Marangoni effects in liquid jets of non-ionic surfactants

The adsorption of nonionic surfactants in the CnE8 family at the air-water interface has been studied on the millisecond timescale in a free liquid jet. The amount of adsorbed surfactant was measured by ellipsometry. The rates of adsorption are compared with a diffusion-controlled adsorption model. In the case of C10E8, which is below its cmc, the monomer diffusion coefficient provides a good fit to the experimental data. For n = 12, 14, and 16, micelles control the mass transport. The best fit diffusion coefficients are close to, but not identical with, the literature values for the micellar diffusion coefficients. Laser Doppler velocimetry was used to measure the change in surface velocity arising from adsorption of the surfactant, for n = 12, 14, and 16. There was a qualitative correlation between the retardation of the surface velocity and the surface tension gradients.