Hybrid Sol Gel Films Research Articles

Application of CeH–V/ sol–gel composite coating for corrosion protection of AM60B magnesium alloy

Application of a composite coating on AM60B magnesium alloy consisting of cerium–vanadium conversion coating and a hybrid sol–gel layer was investigated. Scanning electron microscopy and energy dispersive X-ray spectroscopy analyses revealed a cracked nodular structure for the cerium–vanadium conversion coating which was mainly composed of O, Ce, V, and Mg atoms. All the cracks in the conversion coating were completely sealed by a thin, compact and defect-free hybrid sol–gel film. Potentiodynamic polarization and electrochemical impedance spectroscopy experiments in Harrison's solution showed that the cerium–vanadium conversion coating provides minimal protection against corrosion while the composite coating significantly increases the corrosion resistance of the magnesium alloy. Sol–gel film provides protection against corrosion by sealing cracks in the cerium–vanadium conversion coating and acting as a barrier. Scanning electron microscopy analyses after polarization tests confirmed the results obtained by the electrochemical tests.

High-energy-density hybrid sol–gel dielectric film capacitors with a polymeric charge blocking layer

A dielectric bilayer structure based on a hybrid sol–gel film (2-cyanoethyltrimethoxysilane) with a nano-scale polymeric charge blocking layer (poly(p-phenylene oxide)) has been developed for dielectric energy storage.

Synthesis and characterization of polymer-silica hybrid latexes and sol-gel-derived films

Sol-gel derived organic-inorganic hybrid systems were obtained by applying alkaline-catalyzed co-hydrolysis and copolycondensation reactions of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), isobutyltriethoxysilane (IBTES), diethoxydimethylsilane (DMDES), and vinyltriethoxysilane (VTES), respectively, into a polymer latex functionalized with vinyltriethoxysilane (VTES). The properties of the latex hybrid materials were analyzed by FTIR, water contact angle, environmental scanning electron microscopy (ESEM), TEM and AFM analysis, respectively. FT-IR spectra confirmed that the chemical structures of the sol-gel derived organic-inorganic materials are changed as function of inorganic precursor and SiOSi networks are formed during the co-hydrolysis and copolycondensation reactions. The water contact angle on the sol-gel latex film containing TEOS+VTES increased to 135°±2 compared to 65°±5 for the blank latex, due VTES incorporation into latex material. TGA curves of hybrid sample modifies against neat polymer, the thermal stability being influenced by the presence of the inorganic partner. ESEM analysis showed that the latex hybrid films prepared with different inorganic precursors were formed and the Si-based polymers were distributed on the surface of the dried sol-gel hybrid films. TEM and AFM photos revealed that the latex emulsion morphology was modified due to the VTES incorporation into system.

One-step sol–gel imprint lithography for guided-mode resonance structures

Guided-mode resonance (GMR) structures consisting of sub-wavelength periodic gratings are capable of producing narrow-linewidth optical resonances. This paper describes a sol–gel-based imprint lithography method for the fabrication of submicron 1D and 2D GMR structures. This method utilizes a patterned polydimethylsiloxane (PDMS) mold to fabricate the grating coupler and waveguide for a GMR device using a sol–gel thin film in a single step. An organic–inorganic hybrid sol–gel film was selected as the imprint material because of its relatively high refractive index. The optical responses of several sol–gel GMR devices were characterized, and the experimental results were in good agreement with the results of electromagnetic simulations. The influence of processing parameters was investigated in order to determine how finely the spectral response and resonant wavelength of the GMR devices could be tuned. As an example potential application, refractometric sensing experiments were performed using a 1D sol–gel device. The results demonstrated a refractive index sensitivity of 50 nm/refractive index unit. This one-step fabrication process offers a simple, rapid, and low-cost means of fabricating GMR structures. We anticipate that this method can be valuable in the development of various GMR-based devices as it can readily enable the fabrication of complex shapes and allow the doping of optically active materials into sol–gel thin film.

Hard X-rays for processing hybrid organic-inorganic thick films.

