Dissolution rates of pure nonionic surfactants

Small drops of the pure linear alcohol ethoxylates C12E5 and C12E6 were inj ected into water at temperatures below their cloud points, and the times re quired for their dissolution were measured using videomicroscopy. Separatel y the rates of growth of the various liquid crystalline intermediate phases formed during penetration experiments with these surfactants in vertical l inear cells were measured using videomicroscopy. It was found from both typ es of experiments that the dissolution process was controlled by diffusion, not by kinetics of phase transformation at interfaces. Effective diffusivi ties of the various phases were calculated from the data obtained and were found to be of order 10(-10) m(2)/s. Finally, interferometry was used to me asure concentration distributions as a function of time during dissolution of the lamellar phase of C12E5 Diffusivity iii the micellar solution was fo und to increase with increasing surfactant concentration with a further inc rease occurring at the concentration where the lamellar phase formed. The r esults were consistent with the effective diffusivities determined from the videomicroscopy experiments and with available values in the literature ob tained by other techniques.