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 polymer, poly(ethylene oxide) (PEO), with a cationic surfactant, hexadecyltrimethylammonium chloride (HTAC), is studied by observing the changes in conductivity, specific viscosity (η sp ), and hydrodynamic radius ( R h ) in terms of the solution temperature and PEO molecular weight. The conductivity data show clearly that an interaction between PEO and HTAC occurs at a temperature above 25 °C, as indicated by a decrease in the critical association concentration in the presence of PEO relative to the critical micelle concentration of a surfactant in the absence of PEO. Diminishing hydrophilicity of PEO upon increasing temperature is suggested to induce a stronger interaction between PEO and HTAC. The higher the temperature and the PEO molecular weight are, the more pronounced the peaks in η 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 hydrophobicity of each component.