Glass-like Materials Research Articles

Novel Fluorinated [sgrave]-Conjugated Polysilynes For Optical Waveguides

Abstract Fluorinated polysilynes were prepared by the reductive coupling of trichlorosilanes with molten sodium in a mixture of toluene and diglyme (4:1) as a new synthetic route. Homopolysilynes containing fluorinated organogroups were insoluble in organic solvents due to side reactions. To improve solubility, copolysilynes were synthesized by copolymerization of fluorinated trichlorosilanes with cyclohexyltrichlorosilane. All spectroscopic data indicate that the structure of the resulting polysilynes is a rigid, irregular network of monosubsituted sp3-hybrid silicon atoms that have three neighboring silicon atoms. They exhibit extensive Si-Si [sgrave]-delocalization. delocalization. Upon exposure to deep-UV radiation in air, they undergo photooxidative crosslinking to give insoluble glass-like materials. This photooxidation process is accompanied by a large decrease in refractive index from n= 1.61 to n= 1.485. These results suggest that their potential Applications are as optical waveguides in optical interconnect systems.

Embedding Fullerenes in Thin Sol-Gel Films

ABSTRACTFullerene C60 can be considered an interesting molecule for the preparation of new materials with attractive optical properties. In the present work we report the preparation of sol-gel derived, glass-like materials containing C60 and a C60 derivative prepared by 1,3-dipolar cycloadditions of azomethine ylides to C60. The optical characterisation of the films confirms the presence of C60 and its derivative, in the glass matrix.

Strong nonlinearity under weak pumping. New approach to the problem of optical damage

It is shown that even at homogeneous pumping of glass-like materials macroscopic charge separation takes place. In spite of the strong Coulomb repulsion the pumped volume divides into electron and hole domains. As a result, a strong macroscopic electric field and a contribution to the refractive index appear. 1/ƒ noise in the refractive index fluctuation is predicted.

Preparation of immobilized proteins covalently coupled through silane coupling agents to inorganic supports.

Enzymes were first immobilized on inorganic supports through silane coupling agents over 25 yr ago. Since that initial report, literally hundreds of laboratories have utilized this methodology for the immobilization of enzymes, antigens, antibodies, receptors, and other high and low mol wt compounds. Today silane coupling is one of the commonly used techniques in the arsenal of the biochemist for the binding of material of all sorts to inorganic surfaces. Inorganic materials come in a variety of shapes, sizes, and characteristics. Today silane coupling is one of the most used coupling methods for the preparation of biosensing devices. Sol-gel entrapped enzymes are also produced by the application of silane technology by the polymerization of the silane to form glass-like materials with entrapped protein. This review will discuss the general preparation and characterization of silane coupled proteins with special emphasis on enzymes and describe in detail the actual methods for the silanization and specific chemical coupling of proteins to the silanized carrier.

Synthesis of Novel Fluorinated [sgrave]-Conjugated Silicon-Containing Polymers: Polysilynes and Polysilanes

Abstract The synthesis of fluorinated polysilynes, a new class of silicon-silicon network materials, has been achieved by reductive coupling of fluorinated trichlorosilanes with molten sodium in a mixture of toluene and diglyme (4:1) as a new synthetic route. Homopolysilynes containing fluorinated organogroups were insoluble in organic solvents due to side reactions. To improve solubility, copolysilynes were synthesized by co-polymerization of fluorinated trichlorosilanes with cyclohexyltrichlorosi-lane. All spectroscopic data indicate that the structure of the resulting fluorinated copolysilynes is a rigid, irregular network of monoalkyl sp 3-hybridized silicon units which exhibit extensive Si-Si [sgrave]-delocalization. They are more thermally stable than unfluorinated polysilynes. Upon exposure to deep-UV radiation in air, they undergo photooxidative crosslinking to give insoluble glass-like materials. This photooxidation process is accompanied by a large decrease in refractive index from n = 1.61 to n = 1.485. These results suggest that their potential applications include photoresists and optical waveguides. In order to understand the mechanism of reductive coupling of fluorinated trichlorosilanes, fluorinated linear polysilanes were also prepared.

