Ternary Si-C-N ceramics were derived from silicon containing polymers by thermally induced hybrid processing. These silicon carbonitrides were investigated by impedance spectroscopy depending on the synthesis conditions. The electrical behavior correlates with the solid state reactions and phase transformations, which take place during the processing. It has also been shown that the electrical properties can be controlled in a wide range.

Zirconium and titanium alkoxide derivatives with phosphanyl substituents were synthesized by reaction of the alkoxides with 2-acrylamido-2-methyl-propane sulfonic acid followed by addition of HPPh2 to the acrylic double bond. Alternatively, the phosphinated sulfonic acid was prepared first and then reacted with the alkoxides. The second route is preferred because of the milder reaction conditions, shorter reaction times and avoidance of byproducts. The bifunctional organic ligand is bonded to the titanium or zirconium atom via the sulfonate group, while the PR2 group is available for further reactions such as the coordination of metal compounds.

Organofunctional silica aerogels were prepared by base catalyzed hydrolysis and condensation of Si(OR')4 / RSi(OMe)3 mixtures, followed by supercritical drying. In the trialkoxysilanes, R is of the type (CH2)nA, the group A being an organic function. Amino, ethylenediamino, mercapto, cyano, vinyl, and methacrylate groups were thus incorporated in the aerogels. The sol-gel reaction of a 4:1 mixture of Si(OMe)4 and (vinyl)Si(OMe)3 was exemplarily monitored by Raman spectroscopy. The Raman spectra show that under basic conditions hydrolysis and condensation of Si(OMe)4 is much faster than that of (vinyl)Si(OMe)3. For the other RSi(OMe)3 precursors the reaction rates strongly depend on the electronic properties and the polarity of the functional organic group. Addition of the aminopropyl and cyanoethyl substituted precursors to Si(OR)4 results in shorter gel times relative to pure Si(OR')4, while the mercaptopropyl, methacryloxypropyl and vinyl substituted precursors retard gelation. Depending on the ratio and the kind of the precursors, 70 - 100 % of the functional organic groups were incorporated into the aerogel network. The hydrophobicity of the aerogels depends on the kind and amount of RSiO1.5 units.

The hydrolysis and self- and cross-condensation kinetics of the hybrid sol tetraethoxysilane and ethyltriethoxysilane were investigated by high resolution 29 Si NMR spectroscopy. A kinetic model in which hydrolysis is reversible and condensation is irreversible was developed. We found excellent agreement between the product distributions measured by 29Si NMR spectroscopy and calculated by the model. The cross-condensation rates for each of the sols were intermediate to the condensation rates of the individual components. Calculations show that for these sols, the concentration of cross-condensed species is a weak function of the relative rates of self-condensation.

Organic laser dyes in methyl modified silicate hosts have been found to have poor photo stability. This could be caused by the instability of either the laser dyes or the host materials themselves. To get a better understanding of the chemical reactions and the relationship between the thermal stability and the microstructures of the hybrid network, the methyl modified silicate materials were investigated by TGA, DTA, 13C and 29Si solid state NMR, FTIR, and AFM as a function of processing conditions. The structural stability is found to directly relate to the reaction and processing conditions and the results will be discussed.

We have studied the different driving forces behind syneresis in methyltriethoxysilane/tetraethoxysilane (MTES/TEOS) gels by aging them in different H2O/EtOH pore fluids. We show using shrinkage, density, contact angle, and N2 sorption measurements, the influence of gel/solvent interactions on the microstructural evolution during drying. Competing effects of syneresis (that occurs during aging) and drying shrinkage resulted in the overall linear shrinkage of the organically modified gels to be constant at ∼50%. Increasing the hydrophobicity of the gels caused the driving force for syneresis to change from primarily condensation reactions to a combination of condensation and solid/liquid interfacial energy. In addition the condensation driven shrinkage was observed to be irreversible, whereas the interfacial free energy driven shrinkage was observed to be partially reversible. Nitrogen sorption experiments show that xerogels with the same overall extent of shrinkage can have vastly different microstructures due to the effects of microphase separation.

Two families of hybrid organic-inorganic composites exhibiting ionic conduction properties, so called ORMOLYTES (organically modified electrolytes), have been prepared by the sol-gel process. The first family has been prepared from a mixture of 3-isocyanatopropyltriethoxysilane (IsoTrEOS), O,O′ Bis (2-aminopropyl)polyethyleneglycol and lithium salt. These materials present chemical bonds between the organic (polymer) and the inorganic (silica) phases. The second family has been prepared by an ultrasonic method from a mixture of tetraethoxysilane (TEOS), polyethyleneglycol and lithium salt. The organic and inorganic phases are not chemically bonded. The Li+ ionic conductivity has been studied by AC impedance spectroscopy up to 100 °C. Values of aσ up to 10−4 Scm−1 have been found at room temperature. The conduction properties have been related to the materials structure using linewidth and relaxation times NMR measurements of 7Li between −100 °C and 90 °C. A systematic study has been done changing the lithium concentration, the polymer chain length and the polymer to silica weight ratio. The structures and the ionic conduction properties of both families are compared with emphasis on the nature of the bonds between the organic and inorganic components.

