Neutron scattering of hydrophobically modified poly(ethylene oxide) in aqueous solutions

The structure of aqueous dispersions of hydrophobically end-capped poly(ethylene oxide) (PEOM) was investigated by small-angle neutron scattering. Two polymers, M16C16 and D32C16, with the same hydrophilic/hydrophobic balance, with either one or two n-hexadeca end groups and average molecular weights, M, 16 000 and 32 000 g mol(-1), respectively, were studied in heavy water. In addition, a sample of poly(ethylene oxide), M = 35 000 g mol(-1), with deuterated n-octadecyl end groups was studied in heavy water and in a heavy water/water mixture (17.6% D2O) to selectively match the PEO chain. In all the cases, the scattering curves were characterized by a main peak which revealed that the polymers were organized in micelles forming an organized liquid structure. In heavy water, the peak maximum scattered intensity, I-max, has a maximum at a concentration corresponding to micelle overlapping, and I-max increases with increasing temperature, at constant concentration. In a mixture containing 17.6% D2O, I-max continuously increases with polymer concentration. This scattering behavior is interpreted on the basis of an analogy between micellar solutions and dilute and semidilute solutions of star-branched polymers.