TITRATION MICROCALORIMETRY OF ADSORPTION PROCESSES IN AQUEOUS SYSTEMS- INTERACTION OF SODIUM DODECYL-SULFATE AND SODIUM DECYLSULFATE WITH POLY(N-VINYLPYRROLIDONE)

Procedures are described for analysing enthalpograms characterising ad sorption by macromolecules in solution recorded using a titration micr ocalorimeter. The experimental procedure involves injecting small aliq uots of a solution containing adsorbate into a sample cell containing a solution of macromolecular adsorbent. Treatments based on both Langm uir and Frumkin adsorption isotherms are described. The procedures are illustrated by application of the derived equations to the interactio n of micelles of sodium dodecylsulfate(aq) and of sodium decylsulfate( aq) with the water-soluble polymer, PVP. The dominant features in the recorded enthalpograms are described using equations developed from th e Frumkin equation. In both cases the adsorption is endothermic attrib uted to hydrophobic interactions between polymer and surfactant. Howev er, an important feature of the analysis is the characterisation of ad sorbate-adsorbate interactions using enthalpic interaction parameters. The enthalpograms are characterised by three composition ranges: (i) micelle deaggregation and weak interaction of monomers with polymer, ( ii) micelle adsorption on to the soluble polymer up to surface saturat ion and (iii) micelle dilution.