A hybrid nanocomposite was prepared from the combination of an epoxy resin with a dispersion of nanometer-sized silica particles prepared by hydrolysis of silicon tetra alkoxides A silane coupling agent was used to improve the filler-matrix interface by crosslinking into the epoxy networks. Silica dispersion caused the increase of nanometer size voids evaluated by the positron annihilation method and the decrease of Vickers hardness. The use of coupling agent also brought about the decrease of nanometer size voids and the increase in hardness.

The potential of vibrational spectroscopy for the study of group IV alkoxides M(OR)4 has been demonstrated in several papers, but only a few of these papers have presented results from on line measurements. The monitoring of different reactions such as the stabilization of the alkoxides with organic additives, the exchange processes between different metal alkoxides (R exchange or M exchange) and the hydrolysis process can be of great importance for the development of new synthetic routes leading to materials which are easier to process. NIR spectroscopy is a very versatile technique but lacks of specificity while IR and Raman give more interpretative results but are not always easy during processing. We used both techniques along with chemometric tools to extract relevant information on our processes. The 2D correlation allowed us to benefit from the specificity of IR and Raman to develop robust NIR methods which are able to be used on line to monitor the different steps of the sol-gel process.

The pyrolytic transformation of hybrid gels containing Si-CH3 and Si-H groups is studied with a novel TG/GC/MS technique. Pyrolysis of a gel precursor for SiOC system shows a main decomposition step with the evolution of many different silanes and siloxane species arising from redistribution of Si-H and Si-O bonds in the polymeric network. B-containing gel, precursor for SiBOC oxycarbide glasses, displays a dramatically different pyrolysis pathway in which the redistribution reactions are completely suppressed and the Si-H and Si-CH3 groups are partially consumed at low temperature (≈ 220°C) to form H2 and CH4.

The hydrolysis of Sn(OAmt)2(acac)2 (TTA) leads to sols, gels or precipitates made of tin oxohydroxo polymers, surface capped with residual organic groups, which are mainly acac ligands. The residual acac/Sn ratio decreases when the hydrolysis ratio H increases. For a given H, the observed gelation-precipitation behavior and the BET surface areas of the resulting xerogels strongly depend on the nature of the solvent.

The synthesis of transparent hybrid organic-inorganic coatings obtained from condensation between 3-isocyanatopropyltriethoxysilane containing grafted azo dyes (ICTES-Red 17) and tetramethoxysilane (TMOS) precursors has been performed. Influence of ICTES-Red 17/TMOS molar composition and thermal curing on both structure and nonlinear optical (NLO) properties of these materials have been investigated. A thermal treatment of ICTES-Red 17/TMOS coatings before poling has been found to improve nonlinear optical responses as well as its stability.

Bioactive ORMOSILS (Organically Modified Silicates) were synthesized by a sol-gel method, with tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS). Ca(II) ions were incorporated into the ormosil monoliths by addition of calcium nitrate. The synthesized samples were examined on the bioactivity by the use of a simulated body fluid (the Kokubo solution). The Ca(II) containing ormosils were bioactive that deposited apatite during soaking in the Kokubo solution. The dissolution of Ca(II) from the sample favored the formation of the hydrated silica, which gave nucleation sites for apatite, while the effect of dissolved Ca(II) ions to increase the degree of supersaturation in the fluid could not be neglected.

A new direct-deposition process for silica thin films was developed using silicon alkoxide solutions. Silica thin films incorporating organic groups, such as methyl (CH3) and phenyl (C6H5 ) groups, were deposited on substrates from aqueous and ethanol solutions of organyltrialkoxysilane. Silica films without organic groups were also formed using ethanol solution of tetraalkoxysilane with aqueous ammonia. Composition of the deposited silica films were influenced by temperature and pH of the solutions and the starting alkoxides. From aqueous solutions containing organyltrialkoxysilane and organic dyes, such as Disperse Red 1 and Rhodamine B, silica films including the dyes were directly prepared on substrates. The composition of silica-organic hybrid films prepared by the deposition method was successfully controlled by selecting the deposition condition and the starting materials.

