Fabrication and characterization of superhydrophobic silica nanotrees

Superhydrophobic silica nanotrees were obtained by sol–gel method with hybrid silica sol and jelly-like resorcinol formaldehyde resin. Rough surfaces were obtained by removing the organic polymer at high temperature. After the films with rough surface were modified by trimethylchlorosilane (TMCS), the wettability of the film changed from superhydrophilic to superhydrophobic. The surface roughness of the silica nanotrees film is about 20 nm, and it is transparent and superhydrophobic with a water contact angle higher than 150°.     

The influence of annealing on electrochromic properties of Al–B–NiO thin films prepared by sol–gel

Al–B–NiO thin films were prepared using the sol–gel process and deposited on Indium tin oxide (ITO)-coated glass substrates via the dip-coating technique for the purpose of developing high performance electrochromic materials. The influence of the anneal on the structural and electrochromic properties of Al–B–NiO films is reported. Thermogravimetry (TG) and differential thermal analysis (DTA), cyclic voltammetry measurements (CV), UV spectrophotometer, atomic force microscopy (AFM) and X-ray diffraction (XRD) have been used to investigate the structural and electrochromic properties. The thickness of the films was determined by spectrophotometric analysis in 350–1,000 nm wavelength. Results showed that the Al–B–NiO thin films treated at high temperature have both the excellent electrochromic properties and good reversibility. The transmittance change (ΔT) of the film treated at 500 °C reaches still ~50% at the wavelength of 550 nm. The microstructure and the surface morphology were considered to play an important role in the electrochromic properties with different temperatures.     

Sol–gel preparation and properties of hydroxypropylcellulose–titania hybrid thin films

Hydroxypropylcellulose (HPC)–titania hybrid thin films were prepared by sol–gel method where titanium tetraisopropoxide Ti(OC₃H₇ ⁱ )₄ was hydrolyzed under acidic conditions in the presence of HPC, followed by dip-coating and drying at 120 °C for 24 h. The viscosity average molecular weight of HPC was 55,000–70,000 or 110,000–150,000, and the TiO₂/(HPC + TiO₂) mass ratio ranged from 0 to 1, which was calculated on the assumption that all Ti(OC₃H₇ ⁱ )₄ is converted into TiO₂. The films were 0.35–1.0 μm thick, transparent in visible region and opaque in ultraviolet (UV) region, where the optical absorption coefficient in UV region increased with increasing titania content. The refractive index increased with increasing titania content, ranging from 1.6 to 1.8 for the hybrid thin films. The pencil hardness increased from 6B to 5H, the durability in hot water significantly increased and the contact angle of water on films increased from 35° to 89° with increasing titania content. Crack-free films could be deposited on organic polymer substrates irrespective of titania or HPC contents, where cracking did not occur at higher HPC contents even when the substrate was bent.     

Elaboration of thin colloidal silica films with controlled thickness and wettability

Silica films with controlled thickness and wettability have been formed by sequential adsorption of colloidal silica nanoparticles and a cationic polyelectrolyte (poly(allylamine hydrochloride) or poly(diallyldimethylammonium chloride)) was used as the binding agent. Whatever be the conditions used, the structure of films appeared dense and non-porous. Thicknesses varying from 12 to 430 nm and wettability varying from 5 to 60° were obtained when the pH or concentration of the silica solution was varied. Quartz crystal microbalance measurements evidenced the formation of regular and reproducible thin films mainly composed of silica nanoparticles. These films contained few polycations due to the formation of long-distance charge pairs between silica nanoparticles and polycations.     

Preparation and characterization of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3-δ</Subscript> thin-film membrane on porous support by dip-coating method

Perovskite-type La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) thin-film membrane prepared by modified Pechini sol–gel process, was successfully deposited on porous support of similar composition using dip-coating method. Fine grain and crack-free film with perovskite structure was obtained at sintering temperature of 800 °C and dwelling time of 60 min. The cross-sectional image indicated that LSCF6428 thin-film membrane coated on the porous support showed excellent adhesion to the support with uniform thickness. The minimum dense layer thickness obtained by dip-coating method was around 0.5 μm. It was found that the oxygen permeability of the supported thin film was lower than that of the perovskite support, which indicated that the pores of the support were reduced by thin-film deposition on the support surface. The reduction in the pore size led to the more selective permeation mechanism contributes to the overall permeation. Successful deposition of LSCF6428 thin-film membrane on porous support can be considered as a promising technique for the preparation of oxygen separation membrane.     

