Interaction of inorganic macromolecular systems with surface-active agents

Abstract

Several inorganic macromolecular systems and ionic surface-active agents have been studied in relation to the effect of the surface-active agents on the stability of colloidal suspensions of the inorganic substances, as well as the effect of the inorganic macromolecules on the critical concentration (CMC) of the surface-active agents. Iron (III) oxide, aluminum oxide, manganese (IV) oxide, and arsenic (III) sulfide comprised the inorganic systems. Potassium salts of a series of fatty acids, alkyl sodium sulfates, alkyl amine hydrochlorides, and alkyl pyridinium chlorides were used as the colloidal electrolytes. The stability of the colloidal suspensions in the presence of the surface-active agents varied inversely with the chain length of the surfactant, in the cases where the surface-active ion possessed a charge opposite in sign to that of the colloidal particle. In such systems the minimum concentration required to cause complete flocculation decreased sharply with increase in chain length of the surfactant. At higher concentrations of the surfactants a restabilization of the inorganic systems was observed owing to recharging of the colloidal particles. Logarithmic plots of chain length versus flocculation values approached straight lines as the concentration of the sols decreased. When the surface-active ion had the same sign of charge as the colloid, flocculation occurred only at high concentrations and was independent of chain length. The flocculation value was the same for all members of a homologous series in the latter case. The critical concentration of the anionic surfactants were found to be higher in iron (III) oxide sols than in water, the difference in CMC values being attributed to adsorption of the surfactant by the iron (III) oxide. In a similar manner, manganese (IV) oxide increased the critical concentration of dodecylamine hydrochloride. The critical concentrations of the surface-active ions were unaltered in the presence of colloid particles of the same sign.