On the nature and role of water structuring in the adsorption of nonionic surfactants on hydrophobic surfaces

• High pressure liquid chromatography (HPLC) results were used to calculate the temperature dependence of the hydrocarbon-water interaction parameter. The temperaturte dependence has been interpreted in terms of water structuring around the hydrocarbon. The role of water structuring is to enhance the solubility of hydrocarbons in water, which is equivalent to a decrease of the hydrocarbon-water interaction parameter. The poor solubility of hydrocarbons in water is not due to the water structuring, but to other factors such as the large energy required to form a cavity in the water for the hydrocarbon. This is a reflection of the very large cohesive forces in liquid water. These results, together with the temperature dependence of the polyethylene oxide-water interaction parameter, have been used to calculate the temperature dependence of the adsorption of a nonionic surfactant, viz. an ethoxylated nonyl phenol with 20 ethylene oxide units (NP-EO20). It is shown, that water structuring causes, an increased adsorption with temperature. Without water structuring a decreased adsorption is predicted.

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