title: Structure and kinetics of fatty acid Langmuir monolayers on zinc salt solutions.
abstract: The adsorption of zinc cations under behenic acid Langmuir monolayers was investigated by means of isotherm measurements, grazing incidence X-ray diffraction and Brewster angle microscopy. The structure of the films was characterized as a function of Zn(2+) concentration, for three different counterions (chloride, iodide, bromide) and at two subphase pHs (5.5 and 7.5). At pH 5.5 and in the studied concentration range, Zn(2+) adsorption leads to a condensation of the fatty acid monolayer with the same phase transitions as over pure water. In contrast, at higher pH the organic X-phase is evidenced immediately above a concentration threshold without any ion organization. Even though Cu(2+) and Zn(2+)cations induce both the fatty acid X-phase, the kinetics of its formation appears strongly different. Indeed, as for Mg(2+) and Cd(2+), the intermediate new I-structure is evidenced in the course of Zn(2+) adsorption although superstructures are observed only for Mg(2+) and Cd(2+). However, for Zn(2+), the I-phase evolves to the final state through a new structure called X' and a continuous X'-X transition. Finally, any effect of the counterion is evidenced neither during the kinetic process nor in the final state.
authors.affiliation: Laboratoire de Physicochimie des Polymères et des Interfaces (LPPI, EA 2528), Institut des Matériaux, Université de Cergy-Pontoise , 5 mail Gay-Lussac Neuville/Oise, 95031 Cergy-Pontoise Cedex, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Cantin
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Fauré
authors.forename: Françoise
authors.initials: F
authors.lastname: Perrot
authors.forename: Michel
authors.initials: M
authors.lastname: Goldmann
mesh_terms: D002413:Cations, Divalent; D005227:Fatty Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015394:Molecular Structure; D012996:Solutions; D014961:X-Ray Diffraction; D015032:Zinc / Q000737:chemistry*
chemical_list: D002413:Cations, Divalent; D005227:Fatty Acids; D012996:Solutions; D015032:Zinc