PHASE-SEPARATION AND MORPHOLOGY IN POLYMER-MODIFIED COLLOIDS

The morphology of films of sterically stabilised polystyrene particles , PS, with added free poly(vinyl alcohol), PVA, and poly(vinyl pyrroli done), PVP, was investigated with scanning electron microscopy and cor related to the phase behaviour and interactions. In the case of the PS /PVP system exhibiting depletion phase separation, large polymer domai ns (ca. 7 mu m) were present in the solid state when free polymer conc entration exceeded ca. 13%. This concentration was well within the two -phase region of the phase diagram. Similar polymer domains were also observed for the homogeneous system PS/PVA. The surface of the films w as sealed at free polymer concentrations of ca. 20% and ca. 40% for PV P/PS and PVA/PS, respectively. The final film morphology reflects non- equilibrium conditions arising from the increase in system viscosity d ue to particle close packing and continuous phase thickening by the fr ee polymer. In the case of PS/PVP systems, incomplete depletion phase separation and phase demixing and prevention of particle restabilisati on gives rise to large free polymer domains in the final film. Bridgin g flocculation was argued to be responsible for the large polymer doma ins, some with internal structure, observed with the PVA/PS systems. ( C) 1997 Elsevier Science S.A.