FRS Study of Diffusional Processes in Block Copolymer/Homopolymer Blends Containing Glassy Spherical Micelles

Forced Rayleigh scattering (FRS) was used to study diffusional processes in block copolymer/homopolymer blend systems forming spherical microdomains. Materials used were an asymmetric polystyrene- block -polyisoprene copolymer ( M n = 74 000, 21 wt % polystyrene) labeled with photosensitive dyes (o-nitrostilbene or fluorescein) at the end of polystyrene block chains (b-PS) and two kinds of homopolyisoprene (HPI) ( M n = 23 000, M n = 90 000). Using the lower molecular weight HPI for blending with the block copolymer, b-PS spheres with coronas of polyisoprene block chains (b-PI) strongly swollen by the matrix HPI are obtained (wet-brush system), whereas the HPI matrix having higher M n yields much less swollen coronas of b-PI (dry-brush system). The differences between these two systems in structural and dynamical behavior were found by small-angle X-ray scattering and FRS studies, respectively. To exclude chain release from the spherical micelles during the measurements, diffusion has been studied close to the T g of b-PS microdomains. Unexpectedly, FRS signals differed strongly if measured well below or slightly above the T g of PS microdomains in both intensity and corresponding diffusional processes.