Swelling of colloidal systems

The role of solvent-particle and particle-particle interactions on the swelling of colloidal systems has been investigated. A density functional theory (DFT) approach is taken here to describe a colloid-solvent mixture and develop phase diagrams that give a qualitative picture of possible transitions as a function of the bulk conditions (density and temperature) and the degree of surface solvophobicity. The solvophobicity of the surface is taken as a measure of how much the surface dislikes the solvent, and is determined from the contact angle of the solvent on the surface. The results demonstrate that the nature of the surface (solvophobic or solvophobilic) is a key factor in shaping the phase diagrams. For example, when the surface is solvophilic, the dominant phase is the crystalline, where surfaces are spaced by one solvent layer, while when the surface is solvophobic, the system is most often found in the collapsed state (the surfaces are in contact). The shape of the phase diagrams also depends on the particle-particle interaction. When only the repulsive part of the wall-wall interaction is considered, the collapsed phase is observed less frequently and the diagrams are insensitive to the strength of the purely repulsive interaction. In contrast, the strength of the attractive surface-surface potential plays a crucial role in shaping the phase diagrams.