The addition of A(OBUs)2EAA to silicon-based materials containing PhTES or Glymo leads to a decrease in the thermal stability of the trifunctional siloxanes. 29Si MAS NMR shows that breaking of the Si-C bond and formation of an extra Si-O bond occurs after heating to 200°C of these materials. MeTES-containing materials are stable up to (at least) 200'C. The preparation of samples using Na[AlOR4] instead of Al(OBus)2EAA showed that the undesired decomposition reaction is caused by octahedral (non-network) aluminum (27Al MAS NMR). Up to 4–5 Si-C bonds are broken per octahedral aluminum, which indicates a catalytic effect.

The spectral editing properties of the 29Si NMR INEPT heteronuclear transfer experiment have been utilized for the identification and characterization of hydrolysis and initial condensation products in methyltrimethoxysilane (MTMS) sol-gel materials. 29Si NMR assignments in MTMS are complicated by a small spectral dispersion (∼0.5 ppm) and two different 29Si-1H J couplings. By using analytical expressions for the INEPT signal response with multiple heteronuclear J couplings, unambiguous spectral assignments can be made. For this organomethoxysilane the rate of hydrolysis was found to be very rapid and significantly faster than either the water- or alcohol-producing condensation reactions. The hydrolysis species of both the MTMS monomer and its initial T1 condensation products follow statistical distributions that can be directly related to the extent of the hydrolysis reactions. The role of the statistical distribution of hydrolysis products on the production and synthetic control of organically modified sol-gels is discussed.

Formation of a Schiff base imine by reacting a primary amine with either an aldehyde or ketone was initiated by an aluminum compound acting as a Lewis acid catalyst. The water byproduct of the reaction then was used as an in situ reagent for subsequent hydrolysis and sol-gel condensation of the aluminum species. These reactions yielded a gel network containing the entrained Schiff base. Two examples of this synthetic approach are described with two different aluminum catalyst/reagents: a diethylaluminum diethylphosphate ester [(CH3CH2)2Al-O-P(O)(OCH2CH3)2] and triethyl aluminum [Al(CH3CH2)3]. Anhydrous ammonia and acetone were used as the Schiff base precursors.

The use of preceramic polymers in diverse ceramic applications requires control of a complex set of chemical characteristics to ease processing and develop suitable ceramic properties. The desirable characteristics of a good precursor system are controllable viscosity (preferably without the use of solvents), inhibition of curing during fabrication followed by rapid curing, minimal release of volatiles during curing, high ceramic yield, and controllable final composition and stoichiometry.

This paper describes the use of chemical concepts to synthesize, modify, and manipulate polymeric precursors to silicates and the importance of curing (crosslinking) mechanisms and processing conditions as critical elements in developing ceramic matrix composites.

In this paper, we present recent NMR investigations on several silsesquioxanes (RSiO1.5)8 with R = H, CH3, CH=CH2, OSi(CH 3)2R′ (R′ = H, CH3, CH=CH2). The octameric polyhedral “cubane like” derivatives were analyzed by means of high resolution 13C and 29Si solid state NMR including CP (Cross-Polarization) and MAS (Magic Angle Spinning) techniques. The CP sequence including variable contact time was used in order to extract quantitative data. The ID IRCP sequence (Inversion Recovery Cross Polarization), based on the standard CP scheme, allowed us to investigate the CP dynamics of the involved sites and to propose a complete spectral editing of the spectra. Furthermore, local molecular motions were determined through the careful analysis of CP dynamics. Finally, the NMR results related to crystalline cubane derivatives were extended to hybrid systems obtained by cross-coupling of monomeric entities (via hydrosilylation).

We present results of fluorescence line narrowing (FLN) and lifetime studies of Eu3+-doped ormosils prepared from Si(OCH3)4 and CH3Si(OCH3)3, (CH3)2Si(OCH3)2, (C2H5)2Si(OCH3)2, and (n-C3H7)Si(OCH3)3 in various proportions. Similar results are also presented for Eu3+-doped gels derived from Si(OCH3)4 and fluorinated Eu3+ precursors (Eu(fod)3, (CF3SO3)3Eu, and (CF3CO2)3Eu·3H2O). The FLN studies indicated that significant Eu3+ clustering occurs in densified samples of both the organically modified and fluorinated compositions. Lifetime studies of the organically modified compositions showed longer Eu3+ lifetimes at low heat treatment temperatures relative to an unmodified sample. The difference in lifetime between modified and unmodified compositions decreased at high heat treatment temperatures as the organic substituents were driven from the matrix. The longest Eu3+ lifetimes were observed when the fluorinated Eu3+ precursors were used and persisted at high heat treatment temperatures. The lifetime studies indicate that the fluorinated precursors, and to a lesser extent organically modified precursors, are effective at reducing the water content in densified gels.