Publication Type Journal Article
Title Structure of Langmuir Monolayers of Perfluorinated Fatty Acids: Evidence of a New 2D Smectic C Phase
Authors Philippe Fontaine Eduardo J. M. Filipe Marie-Claude Faure Tomas Rego Stephanie Tassler Ana Carolina Alves Goncalo M. C. Silva Pedro Morgado Michel Goldmann
Groups MET
Journal MOLECULES
Year 2019
Month October
Volume 24
Number 19
Pages
Abstract Due to the characteristic chain rigidity and weak intermolecular interactions of perfluorinated substances, the phase diagram of Langmuir monolayer formed by perfluorinated molecules has been interpreted so far as displaying only two phases, a 2D gas (G) and a liquid condensed (LC). However, in this work, we presented Grazing Incidence X-ray Diffraction measurements, which exhibit two diffraction peaks on the transition plateau: One is the signature of the hexagonal structure of the LC phase, the second one is associated to the low-density fluid phase and is thus more ordered than expected for a 2D gas or a typical fluid phase. Atomistic molecular dynamics simulations, performed on the transition plateau, revealed the existence of clusters in which domains of vertical molecules organized in a hexagonal lattice coexist with domains of parallel lines formed by tilted molecules, a new structure that could be described as a 2D smectic C phase. Moreover, the diffraction spectrum calculated from the simulation trajectories compared favorably with the experimental spectra, fully validating the simulations and the proposed interpretation. The results were also in agreement with the thermodynamic analysis of the fluid phase and X-ray Reflectivity experiments performed before and after the transition between these two phases.
DOI http://dx.doi.org/10.3390/molecules24193590
ISBN
Publisher
Book Title
ISSN
EISSN 1420-3049
Conference Name
Bibtex ID ISI:000496242300175
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