Macroporous silicate thick films were prepared by a sol-gel dip-coating method accompanied by the phase separation using methyl-trimethoxysilane (MTMS), nitric acid and dimethylformamide (DMF) as starting components. The morphology of the film varied to a large extent depending on the time elapsed after the hydrolysis until the dipping of the coating solution. On a glass substrate, the films prepared by early dipping had inhomogeneous submicrometer-sized pores on the surface of the film. At increased reaction times, relatively narrow sized isolated macropores were observed and their size gradually decreased with the increase of reaction time. On a polyester substrate, in contrast, micrometer-sized isolated spherical gel domains were homogeneously deposited by earlier dippings. With an increase of reaction time, the volume fraction of the gel phase increased, then the morphology of the coating transformed into co-continuous gel domains and macropores, and finally inverted into the continuous gel domains with isolated macropores. The overall morphological variation with the reaction time was explained in terms of the phase separation and the structure freezing by the forced gelation, both of which were induced by the evaporation of methanol during the dipping operation.

ORMOCER®*s (inorganic-organic hybrid polymers) with low Si-OH content were synthesized by a new sol-gel route. Optimization of the sol-gel process parameters (catalyst, temperature etc.) was performed in order to achieve reproducible low cost materials which are photo-patternable even in higher layer thicknesses up to 150 μm within one step without cracking or delamination. The materials combine low losses in the NIR region (0.2 dB/cm at 1310 nm and 0.5 dB/cm at 1550 nm without fluorination!) with low dielectric constants (3.3 at 10 kHz).

Beside the dielectric and optical properties the materials have a variety of additional advantages for interconnection technology: good wetting and adhesion on various substrates (e.g. glass, silicon and several polymers), low processing temperatures (postbake below 160 °C), high thermal stability (up to 270 °C) and a tunable refractive index.

Details of chemical synthesis and characterization as well as photo-lithographic processing of ORMOCER® materials are presented.

Inorganic-organic hybrid polymers were prepared by radical polymerization of methacrylic acid or methyl methacrylate with the (meth) acrylate-substituted oxozirconium and oxotitanium clusters Zr6(OH)4O4(OMc)12(OMc = methacrylate), Zr4O2(OMc)12, Ti6O4(OEt)8(OMc)8 and Ti4O2(OPri)6(OAcr)6(OAcr = acrylate). A few mol% of cluster is sufficient for an efficient cross-linking of the polymer chains. Small-angle X-ray scattering data indicate that the cluster size is retained in the polymers and that the microstructure of the cluster cross-linked samples can be described by a dispersion of identical spherical or disk-shaped clusters in the polymer. The obtained hybrid polymers exhibit a higher thermal stability because depolymerization reactions are inhibited. Contrary to undoped poly (methyl methacrylate), the cluster cross-linked polymers are insoluble but swell in organic solvents. The solvent uptake upon swelling decreases with an increasing amount of polymerized cluster.

In recent years great advances have been made in the synthesis of organic-inorganic hybrid materials, whether they are oligomeric, multipodal, polymeric or dendritic in structure. Of particular interest are liquid-crystalline systems, as the control of the soft self-assembly behaviour of these systems allows for the addressing of the macroscopic properties of these materials.

The investigations of silsesquioxane and siloxane cores decorated with suitable organic groups of linear and branched structures leading to liquid-crystalline phase behaviour is presented. The structural and chemical features which govern the phase behaviour will be discussed. Important features are the size, geometry, structure and flexibility of the inorganic core, the flexibility, branching and length of the spacer linking inorganic cores and the organic groups, which promote liquid-crystalline phase behaviour. The effects of a variety of mesogenic structures on the liquid-crystalline phase behaviour and stability range will be discussed.

