The series of inorganic-organic hybrid materials were prepared from silane precursors by the sol-gel process. The resulted perfluorinated organosilicate liquid oligomers were applied on glass substrates and cured by heat yielding hard, clear and well adhering films. The films porosity, water contact angle, refractive index, and absorption in UV-Vis and IR were measured to characterize optical and physicochemical properties of the prepared films. The perfluorinated organosilicate films exhibited excellent optical transparency, low refractive indices, low porosity as well as non-wetting, hydrophobic behavior.
Specialty optical fibers operating in harsh aerospace environments are typically exposed to high temperatures and
elevated humidity. This calls for better performing protective coatings. Recently developed sol-gel derived inorganicorganic
hybrid materials called hybrid glass offered improved protective performance as compared to standard dual
polymer coated fibers [1]. In this paper we examine the effectiveness of online UV curing for the protective ability of
hybrid glass coatings. For this purpose two types of UV-curable hybrid glass candidates representing two different
concentrations of acrylate groups were applied online to silica fibers as single and dual coats. Samples of fibers were
collected and subjected to dynamic fatigue testing by two-point bending. The stress corrosion parameter, n, as well as the
strength of the fibers were determined. Both the strength and n were higher for fibers with two layers of coating as
compared to single coatings even when the thickness of both one and two layer coatings was the same. This may be
caused by the greater degree of cross linking of the inorganic component when the coating is exposed twice to the heat
generated in the UV chamber. Coating materials with reduced acrylate group content had higher values of the fatigue
parameter n but at the same time reduced strength.
Key requirements for specialty optical fibers engaged in various aerospace applications are extended lifetime and superb performance combined with small fiber diameter, minimal bend radius and ease of terminations. To address these requirements, the use of novel inorganic -organic materials called hybrid glass was proposed as single and double coats. Several types of hybrid glass candidate materials were applied on line on silica fibers as 7-35 μm thick single- or double -layer coats. The hybrid glass applied on silica fibers formed a non-strippable glasslike layer that was permanently bonded to the fiber surface. SEM analysis showed smooth, crack-free surfaces of the coatings and their strong adherence to the glass surface. To evaluate the protective ability of the hybrid coatings, the 2-point bending testing (dynamic fatigue) was controlled in a controlled temperature and humidity environment. Dynamic fatigue plots, the stress corrosion parameter n, Weibull strength distribution plots and average bending strength were calculated from the 2-point bending test data for each type of coated fiber tested. Two polymer coated fibers were used as reference and were tested as well. The hybrid glass coatings offered higher values for both fiber strength and n than those found for reference fibers. The UV induced photopolymerization of coating materials crosslinked the inorganic- network. The UV curing contributed also to the condensation process of inorganic constituents of the coatings and their permanent bonding to the silica fiber surface.
UV-curable hybrid glass materials, when applied as thin coatings on optical fibers are already known to result in fibers enhanced mechanical strength as well as thermal and environmental stability [1]. These materials, when fully cured offer refractive index in the range 1.470-1.50 measured at 1300 nm. In search for low optical loss and lower refractive index claddings the hybrid glass composition was altered to result in UV curable two component formulation HG-LI (1+2) of refractive index 1. 380 The goal of this study was fabrication and valuation of the optical, mechanical and thermal properties of the silica fibers cladded with this novel hybrid glass material. The silica fibers were drawn and cladded by HG-LI-(1+2) and HG-LI-2. For control fibers, soft silicone resin and hard silicone resin were used as cladding for the same silica preform rod. The basic optical (spectral attenuation) and mechanical characteristics (tensile strength, n parameter) for hybrid glass cladded fibers were performed. Thermo Gravimetric Analysis (TGA) was performed as well. The results showed that hybrid glass cladding has the onset decomposition temperature exceeding 300 °C, whereas the NA values of the silica fiber cladded by HG-LI-(1+2) and HG-Li-2 were 0.31 and 0.33, respectively.
In this study, SiO2/Al2O3/Er2O3 (SAE) nanopowders were fabricated by the Combustion Flame − Chemical Vapor Condensation (CF-CVC) technique with average primary particle sizes ranging from 10-30 nm. Fluorescence and lifetime measurements were made both on as-prepared powders, as well as heat treated powders, to compare the thermal annealing effects on optical properties. At an annealing temperature of 1000°C, the SAE became partially devitrified with extremely broad (FWHM ≈ 78 nm) and flat emission spectra, which is highly desirable for Wavelength Division Multiplexing (WDM) in optical amplifiers. The unique optical properties of the powders at this temperature, are attributed to the formation of a metastable phase consisting of an uniform nano-scale dispersion of a metastable intermediate SiO2 (Al,Er)2O3 phase in an amorphous SiO2 matrix. At higher heat treatments (1400°C), a dual-phase equilibrium structure was formed, consisting of a pyrochlore phase in a crystobalite matrix.
Polymeric UV curable coatings have been successfully employed over 25 years to protect freshly drawn optical fibers from mechanical damage and to prevent microbending losses. Although present dual acrylate coatings provide satisfactory protection, they are water permeable and do not effectively protect the fiber surface from water corrosion. Rapidly growing market calls for next generation protective materials that would provide with enhanced fiber reliability even in hot, humid and other harsh environments. The general concept of such “hermetic” polymeric coatings design is presented. The key aspects of the design include the use of interpenetrating polymeric network (IPN) and organic-inorganic silica based hybrids derived by sol-gel process. Such coatings may offer superior moisture barriers and surface passivation while remaining otherwise equivalent to commercial acrylates from a processing perspective. Simultaneously, these coatings may offer other potential advantages such as significant thickness reduction, higher temperature performance and lower thermal expansion coefficients.
