Stopped-flow 19F NMR studies of surfactant precipitation

The kinetics of the phase change in surfactant solutions is studied by 19F stopped-flow NMR. In the aqueous solution of sodium perfluooctanoate, we observe precipitation and crystal growth induced by the addition of NaCl solution to the system. The time dependences of the NMR signal intensity and chemical shift, evaluated in the framework of a single model, narrow the range of possible scenarios, the most plausible of which is monomer incorporation into the growing crystals. In accordance to existing models of crystallization, both the nucleation rates and the crystal growth rates are strongly dependent on the magnitude of supersaturation.