title: Adsorption of multiple ammonium salts at the air/solution interface.
abstract: The interfacial behavior of aqueous solutions of newly synthesized bis- and tris-ammonium salts (i.e., bis[2-hydroxy-3-(dodecyldimethylammonio)propyl]alkylamine dichlorides and bis[2-hydroxy-3-(dodecyldimethylammonio)propyl]dialkylammmonium trichlorides, respectively) was analyzed, both experimentally and theoretically. The dynamic and equilibrium surface tension of multiple ammonium salt solutions was measured by using a pendant drop shape analysis method. The determined surface tension isotherms indicated the lack of significant differences in surface activity between bis- and tris-ammonium salts, contrary to the expectations for divalent and trivalent surfactant ions. That effect was explained by assuming the formation of multiple surfactant ion-counterion associates. Taking into account the association process, a good correlation between experimental data and theoretical predictions was obtained by means of the "surface quasi two-dimensional electrolyte" (STDE) model of ionic surfactant adsorption. The degree of association necessary to explain the lack of difference in surface activity between bis- and tris-ammonium salts was in quantitative agreement with the results of measurements of the concentration of free chloride anions in the surfactant solution.
authors.affiliation: Faculty of Chemistry, Wrocław University of Technology, Wybrzeze Wyspiańskiego 27, 50-370 Wrocław, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Wegrzyńska
authors.forename: Grazyna
authors.initials: G
authors.lastname: Para
authors.forename: Jan
authors.initials: J
authors.lastname: Chlebicki
authors.forename: Piotr
authors.initials: P
authors.lastname: Warszyński
authors.forename: Kazimiera A
authors.initials: KA
authors.lastname: Wilk