Surface layer thickness in non-aqueous polymer dispersions stabilised by AB block copolymers of polystyrene and poly(dimethyl siloxane)

Abstract

Well defined non-aqueous dispersions of poly(methyl methacrylate) and polystyrene particles in n-alkanes have been stabilised by AB block copolymers of polystyrene and poly(dimethyl siloxane) having a narrow molecular weight distribution. The thickness of the surface layer was determined from viscosity studies of the dispersions as a function of the molecular weight of the poly(dimethyl siloxane) chains in the range (3–48)× 10³. The thickness of the surface layer was also obtained from results for the surface area occupied per stabilising chain and the mean separation distance between adjacent stabilising chains which were estimated from surface coverage data. The dimensions of the surface layer suggest that short poly(dimethyl siloxane) chains with molecular weights below 10⁴ are in an extended chain conformation. At higher molecular weights, the conformation of the stabilising chains is intermediate between random coil and extended chain conformations. The close packing of the stabilising chains at the particle—liquid interface may contribute to the formation of an extended chain conformation.