title: Self-assembly of (perfluoroalkyl)alkanes on a substrate surface from solutions in supercritical carbon dioxide.
abstract: Toroidal self-assembled structures of perfluorododecylnonadecane and perfluorotetradecyloctadecane have been deposited on mica and highly oriented pyrolytic graphite surfaces by exposure of the substrates to solutions of the (pefluoroalkyl)alkanes in supercritical carbon dioxide. Scanning force microscopy (SFM) images have displayed a high degree of regularity of these self-assembled nanoobjects regarding size, shape, and packing in a monolayer. Analysis of SFM images allowed us to estimate that each toroidal domain has an outer diameter of about 50 nm and consists of several thousands of molecules. We propose a simple model explaining the clustering of the molecules to objects with a finite size. The model based on the close-packing principles predicts formation of toroids, whose size is determined by the molecular geometry. Here, we consider the amphiphilic nature of the (perfluoroalkyl)alkane molecules in combination with incommensurable packing parameters of the alkyl- and the perfluoralkyl-segments to be a key factor for such a self-assembly.
authors.affiliation: Faculty of Physics, M. V. Lomonosov Moscow State University, Vorob'evy Gory, 119992 GSP-2, Moscow, Russia. glm@spm.phys.msu.ru
authors.forename: Marat O
authors.initials: MO
authors.lastname: Gallyamov
authors.forename: Ahmed
authors.initials: A
authors.lastname: Mourran
authors.forename: Bernd
authors.initials: B
authors.lastname: Tartsch
authors.forename: Rostislav A
authors.initials: RA
authors.lastname: Vinokur
authors.forename: Lev N
authors.initials: LN
authors.lastname: Nikitin
authors.forename: Alexei R
authors.initials: AR
authors.lastname: Khokhlov
authors.forename: Kjeld
authors.initials: K
authors.lastname: Schaumburg
authors.forename: Martin
authors.initials: M
authors.lastname: Möller
mesh_terms: D000473:Alkanes / Q000032:analysis / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D025924:Chromatography, Supercritical Fluid / Q000379:methods; D003460:Crystallization / Q000379:methods*; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D011312:Pressure; D012996:Solutions; D013499:Surface Properties
chemical_list: D000473:Alkanes; D012996:Solutions; D002245:Carbon Dioxide