Permeation studies on transparent multiple hybrid SiO<Subscript>2</Subscript>-PMMA coatings-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> barriers on PEN substrates

In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO₂ (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al₂O₃ thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al₂O₃ by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10⁻³ g/m²-day to about 9 × 10⁻⁵ g/m²-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al₂O₃ layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.     

TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hybrid nanomaterials: synthesis and variable UV-blocking properties

Silica and core–shell structured titania/silica (TiO₂/SiO₂) nanoparticles with particles size ranging from tens to hundreds of nanometers were prepared and deposited onto cotton fabric substrates by sol–gel process. The morphologies of the nanoparticles were characterized by field-emission scanning electron microscope (FE-SEM). The photocatalytic decomposition properties as well as UV-blocking properties of the fabrics treated with SiO₂ and TiO₂/SiO₂ nanoparticles were investigated.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Nanosized TiO<Subscript>2</Subscript> particles decorated on SiO<Subscript>2</Subscript> spheres (TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>): synthesis and photocatalytic activities

Nanosized TiO₂ and nano-anatase TiO₂ decorated on SiO₂ spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO₂ nano particle and TiO₂ grafted on SiO₂ sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO₂/SiO₂ particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO₂ particles.     

Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.     

Comparison of the annealing behavior of thin Ta films deposited onto Si and SiO<Subscript>2</Subscript> substrates

Structural changes at annealing temperatures (T_an) of 500–1,100°C were investigated for thin Ta films which were sputter-deposited onto pure Si substrates and onto thermally oxidized Si. In the as-deposited state, the Ta layers predominantly consist of metastable tetragonal -Ta, whereby the [001] texture is independent of the substrate material. At lower annealing temperatures, the microstructural evolution is essentially the same for both Ta films. Incorporation of O atoms causes an increase of the intrinsic compressive stress, and diffusion of C atoms into the Ta layer leads to the formation of Ta₂C. Additionally, a partial transformation of the original -Ta phase into a second phase with tetragonal unit cell (denoted as -Ta) occurs. For the Ta/Si system, the formation of a Ta–Si intermixing layer is initiated at T_an=550°C, and nucleation of crystalline TaSi₂ occurs at T_an=620°C. The formation of a second Ta silicide was not detected up to T_an=900°C. In the case of the Ta film deposited onto the SiO₂ substrate, the metastable -Ta and the -Ta transform completely into the thermodynamically stable cubic -Ta at T_an=750°C. A marked reaction with the substrate indicated by the formation of Ta₂O₅ and Ta₅Si₃ occurs at T_an=1,000°C.     

Mechanical and optical properties of SiO<Subscript>2</Subscript> thin films deposited on glass

The optical and mechanical properties of amorphous SiO₂ films deposited on soda-lime silicate float glass by reactive RF magnetron sputtering at room temperature were investigated in dependence of the process pressure. The densities of the films are strongly influenced by the process pressure and vary between 2.38 and 1.91 g cm^?3 as the pressure changes from 0.27 to 1.33 Pa. The refractive indices of the films shift between 1.52 and 1.37, while the residual compressive stresses in the deposited films vary in the range from 440 to 1 MPa. Hardness and reduced elastic modulus values follow the same trend and decline with the increase of process pressure from 8.5 to 2.2 GPa and from 73.7 to 30.9 GPa, respectively. The abrasive wear resistance decreases with the density of the films.     

Synthesis and characterization of a new hybrid TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> filler for lithium conducting gel electrolytes

This paper describes the synthesis and properties of a new type of ceramic fillers for composite polymer gel electrolytes. Hybrid TiO₂-SiO₂ ceramic powders have been obtained by co-precipitation from titanium(IV) sulfate solution using sodium silicate as the precipitating agent. The resulting submicron-size powders have been applied as fillers for composite polymer gel electrolytes for Li-ion batteries based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF/HFP) copolymeric membranes. The powders, dry membranes and gel electrolytes have been examined structurally and electrochemically, showing favorable properties in terms of electrolyte uptake and electrochemical characteristics in Li-ion cells.     

Phase relationships in the SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> system

Phase equilibria in a miscibility gap of the SiO₂-TiO₂ system were studied. A visual polythermal analysis and annealing of samples were performed in a Galakhov microfurnace. The microstructure and composition of the obtained samples were investigated by scanning electron microscopy and electron probe microanalysis. A critical analysis of the experimental data was made. Thermodynamically optimized based on the sub-regular solution model, a phase diagram of the SiO₂-TiO₂ system was constructed.     

FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

Dielectric and tunable properties of highly (110)-oriented (Ba<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>)TiO<Subscript>3</Subscript> thin films deposited on Pt/LaNiO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrates

Highly (110)-oriented Ba_0.65Sr_0.35TiO₃ films were deposited on Pt/LaNiO₃/SiO₂/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented ferroelectric films with perovskite structure. The as-grown Ba_0.65Sr_0.35TiO₃ films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16, respectively. These results indicate that the highly (110)-oriented Ba_0.65Sr_0.35TiO₃ film is a promising candidate for the applications in microwave tunable devices.     

Study on parylene/SiO<Subscript>2</Subscript> composite films for protection of KDP crystals

In this paper, parylene/SiO₂ composite films were reported to protect KDP crystals, indispensable cells in ICF experiments, from moisture. FTIR, UV-NIR spectra and XPS were used to analyze the properties of films. Laser damage threshold of films was also measured. With porous silica coating on surface of parylene film, the transmittance of dual layers can be raised to more than 91%. KDP crystals with poly(p-xylylene)/SiO₂ coating could work well in ambient atmosphere for more than half a year.     

