A calorimetric study of adsorption and deaggregation in aqueous solution

• Main Author: Irlam, Keith David
• Published: University of Leicester 1998
• Subjects: 541
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.696458

This thesis reports a study of adsorption of small molecules by macromolecules and the deaggregation of micelles in aqueous solution. These phenomena were investigated using an isothermal titration microcalorimeter. Procedures are described for the analysis of enthalpograms which characterise the adsorption of anionic surfactants, sodium dodecylsulphate (aq), copper dodecylsulphate(aq) and sodium decylsulphate(aq) by a water soluble polymer Poly (N-vinlypyrrolidone)PVP(aq). The application of equations based on both Langmuir and Frumkin adsorption isotherms are discussed. Characteristics features of the enthalpograms for the adsorption are described using equations developed from the Frumkin equation. The adsorption was endothermic as a consequence of hydrophobic interactions between polymer and surfactant. The analysis describes absorbate-absorbate interactions using enthalpic interaction parameters. Critical micelle concentrations (cmc) of copper, cadmium and nickel dodecylsulphate(aq) in aqueous solution were measured. The calorimetric plots showed an extrema which corresponded to the cmc which was in close agreement with literature values based on surface tension measurements. Enthalpograms for deaggregation of micelles formed by alkyl trimethylammonium bromide surfactants were classified into three types, A, B, and C. The classification is based on the shape of the plot of the enthalpy of dilution as a function of surfactant concentration. The effect of the cmc and the enthalpogram of added benzoates to n-hexadecyltrimethylammonium bromide(aq) was investigated. The cmc was reduced and the classification changed from Type A to Type B in all cases. This pattern was accounted for in terms of adsorption of benzoate ions into the Stern layer of the micelles.