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Journal Article 
Multilayers of perfluorinated fatty acids 
Knochenhauer, G; Penacorada, F; Reiche, J; Barberka, TA; Brehmer, L; Tredgold, RH 
Materials Science and Engineering C: Materials for Biological Applications
ISSN: 0928-4931
EISSN: 1873-0191 
We have formed Y layers of perfluorododecanoic acid CF3(CF2)(10)COOH by thermal evaporation in vacuo and of perfluorotetradecanoic acid CF3(CF2)(12)COOH by thermal evaporation and by the Langmuir-Blodgett (LB) technique. We have obtained the bilayer spacing of both these materials by X-ray diffraction and have also studied the in-plane structure of these materials by means of grazing incidence diffraction (GID). Computer modelling was used to interpret the results obtained. For the perfluorododecanoic acid, we find two stable untwisted phases at 25 degrees C and a combination of these two predicts both the Bragg peaks arising from the layer structure and the GID results. Our experimental results show that the perfluorotetradecanoic acid exists in the generally accepted helical structure. Computer modelling leads to the conclusion that closely packed perfluorinated chains with 12 or less carbon atoms should exist in an untwisted state while molecules having mon than 12 carbon atoms show the onset of the helical conformation. (C) 1999 Elsevier Science S.A. All rights reserved. 
perfluorinated materials; Langmuir-Blodgett (LB) films; molecular modelling; X-ray diffraction 
• ^Per- and Polyfluoroalkyl Substances (PFAS)
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