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Triphenylene silanes for direct surface anchoring in binary mixed self-assembled monolayers

: Mansueto, M.; Sauer, S.; Butschies, M.; Kaller, M.; Baro, A.; Woerner, R.; Hansen, N.H.; Tovar, G.; Pflaum, J.; Laschat, S.


Langmuir. The ACS journal of surfaces and colloids 28 (2012), No.22, pp.8399-8407
ISSN: 0743-7463
ISSN: 1520-5827
Journal Article
Fraunhofer IGB ()

New triphenylene-based silanes 2-(-(chlorodimethylsilyl)-n-alkyl)-3, 6,7,10,11-penta-m-alkoxytriphenylene 4 (Tm-Cn) with n = 8 or 9 and m = 7, 8, 9, 10, or 11 were synthesized, and their self-assembly behavior in the liquid state and at glass and silicon oxide surfaces was investigated. The mesomorphic properties of triphenylene silanes 4 (Tm-Cn) and their precursors 3 (Tm-Cn) were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. From the small-angle X-ray scattering (SAXS) regime, a preferential discotic lamellar mesophase can be deduced, and wide-angle X-ray scattering (WAXS) highlights the liquid-like characteristics of the alkyl side chains. To transfer these bulk structural properties to thin films, self-assembled monolayers (SAMs) were obtained by adsorption from solution and characterized by water contact angle measurements, null ellipsometry, and atomic force microscopy (AFM). Employing the concen tration as an additional degree of freedom, binary SAMs of 2-(-(chlorodimethylsilyl) -undecyl)-3,6,7,10,11-penta-decyloxytriphenylene 4 (T10-C11) were coassembled with chlorodecyldimethylsilane or chlorodimethyloctadecylsilane, and their capability as model systems for organic templating was evaluated. The structure of the resulting binary mixed SAMs was analyzed by water contact angle measurements, null ellipsometry, and X-ray reflectivity (XRR) in combination with theoretical modeling by a multidimensional Parratt algorithm and AFM. The composition dependence of film thickness and roughness can be explained by a microscopic model including the steric hindrance of the respective molecular constituents.