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 e xchange kinetics of polymeric micelles under equilibrium conditions. Measur ements were performed on the system PEP-PEO/DMF exploiting the large differ ence in scattering length density of protonated and deuterated species. In contrast to theoretical predictions the observed kinetics consists of two w ell-separated processes. From temperature-dependent measurements the corres ponding activation energies E-A could be determined. A comparison on the ba sis of a scaling prediction of Halperin and Alexander indicates that the fa st process can be associated with a single unimer insertion/expulsion mecha nism. The slow process, on the other hand, could not be explained on the ba sis of available microscopic models.