Most conventional techniques for measuring adsorption at the liquid/air interface on fast timescales rely on measuring the change in the interfacial tension as adsorption takes place. This approach works well for solvents such as water, which has a large interfacial tension, but becomes more problematic for less polar solvents such as oil. It is therefore useful to investigate other, more direct, techniques which have the potential to extend the range of systems currently accessible. In this dissertation, Second Harmonic Generation (SHG) and Ellipsometry were applied to the problem of surfactant adsorption at the liquid/air interface, on the millisecond timescale. To measure dynamics on this timescale, SHG and ellipsometry experiments were performed on surfactants adsorbing at the surface of a liquid jet. The principle behind these experiments is that on emergence from the nozzle of the jet, the surfactant surface concentration is not at its equilibrium value and will therefore equilibrate over time. By measuring the surface surfactant concentrations at different distances from the orifice it was therefore possible to obtain a measure of adsorption as a function of time for a given jet speed. In the ellipsometry experiments, the adsorption kinetics of the cationic surfactant, CTAB, were measured. Interpretation of the data was made easier by converting the coefficient of ellipticity directly to a surface concentration using a calibration curve obtained from neutron reflection data. The experimental data obtained were compared with theoretical models for diffusion limited adsoprtion and found to give good agreement. In the SHG experiments, a number of systems were studied, including Nitrophenol, Triton X-100 and the Alkyl-Anilines. For each system, the SHG signal was found to be invariant with time and possible reasons for this finding are discussed in each case.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:604860 |
| Date | January 1999 |
| Creators | Hutchison, J. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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