Morphological changes induced by addition of polystyrene onto dextran-b-polystyrene block copolymer solutions
Résumé
We discuss the effect of adding various amounts in solution of a linear PS standard of Mn = 25,000 g/mol onto a pre-formed nanostructure obtained by self-assembly of dextran40-block-polystyrene270 (dex40-b-PS270). Since there is no common solvent for such a hybrid except mixtures of tetrahydrofuran and dimethylsulfoxide for high PS content, the self assembly is investigated by means of dynamic and static light scattering from dilute solutions of blends using such mixtures. By so dramatically and artificially increasing the hydrophobic mass fraction, the resulting blends exhibit solution properties which depend on the amount of the added PS. It is demonstrated that the dex40-b-PS270 block copolymer can tolerate quite large amounts of the PS additive giving rise, as expected, to a morphological transition when compared to the parent nanostructures, while higher amounts of the PS additive lead to the precipitation of the blends. Interestingly, blend of a given composition exhibits the same vesicular morphology as in the case of the dex40-b-PS775 copolymer of the same composition, that is, free of any PS additive.