Partitioning of Inert Colloids Particles in Phase-Separated Polymer Solutions and their interfacial behaviour on phase boundaries

Phase separation commonly occurs in solutions containing two different incompatible polymers due to insufficient interdroplet repulsion forces and thus their coalescence. Segregative phase separation is the main type in this study, depending on the concentration when there’s no specific interaction between components in analysed solution system. Introducing particles is considered to be a effective way to stabilize this unstable emulsion system.

The work focuses on the phenomenon that added inert small particles show a strong tendency to congregate into one but not the other of two phases in phase separated polymer solution system. A number of previous experimental studies by different groups indicates the wide general existence of this phenomenon. Computer simulation program is utilized here to simulate and calculate distribution of particles into each phase; using simplified model. We use the Flory-Huggins theory and Self-Consistent-Field (SCF) calculations to imitate the phase separation situation and obtain the free energy per unit area (i.e., interfacial tension) resulting from the depletion of polymers around particles in two phases to figure out whether the difference in this free energy between two phases is sufficient to induce particles to partition completely into a single phase. Self-Consistent-Field calculations, often implemented on a lattice model, allow for the variation in the volume fraction of each polymer present in a phase, to be monitored as a function of distance away from a solid interface. Indeed we find this to be the case with a strong preference for inert particles to reside in the phase enriched with smaller polymers. Several more cases for changing degree of incompatibility of two polymers, size of polymers, initial proportion of polymers are explored and discussed. In addition, the contact angle θ produced by introduced particles and the interface between two phases is approaching 90° as long as the degree of incompatibility is sufficiently large.

Experiment of observing the tendency of added fluorescent particles (Carboxyl-modified polystyrene P(S/V-COOH), Surf Green) in phase-separated solution containing κ-carrageenen and konjac gum has been done in this study. We have made phase diagram for concentration ranging from 0.1 wt% to 1.0 wt% for two polysaccharides. The result shows mixture made of higher concentrations of two solutions are prone to phase separate. And the introduced fluorescent particles observed by confocal microscopy prefers to aggregate into the phase enriched with κ-carrageenen, the smaller polysaccharide. This result just verifies the theoretical deduction to some extent.