Effect of polycarbonic acids on the molecular mobility of cationic surfactants in micelles

The rotational mobility of a spin probe in the micelles of alkyltrimethylammonium bromides and in their complexes with poly(acrylic acid) and poly(methacrylic acid) has been studied at pH 6. Formation of the polyelectrolyte-surfactant complexes (PSC) causes the decrease in the molecular mobility of surfactant ions in the PSC micelles as compared with the micelles of the free surfactant. It was found that the surfactant ion mobility in PSC micelles is almost independent of the complex composition and even its phase state. The chemical structure of the polyacid has little effect on the molecular mobility of the surfactant ions in the micelles of the complexes. It was shown that the rotational mobility of the surfactant ions in micelles depends on the hydrocarbon chain length of surfactant molecules. Increase in surfactant ion alkyl chain length causes the decrease of their molecular mobility in micelles. Dissociation of the ionic bonds between polyelectrolyte and the surfactant as a result of the increase in the concentration of NaCl in the solution leads to the enhancement of the mobility of the surfactant ions in PSC micelles. It was shown that solubilization of isopropyl alcohol in complex micelles leads to an increase of surfactant ion mobility even at a very low(<10%) alcohol concentration, i.e. at the conditions when the complexes are still stable. (C) 1999 Elsevier Science B.V. All rights reserved.