Preparation of LiCoPO<Subscript>4</Subscript> powders and films via sol–gel

Lithium intercalation materials are of special interest as cathodes in rechargeable batteries. An uncomplicated sol–gel process has been used for the synthesis of Li–Co phosphates powders and, for the first time, of LiCoPO₄ films. The powders were prepared from aqueous solutions, containing Li, Co and phosphate precursors to which acid citric and ethylene glycol was added, during the drying process at 75 °C. The X-ray diffraction patterns of the prepared powders confirmed the presence of LiCoPO₄ with an olivine-like structure as main phase. The morphological investigations of the powder showed a platelet-like structure with an average grain size of 0.75 μm. The films of LiCoPO₄ were deposited onto ITO glass substrates with the combination of the dip-coating process under the same conditions. Finally, the films were annealed in inert atmosphere at 300 °C. The morphological investigations reveal a smooth and homogeneous surface of the prepared Li–Co phosphate films. The preliminary electrical investigation on the prepared LiCoPO₄ films showed lithium ions electrochemical activity in the range 3.0–4.5 V.     

Improved sintering and electrical properties of La-doped CeO<Subscript>2</Subscript> buffer layer for intermediate temperature solid oxide fuel cells using doped LaGaO<Subscript>3</Subscript> film prepared by screen printing process

Effects of a sintering agent for La-doped ceria (LDC) as a buffer layer to prevent a chemical reaction between Ni in anode and Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte during sintering were studied for improving sintering and electrical properties. Electrochemical performance of anode-supported solid oxide fuel cells (SOFCs) using LDC and LSGM films prepared by screen printing and co-sintering (1,350 °C) was also investigated. The prepared cell with dense LDC (ca. 17 μm) and LSGM electrolyte (ca. 60 μm) films showed an open circuit voltage close to the theoretical value of 1.10 V and a high maximum power density (0.831 W cm^–2) at 700 °C. The addition of 1 wt.% LSGM to porous LDC buffer layer was effective for improving the sintering density and electrical conductivity, resulting in the high power density due to the decreased internal resistance loss.     

Influence of single layer thickness on the performance of undoped and Mg-doped CuCrO<Subscript>2</Subscript> thin films by sol–gel processing

Transparent conductive thin films of copper chromium oxide were processed on borosilicate glass by sol–gel technique. The resistivity of the films was decreased by lowering the single layer thickness of multi-layer stacks deposited by dip-coating, as well as by doping with magnesium. The additional effort of increasing the number of coating cycles from four to fifteen and sintering after each coating resulted in denser films with increased crystallite size. But whereas conductivity was improved by this procedure, the transmittance of the thin films simultaneously dropped by more than 10%. The optimum values obtained for an Mg-doped sample were ρ = 0.38Ω cm at T = 26.8%.     

Effect of co-sintering temperature on the performance of SOFC with YSZ electrolyte thin films fabricated by dip-coating method

Anode-supported yttria-stabilized zirconia (YSZ) electrolyte thin films were fabricated by the dip-coating method using the simple methylethylketone/ethanol-based YSZ suspension. Influences of the sintering temperature on the performance of solid oxide fuel cells were studied. Fully dense YSZ electrolyte thin films were obtained after being sintered at 1,300 °C as well as at 1,400 or 1,500 °C through SEM observation. The open circuit voltages of the cells all reached above 1.10 V at the testing temperatures. The testing results proved that both the anode performance and the electrolyte conductivity sintered at 1,300 °C were superior to those sintered at 1,400 or 1,500 °C. Investigation on the cell voltage drop under operation condition revealed, that the sintering temperature has more significant effect on the performance of the electrodes than on the electrolyte.     

