Raman spectra of oligomeric species obtained by tetraethoxysilane hydrolysis-polycondensation process

Gnado, J.; Dhamelincourt, P.; Pelegris, Christine; Traisnel, Michel; Mayot, A. Le Maguer

doi:10.1016/s0022-3093(96)00526-1

Cited by 49 publications

(44 citation statements)

References 31 publications

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“…The signal around 600 cm -1 comprised both dimer (∼594 cm -1 ) and end groups of chains (∼602 cm -1 ). 14,19 The additional vibrations at ∼430 and ∼882 cm -1 were caused by ethanol as verified by reference measurements and the literature. 14,22 However, an additional signal at ∼565 cm -1 could not immediately The Journal of Physical Chemistry C ARTICLE be identified.…”

Section: ' Introductionsupporting

confidence: 71%

“…The present descriptions of the possible reaction pathways in acidic media even are ambiguous. Several authors adhere to a model of linear chain growth, 8,14,19 while others reported cyclization reactions competing with chain extension. 57,58 Theoretical predictions of gelation times were in better agreement with experimental data when cyclization was accounted for.…”

Section: ' Introductionmentioning

confidence: 99%

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²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

et al. 2011

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ABSTRACT:The initial molecular steps of the acid-catalyzed silica sol-gel process departing from tetraethylorthosilicate (TEOS) were investigated by in situ 29 Si NMR and UV-Raman spectroscopy. The use of a substoichiometric H 2 O:TEOS molar ratio (rvalue 0.2-1.2) slowed the silicate oligomerization reaction and allowed unraveling the initial steps of silica condensation. Molecular modeling confirmed Raman signal and 29 Si NMR shift assignment. A comprehensive listing of all Raman and 29 Si NMR assignments is provided, including unique Raman assignments of cyclosilicates and the linear tetramer. The combination of experiment and modeling allowed an analysis of the reaction kinetics. The derived kinetic model and the experimental observation both revealed that the H 2 O: TEOS molar ratio had a strong influence on the reaction kinetics but not on the reaction pathways. The multianalytical approach led to development of an oligomerization scheme. As dominant oligomerizations, chain growth, cyclodimerization, and branching were identified. Under the investigated conditions, chains did not grow longer than pentamer, and ring sizes were limited to 6-rings. Chains of 4 Si atoms and 4-rings were abundant species. Branched rings and chains were formed by attachment of dimers and trimers. Gelation proceeded from branched 4-rings and branched chains with limited hydroxyl functionalities.

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Section: ' Introductionsupporting

confidence: 71%

Section: ' Introductionmentioning

confidence: 99%

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

et al. 2011

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“…Band C is mainly due to CH 2 twist mode, 3133,35,36 and the peak position is slightly different between ethanol (ca. 1275 cm ¹1 ) and TEOS (ca.…”

Section: ¹1mentioning

confidence: 94%

Macroscopic Phase Separation in a Tetraethoxysilane–Water Binary Sol–Gel System

Kajihara¹,

Kuwatani²,

Maehana³

et al. 2009

Bulletin of the Chemical Society of Japan

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A procedure to prepare macroporous silica gels from an acid-catalyzed tetraethoxysilane (TEOS)water binary system was developed, and the macroscopic morphology formation was examined at a range of conditions under controlled reaction temperature. This procedure involves two-step mixing of TEOS and water containing pH control agents. The gel morphology is significantly influenced by the solution composition in each mixing step, even if the overall solution composition is unchanged. The macroscopic morphology is formed by phase separation between hydrophobic silica oligomers modified by unhydrolyzed ethoxy groups and hydrophilic solvent mixture consisting of water and ethanol generated from TEOS. The morphology can be described as an aggregation of macroscopic particles, which are most likely formed by the spinodal decomposition and subsequent fragmentation of the silica-rich phase occurring at the solvent-rich side of a miscibility gap. The resultant macroporous gels are dried in a relatively short time to obtain crackfree monolithic silica xerogels, which are useful as silica glass precursors.Solgel synthesis of silicates has been extensively studied, mainly because the precursors (silicon alkoxides) are easy to handle due to their moderate reactivity and their various derivatives including those modified with organic functional groups are commonly available. Solgel method is widely used to form various functional silicates, such as monolithic gels and glasses, films, and powders. In the solgel method silica glasses are obtained by sintering monolithic silica xerogels. The low processing temperature as compared with vapor-phase and conventional fusion methods is beneficial in suppressing devitrification and weight loss during manufacturing of silica glasses. However, the utility of the sol gel method is limited by fracture associated with shrinkage during drying, which originates from evaporation induced capillary force and its inhomogeneous propagation in gel monoliths.1 The capillary force is decreased by decreasing the surface tension of pore liquid and the inhomogeneous shrinkage is suppressed by slowing down the drying. Thus, various techniques, including careful control of drying conditions, 25 incorporation of solvents of low surface tension (often termed "drying control chemical additives," DCCAs), 68 and supercritical drying, 9 have been developed to obtain monolithic silica xerogels. The capillary force is also decreased by increasing the pore size. A notable approach is dispersing particulate silica fillers in the precursor solution. 1015 In this method the pores can be easily enlarged by increasing the size of the fillers. Furthermore, the fillers mechanically strengthen the gel framework, making it possible to greatly alleviate the fracture problem. Another method is to utilize macropores formed by phase separation between silica gel and solvent phases. In alkoxide-based gelling systems macroscopic phase separation is induced by incorporating additives such as organic polymers, 16,17 polar organ...

