Characterization of polystyrene-block-poly(4-vinyl-pyridine) block copolymer micelles in toluene solution

Polystyrene-block-poly(4-vinylpyridine) diblock copolymer micelles of various compositions and molecular weights were characterized in toluene. Static light scattering, quasielastic light scattering and viscosity measurements were used to determine the basic micellar characteristics (aggregation number, micellar size, geometry and polydispersity). Depending on the copolymer under investigation, two different geometries (spherical and non-spherical geometry) were observed. The micelles which are spherical in shape have aggregation numbers in the range 200-600 while the non-spherical micelles have a much larger aggregation number (ranging between 600-1000). The sizes of the micelles remain unchanged in our concentration range (10(-3)-5 . 10(-3) g/mL) and no critical micelle concentration could be detected in the concentration range from 10(-5) to 10(-3) g/mL. A detailed analysis of the structural parameters of the micelles which are spherical in shape, reveals that the core-shell interfacial area per copolymer chain as well as the volume fraction of the copolymer in the shell are relatively constant, and that the core is almost not swollen by the solvent. Mixed uniform micelles were observed after mixing equal amounts of two solutions containing micelles differing in size and molecular weight. The reequilibration rate was found to be very fast.