{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,13]],"date-time":"2026-03-13T15:48:10Z","timestamp":1773416890186,"version":"3.50.1"},"reference-count":39,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2019,10,5]],"date-time":"2019-10-05T00:00:00Z","timestamp":1570233600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>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 \u201c2D smectic C\u201d 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.<\/jats:p>","DOI":"10.3390\/molecules24193590","type":"journal-article","created":{"date-parts":[[2019,10,7]],"date-time":"2019-10-07T03:34:01Z","timestamp":1570419241000},"page":"3590","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Structure of Langmuir Monolayers of Perfluorinated Fatty Acids: Evidence of a New 2D Smectic C Phase"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3394-6508","authenticated-orcid":false,"given":"Philippe","family":"Fontaine","sequence":"first","affiliation":[{"name":"Synchrotron SOLEIL, L\u2019Orme des Merisiers, Saint Aubin, BP48, 91192 Gif sur Yvette CEDEX, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4440-7710","authenticated-orcid":false,"given":"Eduardo J. M.","family":"Filipe","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"given":"Marie-Claude","family":"Faur\u00e9","sequence":"additional","affiliation":[{"name":"Institut des NanoSciences de Paris, UMR 7588 CNRS, Sorbonne Universit\u00e9, 4 place Jussieu, 75252 Paris CEDEX, France"},{"name":"Facult\u00e9 des Sciences Fondamentales et Biom\u00e9dicales, Universit\u00e9 de Paris, 45 rue des Saints-P\u00e8res 75006 Paris CEDEX, France"}]},{"given":"Tomas","family":"Rego","sequence":"additional","affiliation":[{"name":"Institut des NanoSciences de Paris, UMR 7588 CNRS, Sorbonne Universit\u00e9, 4 place Jussieu, 75252 Paris CEDEX, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5050-6291","authenticated-orcid":false,"given":"Stephanie","family":"Ta\u00dfler","sequence":"additional","affiliation":[{"name":"Synchrotron SOLEIL, L\u2019Orme des Merisiers, Saint Aubin, BP48, 91192 Gif sur Yvette CEDEX, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7235-2900","authenticated-orcid":false,"given":"Ana Carolina","family":"Alves","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"},{"name":"Institut des NanoSciences de Paris, UMR 7588 CNRS, Sorbonne Universit\u00e9, 4 place Jussieu, 75252 Paris CEDEX, France"}]},{"given":"Gon\u00e7alo M. C.","family":"Silva","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6190-9611","authenticated-orcid":false,"given":"Pedro","family":"Morgado","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8587-5644","authenticated-orcid":false,"given":"Michel","family":"Goldmann","sequence":"additional","affiliation":[{"name":"Synchrotron SOLEIL, L\u2019Orme des Merisiers, Saint Aubin, BP48, 91192 Gif sur Yvette CEDEX, France"},{"name":"Institut des NanoSciences de Paris, UMR 7588 CNRS, Sorbonne Universit\u00e9, 4 place Jussieu, 75252 Paris CEDEX, France"},{"name":"Facult\u00e9 des Sciences Fondamentales et Biom\u00e9dicales, Universit\u00e9 de Paris, 45 rue des Saints-P\u00e8res 75006 Paris CEDEX, France"}]}],"member":"1968","published-online":{"date-parts":[[2019,10,5]]},"reference":[{"key":"ref_1","unstructured":"Karsa, D.R. 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