Arylsilsesquioxane gels and related materials. New hybrids of organic and inorganic networks

Molecular building blocks for the preparation of amorphous hybrid organic-inorganic network materials have been synthesized. Hydrolysis and condensation of bis(triethoxysilyl)aryl 1-4 and -ethynyl 5 monomers results in formation of aryl- and ethynyl-bridged polysilsequioxanes in the form of xerogels. The gels were glasslike materials composed of uniform aggregate of particles between 50 and 80 nm in diameter. Atomic force microscopy was used to examine the fine grained aggregate characteristics of phenyl-bridged polysilsesquioxane

Development of New Polymeric Materials for Linear Waveguides

AbstractWe have evaluated the use of either poly(phenylene) prepared via spin-coatable polymeric precursors or fluorinated polysilynes for optical waveguides. Poly(phenylene) precursors were converted into poly(phenylene) by either curing at 300 °C or by deep-UV exposure in the presence of a photoacid generator. The poly(phenylene)s have a number of desirable properties for optical waveguide applications including good near IR transmission, low dielectric constant, thermal and environmental stability and ease of pattern fabrication using microlithographic techniques. Copolysilynes were spin-coated onto various types of substrates and then exposed by deep-UV radiation. Upon exposure of deep UV irradiation in the presence of air, they undergo photooxidative crosslinking to give insoluble glass-like materials. This photo-oxidation process is accompanied by a large decrease in refractive index from n=1.61 to n= 1.485. The photooxidation results suggest that their potential applications are as photoresists and optical waveguides.

Ion Conductivity in Crystalline and Glass-Like Fluoride Materials

Ion Conductivity in Crystalline and Glass-Like Fluoride Materials

Structural modification to glass-like materials under laser irradiation

Laser-induced changes in glasslike materials may involve the expansion of gas trapped in materials that contain voids, with the resultant growth of bubbles around the voids, which serve as nucleation sites. If the trapped gas is initially frozen in out of equilibrium, this process will lead to irreversible changes in the material. This paper examines theoretically the process of laser-induced bubble growth in a glasslike material and the concomitant changes in the bulk properties of the material. It is pointed out that the theoretical treatment of this laser material interaction can be tested by measuring the gas-bubble distribution function and porosity in a sample of quartz-fiber material after laser irradiation. The foaming of the surface of the material can be measured and used to deduce the frozen-in pressure in the bubbles. 5 refs.

Heat capacity of glasslike materials: The free volume approach

The experimental quasi-linear temperature dependence of the heat capacity of glasses is explained in terms of the free volume concept. The state number density n(0) is calculated as a function of microscopic system parameters. It is noted that the proposed model is also suitable for investigation of the dissipation properties of glasses and proteins.

Formation of glass-like materials from ethyl silicate

The alkyl silicates, especially ethyl silicate, are used as binders in the foundry and refractory industries because they form rigid coherent gels which do not contain fluxing agents. The preparation of glass-like materials from technical ethyl silicate (SiO 2 equivalent of 40% w/w) has been studied, using certain four-covalent organotin compounds as catalysts for the neutral hydrolysis and gelation reactions. Clear, transparent, glass-like gels can be formed, particulary if the water content is greater than 16%. Systems with a water content under 16%, desirably between 8–16% show good fibre-forming ability, dibutyltin diacetate being the preferred catalyst. These systems show a better fibre-forming ability than do similar systems using tetraethoxysilane. Viscosity measurements suggest that this is because the technical ethyl silicate contains a mixture of linear polysilicate oligomers.

ChemInform Abstract: HEAT‐RESISTANT NONSILICATE POROUS GLASSLIKE MATERIAL

AbstractDie untersuchten Na‐Borat‐ Gläser enthielten als 3. Komponenten (X) eine Kombination von hitzebeständigen Oxiden.

