Influence of the Deposition Process on the Structure of Grafted Alkylsilane Layers

Abstract

Monofunctional alkylsilanes, CH3(CH2) n - 1Si(CH3)2R with n varying from 4 to 30 and the hydrolyzable group R = Cl or N(CH3)2, were deposited on quartz slides and on nanometric silica. Due to the presence of only one hydrolyzable group for these alkylsilanes, silane monolayers result from the grafting process. Two methods for silanization were considered: deposition from a solvent (derived from Sagiv's process) and vapor phase deposition (derived from Kovats's process). In vapor phase deposition, the physisorbed water is mainly removed from the surface during the conditioning of the specimens, whereas this is not the case for the solvent method. In addition, the two deposition processes do not take place at the same temperature: the silane needs to be heated under vacuum for the vapor deposition method, whereas the reaction takes place at room temperature for the solvent method. Characterizations of the grafting efficiency and of the structure of the grafted layers were performed with different techniques including contact angle measurements, cross polarization magic angle spinning 29Si NMR, and gas chromatography. The comparison between the two methods of deposition showed that the grafting process has a great influence on the resulting monolayers. By considering the wetting behavior, we can evidence that silane monolayers deposited from a toluene solution are less well-ordered than those resulting from the vapor phase method. In fact, the choice of the solvent for deposition is crucial. This effect is due to the competition between the solvent and the silane molecules to reach the silica surface. This competition, which infuences the packing density of the grafted layer, is dependent on the polarity and the shape of the solvent molecules and on the deposition process.

Functional Covalent Chemistry of Carbon Nanotube Surfaces

“…With respect to Si-containing complexes, organosilanes have been previously used as coupling agents on hydroxylated surfaces for generating organic coatings, [79] with the idea that the electrical properties of carbon nanotubes can be appropriately adjusted through rational chemical functionalization. For instance, the application of a dc electric field can enhance the assembly of silane-modified SWNTs into ordered films with rectifying diode behavior.…”

Microchannel wall coatings for protein separations by capillary and chip electrophoresis

“…Toluene was chosen as the silanization solvent because of its higher boiling point and better environmental compatibility compared to other suitable organic solvents such as carbon tetrachloride or benzene [32][33][34]. Coatings prepared using toluene as the silanization solvent had superior stability compared to those prepared either with 95% ethanol, or with an aqueous solvent with an acetic acid catalyst.…”

Preparation, morphological characterization, and activity of thin films of horseradish peroxidase

“…Proteins could be anchored to the immobilized organic material by chemical reaction with the reactive groups of the coupling agents. Because the properties of the organic layers are fundamental, much effort has been done to improve the organic-layer deposition processes and to characterize the films to obtain the desired coating morphology (Duchet et al, 1997;Gauthier et al, 1996;Karrash et al, 1993). However, when enzymes are the material to be deposited, few data are available to correlate deposition protocols to morphology and biological activity of the protein layer.…”