Mechanical properties and microstructure of bioactive ORMOSILs containing silica particles

We synthesized organically modified silicate (ORMOSILs) gels with colloidal silica (CS) (AEROSIL®) starting from polydimethylsiloxane (PDMS), tetraethoxysilane (TEOS) and calcium nitrate (Ca(NO₃)₂·4H₂O) through sol–gel processing. Dynamic mechanical analysis indicated that relative height of the tanδ peak at about −100 °C increased with an increase in the relative content of the inorganic components. This peak growth was accounted for by the relative increase in PDMS–colloidal silica particle interactions. The colloidal silica could control the mechanical behavior of the hybrids. The gel of a specific composition could deposit apatite within 3 days of soaking in the simulated body fluid (SBF), since it included many calcium ions on the surface.     

Studies on the effect of organic additives on the monolithicity and optical properties of the rhodamine 6G doped silica xerogels

Rhodamine 6G (R6G) laser dye doped silica xerogels were prepared by sol–gel processing using tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] precursor, citric acid (CTA) catalyst and ethanolic R6G in the presence of various organic additives such as formamide (FA), N′methylformamide (N′MF), dimethylformamide (DMF), acetamide (AA), glycerol (GLY), oxalicacid (OXA), ethyleneglycol (EG) and diethyleneglycol (DEG). The organic additive/TEOS molar ratio was varied from 0.001 to 0.1 by keeping the TEOS/EtOH/H₂O/CTA/R6G molar ratio constant at 1:5:7:1.2×10⁻³:9.2×10⁻⁶. It was found from the spectral studies of the additive modified R6G doped silica xerogels that the absorption maxima at 530 nm and emission maxima at 565 nm were increased with the addition of organic additive and with the increase of the additive/TEOS molar ratio. The transparency of the R6G doped silica xerogels was increased with the increase of additive/TEOS molar ratio from 0.001 to 0.1 with OXA, DEG and EG and in the case of DMF, N′MF, FA, AA and GLY, the transparency of the samples increased up to 0.014 of additive/TEOS molar ratio and then decreased for >0.014 of additive/TEOS molar ratio. Monolithic samples were obtained with all the organic additives. The percentage volume shrinkage of the samples was less EG and DEG and more with OXA additives.     

Structural and optical properties of vanadium pentoxide sol–gel films

The V₂O₅ films were obtained using sol–gel procedure. The composition and mesostructure of the layers were investigated with the UV and Raman spectroscopy, as well as with electron microscopy. We showed that the changes in the properties of thin layers accompanying the variation of film thickness are connected with the changes in the microstructure of the film rather than with changes in its composition. The thin V₂O₅ layers obtained in the present study are composed of disordered clusters; their mean size is 4–13 nm.     

Stability of second-order nonlinear optical properties in sol–gel matrix bearing silylated chalcone and disperse red 1

We report the syntheses of two triethoxysilanes for thin film fabrication. One silane (SGDR1) contains disperse red 1 (DR1) which is a second-order nonlinear optical (NLO) active chromophore. The other silane (SGCHC) bears a chalcone derivative. In order to improve the poor temporal stability of second-order NLO effects in the resulting poled sol–gel film, photo-crosslink was induced between the double bonds in chalcone units after mixing SGDR1 and SGCHC. Under UV exposure, the photocrosslink was studied with UV–visible absorption and IR vibrational spectroscopy. The decaying behavior of the molecular order parameter (A₂) after corona poling was investigated using polarized absorption spectroscopy (PAS). Second-order non-linear optical properties of the sample were studied using second-harmonic generation (SHG) and linear electro-optic (E/O) signal measurement. Poled and UV-cured film of SGDR1/SGCHC exhibited much better stability than thermally poled sample with respect to the molecular order parameter and linear electro-optic effect.     

Dielectric and piezoelectric properties of sol–gel derived Ca doped PbTiO3

Synthesis of Ca doped PbTiO₃ powder by a chemically derived sol–gel process is described. Crystallization characteristics of different compositions Pb_1−xCa_xTiO₃ (PCT) with varying calcium (Ca) content in the range x = 0–0.45 has been investigated by DTA/TGA, X-ray diffraction and scanning electron microscopy. The crystallization temperature is found to decrease with increasing calcium content. X-ray diffraction reveals a tetragonal structure for PCT compositions with x ≤ 0.35, and a cubic structure for x = 0.45. Dielectric properties on sintered ceramics prepared with fine sol–gel derived powders have been measured. The dielectric constant is found to increase with increasing Ca content, and the dielectric loss decreases continuously. Sol–gel derived Pb_1−xCa_xTiO₃ ceramics with x = 0.45 after poling exhibit infinite electromechanical anisotropy (k_t/k_p) with a high d₃₃ = 80 pC/N, ′ = 298 and low dielectric loss (tan δ = 0.0041).     