Hard X-rays, deriving from a synchrotron light source, have been used as an effective tool for processing hybrid organic-inorganic films and thick coatings up to several micrometres. These coatings could be directly modified, in terms of composition and properties, by controlled exposure to X-rays. The physico-chemical properties of the coatings, such as hardness, refractive index and fluorescence, can be properly tuned using the interaction of hard X-rays with the sol-gel hybrid films. The changes in the microstructure have been correlated especially with the modification of the optical and the mechanical properties. A relationship between the degradation rate of the organic groups and the rise of fluorescence from the hybrid material has been observed; nanoindentation analysis of the coatings as a function of the X-ray doses has shown a not linear dependence between thickness and film hardness.

Assessment of ZnO nanoparticles as anticorrosive pigment in hybrid sol–gel films

Abstract The present work is focused on the study of sol–gel hybrid films doped with 0.5% (w/w) ZnO nanoparticles and applied on commercial tinplate. The sol–gel matrix was prepared from two precursors: tetra- n -propoxyzirconium (TPOZ) and 3-glycidoxypropyltrimethoxysilane (GPTMS). The incorporation of particles was carried out by two procedures: as received or after functionalization with GPTMS precursor. The interfacial chemistry of the ZnO was studied by the evaluation of the particle size (hydrodynamic diameter) and the zeta potential. The obtained results indicated that particle size was not affected by the chemical treatment. However the zeta potential changed from positive values (+19 mV) for as received ZnO, to negative ones (−44 mV) when they were treated, which corroborated the effectiveness of the functionalization process. The anticorrosive properties of the sol–gel films were evaluated by Electrochemical Impedance Spectroscopy (EIS) technique. The results showed a clear effect of ZnO nanoparticles on the barrier properties of the film, which was more evident when those had been functionalized. An additional inhibiting action was proposed, based on the higher impedance values observed for doped samples.

Porous inorganic thin films from bridged silsesquioxane sol–gel precursors

A sol–gel process was exploited to produce porous inorganic thin films from phenyl-bridged silsesquioxanes. The evolution of both structural and optical properties of the starting hybrid sol–gel films were monitored, during synthesis and successive thermal curing steps, by Fourier transform infrared (FT-IR) spectroscopy, differential thermal analysis (DTA), thermogravimetric analysis (TGA) and spectroscopic ellipsometry (SE). Involved chemical species, structural and chemical modifications were identified when thermal treatments at increasing temperatures in the range of 60–800°C were applied to the hybrid films. The progressive formation of a crosslinked silica network, template elimination and film densification were observed, resulting in completely inorganic porous thin films of low refractive index. The distinctiveness of this system directly comes from the extremely controlled and uniform dispersion of the porogen at a molecular level, which is intrinsic to the bridged silsesquioxane precursor choice. A quantitative porosity analysis was performed by environmental ellipsometric porosimetry (EEP), studying inorganic film optical and mechanical properties under different relative humidity conditions. A transmission electron microscopy (TEM) in-situ characterization of porosity size and distribution confirms the presence of a spatially structured organization of pores of a few nanometers in diameter.

Effect of the surface chemical treatment on the properties of a sol–gel film on AA1050

Silane sol–gel coatings have been widely studied as a potential strategy to protect aluminium and aluminium alloys components and were proved to be suitable both as a chemical conversion treatment alone and as a coupling agent between the underling substrate and an organic coating. Compared with many aluminium alloys, only little investigation was carried out on the application of sol–gel coatings on AA1XXX. Despite pure aluminium shows lower mechanical resistance with respect to aluminium alloys, however, the high thermal conductivity makes it suitable in a huge variety of applications, such as heat exchanger constructions as well as cooling systems. The present work is devoted to the study of the effect of the surface chemical pretreatment on the structural and corrosion protection properties of a hybrid sol–gel film. Different surface chemical treatments of the 1050 aluminium alloy prior sol–gel deposition were tested: alkaline etch, acidic passivation and boiling water immersion (to promote the formation of pseudo‐boehmite). Films of 1 :1 molar ratio of GLYMO : MTES were obtained on AA1050 from a 5wt% solution in acidified water. The effect of the chemical surface treatment on the AA1050 substrate was investigated both in terms of morphology by means of scanning electron microscopy and in terms of surface chemistry by means of Fourier Transform Infrared Spectroscopy (FT‐IR) exploiting attenuated total reflectance (ATR) geometry. The structure and the chemical properties of the different coatings were investigated by means of FT‐IR. The characterization of the different protective coatings was carried out by means of electrochemical impedance spectroscopy measurements and potentiodynamic curves. Copyright © 2015 John Wiley & Sons, Ltd.

