Occurrence, Shape, and Dimensions of Large Surface Hemimicelles Made of Semifluorinated Alkanes. Elongated versus Circular Hemimicelles. Pit- and Tip-Centered Hemimicelles
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- 作者：Guifang Zhang ; Pascal Marie ; Mounir Maaloum ; Pierre Muller ; Nicole Benoit ; and Marie Pierre Krafft
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：July 27, 2005
- 年：2005
- 卷：127
- 期：29
- 页码：10412 - 10419
- 全文大小：278K
- 年卷期：v.127,no.29(July 27, 2005)
- ISSN：1520-5126
文摘
The formation of large (~20-35 nm) surface hemimicelles in monolayers of semifluorinatedalkanes, CnF2n+1CmH2m+1 (FnHm), observed after transfer onto silicon wafers, is a general phenomenon.F6H16 and F8H14 exclusively form highly monodisperse circular hemimicelles, organized in a hexagonalarray. The other FnHm investigated form both circular and elongated hemimicelles. The longer FnHm is,the larger the area fraction of elongated micelles; both the hydrocarbon block (H-block) and the fluorocarbonblock (F-block) affect this area fraction. The length of the elongated micelles increases with the total lengthof the diblocks. The diameter of the circular micelles increases with the length of the H-block but,unexpectedly, not with that of the F-block. Model calculations account for these observations. Closeexamination of the circular micelles showed that they generally present a pit or a tip at their center. Thewidth of the elongated micelles is comparable to the radius of the circular micelles, suggesting that thelatter arise from a partition of elongated micelles, followed by coalescence of the edges of the resultingfragments. The elongated micelles become shorter and fewer when surface pressure increases, furthersuggesting a conversion of elongated into circular micelles. This conversion is reversible. The surfacepressure-molecular area isotherms do not present any feature that forebears the existence of hemimicelles.The obtaining of stable surface patterns from simple, "nonpolar" molecular fluorocarbon/hydrocarbon diblocksopens a new approach for producing featured nanostructures from organic templates.