Micelle templated co-condensation of tetraethoxysilane and 3-(2,4-dinitrophenylamino)-propyltriethoxysilane was used to covalently attach an organic chromophore into silica materials with MCM-41 architecture. Hexagonally highly-ordered mesoporous dye-functionalized silica materials with various dye contents (up to 43 wt%) were precipitated from alkaline and acidic aqueous solutions containing cetyltrimethylammonium bromide (C16TMAB) surfactant. These materials were obtained in the form of powders, excluding their use in thin film applications, such as required for membrane and optical devices. Therefore, an evaporation-induced self assembly process was used to prepare transparent mesostructured dye-functionalized silica thin films and monoliths. Analogous materials with increased pore channel sizes were fabricated by addition of the micelle swelling agent 1,3,5-trimethylbenzene to the reaction mixture or by replacing C16TMAB surfactant by an amphiphilic triblock copolymer (poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide)). This synthetic route was also used to produce bimodal mesostructured dye-modified silica materials using both latex spheres and C16TMAB micelles as organic structure-directing agents.

Organically modified silica gels and dye-doped silica gels have been patterned into micrometer-scale structures on a substrate using micro molding in capillaries (MIMIC). This approach is from a class of elastomeric stamping and molding techniques collectively known as soft lithography. Soft lithography and sol-gel processing share attractive features in that they are relatively benign processes performed at ambient conditions, which makes both techniques compatible with a wide variety of organic molecules, molecular assemblies, and biomolecules. The combination of sol-gel and soft lithography, therefore, holds enormous promise as a tool for microfabrication of materials with optical, chemical, or biological functionality that are not readily patterned with conventional methods. This paper describes our investigation of micro-patterned organic-inorganic hybrid materials containing indicator dyes for microfluidic sensor applications. Reversible colorimetric pH sensing via entrapped reagents is demonstrated in a prototype microfluidic sensor element. Patterned structures range from one to tens of micrometers in cross-section and are up to centimeters in length. Fundamental chemical processing issues associated with mold filling, cracking and sensor stability are discussed.

Ca (II) containing porous hybrids of gelatin and 3-(glycidoxypropyl) trimethoxysilane (GPSM) were prepared with sol-gel processing and freeze-drying techniques. The freezing temperature could control porosity and pore size of the hybrids. The biodegradation rate of the hybrids in a Tris buffer solution decreased with an increase in GPSM content. The bone-like apatite layer could form on the Ca (II) containing porous gelatin-silicate hybrids when they were soaked in a stimulated body fluid (SBF), hence they were applicable to be the bioactive scaffolds for bone tissue engineering.

Vitamin E-TPGS (α-tocopheryl polyethylene glycol 1000 succinate) was found to be an effective template for the preparation of a novel hexagonal mesoporous silica referred to as DAM-1 (Dallas Amorphous Material-1). Depending upon the temperature and gel composition various morphologies can be achieved, including spheres, gyroids, discoids, hexagonal plates and rods. Characterization of these composites as well as a preliminary evaluation of DAM-1 as a drug delivery system under physiological conditions is also presented.

Si-alkoxides in gas phase are reactive towards the surface of animal cells, depositing a homogeneous layer of porous silica. This encapsulation method preserves cell viability and does not alter the hindrance of the biological load.

In the prospective use for the design of a hybrid bioartificial liver, hepatocytes in a collagen matrix can be entrapped by the siliceous deposit which provides definite mechanical stability to the collagen matrix and molecular cutoff vs. high molecular weight proteins, including immunoglobulins. The functionality of the encapsulated cell load is maintained for the expressions of typical liver and pancreas metabolic activities.

Lateral thinking in biomimetic materials chemistry has permitted chemists to create fascinating structures that mimic the biomaterials optimized by Nature. The integration of organic and inorganic chemistry at multiple length scales gives optimal performance characteristics to biomaterials, such as bone. In a similar fashion, lateral thinking in our lab has enabled us to consolidate the chemistry of inorganic surfactant-templated mesoporous materials with the organic-inorganic hybrid structure of amorphous xerogels. A new class of materials, periodic mesoporous organosilicas (PMOs), has emerged that marries organic and solid-state chemistry in the channels of hexagonally ordered mesoporous materials. Various organic and organometallic groups may be integrated into the framework, creating materials with novel, tunable properties. Surfactant can be solvent-extracted or ion-exchanged to create a high surface area PMO with the framework and the organic group intact. This renders the organic groups accessible for reaction to give a new type of “chemistry of the channels”.

