The drag reduction of poly(ethylene oxide)-carboxylate soap mixtures

Abstract

The interaction of poly(ethylene oxide) with a homologous series of carboxylate soaps has been detected through measurements of drag reduction under turbulent flow conditions. The plots of percentage drag reduction at constant polymer concentration versus soap molarity are quite similar to literature data reported for the effect of several anionic surfactants on the reduced viscosity of a nonionic polypeptide. At low soap concentrations, the drag reduction of poly (ethylene oxide) is suppressed and falls to a minimum value. As the concentration is increased further the drag reduction rises above the value in pure water to one almost 75% greater in the stronger soap solutions. When the soap concentration corresponding to the minimum in the plot ( C M ) is plotted against the critical micelle concentration (cmc) the simple relation C M = 0.225 cmc is obtained. Such a result strongly suggests a cooperative micelle formed between soap and polymer at this point. Furthermore, the enhanced drag reduction obtained is consistent with the model of surfactant molecules hydrophobically bonded to the polymer chain in which repulsion between adjacent polar surfactant groups promotes expansion of the polymer coil.