Preparation and optical characterization of catalyst free SiO<Subscript>2</Subscript> sonogel hybrid materials

The synthesis of sol-gel materials induced by ultrasonic irradiation (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic, mechanical and optical properties. Ultrasonic irradiation, instead of commonly used basic- or acidic-catalyst was used to produce acoustical cavitation within the liquid H₂O/tetraethyl-ortosilicate (TEOS) reactants. This procedure forms a hydrolyzed-TEOS colloidal dispersion (sol) which produces, after drying, a highly pure SiO₂ network. The resulting SiO₂ glass exhibits high porosity and allows the inclusion of several organic compounds in the colloidal sol-state. Novel, optical active synthesized liquid crystalline (LC)-azo-compounds, bent shaped mesogens, cis- and trans-poly(1-ethynylpyrene)s, as well as fullerene (C₆₀) spheres and classical organic dyes were successfully incorporated as dopant agents within the novel catalyst free (CF) SiO₂-sonogel host matrix. Absorption and fluorescence spectroscopy studies were carried out in order to characterize the optical performance of both the CF-sonogel and several hybrid composites The pulsed laser photoacoustic technique (LPAT) was implemented to determine thermodynamic phase transitions of LC-based hybrids and laser induced damage (photo-degradation) in dye-based composites. Finally, comparative morphology studies between undoped reference samples and some doped composites were performed by Atomic Force Microscopy (AFM), where an optimal TEOS/dopant concentration ratio, to obtain good mechanical properties among the studied samples, has been found.     

Photoelectrochemical study of electrodeposited TiO<Subscript>2</Subscript> thin films onto F:SnO<Subscript>2</Subscript> substrates

TiO₂ thin films have been effectively fused onto F:SnO₂ (FTO) substrates via the electrodeposition method. The influence of deposition temperature on the synthesis of F:SnO₂ substrates and relative information of as-deposited and annealed TiO₂ thin films have been studied. Novel TiO₂ microspheres are detected on F:SnO₂ substrates at an optimized electrodeposition potential. Raman bands approve the creation of single-anatase-phase TiO₂. The optimized deposition surroundings show a decrease in the band gap of F:SnO₂ substrates and TiO₂ thin films. The determined photoelectrochemical properties of annealed TiO₂ thin films indicate a fill factor of 51% and power conversion efficiency of 0.15% for application in solar cells.     

Carbon ceramic electrodes modified with mixed oxides SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> for determination of levofloxacin

The preparation of a carbon ceramic electrode modified with SnO₂ (CCE/SnO₂) using tin dibutyl diacetate as precursor was optimized by a 2³ factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO₂ provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO₂, indicating that SnO₂ when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10^?5 to 6.97×10^?4 mol L^?1 with quantification and detection limits of 3.80×10^?5 mol L^?1 (14.07 mg L^?1) and 1.13×10^?5 mol L^?1 (4.18 mg L^?1), respectively.     

Stabilization of Oil-in-Water Emulsions with SiO<Subscript>2</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles

Stabilization of oil-in-water Pickering emulsions with SiO₂ and Fe₃O₄ nanoparticles has been studied. Emulsions containing three-dimensional gel networks formed by aggregated nanoparticles in the dispersion media have been shown to be stable with respect to flocculation, coalescence, and creaming. Concentration ranges in which emulsions are kinetically stable have been determined. Stabilization with mixed Ludox HS-30 and Ludox CL SiO₂ nanoparticles leads to the formation of stable emulsions at a weight ratio between the nanoparticles equal to 2 and pH 6.7. In the case of stabilization with Ludox CL and Fe₃O₄ nanoparticles, systems resistant to aggregation and sedimentation are obtained at pH 8. The use of mixed Ludox HS-30 and Fe₃O₄ nanoparticles has not resulted in the formation of emulsions stable with respect to creaming, with such emulsions appearing to be resistant only to coalescence at pH 2–6.     

Preparation and characterization of poly(phthalazinone ether ketone)/SiO<Subscript>2</Subscript> hybrid composite thin films with low friction coefficient

Organic–inorganic poly(phthalazinone ether ketone) (PPEK)/SiO₂ hybrid composite thin films were prepared by the dip-coating method on pre-cleaned glass substrates. The covalent bonds between organic and inorganic phases were introduced by an in-situ O-acylation reaction of isocyanatopropyltriethoxysilane (ICPTES) with the borohydride-reduced PPEK forming a polymer bearing triethoxysilyl groups. Theses groups were subsequently hydrolyzed with tetraethoxysilane (TEOS) and allowed to form a network via a sol–gel process. The polymer hybrid composite exhibited good thermal stability and a higher glass transition temperature as compared with the pure resin. Atomic force microscope, water contact angle measurement and scanning electron microscope were used to characterize the polymer hybrid thin films. The tribological experiment showed that the films have very low friction coefficient (about 0.1) and good anti-wear properties, without failure even after sliding for 18,000 s under modest loads. The improved tribological properties of the modified substrate were attributed to good adherence of PPEK/SiO₂ hybrid films on the substrate and synergy of both PPEK matrix and silica particles.