title: Mixing of partially fluorinated carboxylic acids with their hydrocarbon analogs at the air-water interface.
abstract: The mixing behavior of 1-(perfluorobutyl)undecanoic acid-pentadecanoic acid (C15), 1-(perfluorohexyl)undecanoic acid-heptadecanoic acid (C17), and 1-(perfluorooctyl) undecanoic acid-nonadecanoic acid (C19) mixtures was investigated at the air-water interface. The compression isotherms of the fluorocarbon acid-hydrocarbon acid mixtures were recorded at various compositions on hydrochloric acid (pH 1.9, 37+/-2 degrees C) as a subphase. The phase transition, limiting molecular area, area at collapse pressure, and collapse pressure were determined for all pi-A isotherms. The mixing behavior was assessed by analyzing the concentration dependence of the average molecular area at constant film pressure (area/mole fraction or A-X diagram) and the concentration dependence of the phase transition, where possible. All three acid mixtures show a negative deviation from ideal behavior at surface pressures between 5 and 20 mN/m, which is indicative of an attractive interaction of both compounds in the mixed monolayer at the air-water interface. The miscibility apparently decreases with increasing chain length of the carboxylic acids (C15>C17>C19).
authors.affiliation: Graduate Center for Toxicology, University of Kentucky, Lexington, Kentucky 40536, USA. hjlehm1@uky.edu
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Lehmler
authors.forename: Paul M
authors.initials: PM
authors.lastname: Bummer
mesh_terms: D000388:Air; D002264:Carboxylic Acids / Q000737:chemistry*; D005461:Fluorine / Q000737:chemistry*; D006838:Hydrocarbons / Q000737:chemistry*; D015394:Molecular Structure; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D006838:Hydrocarbons; D014867:Water; D005461:Fluorine