title: Effect of the molecular structure on the hierarchical self-assembly of semifluorinated alkanes at the air/water interface.
abstract: Semifluorinated alkanes (C(n)F(2n+1)C(m)H(2m+1)), short FnHm display local phase separation of mutually incompatible hydrocarbon and fluorocarbon chain moieties, which has been utilized as a structure-forming motif in supramolecular architectures. The packing of semifluorinated alkanes, nominally based on dodecyl subunits, such as perfluoro(dodecyl)dodecane (F12H12) and perfluoro(dodecyl)eicosane (F12H20), as well as a core extended analogue, 1,4-dibromo-2-((perfluoroundecyl)methoxy)-5-(dodecyloxy)benzene) (F11H1-core-H12), was studied at the air/water interface. Langmuir monolayers were investigated by means of neutron reflectivity directly at the air/water interface and scanning force microscopy after transfer to silicon wafers. Narrowly disperse surface micelles formed in all three cases; however, they were found to bear different morphologies with respect to molecular orientation and assembly dimensionality, which gives rise to different hierarchical aggregate topologies. For F12H12, micelles of ca. 30 nm in diameter, composed of several circular or "spherical cap" substructures, were observed and a monolayer model with the fluorocarbon block oriented toward air is proposed. F12H20 molecules formed larger (ca. 50 nm diameter) hexagonally shaped surface micelles that were hexagonally, densely packed, besides more elongated but tightly interlocked wormlike structures. Conversely, F11H1-core-H12 films organized into linear rows of elongated surface micelles with comparable width, but an average length of ca. 400 nm, apparently formed by antiparallel molecular packing.
authors.affiliation: Bio-Organic Materials Chemistry Laboratory, Institute of Electronic Structure & Laser, Foundation for Research and Technology-Hellas (FORTH), Heraklion, Greece.
authors.forename: Laurence
authors.initials: L
authors.lastname: de Viguerie
authors.forename: Rabea
authors.initials: R
authors.lastname: Keller
authors.forename: Ulrich
authors.initials: U
authors.lastname: Jonas
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Berger
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Clark
authors.forename: Christopher O
authors.initials: CO
authors.lastname: Klein
authors.forename: Thomas
authors.initials: T
authors.lastname: Geue
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Butt
authors.forename: Dimitris
authors.initials: D
authors.lastname: Vlassopoulos
mesh_terms: D000388:Air; D000473:Alkanes / Q000737:chemistry*; D054879:Halogenation; D033363:Neutron Diffraction; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D000473:Alkanes; D014867:Water