Organic/inorganic hybrid mesoporous films exhibiting ordered mesophases were prepared by a simple dip-coating procedure. Beginning with a homogeneous solution of tetraethoxysilane, organoalkoxysilane ((R'Si(OR)3, R' is a non-hydrolyzable functional ligand) surfactant, we relied on solvent evaporation to induce micellization and continuous self-assembly into hybrid silica-surfactant thin film mesophases. Surface acoustic wave (SAW)-based nitrogen sorption measurements indicate that the films have high surface areas and unimodal pore diameters after removal of surfactants.

The demand for multi-purpose, high-performance polymer systems has resulted in a need for advancing polymer properties beyond what traditional systems can offer. Only through control/alteration at the molecular level can one maximize property enhancements to meet current military and commercial needs. Over the last seven years the Air Force Research Laboratory has developed and incorporated discrete Si-O frameworks (POSS = Polyhedral Oligomeric Silsesquioxanes) into traditional organic polymer systems. This research has resulted in new hybrid inorganic-organic polymer systems with remarkable enhancements in mechanical and physical properties including dramatic increases in both glass transition and decomposition temperatures, reduced flammability, increased moduli and oxidation resistance. We have shown that these enhancements result from the chemical composition (Si-O core) and size (∼15 A in diameter) of the POSS frameworks, and can be copolymerized, grafted, or even blended using traditional processing methods. Recently, we have focused our efforts on understanding and controlling the molecular level interactions between POSS frameworks and the polymer matrix. The development of new POSS monomers has allowed us to study how functionality, size, and geometry enhances the bulk properties of these hybrid materials. For example, increasing the solubility of side groups on the POSS framework results in greater POSS-polymer matrix interactions and increased Tg and storage moduli. Recent studies with POSS blends have resulted in increases in hardness, and reductions in dielectric constants and coefficients of thermal expansion. New results in polymer synthesis, characterization, and applications will be discussed with a strong emphasis on the versatility of this new nanotechnology to many polymer systems.

The basic tetrahedra of silica are readily assembled into eight cornered cages known as cubic silsesquioxanes ([RSiO1.5]8). Silsesquioxane cubes represent one of the smallest possible units of ceramic silica. The corners of these nanometer-sized ceramic cubes are readily functionalized with reactive groups and incorporated into organic polymers. In this work, we characterize the structures that result from varying the length of the flexible organic segments used to connect the cubes in a series of hybrid network materials. For very short organic segments, steric hindrances inhibit high degrees of network conversion and the resulting network is very inhomogeneous. As the length of the flexible organic segment increases, the added degrees of freedom allow a more ‘ordered’ glassy material to evolve. If the length of the organic segment becomes very long in comparison to the size of the cube, a disordered polymer-like network is obtained.

This work successfully prepared an UV curable organic-inorganic hybrid material consisting of organic modified colloidal silica. Applications of UV curable organic-inorganic hybrid materials include abrasion resistant coatings, photo-patternable thin films and waveguides. Colloidal silica containing reactive functional groups were also prepared by reacting organic silane and tetraethyl orthosilicate (TEOS) using sol-gel process. In addition, the efficiency of grafting organic moiety onto silica nanoparticles was investigated by applying TGA and FTIR techniques. Experimental results indicated a strong interdependence between surface modification efficiency and solution pH. Acrylate-SiO2 hybrid formation could result in a shifting of thermal degradation temperature of organic component from about 200°C to near 400°C. In addition, the stability of organic modified colloidal silica in UV curable formula and the physical properties of resulting coatings were discussed. Furthermore, the morphology of organic modified colloidal silica was investigated by performing TEM and SEM studies‥

