Self-Assembly of the Perfluoroalkyl-Alkane F14H20 in Ultrathin Films
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- 作者：Ahmed Mourran ; Bernd Tartsch ; Marat Gallyamov ; Sergei Magonov ; Denitza Lambreva ; Boris I. Ostrovskii ; Igor P. Dolbnya ; Wim H. de Jeu ; and Martin Moeller
- 刊名：Langmuir
- 出版年：2005
- 出版时间：March 15, 2005
- 年：2005
- 卷：21
- 期：6
- 页码：2308 - 2316
- 全文大小：823K
- 年卷期：v.21,no.6(March 15, 2005)
- ISSN：1520-5827
文摘
Scanning force microscopy on monomolecular films of eicosylperfluorotetradecane, F(CF2)14(CH2)20H,on mica, silicon oxide, or water revealed spontaneous organization to well-defined nanoscopic ribbon andspiral or toroidal superstructures. Whether ribbons or nanospirals were formed depended on the solventfrom which the molecular monofilm was cast. Ribbons were observed when a hydrocarbon or a perfluorocarbonsolvent was used, e.g., decalin or perfluorodecalin. When the compound, however, was deposited fromnonselective hexafluoroxylene, the molecules assembled into spirals of defined size. The spirals/toroidstransformed to ribbons when exposed either to decalin or perfluorodecalin vapor, and the ribbons transformedto toroids when exposed to hexafluoroxylene vapor. These changes could be observed in situ. Scanning forcemicroscopy yielded an identical height and width for the bands forming the spirals and for the parallelflat ribbons. X-ray reflectivity yielded a height of 3.61 ± 0.05 nm, again identical for both morphologies.Yet, the length of the extended F(CF2)14(CH2)20H molecule, i.e., 4.65 nm, exceeds the layer thicknessobtained from X-ray reflectometry. It is, however, consistent with an arrangement where the fluorinatedchains are oriented normal to the surface layer and where the alkyl segments are tilted with a 122
anglebetween the two segments. Within the plane defined by the tilt, this angle allows a dense packing of thealkyl segments compensating for the larger cross-section of the fluorocarbon segment. The tilt plane definesan "easy" direction along which the monolayer structure can preserve order. In the plane perpendicularto this axis, long-range ordered dense packing of the alkyl chains is not possible. Incommensurable packingcan in principle explain the finite and regular width of the ribbons and the stepwise turn in the spirals.
anglebetween the two segments. Within the plane defined by the tilt, this angle allows a dense packing of thealkyl segments compensating for the larger cross-section of the fluorocarbon segment. The tilt plane definesan "easy" direction along which the monolayer structure can preserve order. In the plane perpendicularto this axis, long-range ordered dense packing of the alkyl chains is not possible. Incommensurable packingcan in principle explain the finite and regular width of the ribbons and the stepwise turn in the spirals.