Structure of (deuterated PEO) (PPO) (deuterated PEO) block copolymer micelles as determined by small angle neutron scattering

The structure of(deuterated ethylene oxide)(23)-(propylene oxide)(34)-(deuterated ethylene oxide)(34) block copolymer micelles was studied in the unimer-to-micelle transition region using small angle neutron scattering (SANS). A three-parameter core-corona model fit to the set of scattering curves obtained with various mixtures of D2O and H2O as the solvent yielded the aggregation number, the core and corona radii, and the water contents of the core and the corona. The results showed that the micellar core cannot consist of PPO only but must contain significant quantities of water. The micelle aggregation number increased with temperature while the core and corona radii were constant over a 10 degrees C temperature region above the critical micellization temperature. The values of the corona radius obtained from the model fit (56-57 +/- 3 Angstrom) are in a good agreement with the hydrodynamic radius of the micelle (56-61 +/- 2 Angstrom) measured by dynamic light scattering.