Poly(methyl methacrylate) (PMMA)/silicate interpenetrating networks (IPNs) have been synthesized in formic acid solutions. The fast gelation times observed in these solutions reduced the phase separation of the polymer, and the 50% by weight PMMA/silicate hybrid showed virtually no evidence of a glass transition (Tg) from thermomechanical data. 2H NMR showed that the PMMA is extremely mobile in the wet gels, and liquid-like 2H NMR spectra are observed even after prolonged aging of the samples. A 2H static NMR lineshape, indicative of the rigid polymer, does not occur until polymer to solvent ratios of approximately 0.2 (weight basis) are attained. Motional narrowing of the 2H resonances is not observed in the vacuum-dried IPNs below 180 °C. In contrast, pure PMMA shows motional narrowing between 150 and 180 °C. There was little evidence of isotropic motion of the polymer chains, for low polymer concentrations, up to the highest temperature studied (200 °C). The percentage of polymer undergoing isotropic motion increased with polymer content, and as a function of the aging time before solvent stripping.

Two molecular probes, pyranine (8-hydroxy 1,3,6-trisulfonated pyrene) and cytochrome c, are used to probe two different aspects of sol-gel SiO2 films. Pyranine is used as an in-situ fluorescence probe to monitor the chemical evolution during sol-gel thin film deposition of silica by the dip coating process. The sensitivity of pyranine luminescence to protonation/deprotonation effects is used to quantify changes in the water/alcohol ratio in real time as the substrate is withdrawn from the sol reservoir. Correlation of the luminescence results with the interference pattern of the depositing film allows the solvent composition to be mapped as a function of film thickness. Cytochrome c is used as a probe of the rotational mobility of a large molecule in the pores of sol-gel SiO2 films. A.C. dipolar relaxation measurements show that the biomolecule remains mobile but experiences a ten-fold increase in local microviscosity.

Polyimide-silica materials have been prepared via the sol-gel process by mixing tetramethoxysilane with a polyamic acid. Two polyamic acids have been used. The first is obtained with an equimolar mixture of oxydianiline (ODA) and pyromellitic dianhydride (PMDA) in dimethyacetamide. The second is prepared with a mixture of PMDA with aminopropyltrimethoxysilane (APrTMOS).

The microstructure of the materials obtained with these two polyamic acids are drastically different. The presence of both amino and methoxy side-groups on the APrTMOS enables a chemical bonding between the organic and the inorganic networks resulting in the formation of homogeneous films. On the other side, no chemical bond is provided by the ODA-PMDA polyamic acid resulting in a biphasic microstructure where pure silica particles are embedded in a polyimide matrix.

These two types of materials have been characterized in order to point out the key parameters of their microstructure. 29Si NMR, thermogravimetric analysis, scanning electron microscopy and infra-red spectroscopy have been used to study materials containing various proportions of TMOS and prepared with various hydrolysis ratios.

Novel abrasion resistant coatings have been successfully prepared by the sol-gel method. These materials are spin coated onto bisphenol-A polycarbonate, diallyl diglycol carbonate resin (CR-39) sheet, aluminum, and steel substrates and are thermally cured to obtain a transparent coating of a few microns in thickness. Following the curing, the abrasion resistance is measured and compared with an uncoated control. It was found that these hybrid organic/inorganic networks partially afford excellent abrasion resistance to the polycarbonate substrates investigated. In addition to having excellent abrasion resistance comparable to current commercial coatings, some newly developed systems are also UV resistant. Similar coating formulations applied to metals can greatly improve the abrasion resistance despite the fact that the coatings are lower in density than their substrates.

Coatings were prepared from suspensions containing colloidal silica (20nm) in isopropanol and 3-glycidoxypropyltrimethoxysilane (GPS). Thicker coatings without cracks were achieved by increased addition of GPS. The microstructure of the resultant coatings contained well packed colloids with some pore space. When high amounts of GPS were added (i.e., GPS:silica weight ratio (R) greater than 0.5), polymeric material appeared and covered the necks between particles and filled in pores. 29Si NMR of coating suspensions (R=l) showed GPS hydrolysis within a few minutes and GPS adsorption on the silica surface within a few hours. The excess silane remained in solution and further polymerized, instead of forming a thick multilayer on the colloids. Diffuse reflectance IR spectroscopy data suggests saturated surface coverage beginning around 2 to 3 molecules/nm2 based on observed depletion of silica surface hydroxyls.

