Micellar Kinetics of a Fluorosurfactant through Stopped-Flow NMR

摘要

~(19)F NMR chemical shifts and transverse relaxation times T_2 were measured as a function of time after quick stopped-flow dilution of aqueous solutions of sodium perfluorooctanoate(NaPFO)with water.Different initial concentrations of micellar solution and different proportions of mixing were tested.Previous stopped-flow studies by time-resolved small-angle X-ray scattering(TR-SAXS)detection indicated a slow(approx 10 s)micellar relaxation kinetics in NaPFO solutions.In contrast,no evidence of any comparable slow(> 100 ms)relaxation process was found in our NMR studies.Possible artifacts of stopped-flow experiments are discussed as well as differences between NMR and SAXS detection methods.Upper bounds on the relative weight of a slow relaxation process are given within existing kinetic theories of micellar dissolution.