Functionalisation of the template-free and template-structured silica films synthesised on glass substrates by sol–gel technique

Possibility of the post-synthesis functionalisation of the template-free and template-structured silica films of ca. 200 nm thickness on glass slides was evaluated. The films were prepared by dip-coating from TEOS sol–gel precursor in the absence or presence of CTAB template. It has been found out that the template-structured silica films can be functionalised with Ag nanoparticles via [Ag(NH₃)₂]NO₃ ion-exchange or with adsorbed Methylene Blue (MB) cationic dye due to the presence of the well-organised mesopores after template removal. In contrast, only the external geometric surface of the template-free silica films appeared to be accessible for modifier molecules. Possibility of functionalisation of the multi-layered template-structured silica film depends on the sequence of dip-coating and calcination steps upon their preparation. When preparation includes reiteration of dip-coating and calcination steps, only the latest top silica film appears to be accessible to modifier molecules. When preparation includes successive dip-coating cycles accomplished by calcination of the final multi-layered film, all pores appear to be accessible since their formation occurs via simultaneous removal of the template molecules over the whole thickness of the multi-layered template-structured silica film.     

The influence of polyvinylpyrrolidone on thick and optical properties of BaTiO<Subscript>3</Subscript>:Er<Superscript>3+</Superscript> thin films prepared by sol–gel method

Erbium (Er³⁺) 0.5% mol doped barium titanate (BaTiO₃) thin films were elaborated via sol–gel method and dip-coating technique using titanium alkoxide and barium pentanedionate. Two syntheses were performed [with and without polyvinylpyrrolidone (PVP)] in order to obtain thick films. The BaTiO₃:Er³⁺ thin films prepared from the sol with PVP were elaborated with 1 layer and those without PVP and were elaborated with 17 layers. In both cases, the films were deposited on silica quartz substrates. Both BaTiO₃:Er³⁺ films presented a cubic phase, as determined by X-ray diffraction. BaTiO₃:Er³⁺ films elaborated with PVP via single-step dip coating produced crack-free films with thicknesses of ~800 nm. SEM micrographs for the obtained BaTiO₃:Er³⁺ films revealed high homogeneity and density. Mapping images obtained from BaTiO₃:Er³⁺ revealed homogeneous distribution of Er³⁺ ions on the surface. XPS analyses of the chemical state and chemical environment of the constituent elements in the compositions showed that Er³⁺ ions in (Ba_1−x Er _x )TiO₃ are in mixed valence of Er³⁺/Er²⁺. The BaTiO₃:Er³⁺-PVP film exhibited luminescent properties under near-infrared excitation, as revealed by green emissions. The BaTiO₃:Er³⁺-PVP film has good potential for optical applications.     

Preparation of amino-functionalized mesoporous silica thin films with highly ordered large pore structures

Highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of triblock copolymer Pluronic P123 surfactant species under acidic conditions by sol-gel dip-coating. The effect of the sol aging on thin films organization is systematically studied, and the optimal sol aging time is obtained. The amino-functionalized mesoporous silica thin films exhibit a long-range ordering of 2D hexagonal (p6mm) mesostructure with a large pore size of 8.3 nm, a large Brunauer–Emmett–Teller (BET) specific surface area of 680 m² g⁻¹ and a large pore volume of 1.06 cm³ g⁻¹ following surfactant extraction as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM), and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for the amino-functionalized mesoporous silica thin films is calculated to be 3.2 amino-groups per nm². Moreover, the functionalized thin films display improved properties for immobilization of cytochrome c in comparison with pure-silica mesoporous thin films.     

