MICELLIZATION OF POLYSTYRENE POLY(ETHYLENE OXIDE) BLOCK COPOLYMERS IN WATER .5. A TEST OF THE STAR AND MEAN-FIELD MODELS

PS-PEO di- or triblock copolymer micelles of various compositions and molecular weights in water were investigated by light scattering. Characteristic micelle sizes (hydrodynamic radius (R(h)) were resolved from a secondary association by a combination of static and quasi-elastic light scattering signals. The R(h) values for the micelles are in good accord with the scaling relationship of Halperin's star model. The star model then was incorporated into our data analysis to obtain aggregation number N and core radii R(c). With these parameters we are able to test the validity of the Noolandi-Hong mean density micelle model by using their equations to calculate the Flory-Huggins chi parameters for the interaction of PEO-water and PEO-PS. The chi values we obtained are in very good agreement with values in the literature. We found a monotonic dependence of chi-PEO water on PEO concentration. We note not only that these chi parameters are very difficult to determine by other methods but also that two theoretical models with very different sets of assumptions receive quantitative support from our measurement.