Solid State NMR and EIS Examination of SiO<sub>2</sub>-Epoxy Hybrid Coatings on Stainless Steel

Sol-gel SiO2 and hybrid films were deposited on 316L stainless steel by the dip process. Epoxy bisglycidyl hydroquinone (EBH) was used as an organic component in hybrid films. Both coatings were uniform and homogeneous and displayed good adhesion to the substrates. The thickness of hybrid coatings was greater than that of SiO2 coatings. Thermal condition preparation has significant influence on spectroscopic properties of samples. These features are due to changes of morphology of epoxy-silica hybrid compared to unmodified silica-gels and are related to decomposition at higher temperature. The corrosion behaviour of 316L stainless steel samples coated with SiO2 and hybrid films was studied in Ringer’s solution by electrochemical impedance spectroscopy. SiO2 and silica-based hybrid coatings produced by the sol-gel method offers a good protection against corrosion of stainless steel in Ringer’s solution. In contrast to the SiO2-coated samples and the hybrid coating heated to 200°C, the behaviour of the hybrid coating heated to 300°C changed from resistive to a barrier-like one during exposure to the solution. This change was found to be a transient effect only. During 1-month exposure to Ringer’s solution the coating lost its barrier properties.

Corrosion Behavior of Hybrid Sol-Gel Films Reinforced with Electrospun Nanofibers

The aim of this paper is to evaluate the efficiency of hybrid sol-gel coatings reinforced with electrospinning nanofibers doped with cerium nitrate and ceria particles to increase the corrosion properties of the coating. Poly(vinyl alcohol) solutions doped with cerium nitrate and ceria were electrospun onto clean commercial aluminum alloy AA2024-T3 plates and then coated with a hybrid sol-gel system using the dip-coating procedure. The hybrid materials synthesized via sol-gel chemistry were prepared from inorganic-organic precursors: zirconium (IV) propoxide and 3-glycidoxypropyltrimetoxysilane. The electrochemical impedance spectroscopy technique was applied to evaluate the electrochemical properties of the film whereas scanning electron microscopy and atomic force microscopy were employed to characterize the surface characteristics. The incorporation of nanofibers into the sol-gel system provides good barrier properties that increase the corrosion resistance of the aluminum at longer exposure times in saline media. This protection depends of the type of inhibitor loaded within the electrospun nanofibers.

Selective electrochemical sensor for theophylline based on an electrode modified with imprinted sol–gel film immobilized on carbon nanoparticle layer

A novel electrochemical sensor based on an imprinted hybrid sol–gel film for selective and sensitive determination of theophylline was developed. The imprinted hybrid sol–gel film was prepared by using a new organosilane synthesized as a functional precursor, theophylline as a template and tetraethoxysilane as a matrix forming precursor. The mixture was allowed to hydrolyze, and then spin coated on glassy carbon electrode covered by carbon nanoparticles with sulfonic acid groups that were introduced for immobilization of imprinted sol–gel film and for enhancement of electronic transmission. The morphology and performance of the imprinted film were investigated in detail by scanning electron microscopy, FTIR Spectroscopy, cyclic voltammetry and differential pulse anodic stripping voltammetry. Molecularly imprinted sol–gel was employed to achieve a suitable conformation for electrochemical oxidation of theophylline and also to improve the selectivity of the sensor. The results showed that the imprinted film exhibited selectivity toward theophylline compared to the random sol–gel film prepared in the absence of the template. The imprinted sensor was also successfully employed to detect theophylline in a drug sample.

