Environmental pressures are driving detergent formulations to become ever-more sophisticated blends of stabilisers; new formulations of drugs require elaborate stabilisation as they pass from manufacturer to patient; cosmetics and paints increasingly mix colloidal dispersions of different origins into the one final product. The stability of the dispersion in each of these multicomponent systems poses significant problems and the interactions of hydrosoluble neutral polymers with surfactants and their adsorption onto particles is key for the understanding of the mechanism of colloidal stability.

The interactions between poly(vinyl pyrrolidone), PVP, sodium dodecyl sulfate, SDS, and a non-ionic alcohol ethoxylate surfactant have been previously investigated. It was demonstrated that the alcohol ethoxylate does not bind to PVP and desorbs bound SDS from the polymer. We report the effect of non-ionic alcohol ethoxylate surfactant, C13E7, on the PVP/SDS/silica system as studied by photon correlation spectroscopy, solvent relaxation NMR and SANS. Our results confirmed that, in the absence of SDS, C13E7 is non-interacting and does not affect the layer thickness of the adsorbed PVP. As SDS is added, the layer thickness increases due to Coulombic repulsion between micelles in the polymer layer. When C13E7 is progressively added to the system, it forms mixed micelles with SDS, the total charge per micelle reduces so the repulsion between micelle and silica surface that would otherwise cause the PVP to desorb is reduced. Thus, the polymer layer appears to be more strongly adsorbed but also more stretched. The structural conformation of the layer was also investigated by SANS.

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Last edited: Friday September 10, 2010

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