Optimization of hybrid sol–gel coatings by combination of layers with complementary properties for corrosion protection of AA2024

The coating system usually employed for corrosion protection of metal substrates consists of different layers which can be constituted of a chemical conversion coating applied on the metal surface followed by a number of organic layers. Hybrid films prepared by the sol–gel method provide a good approach as protective layers on metallic surfaces, although it is necessary to combine the barrier functionality with an active protection mechanism to avoid corrosion when the coating is damaged. Previous works have shown that it is very difficult to reach this result in a mono-layer sol–gel because the amount of inhibitors incorporated tends to increase significantly the porosity of the coating and reduces drastically the barrier properties. This work presents the characterization of a multi-layer sol–gel hybrid inorganic–organic coating system with a structure composed of an intermediate cerium inhibited layer deposited between two un-doped layers on AA2024 alloy. The comparison between the inhibited system and a bi-layer non-inhibited one has allowed to assess the migration of the cerium ions into the hybrid coating towards the substrate corresponding to the improvement of the corrosion properties. The combination of the physical barrier and the active protection enables to obtain an effective protective system.     

Subwavelength Grating Waveguide Structures Proposed on the Low-Cost Silica–Titania Platform for Optical Filtering and Refractive Index Sensing Applications

The sol–gel dip-coating method is a cost-efficient way for the realization of thin films on a planar substrate. In this work, high-quality, low-loss, and low-surface roughness silica–titania thin films are deposited on a glass substrate with the sol–gel dip-coating method. This platform works in the visible to near-IR wavelength ranges and can be useful for several eye-catching photonic components. The paper is comprised of two parts: the first part deals with the development of a low-cost silica–titania waveguide system, whereas the second part provides detail on the numerical modeling of the SWG waveguide filter and SWG waveguide FP-sensor design. The SWG waveguide NIR-stopband filter can achieve an ER of >40 dB and 3-dB bandwidth of 110 nm designed at optimized parameters. The SWG waveguide-FP structure proposed in this work act as a refractive index sensor where the sensitivity is ~120 nm/RIU by reducing the width of the waveguide. This sensitivity can be further enhanced by reducing the waveguide height. We believe that this work is quite important for the realization of low-cost integrated photonic devices based on the silica–titania platform developed via the sol–gel dip-coating method.     

Physicochemical Characterization and Drug Release Properties of Methyl-Substituted Silica Xerogels Made Using Sol–Gel Process

In this work, a multi-analytical approach involving nitrogen porosimetry, small angle neutron and X-ray scattering, Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies, X-ray diffraction, thermal analysis and electron microscopy was applied to organically modified silica-based xerogels obtained through the sol–gel process. Starting from a tetraethoxysilane (TEOS) precursor, methyltriethoxysilane (MTES) was added to the reaction mixture at two different pH values (2.0 and 4.5) producing hybrid xerogels with different TEOS/MTES molar ratios. Significant differences in the structure were revealed in terms of the chemical composition of the silica network, hydrophilic/hydrophobic profile, particle dimension, pore shape/size and surface characteristics. The combined use of structural characterization methods allowed us to reveal a relation between the cavity dimensions, the synthesis pH value and the grade of methyl substitution. The effect of the structural properties on the controlled Captopril release efficiency has also been tested. This knowledge facilitates tailoring the pore network for specific usage in biological/medical applications. Knowledge on structural aspects, as reported in this work, represents a key starting point for the production of high-performance silica-based hybrid materials showing enhanced efficacy compared to bare silica prepared using only TEOS.     

The Impact of Multiple Functional Layers in the Structure of Magnetic Nanoparticles and Their Influence on Albumin Interaction

In nanomedicine, hybrid nanomaterials stand out for providing new insights in both the diagnosis and treatment of several diseases. Once administered, engineered nanoparticles (NPs) interact with biological molecules, and the nature of this interaction might directly interfere with the biological fate and action of the NPs. In this work, we synthesized a hybrid magnetic nanostructure, with antibacterial and antitumoral potential applications, composed of a magnetite core covered by silver NPs, and coated with a modified chitosan polymer. As magnetite NPs readily oxidize to maghemite, we investigated the structural properties of the NPs after addition of the two successive layers using Mössbauer spectroscopy. Then, the structural characteristics of the NPs were correlated to their interaction with albumin, the major blood protein, to evidence the consequences of its binding on NP properties and protein retention. Thermodynamic parameters of the NPs–albumin interaction were determined. We observed that the more stable NPs (coated with modified chitosan) present a lower affinity for albumin in comparison to pure magnetite and magnetite/silver hybrid NPs. Surface properties were key players at the NP–biological interface. To the best of our knowledge, this is the first study that demonstrates a correlation between the structural properties of complex hybrid NPs and their interaction with albumin.     