Sol–gel elaboration and structural investigations of Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> planar waveguides

Europium actived Lu₂O₃ sol–gel transparent and crack free films were deposited by dipping on silica substrates. The film microstructure was studied by waveguide Raman spectroscopy (WRS) with annealing temperatures from 400 up to 1,000 °C and X-ray diffraction. The WRS results and TEM observations were correlated and showed that crystallization of the lutetium oxide phase into cubic phase occurs at 600 °C and is stable up to 1,000 °C, the crystallite size increasing between ±38 nm with annealing temperature ranging from 600 to 1,000 °C. Opto-geometrical parameters were determined by m-lines spectroscopy using four different wavelengths of laser sources in order to confirm the step-index profile of the as-prepared waveguides. The Eu³⁺ doped films heat-treated at 1,000 °C presented a constant thickness for the wavelengths 493, 543, 594 and 632.8 nm and a density of 8.4 g cm⁻³. High-resolution X-ray images were obtained.     

Preparation of mesoporous hydroxyapatite films used as biomaterials via sol–gel technology

The mesoporous hydroxyapatite films (MHFs) have been developed on glass slides by sol–gel dip-coating technology using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent and the effects of pH value and calcination temperatures on the surface morphology and the mesostructure have been discussed. The phase composition, surface morphology, mesostructure and surface wettability were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, N₂ adsorption–desorption isotherms and water contact angle analyzer, respectively. The continuous thin films consisted of mesoporous hydroxyapatite particles (~50 nm) with mesopores (~2 nm) within the particles have been obtained after being prepared in the condition of concentration of CTAB 0.09 M, pH of sol 3.0, reaction temperature 60 °C and calcination temperature 550 °C. In vitro cell culture, the mesoporous films, which possessed favorable surface wettability resulting from the special pore structure, have exhibited a high degree of MC3T3-E1 cell attachment and spreading, suggesting a better bioactivity. Therefore, the MHFs can be expected to have potential application for decreasing the ion release of implant and improving the bioactivity as a coating on material surface.     

Sol–gel-derived nanocomposite coatings filled with inorganic fullerene-like WS<Subscript>2</Subscript>

Silica coatings filled with nanoscaled inorganic fullerene-like tungsten disulphide (IF-WS₂) have been prepared through a sol–gel process on stainless steel substrates, and the structure and mechanical properties have been investigated. The precursor was prepared from a mixture of colloidal silica, 3-glycidoxypropyltrimethoxysilane (GLYMO), water and ethanol, adjusted to pH 4 with HNO₃. In this solution WS₂ is dispersed and in some cases immediately before coating ethylenediamine (ED) is added. The stainless steel substrates are dip-coated, dried in air and heat-treated in the temperature range of either 150–360 °C in air or up to 900 °C in vacuum. The solidification process is followed by differential thermal analysis (DTA). The resulting brown coloured coatings have a thickness of 1.5–4 μm. Scanning electron microscopy investigations (SEM) show that the WS₂ nanoparticles are embedded as small aggregates in a hybrid silica matrix. X-ray diffraction (XRD) measurements prove that most of the tungsten disulphide embedded in the matrix can be protected against oxidation even after curing the samples at temperatures up to 900 °C. Hardness and modulus of the hybrid silica films were measured through an instrumented indentation test. Increasing the temperature of the heat treatment yields an increase of hardness from 0.3 to 1 GPa and of modulus from 3 to 17 GPa. The amount of up to 10 wt.% WS₂ in the coatings has no remarkable influence on hardness and modulus of the samples.     

Preparation of YSZ thin films for intermediate temperature solid oxide fuel cells by dip-coating method

By studying the effects of different solvents, dispersants and solid loading amount on the suspension stability from sedimentation and viscosity experiments, a simple, effective and highly stable YSZ particle suspension based on MEK/EtOH was developed for dip-coating anode supported electrolyte films for intermediate temperature solid oxide fuel cells (IT-SOFCs). The morphologies of the prepared YSZ thin films from different dip-coating times were studied by scanning electron microscopy (SEM), and a film with a thickness of 16 μm by twice dip-coating was determined to be homogeneous, crack-free and well adherent to the anode substrate. The single cell assembled with this film presents an open-circuit voltage (OCV) of 1.01 V, and a maximum power density of 262 mW cm⁻² under H₂ as the fuel at 800 °C.     

