On the swelling behavior of linear end-grafted polystyrene in methanol\toluene mixtures

Neutron reflectivity measurements have been performed with polystyrene (PS) brushes of different graft densities ranging from =0.020 to =0.051 in contact with toluene\methanol mixtures of different composition. The brushes were prepared by a grafting-from procedure resulting in linear chains of average molecular weight n=300,000 g mol–1. The recorded reflectivity curves could be analyzed to a first approximation by assuming a flat scattering length density profile within the brush normal to the surface with a moderate Gaussian smearing of the interface brush\solvent. With increasing toluene content a substantial thickness increase was found with the swollen brush at 70 vol.% being 3.7 times thicker than the dry collapsed film. At low toluene contents the preferential incorporation of this good solvent for the PS brush exceeds a factor 3.5 relative to the molar ratio of the bulk solvent mixture with methanol.