Preparation of Polymer-stabilized Palladium–silver Bimetallic Nanoparticles by γ-irradiation and their Catalytic Properties for Hydrogenation of cis,cis-1,3-Cyclooctadiene

Polyvinypyrrolidone (PVP)-stabilized Pd-Ag bimetallic colloids were successfully prepared in an acetone:2-propanol solution mixture of palladium acetate and silver perchlorate, and in an aqueous solution of palladium nitrate and silver nitrate by γ-irradiation. The prepared PVP-stabilized bimetallic nanoparticles were characterized by UV, TEM, XRD, and XPS. In Pd–Ag bimetallic nanoparticles, the XPS data indicated that the constituent elements were in the metallic state, and the palladium atoms were concentrated on the surface of the alloy cluster. These PVP-stabilized bimetallic nanoparticles were used as catalysts for hydrogenation of cis,cis-1,3-cyclooctadiene (COD).     

Complex anticorrosion coating for ZK30 magnesium alloy

This work aims at developing a new complex anticorrosion protection system for ZK30 magnesium alloy. This protective coating is based on an anodic oxide layer loaded with corrosion inhibitors in its pores, which is then sealed with a sol–gel hybrid polymer. The porous oxide layer is produced by spark anodizing. The sol–gel film shows good adhesion to the oxide layer as it penetrates through the pores of the anodized layer forming an additional transient oxide–sol–gel interlayer.The thickness of this complex protective coating is about 3.7–7.0 μm. A blank oxide–sol–gel coating system or one doped with Ce³⁺ ions proved to be effective corrosion protection for the magnesium alloy preventing corrosion attack after exposure for a relatively long duration in an aggressive NaCl solution.The structure and the thickness of the anodized layer and the sol–gel film were characterized by scanning electron microscopy (SEM). The corrosion behaviour of the ZK30 substrates pre-treated with the complex coating was tested by electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET), and scanning ion-selective electrode techniques (SIET).     

Optical properties of ZnO/BaCO3 nanocomposites in UV and visible regions

Pure zinc oxide and zinc oxide/barium carbonate nanoparticles (ZnO-NPs and ZB-NPs) were synthesized by the sol–gel method. The prepared powders were characterized by X-ray diffraction (XRD), ultraviolet–visible (UV–Vis), Auger spectroscopy, and transmission electron microscopy (TEM). The XRD result showed that the ZnO and BaCO₃ nanocrystals grow independently. The Auger spectroscopy proved the existence of carbon in the composites besides the Zn, Ba, and O elements. The UV–Vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is redshifted by adding barium carbonate. In addition, the optical parameters including the refractive index and permittivity of the prepared samples were calculated using the UV–Vis spectra.

PACS

81.05.Dz; 78.40.Tv; 42.70.-a.     

Polymer/silica nanohybrids by means of tetraethoxysilane sol–gel condensation onto waterborne polyurethane particles

Stable waterborne polyurethane/silica hybrid dispersions were obtained by sol–gel reaction of tetraethoxysilane added to previously synthesized waterborne polyurethane nanodispersions. Two series of polyurethane/silica nanostructures with different silica contents were synthesized using pure polyurethane particles and polyurethane particles previously functionalized with (3-aminopropyl)triethoxysilane (APTES) as colloidal templates. The optimum experimental conditions for tetraethoxysilane sol–gel reaction (T = 75 °C and semi batch polymerization conditions) leading to the formation of silica/polyurethane aqueous nanodispersions were established. The presence of silica was confirmed using TGA, FTIR, ²⁹Si NMR and TEM. TEM images showed an excellent final dispersion of the silica nanoparticles in the polymer matrix when silane functionalized polyurethane nanoparticles were used.     

