title: Investigation of Mixed Surfactant Films at Water Surface Using Molecular Dynamics Simulations.
abstract: Multicomponent Langmuir monolayers are important models of organic coatings of naturally occurring water-vapor interfaces such as the surfaces of oceans or aerosol particles. We investigated mixed monolayers comprised of palmitic acid, C15H31COOH (PA) and 1-bromoalkanes of different chain length (C5, C10, and C16) at the air-water interface employing classical molecular dynamics simulations. Different composition ratios and lateral compression of the monolayers were considered. The structural parameters, such as density profiles, and deuterium order parameter, evaluated as functions of composition and the lateral film packing, provide microscopic information about organization and dynamics of the mixed monolayers. Simulations demonstrate that stable and well mixed monolayers are formed by the mixtures of PA and BrC16H33 (BrCl6), whereas the two considered shorter bromoalkanes, BrC5H11 (BrC5) and BrC10H21 (BrC10), do not form stable films. This is in accord with earlier experimental studies. Under high lateral pressures, in PA/BrC10 mixed systems molecules of the bromoalkane readily flip in the monolayer and subsequently leave the film, while the molecules of the longer BrC16 are expelled from the PA film but no flipping occurs. These results suggest that the film collapse under pressure is preceded by squeezing-out of bromoalkanes from the PA monolayer.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 16610, Prague 6, Czech Republic.
authors.forename: Alena
authors.initials: A
authors.lastname: Habartová
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 16610, Prague 6, Czech Republic.
authors.forename: Martina
authors.initials: M
authors.lastname: Roeselová
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , v.v.i., Dolejškova 3, 18223 Prague 8, Czech Republic.
authors.forename: Lukasz
authors.initials: L
authors.lastname: Cwiklik