Polymer-surfactant interactions: Thermodynamics of some polypropylene glycols in sodium dodecylsulfate aqueous solutions at 298.15 K. Comparison withcationic CTAB aqueous solutions

Interactions between poly(propylene) glycols and sodium dodecylsulfate, in aqueous solutions were investigated through thermodynamic analysis. Densiti es and heat capacities, measured with the corresponding well-known Picker a pparatus, were determined as a function of the surfactant concentration at 298.15 K. The apparent and transfer molar volumes and heat capacities of th e solutes, surfactant and polymer, were deduced therefrom. From the analysi s of their variations as a function of the surfactant concentration, it was shown that mainly strong hydrophobic interactions are involved between sol utes, similar to the medium chain (C-4-C-6) 1-alcohols in equivalent surfac tant systems. However, the large variations of these properties observed cl ose to the critical micellar concentration signify profound structural chan ges in micelles caused by the presence of the polymer. Comparison with hexa decyltrimethyl ammonium bromide solutions shows a similar pattern of aggreg ation and complex formation although the strength and nature of the interac tions are somewhat different.