Interactions between Alkyl Alcohol and Ionic Surfactant in the Adsorption Layer and Insoluble Monolayer

The surface adsorption of the aqueous solutions of octylalcohol-sodium decylsulfate, n-octylalcohol-decyltrimethyl-ammonium bromide, n-oclylalcohol-decylammoriium bromide mixtures and the surface pressure-molecular area relationships of the mixed insoluble monolayer of octadecylalcohol-sodium octadecyl-sulfate, octadecyltrimethylammonium bromide have been studied. The results show that (1) the surface activity of ionic surfactant, irrespective of whether it is anionic or cationic, is much enhanced by the addition of a small amount of octylalcohol; the surface adsorptions of the two components are mutually enhanced at a dilute solution concentration and depressed near the saturation adsorption; the molecular interaction parameters, Pa of all the binary systems studied have large negative values; (2) the mixed insoluble film of octadecylalcohol-octadecyl trimelhyl-ammonium bromide (or sodium octadecylsulfate) is more condensed than the single component; a negative value of surface excess free energy, Gxs, is obtained. A conclusion has been made: the interactions between alkyl alcohol and ionic surfactant in the adsoiption layer and insoluble monolayer are essentially due to the hydrophobic effect of HC-chain and the ion-dipole interaction between polar heads, and H-bonding is not the determining factor.