No abstract

The morphology of surfaces modified by π-conjugated arylsilanes depends on various parameters such as the nature and the number of the hydrolyzable functions or the length of the aromatic segment. The grafting of phenyltrichlorosilane and phenyltrimethoxysilane leads to multilayers even when the reactions are carried out at 0 °C, the films obtained from phenyltrichlorosilane being much thicker than the one obtained from phenyltrimethoxysilane. A submonolayer is obtained using phenyltriethoxysilane. Whereas the trifunctional phenyltrichlorosilane forms an inhomogeneous multilayer, the difunctional phenyldichlorosilane (PhSiHCl2) and the monofunctional phenylchlorosilane (PhSiH2Cl) (the SiH bond is not reactive under these experimental conditions) deposit as dense homogeneous monolayers. For these two phenylchlorosilanes, the surface analytical data are similar except for contact angle measurements, which can be explained by a different orientation of the phenyl group at the surface. Concerning the influence of the length of the aromatic segment on the quality of the film, styryltrimethoxysilane and methylstilbenyltrimethoxysilane lead to dense monolayers indicating that adding a short group such as the vinyl group is sufficient to induce an organization between aromatic groups and to achieve a dense monolayer.

Silylation reactions of oxidized silicon(1,0,0) wafers with octadecylchlorosilanes were performed to determine the influence of the number of hydrolyzable functions on the quality of the film deposited on the surface. Octadecylchlorosilane (C18H37SiH2Cl) and octadecyldichlorosilane (C18H37SiHCl2) were synthesized and compared to the well-studied octadecyltrichlorosilane (C18H37SiCl3). The grafting reactions in CCl4 solutions were monitored by in situ internal reflection FTIR spectroscopy. The surfaces were also analyzed by wettability, ellipsometry, and atomic force microscopy (topography and friction). As expected, the Si-H bonds are unreactive under these reaction conditions, indicating that the monochlorosilane and the dichlorosilane behave as mono-and difunctional species, respectively. The surfaces obtained after grafting of octadecyltrichlorosilane and octadecyldichlorosilanesthat is, in cases where cross-linking is possiblesare similar with a very dense film of organized alkyl chains in the all-trans configuration. On the other hand, in the case of octadecylchlorosilane where no cross-linking is possible, a less organized film of monografted species is obtained.