Time-resolved SANS for the determination of unimer exchange kinetics in block copolymer micelles

A time-resolved SANS method was developed for the determination of unimer exchange kinetics of polymeric micelles under equilibrium conditions. Measurements were performed on the system PEP-PEO/DMF exploiting the large difference in scattering length density of protonated and deuterated species. In contrast to theoretical predictions the observed kinetics consists of two well-separated processes. From temperature-dependent measurements the corresponding activation energies E-A could be determined. A comparison on the basis of a scaling prediction of Halperin and Alexander indicates that the fast process can be associated with a single unimer insertion/expulsion mechanism. The slow process, on the other hand, could not be explained on the basis of available microscopic models.