ON THE FORMATION OF CATANIONIC SURFACTANT PRECIPITATE

The morphology, structure and composition of catanionic surfactants formed during spontaneous batch precipitation from equimolar mixtures of alkylammonium chlorides and sodium alkyl sulfates, both with alkyl chains containing 10, 12 and 14 carbon atoms, were investigated by elemental, X-ray and IR analysis. - Size distribution data are used to assess the mechanisms which control the precipitation at different stages of the process. Under experimental conditions employed (low surfactant concentration, high ionic strength) practically pure decylammonium decyl sulfate, dodecylammonium dodecyl sulfate or tetradecyl-ammonium tetradecyl sulfate were formed. Crystalline catanionic surfactant particles exhibited low symmetry and interplanar spacings typical for lamellar structure. Great similarity of IR spectra obtained for the systems with alkyl chains containing 12 or 14 carbon atoms indicates essentially the same type of electrostatic interactions between the headgroups in these systems. - Catanionic surfactant formation could be described by a general equation of the type d(v50) = at(b). Determined values of the coefficient a and exponent b varied with the length of alkyl chain and the type of the rate - controlling process (growth, recrystallization and/or dissolution). Microscopic observation showed the coexistence of crystalline and liquid crystalline phase in aged systems.