Radiotracer studies of the adsorption of surface active substances at aqueous surfaces, 6

The surface tension and adsorption were observed by the Wilhelmy plate and radiotracer methods at the air-solution interface of an aqueous solution of urea and α-dodecyl-ω-hydroxyhexa(oxyethylene) (D(EO)6). The adsorption of D(EO)6 was dependent on the concentration of urea below the CMC values, but above the values it was independent of the concentration. Urea adsorption occurs positively for low-surface packing of the poly(oxyethylene) group of D(EO)6, but negatively for the closest packing of the group and high concentrations of urea. It was confirmed that D(EO)6 adsorption took place at the solution surface according to the Gibbs adsorption isotherm, which was taken into account as an activity coefficient in an empirical equation for the interactions of D(EO)6 and urea in solution. Urea adsorption for the adsorbed monolayer of D(EO)6 above the CMC value was interpreted assuming that urea, as for the nonionic micelle, was nonpenetrating, which was examined by gel permeation. (auth.)