Hybrid Nanoparticles and Composite Hydrogel Systems for Delivery of Peptide Antibiotics

The growing number of drug-resistant pathogenic bacteria poses a global threat to human health. For this reason, the search for ways to enhance the antibacterial activity of existing antibiotics is now an urgent medical task. The aim of this study was to develop novel delivery systems for polymyxins to improve their antimicrobial properties against various infections. For this, hybrid core–shell nanoparticles, consisting of silver core and a poly(glutamic acid) shell capable of polymyxin binding, were developed and carefully investigated. Characterization of the hybrid nanoparticles revealed a hydrodynamic diameter of approximately 100 nm and a negative electrokinetic potential. The nanoparticles demonstrated a lack of cytotoxicity, a low uptake by macrophages, and their own antimicrobial activity. Drug loading and loading efficacy were determined for both polymyxin B and E, and the maximal loaded value with an appropriate size of the delivery systems was 450 µg/mg of nanoparticles. Composite materials based on agarose hydrogel were prepared, containing both the loaded hybrid systems and free antibiotics. The features of polymyxin release from the hybrid nanoparticles and the composite materials were studied, and the mechanisms of release were analyzed using different theoretical models. The antibacterial activity against Pseudomonas aeruginosa was evaluated for both the polymyxin hybrid and the composite delivery systems. All tested samples inhibited bacterial growth. The minimal inhibitory concentrations of the polymyxin B hybrid delivery system demonstrated a synergistic effect when compared with either the antibiotic or the silver nanoparticles alone.     

Synthesis and Characterization of Titania Nanoparticles on the Surface of Microporous Perlite Using Sol–Gel Method: Influence of Titania Precursor on Characteristics

Titania colloidal nanoparticles have been successfully fabricated by a very simple and inexpensive sol–gel spin-coating method on the surface perlite granules. This was achieved by adjustment of the sol–gel parameters such as the precursors, spin-coating time and heating processes. Five samples were prepared using different titania e.g. Millennium, Degussa P25, titania nanoparticle, sol–gel derived titania and rutile nanoparticles precursors. Titania nanoparticles were grown on perlite granules by the controlled immobilization of titania. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the growth and morphology of the titania coating on perlite granules. The results showed surface modification of perlite granules with uniform coating of titania on supports and confirmed that the coatings are composed of aggregated crystallites of 11–61 nm in diameter, good compositional uniformity and good adherence of the fabricated titania layer on perlite granules. The synthesis of adsorptive supports for immobilization of powdery photocatalysts would show significant improvements in both practical use and degradation efficiency of photocatalysis in environmental protection.     

Self-repairing coating for corrosion protection of aluminum alloys

The development of effective anticorrosion pre-treatments for metallic substrates is an issue of great importance for durability of metal structures and components. In this work, we proposed and demonstrated the concept of self-repairing coating for corrosion protection of aluminum alloys, using cagelike oil core/silica gel shell particles. These micron-scale, cagelike smart microspheres with opened and closed pores were successfully fabricated, and at the same time encapsulated repairing agent (methyl methacrylate) and catalysts (potassium persulfate and sodium thiosulfate) into the microspheres, respectively. Such smart particle composites (SPCs) were prepared based on an interfacial self-assembly process and sol–gel reaction. They were then self-assembled on the AA2024 aluminum alloy surface, followed by the application of a sol–gel film. The hybrid film worked as a primer coating featuring the self-repairing property. Both the EIS and SEM/EDS data demonstrated that the encapsulated repairing agent was released as a response to external stimulus (scratches) and polymerized to repair the coating defects. By comparing the corrosion rate of AA2024 in three coating systems, the self-repairing effect is quantified to be 22% after 2 h immersion in deoxidized 3% NaCl solution.     

Magnetic resonance of the NiFe2O4 nanoparticles in the gigahertz range

We report an adjustable magnetic resonance frequency from 1.45 to 2.54 GHz for NiFe₂O₄ nanoparticles which were prepared by a sol–gel process. X-ray diffraction and scanning electron microscopy results indicate that the samples are polycrystalline nanoparticles, and the size of the particles increases obviously with the thermal treatment temperature. The consequence of the surface composition suggests that the oxygen defects are present in the nanoparticle surface, and this surface magnetic state can show a strong surface anisotropy. With decreasing size of the particle, the surface magnetic effect is predominant, resulting in an increase of resonance frequency for NiFe₂O₄ nanoparticles. This finding provides a new route for NiFe₂O₄ materials that can be used in the gigahertz range.     