Correlation of sol–gel processing parameters with microstructure and properties of a ceramic product

A very high purity MgAl₂O₄ spinel precursor can be prepared via a low temperature process called “Oxide One Pot Synthesis (OOPS)”. Sol–gel processing of such precursors offers the opportunity to prepare spinels with controlled microstructures, which is key to optimizing their properties for application as humidity sensors. Sol–gel processing of a double alkoxide precursor was carried out in buffer solutions in the pH range 8–12, to investigate the effect on the physical properties of the calcined ceramic products. The structure and morphology of the latter were characterized using FTIR, XRD, SEM and BET surface area measurements. Sol–gel processing results in a calcined product with a narrow pore size distribution, which contains a spinel phase of high crystallinity. At higher pH values, increasing amounts of an -Al₂O₃ phase are formed. At all pH values, the calcined product exhibits high water adsorption, up to 0.312 g H₂O/g sample.     

Photoluminescence properties of an oligo-phenylkene vinylene derivative doped in polymer/silica hybrid sol–gel matrix

An oligo-phenykene vinylene derivative 4,4′-(1,4-phenylene dithenylene)-bis-(N-methyl pyridinium iodide) (OPVD) was introduced into poly(hydroxyethyl methacrylate) (PHEMA)-impregnated silica composite film by the sol–gel process. The X-ray diffraction and UV–VIS reveal that this method can restrict the crystallization of OPVD and OPVD molecules tend to form J-aggregates in the composite film. The results of photoluminescence of OPVD in the composite film indicate that as compared with OPVD itself, the emission peak of OPVD in the composite film undergoes a blue shift about 80 nm, fluorescence intensity enhances and the photostability is much better, which make such composite film of more practical significance.     

Photocatalyzed degradation of flumequine by doped TiO2 and simulated solar light

Titanium dioxide was obtained in its pure form (TiO₂) and in the presence of urea (u-TiO₂) and thiourea (t-TiO₂) using the sol–gel technique. The obtained powders were characterized by BET surface area analysis, Infrared Spectroscopy, Diffuse Reflectance Spectroscopy and the Rietveld refinement of XRD measurements. All the prepared catalysts show high anatase content (>99%). The a and b-cell parameters of anatase increase in the order TiO₂ < u-TiO₂ < t-TiO₂, while the c-parameter presents the opposite trend. Because of the interplay in cell dimensions, the cell grows thicker and shorter when prepared in the presence of urea and thiourea, respectively. The cell volume decreases in the order t-TiO₂ > u-TiO₂ > TiO₂. The photocatalytic activities of the samples were determined on flumequine under solar-simulated irradiation. The most active catalysts were u-TiO₂ and t-TiO₂, reaching values over 90% of flumequine degradation after 15 min irradiation, compared with values of 55% for the pure TiO₂ catalyst. Changing simultaneously the catalyst amount (t-TiO₂) and pH, multivariate analysis using the response surface methodology was used to determine the roughly optimal conditions for flumequine degradation. The optimized conditions found were pH below 7 and a catalyst amount of 1.6 g L⁻¹.     

Effects of rare-earth concentration and heat-treatment on the structural and luminescence properties of europium-doped zirconia sol–gel planar waveguides

Sol–gel zirconia films doped with Eu³⁺ concentrations ranging from 0.2% to 10%, were prepared by dip-coating a solution of the starting precursor, zirconium n-propoxide, ethanol, methanol, water, acetic acid and europium nitrate on glass and SiO₂/Si wafer substrates. The ZrO₂sol thus synthesized remains stable for several months. Structural characterization of the zirconia films was performed using Waveguide Raman Spectroscopy. These films present an amorphous phase up to an annealing temperature of 400 °C. Above 400 °C the matrix evolves towards a metastable tetragonal phase. This transformation was found to depend on the concentration of Eu³⁺ ions. Indeed, while for samples doped with 0.2% Eu³⁺ this transformation occurs around 450 °C, in the case of 10% of Eu³⁺ ions, the transition is pushed off to 500 °C. The optical losses of these waveguides were found to be about 0.3 dB cm⁻¹ for samples annealed at 400 °C. The surfaces of the films were characterized using Atomic Force Microscopy and the roughness was measured. The Eu-doped films were investigated using Waveguide Photoluminescence Spectroscopy. The dynamical behaviour of the Eu³⁺ emissions indicated that concentration quenching effect is not observed even when the matrix is doped up to 10%.     

