Coacervation in aqueous cationic soap solutions

Abstract

AbstractThe properties of several coacervating longchain quaternary ammonium salts were studied by means of light‐scattering, viscosity, and diffusion measurements. The aqueous quaternary ammonium‐electrolyte solutions, Hyamine 1622‐NaCl, Hyamine 1622‐NaNO3 and EHDDAB‐NaNO3 systems, which form coacervates, show the following distinctive characteristics as compared to the non‐coacervating Hyamine 1622‐NaAc system: The micellar solute species in a coacervate system is one of relatively low charge density. The addition of electrolyte to a coacervate system produces a tremendous growth of the micellar species prior to two phase formation, in many cases larger than a one hundred fold increase as compared to the salt free solution. The phenomenon of two phase formation in these cationic soap systems shows a pronounced specificity to the anion of the added electrolyte. This specificity may be qualitatively correlated to the ionization properties of the micellar species in the presence of added electrolyte. A relatively narrow electrolyte transition range (ETR) may be described for coacervating systems, intermediate between zero electrolyte concentration and the critical electrolyte concentration necessary for two phase formation, in which a radical reorganization of the soap micelle occurs. Light‐scattering, viscosity and diffusion data for a typical coacervating system, Hyamine 1622‐NaCl‐H2O, indicate that for electrolyte concentrations below the electrolyte transition range, the soap micelle is isotropic. For electrolyte concentration in excess of the electrolyte transition range, the data are consistent with a cylindrical rod‐shaped micellar solute particle.