Novel sol–gel‐derived Ag/SiO2–Al2O3 catalysts for highly selective oxidation of methanol to formaldehyde

Novel Ag/SiO₂–Al₂O₃ catalysts with low silver content prepared by the sol–gel method exhibit excellent catalytic properties in the catalytic oxidation of methanol to formaldehyde. The silver content was as low as 2% and the yield of formaldehyde was achieved as 90.3%, which is 16% higher than that of pumice‐supported silver and even 5–6% higher than that of a commercial electrolytic silver catalyst. XRD, XPS and SEM results reveal that all silver was present as Ag⁺ before catalytic reaction and was partially reduced to the metallic state after the reaction. It was also found that silver was aggregated on the surface after its reduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Self-healing corrosion protection by nanostructure sol–gel impregnated with propargyl alcohol

Zirconia based nanostructured hybrid sol–gel coating, impregnated with propargyl alcohol (PA) to hinder corrosion of mild steel was studied. Zirconia nano-particles (TPOZ) contained sol–gel was synthesized using 3-glycidoxypropyltrimethoxysilane (GPTMS) as precursor and subsequently optimized for internal cohesion as well as adhesion to the mild steel substrate to assess the consequent effect on suppression of corrosion damage in 0.5 M NaCl solution. Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscopy (SEM) results demonstrated the effect of coating integrity on impeding corrosion. Experiments on mild steel specimens coated with hybrid sol–gel films following mechanical polishing render superior corrosion resistance to mild steel in contrast to those undergoing electrochemical polishing with marked lower surface roughness. Results also proved of beneficial effect of low and exact concentration of PA on sol–gel coat's barrier properties evident from diminished corrosion current and other electrochemical indicators.     

Synthesis of antistatic hybrid nanocomposite coatings using surface modified indium tin oxide (ITO) nanoparticles

Several antistatic nanocomposite hybrid coatings based on epoxy-silane developed by sol–gel method are studied. The hybrid sols are prepared by hydrolysis and condensation of GPTMS and TMOS precursors in the presence of an acid, as catalyst, and EDA as curing agent. Considering their good electrical conductivity, indium tin oxide (ITO) nanoparticles are used as antistatic agents. To improve the distribution/dispersion of ITO nanoparticles in the polymer matrix, the surface of nanoparticles is modified with silane groups (m-ITO). The antistatic properties of the coatings, containing various amounts of m-ITO nanoparticles, are investigated through surface electrical resistivity measurements. FTIR is used to screen the reaction of epoxy groups and the effect of EDA on crosslinking in the hybrid coatings. Morphology, nanoparticle distribution and surface roughness of the coatings are studied through SEM and AFM microscopy techniques. Also, homogeneous distribution of ITO nanoparticles within the polymer matrix is confirmed by EDXA elemental mapping. The cubic shape and nanometric size of the nanoparticles in the hybrid coatings are monitored by transmission electron microscopy (TEM).     

Synthesis and Characterization of Core-shell ZrO2/PAAEM/PS Nanoparticles

This work demonstrates the synthesis of core-shell ZrO₂/PAAEM/PS nanoparticles through a combination of sol–gel method and emulsifier-free emulsion polymerizaiton. By this method, the modified nanometer ZrO₂ cores were prepared by chemical modification at a molecular level of zirconium propoxide with monomer of acetoacetoxyethylmethacrylate (AAEM), and then copolymerized with vinyl monomer to form uniform-size hybrid nanoparticles with diameter of around 250 nm. The morphology, composition, and thermal stability of the core-shell particles were characterized by various techniques including transmission electron microscopy (TEM), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal-gravimetry analyzer (TGA). The results indicate that the inorganic–organic nanocomposites exhibit good thermal stability with the maximum decomposition temperature of ~447 °C. This approach would be useful for the synthesis of other inorganic–organic nanocomposites with desired functionalities.     

