Particle-Induced Phase Separation in Aqueous Solutions containing Colloidal Particles and Adsorbing Polymers

Sammanfattning: The influence of added colloidal particles on the phase behaviour of a polymer solution was investigated. Binary, quasi-binary and mixed polymer solutions were used in the study, where at least one of the polymers had an affinity for the surfaces of the colloidal particles. Experimentally, silica and polystyrene latex particles were used as colloidal particles. Theoretical calculations have been performed on these kinds of systems using the Flory-Huggins theory extended in two different ways to account for the effects of the particles. Added colloidal particles decreased the stability of the polymer solution. One mechanism that lead to the decreased stability in solutions close to phase separation was capillary-induced phase separation (CIPS). The occurrence of CIPS was seen to depend on different parameters in the solutions, such as the types of polymer and particles, the length of the polymer, the particle concentration and the amount of salt. Another mechanism giving decreased stability of the solutions was adsorption of polymer molecules to the surfaces of the colloidal particles. This creates a “new” kind of particle that interacts unfavourably with the bulk in a mixed polymer solution rich in the polymer with less affinity for the surfaces of the colloidal particles. The interactions between the colloidal particles and the bulk can also be affected by surfactants adsorbing to the surfaces of the colloidal particles, which was shown in a quasi-binary polymer solution.