Inorganic/organic gels are prepared by hydrolyzing silica-containing alkoxides. Organics are introduced either by functionalizing the silica chemical hybrids) or by dissolving organic polymer in the solvent (physical hybrids). When the organic is a linear polymer, such as poly(vinyl acetate) or poly(ethylene oxide), the interactions between the organic and inorganic components are largely through surface hydroxyl groups. These interactions are responsible for the degree of visible light transmission.
Two formulations based on perfluorinated polymer were prepared for use as UV-curable optical cladding for silica fibers. In the first formulation an adhesion promoting agent based on fluoroacrylate resin was synthesized and mixed with the experimental product Defensa 7702++ in order to promote wetting and chemical adhesion to the silica fibers. In the second formulation, wetting and physical adhesion between the liquid coating and the silica fibers were achieved by increasing the viscosity of the starting coating by addition of unsaturated perfluorinated polymer into Defensa. Both formulations were used as primary coatings on dual coated silica optical fibers. The mechanical behavior of the formulations was characterized by the strip test, the pull-out test and zero stress aging in 90 degrees Celsius pH 7 buffer. The results show that both formulations exhibit better wetting-adhesion characteristics than unmodified starting coating and that the strength degradation during zero- stress aging was lower for the fiber coated with the formulation of higher viscosity.
Two types of hybrid gels based on silica and perfluorinated polymers have been prepared. The first type involves a perfluorinated polymer containing acrylate groups. Perfluoropolyether diol diacrylate (PFDA) was functionalized by reacting it with (3-mercapto-propyl) trimethoxysilane by a Michael addition. The resulting silyl derivative (PFDAS) was able to copolymerize with a silica precursor, tetraethylorthosilicate (TEOS), resulting in perfluorinated polymer/silica hybrid gels. For the second type, perfluoroalkylsilane (FAS), vinyltriethoxysilane (VTES), and TEOS were polymerized in one step. In both cases, the gels were transparent, crack-free and water repellent. Since the inorganic and organic components are covalently bonded to each other, these materials can be classified as organic/inorganic copolymers.
Rhodamine 6G-doped hybrid gels were prepared by a sol-gel route. The inorganic component tetraethyl orthosilicate (TEOS) and the organic component glycerol propoxy triacrylate (GPTA) were simultaneously polymerized to create interpenetrating silica-GPTA networks. Crack-free, transparent dried gels in the shape of rods and fibers were obtained. Lasing properties of the hybrid rod-shaped monoliths were determined as a function of rhodamine concentration. In addition, gels in the shape of fibers were evaluated as fiber lasers for detecting ammonia vapor.
Three kinds of UV-curable organically modified silicates have been prepared to be used as protective coatings for optical fibers. The synthesis involves the reaction of the thiol group of 3-mercaptopropyl-trimethoxysilane with a C equals C bond in one of the acrylic groups of three commercially available aliphatic triacrylates. The methoxysilyl groups of the synthesized diacrylate methoxysilanes were subjected to hydrolysis and condensation to form Si-O-Si units. Transparent, viscous, solvent-free resins were obtained that hardened in seconds when exposed to UV radiation. The coating derived from the reaction with glycerol propoxy triacrylate (GPTA) proved to adhere the best of the three to both plastic and glass substrates. It was then tested as a protective coating for silica fibers. Reliability tests were carried out including bending strength and fatigue tests at pH 7 and 10. The results show improved water resistance of the coated fiber in neutral conditions.
Rod shaped silica-poly(vinyl acetate) (PVAc) gels have been prepared by a sol gel process. In situ polymerization of tetraethoxysilane (TEOS) was accomplished in the presence of low molecular weight PVAc by dissolving various amounts of PVAc in a mixture of TEOS, ethanol, water and hydrochloric acid (HCl). Gelation of this mixture was carried out between room temperature and slightly above. Silica-PVAc rods recovered from cylindrical molds were homogeneous and transparent. Gels with weight percents of PVAc ranging from 2% to 50% were prepared. Silica-PVAc gels have higher flexure strengths, less brittle character and improved water durability in comparison with pure sol- gel silica.
Fluorescence properties of the methyl methacrylate solutions of two kinds of aromatic methacrylate monomers: 9-methyl,10-methacryloyloxymethylanthracene and 9- methacryloyloxymethylanthracene were studied. The concentration of anthracene fluors in methyl methacrylate corresponding to the maximum fluorescence yield has been found, and some parameters describing the excitation and deactivation of the excitation energy of the studied system have been calculated. Next polymer rods have been prepared by copolymerization of methyl methacrylate and two studied fluors of anthracene. The absorption and emission spectra, fluorescence lifetimes, quantum efficiency, and Verdet constants were measured for the obtained polymer rods. The studied anthracene fluors can be useful, at small concentrations, as wavelength shifters in polymethyl methacrylate-core polymeric optical fibers whereas higher concentrations of anthracene fluors can be used to get some enhanced magneto-optical properties of the polymers.
Polymethyl methacrylate (PMMA) rods have been prepared under various polyme- rization conditions. All the obtained rod-preforms were subjected to a drawing process to examine their thermoplastic properties. The mechanical and optical properties of the drawn PMMA fibres were determined with respect •to the preparation and drawing conditions of the rods. Polystyrene - core polymer optical fibres (POF) manufacturing as well, as gra- dient - index (GRIN) polymer rod preparation were also briefly reviewed.
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