Thermodynamics of Interaction between Some Cellulose Ethers and SDS by Titration Microcalorimetry

A titration calorimetric study of the interaction between nonionic cellulose ethers and ionic surfactant (SDS) has been extended to a larger number of polymers to explore the effect of variation of polymer hydrophobicity on the energetics of the process. "Hydrophobicity" as used here is an overall effect of the nature, degree, and number of substituents and is characterized by the cloud point and (aqueous) surface tension lowering abilities of the polymer. A direct correlation is found between the extent of "hydrophobicity" and the endo-enthalpic peak in the initial SDS concentration region of interaction. However, the overall mechanism of interaction is similar for all the polymers, being dominated by polymer-surfactant interactions initially and converting into a surfactant-surfactant interaction process at higher SDS concentrations. The importance of polymer characteristics thus becomes weaker at the later stages of the process. Differences between the polymers is also reduced by an increase of temperature, leading to a near overlap of observed enthalpy curves at 40 degrees C. The energetics of interaction are also mirrored by the isothermal surfactant binding curves and the changes in macroscopic and microviscosity of the system. Copyright 1999 Academic Press.