Structural and morphological study of gamma‐irradiation synthesized silver nanoparticles

Silver nanostructured particles with controlled size, shape, and morphology were achieved by gamma irradiation of aqueous solution containing AgNO_3, ploy (vinyl pyrrolidone), (PVP) or mixture of PVP and ploy (vinyl alcohol), (PVA). The reaction condition parameters such as solvent content, polymer type and irradiation dose were investigated. The physico‐chemical properties and morphological structures of the as‐prepared sliver nanostructures were characterized using UV/VIS spectroscopy, TEM, XRD, and Fourier transform infrared spectroscopy (FTIR) spectroscopy. Hexagonal and nanorods structures of sliver nanoparticles having single surface plasmon resonance peak and triangular (nanoprism) nanoparticles having different surface plasmon resonance peak were obtained. The XRD patterns of the as‐prepared silver nanostructure show four diffraction peaks at 2θ of 38.4°, 44.5°, 64.6°, and 77.6° of the face‐centered cubic structure silver nanoparticles. FTIR measurements indicated that the sliver nanoparticles were coordinated through the functional groups of PVA and/or PVP. POLYM. COMPOS., 38:2687–2694, 2017. © 2015 Society of Plastics Engineers     

Sol–Gel Synthesis of Doped Vitreous Materials with the Use of Modified Aerosils

A novel variant of the sol–gel synthesis of silica glasses and optical composites containing transition-metal ions and nanoparticles is developed. Xerogels and glasses containing 10- to 46-nm particles are prepared with the use of aerosils modified by chromium oxide. The structural and physicochemical properties of chromium oxide–modified silica samples are investigated by X-ray powder diffraction, differential thermal analysis, thermal gravimetric analysis, and IR spectroscopy. The optical properties of transparent samples are examined using the transmission spectra and the refractive index distribution over the cross section of the xerogel preform. Xerogels and glasses containing nanoparticles of metallic copper and Cu _x Se are formed in the tetraethoxysilane–aerosil–copper nitrate system. An analysis of the optical properties of the nanocomposites demonstrates that SiO₂ : Cu _x Se nanocomposites can be used as passive Q switches.     

Layer by Layer Deposition of Polyethylene Glycol Capped Silver Nanoparticles/Chitosan on Polyethylene Substrate

Multilayers of silver nanoparticles and chitosan were deposited on polyethylene film by a layer-by-layer (LBL) self-assembly technique. Silver nanoparticles with a size of about 5 nm were prepared by chemical reduction and then fabricated onto a polyethylene (PE) substrate, which led to the formation of a colored film with the thicknesses of 2, 4, 8, 12, and 20 layers. Silver nanocomposites were characterized by atomic force microscopy (AFM) and UV-visible spectroscopy, X-ray diffraction (XRD), and infrared spectroscopy (FTIR). Results showed that nanoparticles deposited homogenously on the surface of the polyethylene film. LBL silver nanocomposites showed considerable antimicrobial activity by agar diffusion test.     

Influence of substrate composition on corrosion protection of sol–gel thin films on magnesium alloys in 0.6 M NaCl aqueous solution

The corrosion protection behaviour of organic–inorganic hybrid thin films on AZ31 and AZ61 magnesium alloy substrates has been studied. These films were prepared by a sol–gel dip-coating method. The organopolysiloxane precursors were γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethoxysilane (TMOS). An attempt was made to determine the possible relationships between the degradation of the sol–gel film and composition of the metal substrate during the exposure of the metal/coating system to 0.6 M NaCl aqueous solutions. For this purpose electrochemical impedance spectroscopy (EIS) and hydrogen evolution measurements were applied. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the sol–gel films formed on the surface of AZ61 alloy were far more perfect and uniform than those formed on the AZ31 alloy. This behaviour was attributed to the effect of the native oxide film initially present on the surface of the AZ61 alloy, which inhibited the attack of magnesium. Results indicated that the sol–gel coated AZ61 substrate tended to develop corrosion products slower than the sol–gel coated AZ31 substrate, trend that could change by prolonging exposure time. After 6 days of immersion, a clear inhibitive effect of the corrosion products formed during the test was observed in the case of the sol–gel coated AZ31, but not with the coated AZ61 alloy substrate, a phenomenon explained by the carbonate enrichment observed by XPS.