Perfluorinated chains (-CF2CF2CF2-) are not only highly hydrophobic but also lyophobic, i.e. they segregate hydrogenated chains. Mixtures of alkanes and perfluoroalkanes are known to be highly non-ideal systems, exhibiting large regions of liquid–liquid immiscibility and large positive excess properties.
Semifluorinated alkanes (CnF2n+1CmH2m+1 , FnHm) are diblock molecules in which a perfluorinated and a hydrogenated segment are covalently bonded together to form a single chain. Although not possessing a hydrophilic group, the simultaneous presence of the antagonist segments gives FnHm the required amphiphilicity to form various supramolecular structures. These are potential candidates for numerous applications, from medicine to smart-materials and tailored interfaces. Among them, the nano-structuration exhibited by Langmuir films of these so-called “primitive surfactants” is particularly striking [1,2,3]. A hexagonal 2D packing of domains of circa 30 nm of diameter is observed at the surface of water or of an adequate solid substrate. In spite of all efforts, the origin and structure of the nano-domains are yet to be understood. The non-coalescence of the domains under compression is particularly puzzling.
In this work Molecular dynamics simulations have been successfully used to model the formation, structure and size of the FnHm nano-domains. The ultimate aim is to understand, and thus control, how the simultaneous presence of mutually phobic hydrogenated and perfluorinated chains induces organization.
[1] P.Fontaine, MC.Fauré, L.Bardin, E.J.M. Filipe, M.Goldmann, Langmuir, 30, 15193 (2014).
[2] L.Bardin, MC.Fauré, E.J.M. Filipe, P.Fontaine, M.Goldmann, Thin Solid Films, 519, 414 (2010).
[3] A. L. Simões Gamboa, E. J. M. Filipe, P. Brogueira, Nano Letters, 2, 1083 (2002).