Electrochemical behavior of hydrophobic silane–zeolite coatings for corrosion protection of aluminum substrate

The anticorrosive properties of a silane–zeolite composite coating applied on a 6061 aluminum substrate was investigated. The composite film, deposited by dip-coating technique, was prepared with different contents of SAPO34 powder (60–90 wt%) with the purpose of evaluating the protective action offered by the zeolite-filled silane matrix. Corrosion protection performance, during immersion in 3.5% NaCl solution, was evaluated by means of a potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). The coating evidenced good barrier properties and high hydrophobicity. The addition of zeolite in the silane matrix induced, as expected, a reduction of cathodic and anodic current. The zeolite improved the barrier properties of the hybrid sol–gel films, enhancing the resistance to localized corrosion attacks. Better results were observed for the sample with 80 wt% of zeolite filler that evidenced still acceptable protective action after 3 days of immersion in the sodium chloride solution.

Corrosion protection of mild steel by one-step electrodeposition of superhydrophobic silica film

Superhydrophobic silica films were deposited onto mild steel substrate for the purpose of corrosion protection. The superhydrophobicity was obtained by one-step electrodeposition of inorganic/organic hybrid sol–gel films from tetraethoxysilane and dodecyltriethoxysilane mixed sol–gel precursors, as a result of simultaneous generation of high roughness and low-energy surface. The corrosion performance was investigated by monitoring the change of water contact angle, by the electrochemical impedance spectroscopy measurements and by iron dissolution test over the whole immersion time. The results show that the superhydrophobic film provides an effective barrier coating for the mild steel interface.

Sol–gel hybrid films based on organosilane and montmorillonite for corrosion inhibition of AA2024

The present work reports the production of films on AA2024-T3 composed of vinyltrimethoxysilane (VTMS)/tetraethylorthosilicate (TEOS) with incorporation of montmorillonite (sodium montmorillonite and montmorillonite modified with quaternary ammonium salt, abbreviated Na and 30B, respectively), generated by the sol–gel process. According to FT-IR analyses the incorporation of montmorillonite does not affect silica network. Electrochemical characterization was performed by electrochemical impedance spectroscopy measurement in 0.05molL−1 NaCl solution. Results indicate that montmorillonite incorporation improves the corrosion protection compared to the non-modified system. Scanning electron microscopy micrographs reveal that high concentrations of montmorillonite provide agglomerations on the metallic surface, which is in detriment of the anticorrosive performance. The VTMS/TEOS/30B films with the lowest concentration (22mgL−1) of embedded clay provide the highest corrosion protection.

Development and characterization of novel organic–inorganic hybrid sol–gel films

Organic–inorganic hybrid films were fabricated by reacting 3-glycidoxypropyltrimethoxysilane with 4,4′-diaminodiphenylether by hydrolysis and condensation reaction with acid catalysis. The chemical bonding between the organic and inorganic phases provides reinforcement to the films, and tetraethoxysilane was added in such a way that silica contents varied from 1 wt% to 3 wt% in the films. Structural characterization of the hybrid films was performed using Fourier transform infrared and nuclear magnetic resonance spectroscopic techniques. The thermal properties studied using thermogravimetric analysis, indicate an improved thermal stability for the films according to the percentage concentration of silica present in them. The water absorption was also found to be reduced for the films with increased silica content. The surface morphology was investigated by means of x-ray diffraction and scanning electron microscopic techniques. The films transparency and homogeneity seem to have been affected severely when the silica content kept on increasing and ultimately led to opaqueness in film.

Why Can Organic Liquids Move Easily on Smooth Alkyl-Terminated Surfaces?

The dynamic dewettability of a smooth alkyl-terminated sol-gel hybrid film surface against 17 probe liquids (polar and nonpolar, with high and low surface tensions) was systematically investigated using contact angle (CA) hysteresis and substrate tilt angle (TA) measurements, in terms of their physicochemical properties such as surface tension, molecular weight/volume, dielectric constant, density, and viscosity. We found that the dynamic dewettability of the hybrid film markedly depended not on the surface tensions but on the dielectric constants of the probe liquids, displaying lower resistance to liquid drop movement with decreasing dielectric constant (ε < 30). Interfacial analysis using the sum-frequency generation (SFG) technique confirmed that the conformation of surface-tethered alkyl chains was markedly altered before and after contact with the different types of probe liquids. When probe liquids with low dielectric constants were in contact with our surface, CH3 groups were preferentially exposed at the solid/liquid interface, leading to a reduction in surface energy. Because of such local changes in surface energy at the three-phase contact line of the probe liquid, the contact line can move continuously from low-surface-energy (solid/liquid) areas to surrounding high-surface-energy (solid/air) areas without pinning. Consequently, the organic probe liquids with low dielectric constants can move easily and roll off when tilted only slightly, independent of the magnitude of CAs, without relying on conventional surface roughening and perfluorination.

