails to describe experimental swelling data of polystyrene particles with toluene in the absence of free or adsorbed surfactants. A modification of the MKA equation is possible by the consideration of a volume work leading to a swelling pressure in analogy to macroscopic gels. With the modified equation a satisfactory description of the experimental data is possible if a size dependence of all the three interaction parameter of the particles with the swelling agent, the swelling pressure, and the interfacial tension of the particles is considered. In the case of particles with diameters below 50 nm and with high surface charge densities an additional electrostatic repulsion contributes to the volume increase during swelling, which is not yet considered in the theory.