Viscoelastic properties of a cationic surfactant and its mixture with a hydrophobically modified polyacrylamide

The rheological behavior of aqueous solutions of the cationic surfactant erucyl his(hydroxyethyl)methylammonium chloride and its mixture with the hydrophobically modified polyacrylamide in the presence of the low-molecular-mass salt KCl and isopropanol was studied. The critical micelle concentration (cmc) of the surfactant was determined by fluorescence spectroscopy. Two regions having different slopes (6.0 and 3.5) were observed on the viscosity versus concentration curves plotted for semidilute solutions of the surfactant in log-log coordinates. It was shown that the greatest slope corresponds to the regime of short unbreakable cylindrical surfactant micelles whose lifetime is longer than the time of reptation, while the smallest slope reflects the regime of long-lived micellar chains of the surfactant which repeatedly decompose in the course of reptation. It was demonstrated that the addition of an associating polymer based on polyacrylamide to the saline solution of the surfactant leads to an increase in viscosity of the system by a factor of 1-3 and improves its heat stability.