FT-Raman Spectroscopic Study of the Structural Evolution in Binary UV-Curable Vinyltriethoxysilane/Tetraethoxysilane Mixtures from the Sol to the Xerogel State

Abstract

Fourier transform Raman spectroscopy was used in order to study acid catalyzed hydrolysis and polycondensation processes from the sol via the gel until the xerogel state in binary mixtures of vinyltriethoxysilane (ViTEOS) and tetraethoxysilane (TEOS). Supplementary 29Si-, 13C-MAS-NMR, and FT-IR data were considered. Intermediate hydrolysates, oligomers, and polycondensates were detected independently of the sample's physical state. Vibrational assignments are given for pure ViTEOS and its partially hydrolyzed intermediates. The corresponding mono-, di-, and tri-hydroxylated species are found to exhibit characteristic νsym(CSiO3) vibrational modes in the 650–672 cm−1 region. Subsequent oligomerization results in a progressive shift of the νsym(CSiO3) bands towards lower wavenumbers. Condensation proceeds faster in ViTEOS–TEOS mixtures than in pure ViTEOS. Assignments for some early oligomeric species and some network connectivity are given. The Raman spectra suggest that the main building blocks of the evolving network are already present in the wet gels. Moreover, it is shown that residual ethoxy groups attached to the siloxane network are still present in xerogels, whereas no silanol groups are detected. The spectra demonstrate that the vinyl groups did not react under the applied conditions. This system has potential for the preparation of UV-curable abrasion-resistant coatings for plastic substrates.

Structure–property correlations in hybrid sol–gel coatings as revealed by Raman spectroscopy

“…It was considered complete when the m(CSiO 3 ) sym and m(SiO 4 ) sym bands disappeared completely [10]. The acrylate component was dissolved in ethanol prior to its addition to prehydrolysed alkoxysilane mixtures as described in Ref.…”

“…The Raman spectra of VTES/TEOS-and GPTMS/ TESSA-based sols, wet gels, and xerogels have been reported recently [10,12]. In these investigations it was shown that FT-Raman spectroscopy may be used to follow the structural evolution from the pure precursor via silanol and oligomer formation to final polycondensation products in xerogels and fully cured materials.…”

Preparation and optical properties of hybrid coatings based on epoxy-modified silane and rhodamine B

“…The important class of solid matrices for luminophores comprises silica, titania and silica-titania oxides obtained by the sol-gel technique [1]. The sol-gel materials have been investigated for various optical applications, such as anti-refractive coatings, planar optical waveguides, optical filters and optical sensors [2][3][4][5][6][7][8]. It has been demonstrated that silica, titania and silica-titania materials may be doped with rare-earth ions and organic dyes via the sol-gel techniques, the spin-top deposition [9] and the sonochemical method [10].…”

Synthesis and properties of an inorganic–organic hybrid prepared by the sol–gel method

“…Such hybrids are promising materials for various applications, e.g. : solid state lasers (optical components), replacements for silicon dioxide as insulating materials in the microelectronic industry, anti-corrosion and scratch resistant coatings, contact lenses or host materials for chemical sensors [1][2][3][4][5][6].…”