Preparation and optical properties of sol–gel derived Er-doped Al2O3–Ta2O5 films

Thin films of the system xAl₂O₃–(100 − x)Ta₂O₅–1Er₂O₃ were prepared by a sol–gel method and a dip-coating technique. The influences of the composition and the crystallization of the films on Er³⁺ optical properties were investigated. Results of X-ray diffraction indicated that the crystallization temperature of Ta₂O₅ increased from 800 to 1000 °C with increased values of x. In crystallized films, the intensities of the visible fluorescence and upconversion fluorescence tend to decrease with an increase in x values, due to the high phonon energy of Al₂O₃; the strongest fluorescence is observed in a crystallized film for x = 4 heat treated at 1000 °C. In amorphous films obtained by heat treatment at relatively low temperatures the Er³⁺ fluorescence could not be observed because strong fluorescence from organic residues remaining in the films thoroughly covered the Er³⁺ fluorescence. On the other hand, the Er³⁺ upconversion fluorescence in the amorphous films was observed to be stronger than that in the crystallized films. The strongest upconversion fluorescence is observed in an amorphous film for x = 75 heat treated at 800 °C.     

Influence of processing conditions on the luminescence of YVO4:Eu nanoparticles

Single-phase YVO₄:Eu³⁺ nanopowders were synthesized by sol–gel combustion method using citric acid as a chelating agent and reducer. The microstructures and photoluminescence (PL) properties of the as-prepared YVO₄:Eu³⁺ nanopowders were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and PL spectroscopy. The luminescence intensities of the YVO₄ nanoparticles doped with 5 mol% Eu³⁺ ions strongly depended on the calcination temperature, the molar ratio of citric acid to nitrates and the amounts of the Li⁺ additive.     

Preparation and optical properties of sol–gel derived organic–inorganic hybrid waveguide films doped with disperse red 1 azoaromatic chromophores

We report here on TiO₂/organically modified silane (ormosil) organic–inorganic hybrid waveguide films doped with disperse red 1 (DR1) azoaromatic chromophores and derived by a low-temperature sol–gel process for photonic applications. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane mixed with tetrabutyl titanate are used as matrix precursor for the hybrid films. Third-order nonlinear and photo-responsive properties of the hybrid films are studied by using a z-scan technique and a UV–vis absorption spectroscopy. Results indicate that the hybrid films have a large third-order nonlinear susceptibility and an obvious trans-to-cis photoisomerization under UV light irradiation. The planar waveguide and structural properties of the hybrid films are also characterized by a prism coupling technique, thermal gravimetric analysis, and Fourier-transform infrared spectroscopy. These results indicate that the as-prepared hybrid films are promising candidates for integrated optics and photonic applications, which allow directly integrating on the same chip waveguide devices with the functionalized devices.     

Study of electrical and optical properties of Mn doped ZnS clusters

A simple, easy approach to the synthesis of manganese Mn doped zinc sulphide (ZnS) clusters is reported. The synthesis of Mn–ZnS clusters involved mixing and drying of zinc acetate, sodium sulphide and acrylic acid in appropriate ratio and adding Mn at proper conditions. These clusters were trapped in polyacrylic acid (PAA) to form PAA capping to provide stability. The clusters were characterized using high resolution SEM for morphological investigation; XRD for its crystalline nature; photoluminescence (PL) for optical characterization and electrical conductivity measurement. Clusters of Mn–ZnS were formed of the size ~ 10 nm.     

Microstructural, photocatalysis and electrochemical investigations on CeTi2O6 thin films

The properties of sol–gel derived CeTi₂O₆ thin films deposited using a solution of cerium chloride heptahydrate and titanium propoxide in ethanol are discussed. The effect of annealing temperature on structural, optical, photoluminescence, photocatalysis and electrochemical characteristics has been examined. Lowest annealing temperature for the formation of crystalline CeTi₂O₆ phase in these samples is identified as 580 °C. The optical transmittance of the films is observed to be independent of the annealing temperature. The optical energy bandgap of the 600 °C annealed film for indirect transition is influenced by the presence of anatase phase of TiO₂ in its structure. Fourier transform infrared spectroscopy investigations have evidenced increased bond strength of the Ti–O–Ti network in the films as a function of annealing temperature. The photoluminescence intensity of the films has shown dependence on the annealing temperature with the films fired at 450 °C exhibiting the maximum photoluminescence activity. The decomposition of methyl orange and eosin (yellow) under UV–visible light irradiation in the presence of crystalline CeTi₂O₆ films shows the presence of photoactivity in these films. The photocatalytic response of CeTi₂O₆ films is found to be superior to the TiO₂ films. In comparison to crystalline films, the amorphous films have shown superior electrochemical characteristics. The 500 °C annealed amorphous films have exhibited the most appropriate properties for incorporation in electrochromic devices comprising tungsten oxide as the primary electrochromic electrode.     

