Macromolecules, Vol.31, No.18, 6226-6233, 1998
Light-scattering studies of concentrated copolymer micellar solutions
We report the analyses of an extensive set of light scattering intensity distributions from triblock copolymer micelles in aqueous solutions. We investigated two Pluronics, P84 (PEO19-PPO43PEO19) and P104 (PEO27-PPO61-PEO27) in an entire range of the disordered micellar phase. Our previous small-angle neutron scattering (SANS) study showed that the micelle is spherical and consists of a compact hydrophobic core and a hydrophilic corona region. In that paper (Liu, Y. C., et al. Macromolecules 1998, 31, 2236-2244), we proposed a "cap-and-gown" model for the microstructure of the micelle, taking into consideration the polymer segmental distribution and water penetration profile in the core and corona regions. We took into account the intermicellar correlation using the adhesive hard-sphere model of Baxter. With this combined model, we obtained consistent trends for important parameters such as the aggregation number, hydration number per polymer in both the core and corona, and surface stickiness. The structure of the micelle stays essentially constant as a function of concentration, but changes rapidly with temperature. In this paper, we propose a new method for data treatment of static light scattering (LS) intensities at all concentrations which is complementary to the SANS technique. This analysis allows us to extract the average aggregation number of polymer chains in a micelle, the average hydrated volume fraction of a micelle, and the volume fraction of polymers in a micelle. These parameters obtained from SANS and LS agree to within experimental error.