Heat-Resistant Nonsilicate Porous Glasslike Material

Substitution of the end-member oxides in the ternary sodium borosilicate system was studied. Replacing SO2 with a combination of beat-resistant oxides Ce, Hf, Th, and Zr (with or without La2O3 and/or Y2O3) was found to produce glasses (droplet like phases present), which after heat treatment decomposed into two immiscible microphases (coarsening process) of which one is water-soluble. The structure of the leached materials or the materials sintered after leaching (CeO2-HfO2-La2O3-ThO2-Y2O3-ZrO2), (CeO2-HfO2-La2O3-ThO2-ZrO3), (CeO2-HfO2-ThO2-YZO3-ZrO2), and (CeO2-HfO2-ThO2-ZrO2) is predominantly glasslike. Some Na2O-B2O3 may be expected to remain unleached in the pores, as has been observed for silica-based materials. However, no evidence for this was found during X-ray diffraction analysis and therefore any such presence if crystalline must be below 1%. The new glasslike materials have a higher sintering temperature (1520°C) than porous silica glass (900° to 1200°C). The specific surface area of the leached glasslike materials is 93.7 to 295.8 m2/g and an average pore radius of 0.4 to 7.3 nm was calculated, A favorable alkali resistance of 5.12 × 10−3 to 1.36 × 10−2 mg/dm2 as well as a water resistance of 5.9 to 13.8 Na2O in mg/g was measured.

Thermal and mechanical properties of linear segmented polyurethanes with butadiene soft segments

AbstractA series of segmented polyurethanes based on a hydroxyl terminated polybutadiene soft segment (HTPBD) have been prepared with varying hard segment content between 20 and 60 weight percent. These materials are linear and amorphous and have no potential for hydrogen bonding between the “hard” and “soft” segments. The existence of two‐phase morphology was deduced from dynamic mechanical behavior and thermal analysis. Both techniques showed a soft segment glass transition temperature, Tgs, at −56°C and hard segment transitions between 20 and 100°C, depending on the urethane content. The low value of Tg, only 8° higher than the Tg of free HTPBD and independent of hard segment concentration indicated nearly complete phase segregation. Depending on the nature of the continuous and dispersed phases, the urethanes behaved as elastomers below 40 weight percent hard segment or as glasslike materials at higher hard segment contents. The effect of thermal history on transitions of the HTPBDurethanes was also investigated and the results suggest that the absence of hydrogen bonding to the soft segment must account for the extraordinary insensitivity to thermal history in dynamic mechanical, thermal and stress‐strain behavior. Comparisons are made to the more common polyurethanes containing polyether and polyester soft segments.

Thermoelectric Power of the Systems AgI-Ag2 XO4 (X=Mo, W)

Abstract Determinations of the initial thermoelectric power were carried out at 1000 K in the whole composition range of the molten systems AgI-Ag2XO4 (X = Mo, W). For the composition XAgI= 0.8 the investigation was extended to the variation of the thermal emf at the “melting point” of the electrochemically noteworthy glass-like phases, obtained through rapid quenching of the melt. The hypothesis that these glass-like materials could keep the melt configuration at room temperature is contradicted by the results on the molten systems; more complex interpretations, based on the behaviour of the thermal emf at the “m.p.” are proposed.

Structure-toxicity relationships of acrylic monomers.

Esters of acrylic acid, in particular methyl methacrylate, have wide applications in a number of industrial and consumer products, forming very desirable nonbreakable glass-like materials. In dentistry, the monomers are used to prepare dentures and a variety of filling and coating materials for the teeth. Surgeons utilize the monomers to prepare a cement which helps anchor prosthetic devices to bone. Special types of acrylic monomers such as the cyano derivatives have found a useful application as adhesive materials. Most of the acrylic acid esters are volatile substances and can produce various levels of toxicity if inhaled. A large number of workers thus exposed to the vapors of these esters can develop clinical symptoms and signs of toxicity. This paper will discuss the toxicity of a large number of acrylic esters, and will attempt to show structure-activity relationships where such data are available. General comments will also be made as to the potential health hazards this variety of esters may present to selected segments of the population.

Some aspects of the mechanical testing of non-metallic solids

Some problems associated with the mechanical testing of several classes of non-metals are reviewed. The difficulties encountered in measuring the elastic properties of rubbers, plastics and fibrous materials are considered and tests on the mechanical strength of glass-like materials are discussed. The significance of static and dynamic hardness measurements on non-metals is then considered in detail and the way in which such quantities as rebound hardness may depend on the conditions of test rather than on the properties of the material being investigated is described.