Coatings were prepared from a suspension of colloidal silica particles containing glycidoxypropyltrimethoxysilane (GPS) and a polyamine curing agent. GPS was first added to an aqueous silica suspension which contained ethanol (30 wt%) to enhance mixing. The addition of GPS to a basic silica suspension favored condensation among the silane monomers and oligomers, resulting in precipitation. By contrast, acidic conditions resulted in slower condensation which allowed adsorption of the silane on silica, as followed by ATR-FI'IR. After GPS addition and aging, the pH of the suspension was increased, a polyamine was added, and coatings were prepared on polyester web. Coatings with GPS modification were denser, adhered better to the polymer substrate, and could be made thicker than unmodified silica coatings.

Organically modified silicates, the so-called Ormosils, based on silica (SiO2) and polydimethylsiloxane (PDMS), can have wide variations of mechanical properties depending on their chemical compositions and processing variables. The random network of the SiO2 is structurally modified by the reactive incorporation of PDMS chains to give materials ranging from hard glassy solids with Vickers number up to 200 Kg/mm2 to rubbery solids with resilience in excess of 75%. The variations of strength, elastic modulus and mechanical damping with temperature have been studied. The chemical stability of rubbery Ormosils as a function of temperature has been measured in air and in nitrogen. Examples of potential applications are presented.

Thermoplastic nanocomposites based on linear polymethacrylates as matrix materials and spherical silica particles as fillers have been synthesized using the in situ free radical polymerization technique of methacrylate monomers in presence of specially functionalized SiO2 nanoparticulate fillers. Uncoated monodisperse silica particles with particle sizes 100 nm and 10 nm were used as reference fillers. For surface modification, the alcoholic dispersions of the fillers were treated with appropriate amounts of methacryloxypropyltrimethoxysilane (MPTS) and acetoxypropyltrimethoxysilane (APTS). Transmission electron microscopy (TEM) was used to investigate dispersion behaviour in dependence on surface modification. Dynamic mechanical properties were measured by dynamic mechanical thermal analysis (DMTA).

Improvement of the fracture toughness of epoxy at cryogenic temperatures has been carried out aiming at cryogenic application. The macroscopic molecular state of hybrid material was studied and the possible mechanism to improve the fracture toughness even at cryogenic temperature was discussed.

Based on the mechanism the hybrid materials were prepared by dispersion of silica through hydrolysis of alkoxide. To connect the silica to epoxy molecule a coupling agent was used. The connection was successfully performed and was confirmed by positron annihilation method. The fracture toughness of the developed hybrid material was found to be approximately 2.6 times higher than that of epoxy itself at liquid helium temperature.

The degree of dispersion of latex particles in latex-modified cement paste was assessed by measurement of the volume electrical resistivity and modeling this resistivity in terms of latex and cement phases that are partly in series and partly in parallel. The assessment was best at low values of the latex-cement ratio; it underestimated the degree of latex dispersion when the latex/cement ratio was high, especially > 0.2.

A method for the preparation of dental restorative composites based on an organicinorganic hybrid material is presented. A sol-gel process was used to produce composites comprised of submicron silica in a polymer matrix. Using alcohols such as, 3-allyloxy-1, 2-propanediol and 2, 3-dihydroxypropyl methacrylate in combination with polysilicic acid or cyclic siloxane precursors, modified siloxanes are produced which can be polymerized photochemically with concurrent hydrolysis and condensation to generate a silica-reinforced polymer with superior mechanical properties and abrasion resistance.

Microporous, crystalline silicates can be synthesized using organic structure-directing molecules whose function is to organize silicate species into particular arrangements that then spontaneously self-assemble into the final crystalline materials. The porosity is obtained by removal of the organic component. We discuss the molecular properties (size, rigidity, hydrophobicity) necessary for the organic component to interact with aqueous silicate species and prepare microporous silicates. It is shown that a strategy to construct large organic molecules in order to prepare large pore crystalline silicates could involve the use of two charge centers if these functionalities are distributed within the molecules such to prevent aggregation in aqueous media. A charge distribution that allows aggregation of the organic molecules at synthesis conditions directs the formation of a locally amorphous, mesoporous silicate rather than a crystalline, microporous material.

We use an organic template approach to prepare microporous silica with controlled pore size and narrow pore size distributions. This was accomplished by fabricating relatively dense hybrid silica matrices incorporating organic template ligands by sol-gel synthesis and then removing the organic ligands to create a microporous silica network. Comparison of computer simulation results and experimental data indicated that using this fugitive template approach, pore volume can be controlled by the amount of organic template added to the system, and pore size can be controlled by the size of the organic ligands.

