School of Chemistry - Theses

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    The adsorption of polydisperse nonionic surfactants at the solid/aqueous interface
    Aston, Jeffrey Roy ( 1987)
    A high resolution capillary gas chromatography technique has been adapted to the analysis of polydisperse non-ionic surfactants. This technique has enabled the complete characterization of the oligomer distributions of very small samples of surfactants (typically 0.1 µg to 0.5 µg). It has made possible the determination of changes in the oligomer distribution on adsorption of surfactant at the solid/aqueous interface. Isotherms have been measured for the adsorption of a series of polyoxyethylene nonylphenol surfactants from aqueous solution on to various solids. These isotherms indicate that the surfactant – surface interaction increases with an increase in the hydrophobicity of the adsorbent. They also show a dependence upon the average length of the ethylene oxide chain and the ratio of the surface area/solution volume. These latter factors affect both the total partition of surfactant between the surface and the solution, and also the selectivity of the solid surface. A detailed study of the adsorption of N8 (a commercial non-ionic surfactant) by a precipitated silica at various surface area/solution ratios, has been undertaken, where the equilibrium surfactant oligomer distributions in the adsorbed and solution phases have been determined. At surfactant concentrations above the critical micelle concentration, the phase separation approach has been used to estimate the surfactant oligomer distributions in free monomer solution and in micelles. This information has been combined with a surface phase model to interpret the results of the adsorption distribution studies.