Deposition of Dense Siloxane Monolayers from Water and Trimethoxyorganosilane Vapor

Abstract

A convenient, laboratory-scale method for the vapor deposition of dense siloxane monolayers onto oxide substrates was demonstrated. This method was studied and optimized at 110 °C under reduced pressure with the vapor of tetradecyltris(deuteromethoxy)silane, (CD(3)O)(3)Si(CH(2))(13)CH(3), and water from the dehydration of MgSO(4)·7H(2)O. Ellipsometric thicknesses, water contact angles, Fourier transform infrared (FTIR) spectroscopy, and electrochemical capacitance measurements were used to probe monolayer densification. The CD(3) stretching mode in the FTIR spectrum was monitored as a function of the deposition time and amounts of silane and water reactants. This method probed the unhydrolyzed methoxy groups on adsorbed silanes. Excess silane and water were necessary to achieve dense, completely hydrolyzed monolayers. In the presence of sufficient silane, an excess of water above the calculated stoichiometric amount was necessary to hydrolyze all methoxy groups and achieve dense monolayers. The excess water was partially attributed to the reversibility of the hydrolysis of the methoxy groups.

Alkylsilane–SiO2 Hybrids. A Concerted Picture of Temperature Effects in Vapor Phase Functionalization

“…The presence of unhydrolyzed alkoxy groups on the alkylsilanes could sterically hinder dense monolayer formation. 14 The samples functionalized with the Octyl(F) show 29 Si spectra similar to corresponding compounds functionalized with the unfluorinated analogue. In the same way, 29 Si NMR spectra of Octyl(F) derivatives ( Figure 10) are characterized by the presence of T n and Q n species, which are as well strongly affected by the functionalization temperature.…”

“…14,32 In the case of Octyl(H) (Figure 4), H_100 shows the highest charge transfer resistance, measured from the semicircle diameter, which is indicative of a low ionic permeability of the electrolyte in the organic structure. The R ct values strongly decrease for H_80 and H_150, indicating a more disordered and nonuniform layer, where the electrolyte can permeate.…”

“…Furthermore, 29 Si NMR spectra proved that higher functionalization temperatures increase the lateral polymerization across the alkylsilane layer. Undesired selfpolymerization of the alkylsilane molecules before vaporization might concur to reduce the functionalization degree at high temperatures, 11,14 along with effects on the surface hydration. 15 Indeed, trialkoxy alkylsilanes are generally believed to first react with water adsorbed at the silica surface to form silanol intermediates, which then undergo condensation reactions with neighboring intermediates and hydroxyl groups on the silica surface.…”

Squish and CuAAC: Additive-Free Covalent Monolayers of Discrete Molecules in Seconds

“…For these reasons, the CuAAC reaction has been adopted for a wide variety of applications including surface immobilization. 12–14 CuAAC has proven to be a useful immobilization strategy on silica, 15 titania, 12,16 gold, 17 diamond, 18,19 and graphitic materials 3,20,21 . The CuAAC reaction is catalyzed by Cu(I) complexes, and therefore requires a reductant when carried out using Cu(II) catalyst precursors, a commonly used method.…”

Whispering Gallery Mode Devices for Sensing and Biosensing

“…The vapor phase deposition requires more equipment as it involves placing the sensor surface in a vacuum chamber under a low pressure of silane vapor. Despite this technical limitation, vapor phase deposition has shown to be more reliable in producing consistent silane films compared with the solution phase deposition [100]. For further information, we suggest the review written by Pujari et al [88] on oxide surfaces covalent functionalization and the review from Goddard et al [101] on the same topic applied to polymers.…”