Preparation and magnetic properties of barium hexaferrite nanorods

The barium hexaferrite nanorods were successfully prepared by sol–gel technique combined with polymethylmethacrylate as template. The crystal structure, morphology and magnetic properties of BaFe₁₂O₁₉ with different shape were investigated with X-ray diffraction, field emission scanning electron microscope and vibrating sample magnetometry. The results show that diameters and lengths of magnetic nanorods are about 60 nm and 300 nm, respectively. The coercivity of rod-shaped BaFe₁₂O₁₉ is increased to 5350 Oe, in comparison with 4800 Oe with plate-shape. The formation mechanism of BaFe₁₂O₁₉ nanorods and reasons resulting in high coercivity are discussed.     

Synthesis, phase transformation and dielectric properties of sol–gel derived Bi2Ti2O7 ceramics

Sol–gel derived Bi₂Ti₂O₇ ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi₂Ti₂O₇ phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ at 850–1150 °C. The single phase of Bi₂Ti₂O₇ reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm⁻² and coercive field is 24 kV cm⁻¹. Thus, the Bi₂Ti₂O₇ did not exhibit ferroelectricity, but the mixed phase of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ did.     

Preparation, patterning and luminescent properties of nanocrystalline Gd2O3:A (A=Eu, Dy, Sm, Er) phosphor films via Pechini sol–gel soft lithography

Nanocrystalline Gd₂O₃:A (A=Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd₂O₃ phosphor films due to an efficient energy transfer from Gd₂O₃ host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd³⁺ in Gd₂O₃ films, respectively.     

Preparation of aluminum doped zinc oxide films and the study of their microstructure, electrical and optical properties

Aluminum doped zinc oxide (AZO) polycrystalline thin films were prepared by sol-gel dip-coating process on optical glass substrates. Zinc acetate solutions of 0.5 M in isopropanol stabilized by diethanolamine and doped with a concentrated solution of aluminum nitrate in ethanol were used. The content of aluminum in the sol was varied from 1 to 3 at.%. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 300 °C and 500 °C for 1 h. The coatings have been characterized by X-ray diffraction, UV-Visible spectrophotometry, scanning electron microscopy, and electrical resistance measurement. The ZnO:Al thin films are transparent (∼ 90%) in near ultraviolet and visible regions. With the annealing temperature increasing from 300 °C to 500 °C, the film was oriented more preferentially along the (0 0 2) direction, the grain size of the film increased, the transmittance also became higher and the electrical resistivity decreased. The X-ray diffraction analysis revealed single-phase ZnO hexagonal wurtzite structure. The best conductors were obtained for the AZO films containing 1 at.% of Al, annealed at 500 °C, 780 nm film thickness.     

Functionalization of multi-wall carbon nanotubes with silane and its reinforcement on polypropylene composites

Multi-wall carbon nanotubes (MWCNTs) were functionalized with a silane coupling agent. The MWCNTs were first coated with inorganic silica by a sol–gel process and then grafted with 3-methacryloxypropyltrimethoxysilane (3-MPTS). The grafting of 3-MPTS onto the MWCNTs surface was confirmed by Fourier-transform infrared spectroscopy, transmission electron microscopy and X-ray photoelectron spectra. Polypropylene (PP) composites filled with raw MWCNTs and functionalized MWCNTs were prepared and characterized. The PP/3-MPTS functionalized MWCNTs composite has higher tensile strength than the PP/raw MWCNTs composite. This is explained by the organic groups of 3-MPTS grafted onto the surface of MWCNTs.     

Deposition and photoluminescence of sol–gel derived Tb:Zn2SiO4 films on SiO2/Si

Tb³⁺ doped Zn₂SiO₄ films have been deposited on SiO₂ buffered Si wafers by sol–gel method. The structures of these films have been investigated with X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results revealed that these films were composed of nanometer-size grains with a Willemite structure and had smooth surfaces. Photoluminescence measurements of the films showed a strong emission from ⁵D₄ to ⁷F₅ at 544 nm. The blue emission from ⁵D₃–⁷F_j was depressed because of cross-relaxation effect. The decay kinetics of the ⁵D₄–⁷F₅ green emission was studied and a best fitting was obtained by a double exponential function. The lifetime of the excited ⁵D₄ state is estimated to be 5.2 ms.