Browsing by Subject "Sol-gel process"

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    Effect of processing options on ultra-low-loss lead-magnesium-niobium titanate thin films for high density capacitors
    (Elsevier, 2013) Chen W.; McCarthy, K.G.; O'Brien, S.; Çopuroǧlu, Mehmet; Cai, M.; Winfield, R.; Mathewson, A.
    This work studies the impact of annealing temperatures on PMNT (lead-magnesium niobate-lead titanate, Pb(Mg0.33Nb 0.67)0.65Ti0.35O3) thin films grown on a silicon substrate. The electrical properties of the thin films, such as dielectric constant and loss tangent, are shown to depend strongly on the annealing temperature, with the best electrical properties being achieved at the highest annealing temperature. It is seen that the perovskite phase is highest in the sample annealed at 750 C indicating that a relatively high temperature is necessary for complete transition of PMNT to the perovskite phase. The sample annealed at 400 C exhibits the lowest loss tangent of approximately 0.007 at a frequency of 1 MHz. © 2012 Elsevier B.V.
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    Nano-structured organically modified silica thin films for functional surfaces
    (2011) Bayındır, Mehmet; Yıldırım, Adem; Budunoglu, Hülya; Yaman, Mecit; Deniz, Hakan; Güler, Mustafa O.
    We report a template-free sol-gel method for preparation of nanoporous ormosil thin films at ambient conditions. The thin films are coated to the surfaces by using colloidal suspensions of ormosil gels. Gels are synthesized by using a trifunctional organosilane monomer, methyltrimethoxysilane (MTMS), with a two-step acid base reaction. We prepared several ormosil thin films on glass, metal, plastic and paper surfaces with different functionalities like superhydrophobic, antireflective, antifogging and ice retarding properties, from gels prepared in different conditions. Also films on flexible substrates exhibits durable surface properties after several bending cycles. In addition, we also demonstrate that these thin films can be used for fluorescent sensing of explosives by doping them with fluorescent dyes.
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    Nanocomposite glass coatings containing hexagonal boron nitride nanoparticles
    (Pergamon Press, 2016) Çamurlu, H. E.; Akarsu, E.; Arslan, O.; Mathur, S.
    Glass coatings composed of SiO2-K2O-Li2O, containing non-modified and fluorosilane modified hexagonal boron nitride (hBN) nanoparticles, were prepared on stainless steel plates through sol-gel spin-coating method. Coatings were examined by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), atomic force microscopy (AFM) and thermo-gravimetric analysis (TGA). 1.3-2.5 μm thick uniform coatings were obtained after curing at 500 °C for 1 h. The coatings adhered well to the steel substrates. It was determined by salt spray tests that the coatings enhance corrosion resistance. The aim of hydrophobic fluorosilane modification of hBN nanoparticles was to enrich hBN quantity on the top surface of the coatings. Coatings containing fluorosilane modified hBN nanoparticles presented slightly lower friction coefficient values than the other coatings.
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    Nature of the Ti-Ba interactions on the BaO/TiO2/Al 2O3 NOx storage system
    (2009) Andonova, S. M.; Şentürk, G. S.; Kayhan, E.; Ozensoy, E.
    A ternary oxide-based NO* storage material in the form of BaOZTiO2Zy-Al2O3 was synthesized and characterized. Thermally induced structural changes occurring on the surfaces of the TiO2Zy-Al2O3 and BaOZ TiO 2Zy-Al2O3 systems were studied in a comparative manner within 300-1273 K via X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and BET surface area analysis. The surface acidity of the studied oxide systems was also investigated via pyridine adsorption monitored by in-situ Fourier transform infrared (FTIR) spectroscopy. BaO/TiO2γ-Al 2O3 ternary oxide was synthesized by incorporating different loadings of (8-20 wt %) BaO onto the TiO2/γ Al 2O3 support material, which was originally prepared using the sol-gel method. In the TiO2Zy-Al2O3 binary oxide support material, anatase phase exhibited a relatively high thermal stability at T < 1073 K. The presence of TiO2 domains on the surface of the alumina particles was found to alter the surface acidity of alumina by providing new medium-strength Lewis acid sites. SEMZEDX results indicate that in the BaO/TiO2γ-Al2O3 system, TiO2 domains present a significant affinity toward BaO and/or Ba(NO3) 2 resulting in a strong Ti-Ba interaction and the formation of overlapping domains on the surface. The presence of TiO2 also leads to a decrease in the decomposition temperature of the Ba(N03) 2 phase with respect to the Ti-free Ba(N03) 2ZyAl2O3 system. Such a destabilization is likely to occur due to a weaker interaction between Ba(N03) 2 and y-Al203 domains in the ternary oxide as well as due to the change in the surface acidity in the presence of TiO 2. At relatively high temperatures (e.g., 873-1273 K) formation of complex structures in the form of BaTiO3, Ba1.23Al 2.46Ti5.54O16, BaTiO5, andor Ba x:AlyTizOn., were also observed. © 2009 American Chemical Society.
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    Robust superhydrophilic patterning of superhydrophobic ormosil surfaces for high-throughput on-chip screening applications
    (Royal Society of Chemistry, 2016) Beyazkilic, P.; Tuvshindorj, U.; Yildirim, A.; Elbuken, C.; Bayındır, Mehmet
    This article describes a facile method for the preparation of two-dimensionally patterned superhydrophobic hybrid coatings with controlled wettability. Superhydrophobic coatings were deposited from nanostructured organically modified silica (ormosil) colloids that were synthesized via a simple sol-gel method. On the defined areas of the superhydrophobic ormosil coatings, stable wetted micropatterns were produced using Ultraviolet/Ozone (UV/O) treatment which modifies the surface chemistry from hydrophobic to hydrophilic without changing the surface morphology. The degree of wettability can be precisely controlled depending on the UV/O exposure duration; extremely wetted spots with water contact angle (WCA) of nearly 0° can be obtained. Furthermore, we demonstrated high-throughput biomolecular adsorption and mixing using the superhydrophilic patterns. The proposed superhydrophilic-patterned nanostructured ormosil surfaces with their simple preparation, robust and controlled wettability as well as adaptability on flexible substrates, hold great potential for biomedical and chemical on-chip analysis.
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    Superhydrophobic, hybrid, electrospun cellulose acetate nanofibrous mats for oil/water separation by tailored surface modification
    (American Chemical Society, 2016) Arslan, O.; Aytac Z.; Uyar, Tamer
    Electrospun cellulose acetate nanofibers (CA-NF) have been modified with perfluoro alkoxysilanes (FS/CA-NF) for tailoring their chemical and physical features aiming oil-water separation purposes. Strikingly, hybrid FS/CA-NF showed that perfluoro groups are rigidly positioned on the outer surface of the nanofibers providing superhydrophobic characteristic with a water contact angle of ∼155°. Detailed analysis showed that hydrolysis/condensation reactions led to the modification of the acetylated β(1 → 4) linked d-glucose chains of CA transforming it into a superhydrophobic nanofibrous mat. Analytical data have revealed that CA-NF surfaces can be selectively controlled for fabricating the durable, robust and water resistant hybrid electrospun nanofibrous mat. The -OH groups available on the CA structure allowed the basic sol-gel reactions started by the reactive FS hybrid precursor system which can be monitored by spectroscopic analysis. Since alkoxysilane groups on the perfluoro silane compound are capable of reacting for condensation together with the CA, superhydrophobic nanofibrous mat is obtained via electrospinning. This structural modification led to the facile fabrication of the novel oil/water nanofibrous separator which functions effectively demonstrated by hexane/oil and water separation experiments. Perfluoro groups consequently modified the hydrophilic CA nanofibers into superhydrophobic character and therefore FS/CA-NF could be quite practical for future applications like water/oil separators, as well as self-cleaning or water resistant nanofibrous structures.
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    Template-free synthesis of organically modified silica mesoporous thin films for TNT sensing
    (American Chemical Society, 2010) Yildirim, A.; Budunoglu, H.; Deniz, H.; Güler, Mustafa O.; Bayındır, Mehmet
    In this paper, we present a facile, template-free sol−gel method to produce fluorescent and highly mesoporous organically modified silica (ORMOSIL) thin films for vapor phase sensing of TNT. An alkyltrifunctional, methyltrimethoxysilane MTMS precursor was used to impart hydrophobic behavior to gel network in order to form the spring back effect. In this way, porous films (up to 74% porosity) are obtained at ambient conditions. Fluorescent molecules are physically encapsulated in the ORMOSIL network during gelation. Fluorescence of the films was found to be stable even after 3 months, proving the successful fixing of the dye into the ORMOSIL network. The functional ORMOSIL thin films exhibited high fluorescence quenching upon exposition to TNT and DNT vapor. Fluorescence quenching responses of the films are thickness-dependent and higher fluorescence quenching efficiency was observed for the thinnest film (8.6% in 10 s). The prepared mesoporous ORMOSIL thin films have great potential in new sensor and catalysis applications.