The retro Diels-Alder reaction was used to modify porosity in hydrocarbon-bridged polysilsesquioxane gels. Microporous polysilsesquioxanes incorporating a thermally labile Diels-Alder adduct as the hydrocarbon bridging group were prepared by sol-gel polymerization of trans-2, 3-bis(triethoxysilyl)norbornene. Upon heating the 2, 3-norbornenylene-bridged polymers at temperatures above 250°C, the norbornenylene-bridging group underwent a retro Diels-Alder reaction losing cyclopentadiene and leaving behind a ethenylene-bridged polysilsesquioxane. Less than theoretical quantities of cyclopentadiene were volatilized indicating that some of the diene was either reacting with the silanol and olefinic rich material or undergoing oligomerization. Both scanning electron microscopy and nitrogen sorption porosimetry revealed net coarsening of pores (and reduction of surface area) in the materials with thermolysis.

Organic/inorganic hybrid materials offer specific advantages for the realization of artificial membranes exhibiting high selectivity and flux as well as good thermal and chemical resistances. Preparations of hybrid membranes able to work in liquid or gas media are described. The influence of physicochemical properties of the membranes on transport parameters was also investigated. Results are discussed related to solution-diffusion theory in dense homogeneous membranes.

Aerogels derived from sol-gel oxides such as silica have become quite scientifically popular because of their extremely low densities, high surface areas, and their interesting optical, dielectric, thermal and acoustic properties. However, their commercial applicability has thus far been rather limited, due in great part to their brittleness and hydrophilicity. In prior work by our research group, modifying silicate gel structures with flexible, organic containing polymers such as polydimethylsiloxane imparted significant compliance (even rubbery behavior) and hydrophobicity. These materials have been referred to as Ormosils. This study expounds on our current efort to extend these desirable properties to aerogels, and in-so-doing, creating novel “Aeromosils”.

Reactive incorporation of hydroxy-terminal polydimethylsiloxane (PDMS) into silica sol-gels was made using both acid and two-step acid/base catalyzed processes. Aerogels were derived by employing the supercritical CO2 technique. Analyses of microstructure were made using nitrogen adsorption (BET surface area and pore size distribution), and some mechanical strengths were derived from tensile strength testing. Interesting Aeromosil properties obtained include optical transparency, surface areas of up to 1200 m2/g, rubberiness, and better strength than corresponding silica aerogels with elongations at break exceeding 5% in some cases.

We investigate the porosity of a series of xerogels prepared from arylene-bridged silsesquioxane xerogels as a function of organic bridging group, condensation catalyst and post-synthesis plasma treatment to remove the organic functionalities. We conclude that porosity is controlled by polymer-solvent phase separation in the solution with no evidence of organic-inorganic phase separation. As the polymer grows and crosslinks, it becomes increasingly incompatible with the solvent and eventually microphase separates. The domain structure is controlled by a balance of network elasticity and non-bonding polymer-solvent interactions. The bridging organic groups serve to ameliorate polymer-solvent incompatibility. As a result, when the polymer does eventually phase separate, the rather tightly crosslinked network limits domain size to tens of angstroms, substantially smaller than that observed in xerogels obtained from purely inorganic precursors where incompatibility drives phase separation earlier in the gelation sequence.

It has been found that inorganic thin films, prepared via sol-gel route, are nonporous or much less porous than bulk gel derived from the same precursor solutions, because of the overlap of rigorous solvent evaporation with continuing condensation during the process of film deposition. The synthetic strategy of this work is to control the condensation reaction by incorporation of terminal ligands through the formation of organic-inorganic network at molecular scales on the thin film coatings. Depending on the nature of the organic groups, the hybrid film can be designed with micropores close to the kinetic diameter of nitrogen as indicated by sorption isotherms and kinetics. The incorporation of the organic groups also renders the porous films with a more hydrophobic surface. AFM, 13C and 29Si MAS/NMR and FTIR data also qualitatively support the proposed microstructures of the hybrid materials.

The titanates MTiO3 ( M =; Ni,Co,Mn ) were prepared by a sol-gel method. The reaction between the metal solution and titanium butoxide leads to the formation of gels. The amorphous gels so obtained under different pH conditions, were calcined at temperatures between 750°C and 1200°C to obtain in some cases high purity, crystalline MTiO3 powders. The characterization of the samples was done by X-ray powder diffraction, differential thermal analysis (DTA), thermal gravimetry (TG) and BET surface measurements.

Inorganic-organic hybrids have been synthesized by reaction of Ti(OC2H5)4 and Ta(OC2H5)5 with silanol-terminated polydimethylsiloxane (PDMS). The chemical modification of the metal alkoxides with ethyl acetoacetate (EAcAc) was carried out in order to obtain a transparent and uniform hybrid. The hydrolysis behavior of Ti(OC2H5)4 modified with EAcAc in the presence of PDMS and the formation of the Ti-O-Si bond in a Ti-O-PDMS hybrid were revealed by FT-IR experiments. Dynamic mechanical measurements showed that a Ta-O-PDMS hybrid was harder than a Ti-O-PDMS hybrid, indicating the effect of metal on the storage modulus of hybrids.