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“…The formation of condensed species from OH-substituted monomeric species could thus be anticipated. 29 Si NMR spectra and Raman spectra recorded on solutions with H2O:TEOS molar ratio between 0.5 and 1.75 and mild acidic conditions (HCl 0.01-0.03 M) have been compared 35,40 ; bands at 600, 576, 554, 534 cm -1 have been assigned to dimers Si2O(OEt)6, linear trimers Si3O2(OEt)8, linear and branched tetramers Si4O3(OEt)10, respectively. These bands are of comparable intensity with respect to the TEOS band at 658 cm -1 except for the bands due to the tetramers that are much weaker.…”

Section: Insert Figurementioning

confidence: 99%

Time-Resolved in Situ Raman and Small-Angle X-ray Diffraction Experiments: From Silica-Precursor Hydrolysis to Development of Mesoscopic Order in SBA-3 Surfactant-Templated Silica

et al. 2007

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Time-resolved in situ Raman spectroscopy and small-angle X-ray diffraction have been combined in order to characterize the formation of hexagonal mesostructured SBA-3 silica. Experiments were performed under identical synthesis conditions in order to correlate the molecular and mesoscopic scales. Cetyltrimethylammonium bromide (CTAB) was used as the structuring agent with tetraethoxysilane (TEOS) as the silica precursor at a constant CTAB/TEOS molar ratio under highly acidic conditions and for various dilutions. Raman spectra allowed quantification of the release of ethanol that was produced solely by hydrolysis of TEOS under the experimental conditions used. The hydrolysis kinetics of TEOS was greatly enhanced in the presence of the surfactant as a result of micellar solubilization and surfactant stabilization of emulsion droplets. At the time of precipitation, the degree of TEOS hydrolysis depended strongly on the TEOS/CTAB concentration, decreasing with increasing concentration. The time evolution of the d-spacing and the full width at half-maximum of the (10) main reflection in the XRD pattern showed two distinct stages that were also strongly dependent on the sol composition. There seemed to be a coexistence of an ordered phase and a disordered one for a longer time in SBA-3 compared with MCM-41, clearly indicating that the ordering process is slower for SBA-3.

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Raman spectra of oligomeric species obtained by tetraethoxysilane hydrolysis-polycondensation process

Cited by 49 publications

References 31 publications

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

Macroscopic Phase Separation in a Tetraethoxysilane–Water Binary Sol–Gel System

Time-Resolved in Situ Raman and Small-Angle X-ray Diffraction Experiments: From Silica-Precursor Hydrolysis to Development of Mesoscopic Order in SBA-3 Surfactant-Templated Silica

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Raman spectra of oligomeric species obtained by tetraethoxysilane hydrolysis-polycondensation process

Cited by 49 publications

References 31 publications

29Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

29Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

Macroscopic Phase Separation in a Tetraethoxysilane–Water Binary Sol–Gel System

Time-Resolved in Situ Raman and Small-Angle X-ray Diffraction Experiments: From Silica-Precursor Hydrolysis to Development of Mesoscopic Order in SBA-3 Surfactant-Templated Silica

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²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry