Thermodynamics of interaction between some cellulose ethers and SDS by titration microcalorimetry - II. Effect of polymer hydrophobicity

A titration calorimetric study of the interaction between nonionic cellulos e 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 characteriz ed by the cloud point and (aqueous) surface tension lowering abilities of t he polymer. A direct correlation is found between the extent of "hydrophobi city" and the endo-enthalpic peak in the initial SDS concentration region o f interaction. However, the overall mechanism of interaction is similar for all the polymers, being dominated by polymer-surfactant interactions initi ally and converting into a surfactant-surfactant interaction process at hig her SDS concentrations. The importance of polymer characteristics thus beco mes weaker at the later stages of the process, Differences between the poly mers is also reduced by an increase of temperature, leading to a near overl ap of observed enthalpy curves at 40 degrees C. The energetics of interacti on are also mirrored by the isothermal surfactant binding curves and the ch anges in macroscopic and microviscosity of the system. (C) 1999 Academic Pr ess.