Effect of temperature and molecular weight on binding between poly(ethylene oxide) and cationic surfactant in aqueous solutions

The formation of a polymer-surfactant complex upon mixing a nonionic polyme r, poly(ethylene oxide) (PEO), with a cationic surfactant, hexadecyltrimeth ylammonium chloride (HTAC), is studied by observing the changes in conducti vity, specific viscosity (Bsp), and hydrodynamic radius (Rh) in terms of th e solution temperature and PEO molecular weight. The conductivity data show clearly that an interaction between PEO and HTAC occurs at a temperature a bove 25 degrees C, as indicated by a decrease in the critical association c oncentration in the presence of PEO relative to the critical micelle concen tration of a surfactant in the absence of PEG. Diminishing hydrophilicity o f PEO upon increasing temperature is suggested to induce a stronger interac tion between PEO and HTAC. The higher the temperature and the PEO molecular weight are, the more pronounced the peaks in eta(sp) and R-h Will be. The amount of surfactant molecules per chain varies with molecular weight, but it is independent of temperature. Our results suggest that the strength of the polymer surfactant interaction increases with the increasing hydrophobi city of each component.