Phase Transitions in Langmuir Films of C10-C16 Perfluorocarboxylic Acids at the Air-Water Interface

Abstract

Perfluorocarboxylic acids (PFCAs) are important precursors in the syntheses of fluorinated polymers. These polymers find a variety of applications in industry due to their water and lipid repelling properties, chemical inertness, and facile processing. Non-stick coatings in cooking pans and gasoline tanks in cars are just two of many common applications that use these fluorinated compounds. Critically, it is the desirable property of chemical stability that prevents perfluorinated compounds from biodegradation. Recent research indicates that low levels of PFCAs (and other fluorinated compounds) are ubiquitous in the environment including the biosphere. How PFCAs interact with their local surroundings on a molecular scale is not fully understood, and the need for more fundamental measurements inspires this investigation. In our study, properties of monolayer films of C10-C16 perfluorocarboxylic acids at the air-water interface were measured. Using a Langmuir-Blodgett trough, the surface pressure of the deposited compound was recorded, while compressing the monolayer at constant temperature. The resulting isotherms are interpreted to determine phase transitions, molecular footprints and collapse pressures of the monolayers.