Temperature dependence of hydrodynamic properties and surfactant-polymer interaction in solution. The EHEC/SDS/water system

Hydrodynamic properties and interactions between ethyl(hydroxylethyl)cellulose (EHEC) and sodium dodecyl sulfate (SDS) in water solution are discussed as a function of temperature in a composition interval of the surfactant ranging from zero up to well above the critical micelle concentration (cmc) and for the polymer concentration from zero up to slightly above the concentration of critical overlap, at temperatures between 20 and 34 degrees C, which is the limit of phase separation. The results from viscometric measurements, equilibrium dialysis, cloud point determinations, and conductometric measurements show a strong interaction when small amounts of SDS are added to an EHEC solution. For solutions with polymer concentrations in the range between 0.15 and 0.25% and a total SDS concentration of about 2 mM, a large increase in reduced viscosity is observed. The reduced viscosity passes through a maximum, followed by a marked decrease for SDS concentrations >5 mM. Further additions of surfactant to the polymer solution result in about half the value of the reduced viscosity displayed by the pure polymer solution. The SDS-EHEC composition, which shows an increase in reduced viscosity, corresponds to the onset of surfactant redistribution. These effects persist at elevated temperatures although they are shifted to somewhat lower SDS concentrations, but a second maximum in reduced viscosity develops upon raising the temperature when the concentration of the added SDS is in the vicinity of the surfactant cmc. At all temperatures the equilibrium dialysis shows that the redistribution increases with added SDS until normal micelles begin to form in the bulk solution. The intrinsic viscosity was found to decrease with increasing amount of redistributed SDS to EHEC. The investigation is part of a study concerning thermodynamic and hydrodynamic interactions in systems containing amphiphiles and uncharged polymers(1-4) of interest for applications, for instance, in drug formulations.