Study of the Packing Density and Molecular Orientation of Bimolecular Self-Assembled Monolayers of Aromatic and Aliphatic Organosilanes on Silica

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• 作者：Matthew B. Smith ; Kirill Efimenko ; Daniel A. Fischer ; Simon E. Lappi ; Peter K. Kilpatrick ; Jan Genzer
• 刊名：Langmuir
• 出版年：2007
• 出版时间：January 16, 2007
• 年：2007
• 卷：23
• 期：2
• 页码：673 - 683
• 全文大小：264K
• 年卷期：v.23,no.2(January 16, 2007)
• ISSN：1520-5827

文摘

Bimolecular self-assembled monolayers (SAMs) of aromatic and aliphatic chlorosilanes were self-assembled ontosilica, and their characteristics were established by contact angle measurement, near-edge X-ray absorption finestructure spectroscopy, and Fourier transform infrared spectroscopy. Three aromatic constituents (phenyltrichlorosilane,benzyltrichlorosilane, and phenethyltrichlorosilane) were studied in combination with four aliphatic coadsorbates(butyltrichlorosilane, butyldimethylchlorosilane, octadecyltrichlorosilane, and octadecyldimethylchlorosilane). Ourresults demonstrate that whereas SAMs made of trichlorinated organosilanes are densely packed, SAMs prepared frommonochlorinated species are less dense and poorly ordered. In mixed systems, trichlorinated aromatics and trichlorinatedaliphatics formed SAMs with highly tunable compositions; their surfaces were compositionally homogeneous withno large-scale domain separation. The homogeneous nature of the resulting SAM was a consequence of the formationof in-plane siloxane linkages among neighboring molecules. In contrast, when mixing monochlorinated aliphatics withtrichlorinated aromatics, molecular segregation occurred. Although the two shortest aromatic species did not displaysignificant changes in orientation upon mixing with aliphatics, the aromatic species with the longest polymethylenespacer, phenethyltrichlorosilane, displayed markedly different orientation behavior in mixtures of short- and long-chain aliphatics.