The broadband dielectric relaxation of a BaTiO3-polymer composite film was studied. The complex dielectric constant data from 10-4 Hz to 1010 Hz reveals the existence of relaxation process at frequency of 10 MHz in the polymer composite. On the basis of Cole-Cole analysis, the relaxation time of the system is of order of 10-8 s. The understanding of the broad dispersion in dielectric behavior of polymer composite materials is needed to support next generation electronic devices used in wireless communication and related applications.

Using a micro-Contact Printing (μ-CP) technique, substrates are prepared with patterns of hydrophilic, hydroxyl-terminated SAMs and hydrophobic methyl-terminated SAMs. Beginning with a homogeneous solution of silica, surfactant, ethanol, water, and functional silane, preferential ethanol evaporation during dip-coating, causes water enrichment and selective de-wetting of the hydrophobic SAMs. Correspondingly, film deposition occurs exclusively on the patterned hydrophilic SAMs. In addition, by co-condensation of tetrafunctional silanes (Si(OR)4) with tri-functional organosilanes ((RO)3Si(CH2)3NH2), we have selectively derived the silica framework with functional amine NH2 groups. A pH sensitive, micro-fluidic system was formed by further conjugation reactions with pH sensitive dye molecules.

The dielectric properties of acrylic resin composites filled with BaTiO3, have been evaluated over a broad frequency range. These materials were used as models to study the dielectric response in polymer composite films for de-coupling capacitance applications. A series of photocurable resin formulations were prepared and photocured into films of approximately 100 μm to 120 μm thick. Dielectric permittivity of the materials was investigated at frequencies from 100 Hz to 10 GHz and temperatures from –140 °C to +150 °C. The dielectric constant of the composites reached 35 at 1 GHz. A high frequency dielectric relaxation process was identified and related to the molecular structure of the polymer matrix.

Polymer encapsulation of inorganic silica nanoparticles was performed through emulsion polymerization of styrene and methyl methacrylate monomers. Two different approaches are described. In a first one, the hydrophilic silica was modified by reacting the coupling agent, 3-trimethoxysilyl propyl methacrylate, which was involved further in propagation reactions. In a second approach, we used the 2–2'- azobis (2-amidinopropane) dihydrochloride cationic initiator to promote interactions of the positively charged growing polymer with the negatively charged silica surface. We demonstrate, using transmission electron microscopy, that the silica beads are successfully encapsulated by the two techniques giving silica/polymer nanoparticles with different morphologies. The influence of some parameters, such as the nature of the surfactant and the monomer concentration, on the efficiency of the encapsulation reaction and the morphology of the encapsulated products are reported.

Photopatternable hybrid inorganic-organic polymers with negative resist behaviour have been developed and tested for evaluation in optical and electrical interconnection technology. They are composed of inorganic oxidic structures cross-linked or substituted by organic groups. The synthesis starts from organosilane precursors reacted by sol-gel-processing in combination with organic crosslinking of polymerisable organic functions. As a result of these functionalities the properties of the ORMOCER®s are adjusted to the particular applications. Systematic variation of composition combined with adaptation to micro system technology allows great flexibility in processing. The main features of these materials are:

• Combined use as dielectric and passivation layers in electrical systems and devices as well as core and cladding for optical applications enables e/o applications with high integration levels.

• Postbaking at moderate temperatures (120 - 170 °C) enables processing on low-cost substrates such as FR-4 (a glass-fibre reinforced epoxy-polymer).

• Easily adaptable to thin film technology: spin-on with planarisation > 90 %, via diameters down to 20 μm and high aspect ratio for optical waveguides have been achieved.

Synthesis, modification of the resins towards technological needs, their thin film technology and the resulting demonstrators will be discussed.