Electrochemical behavior of organic/inorganic films applied on tinplate in different aggressive media

Abstract The corrosion behavior of bare and coated tinplate samples was investigated using two different electrolytes: 0.1 M NaCl and 0.1 M citric acid/sodium citrate buffer solutions. A hybrid sol–gel film was synthesized to coat the tinplate samples. The study was performed by polarization and electrochemical impedance spectroscopy techniques. The morphology characterization was made by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction and mechanical profilometry techniques. The obtained results indicate that the corrosion resistance is strongly dependent on the electrolyte. Better behavior is observed for samples in contact with chloride ions, even though at the end of the experiment numerous pits are observed all over the surface. Samples immersed in the citric/citrate solution undergo severe attack, which can be associated with a faster tin dissolution in presence of citrate ions.

Electrolyte Uptake Kinetics in Doped and Undoped sol-gel Films Using a High Resolution EQCM Oscillator Sensor

The electrolyte uptake kinetics in hybrid sol–gel films was monitored with an electrochemical quartz crystal microbalance (EQCM) oscillator sensor, focused on the effect of particles addition in the film. Undoped and zinc oxide doped sol-gel coatings were immersed in a 0.1M NaCl solution to reproduce seafood environment with the object of study their performances as anti-corrosion coatings for the food packing industry. The electrolyte uptake process was investigated by immersion of doped and undoped sol-gel films in NaCl solution for 24hours. The acoustic load impedance, the shear modulus and the acoustic factor of the films were also calculated before and after immersion in order to determine the gravimetric regime of the sensor. Also, the phase noise performance of the oscillator in the solution was investigated to characterize the oscillator's resolution during the electrolyte uptake process.

Modified Silane Films for Corrosion Protection of Mild Steel

Chromium pre-treatments of metal have been replaced by silane pre-treatments as more environmental friendly option. Corrosion inhibitors and nanoparticles can be added in the silane sol-gel network have been reported to improve corrosion resistance. The present work investigates the effect of cerium nitrate activated nanoparticles additions into a sol-gel hybrid silane matrix coated on low carbon steel substrates. Two different types of nanoparticles and its mixture (silica, alumina and their equimolar mixtures) at the concentration of 250ppm were used. Hybrid sol-gel films have been synthesized from mixture of 3-glycidoxy-propyl-trimethoxy-silane (3-GPTMS) and tetraethyl orthosilicate (TEOS). The electrochemical behavior was studied using DC polarization tests after 24hours of exposure in aerated 0.1M NaCl. The scanning electron microscopy (SEM) confirmed crack-free surface morpohology for the as-prepared substrates after different pre-treatments. The experimental results have shown that addition of cerium nitrate at 250ppm and nanoparticles at 250ppm did not efficiently inhibit the corrosion of low carbon steel, unlike inhibiting properties shown by blank silane film.

Concave micro-lens arrays fabricated from the photo-patternable GeO2/ormosils hybrid sol–gel films

Photo-patternable GeO2/γ-glycidoxypropyltrimethoxysilane hybrid thin films were synthesized by a low-temperature sol–gel spin-coating technique. Optical properties and photochemical activities of the as prepared hybrid sol–gel films baked at different temperature were characterized by atomic force microscopy, prism coupling technique, UV–Visible spectroscopy, and Fourier transform infrared spectroscopy. The thermal stability of the gel powder obtained from the hybrid material sol was also examined by a thermal gravimetric analysis. Advantages for fabrication of concave micro-lens arrays based on the as-prepared photo-patternable hybrid films were demonstrated by a UV-cured imprint technique. Results indicate that the as-prepared photo-patternable hybrid materials have great applicability for the fabrication of photonic components. And the UV-cured imprint technique has advantages of simplicity, cost-effective, mass-production, and potential applications in industry production.