Effects of ferrocenyl group on refractive index of colloidal crystal system formed by polymer-grafted silica in organic solvent

Colloidal crystallization of copolymer-grafted silica containing ferrocenyl groups in organic solvents and effects of ferrocenyl groups on effective refractive index of colloidal crystal systems were investigated. Poly(ferrocenyl metharylate (FeMA)-co-methyl methacrylate (MMA)-grafted silica gave colloidal crystallization in dimethylformamide and acetonitrile. The colloidal crystals exhibited characteristic coloration due to cooperative effects of specific absorption at 400–500 nm by ferrocenyl group and transmission of 700–800-nm light through the crystals. It was observed that effective refractive index of colloidal crystals systems of poly(FeMA-co-MMA)-grafted silica was higher than that of poly(MMA)-grafted silica. Normalized effective refractive index of the system linearly increased with mole fraction of FeMA in grafted copolymer. However, poly(FeMA-block-MMA) did not bring effective increase of the index because of bias formation of ferrocenyl group on silica.     

Biodegradability of sol–gel silica microparticles for drug delivery

The biodegradability of porous sol–gel silica microparticles in physiological buffers has been investigated using a USP4 flow-through dissolution tester. In the open configuration, which most closely models in-vivo conditions, the particles dissolved rapidly at pH 7.4, with a rate dependent on the surface area and media flow rate. In the closed configuration, the fastest dissolving 4 mg silica sample was almost completely dissolved in 100 mL of buffer after 36 h. The initial dissolution rates appeared relatively linear but dropped off as dissolved SiO₂ concentrations approached 20–25 ppm. Addition of serum proteins acted to slow dissolution by 20–30%, suggesting a slower degradation in vivo. Silica microparticles administered for controlled release drug delivery would therefore be expected to be eliminated relatively rapidly from the body, depending on the sample size and local fluid flow conditions.     

Bimodal meso/macro porous hydroxyapatite coatings

Bimodal porous nanocrystalline hydroxyapatite (HA) coatings with pore sizes in the range of meso/macro meter scale have been deposited onto Ti6Al4V substrates by sol–gel method using nonionic surfactant as porous former agent. By increasing the molar ratio between phosphorous source and surfactant to 0.006, a very homogeneous bimodal distribution of pores in the range of 4.5–10 nm and 0.2 μm have been obtained.     

Polysilazane as the source of silica: the formation of dense silica coatings at room temperature and the new route to organic–inorganic hybrids

Xylene solutions of perhydropolysilazane (PHPS) were used as the coating solutions for preparing silica coatings at room temperature. The PHPS-to-silica conversion was achieved by exposing the spin-on coatings to the vapor from aqueous ammonia. In order to examine the significance of the mechanical properties of the PHPS-derived silica coatings, the pencil hardness was measured, which was compared with that of tetraethoxysilane (TEOS)-derived silica coatings. The pencil hardness was over 9H at a load of 1 kg, which was much higher than that of the TEOS-derived silica gel films, and was comparable to that of the TEOS-derived films heat treated at 300 °C. Second, poly(methyl methacrylate) (PMMA)–silica hybrid coatings were prepared from xylene solutions of PMMA and PHPS via exposure to the vapor from aqueous ammonia. Crack-free, optically transparent PMMA–silica hybrid coatings could be prepared, where PHPS-to-silica conversion was confirmed by infrared absorption spectroscopy. The refractive index was around 1.42–1.50, and the contact angle with water increased from 35 to 70° with increasing PMMA content. The pencil hardness greatly increased during the PHPS-to-silica conversion, and was much higher than that of the non-heat treated TEOS-derived hybrid coatings. The durability in tetrahydrofuran (THF) was also evaluated by measuring the reduction in thickness occurring during soaking in THF. The durability decreased with increasing PMMA content, but was much higher than that of the non-heat treated TEOS-derived hybrid coatings. Both the hardness and the durability were comparable to those of the TEOS-derived coatings heated at 300 °C. The hybrid coatings could also be deposited on poly(ethylene terephthalate) substrates, where no cracks were observed at high PMMA contents even when the substrate was bent.