Sol-gel Structure Research Articles

The Effect of the Gelling Agent on the Gelation Rate and the Formed Sol-Gel Structure

In this paper a combination of colloidal silica and different gelling agents are studied in order to observe the effect of gelation rate on the formed sol-gel structure. Proper ratios of sol matrix materials and gelation agents were determined. Sets of samples based on these recipes were prepared with added filling material and tested for mechanical properties. Samples with added solution of NaCl gelling agent showed the highest flexural strength observed and also lower doses of this gelling agent are required for one of the studied sols which can positively effect the final price of product.

Multiscale investigation of waste soybean oil rejuvenated asphalt binder utilising experimental methodologies and molecular dynamics simulations

ABSTRACT To demonstrate the rejuvenation effect of waste soybean oil (WSO) on aged asphalt binder (AB) and realise the efficient combination of laboratory evaluation and numerical simulation. The rheological properties and molecular dynamics simulation of WSO rejuvenated binders were investigated. The results demonstrated that the WSO provided sufficient light components in the AB and reduced the stiffness. The WSO rejuvenated binders were transformed into a sol–gel structure, this resulted in excellent rheological properties. The WSO improved the anti-fatigue performance of rejuvenated binders. The WSO provided sufficient aromatics and a small amount of saturates for the AB. The blending mechanism of WSO and AB was physical blending. The atomic force microscopy micromorphology images showed that the bee-like structure of WSO rejuvenated binders was reduced in quantity compared with that of AB. The dosages of 3–6 wt% of AB content was determined to be the optimum content of WSO. The molecular dynamics results indicated that as the amount of WSO increased, the total volume and the occupied volume increased, while the free volume decreased. The volume fusion parameters increased significantly with an increase in the WSO content. This showed that WSO effectively improved the diffusion capacity of rejuvenated binders.

Surfactant-template sol-gel protective coatings for cast iron corrosion: Effect of the surfactant type and concentration

Different surfactants-template tetraethylorthosilicate-3-mercaptopropyl-trimethoxysilane (TEOS-MPTMS) sol–gel materials are prepared by the hydrolysis of silane precursors, in presence of the surfactant. Three surfactants are used, cationic cetyltrimethylammonium bromide (CTAB), non-ionic TritonTM X-100, and anionic sodium dodecyl sulfate (SDS). Prepared sol–gel materials are applied as protective coatings for cast iron corrosion in 0.5 mol.L-1 HCl. The protection efficiency is estimated by electrochemical measurements. Structural and surface properties of the prepared sol–gel materials are examined by FTIR and scanning electron microscope (SEM) and are affected by the surfactant species and concentration. Surfactant-template sol–gel materials acquire higher porosity than the free material. However, the presence of the surfactant stabilizes the silane network formation, and facilitates the protection performance, especially at lower and intermediates surfactant amounts. The presence of TritonTM X-100 and CTAB enhance the protection performance of the sol–gel coatings, average efficiencies are 95 and 86 %, respectively. On the other hand, SDS-template sol–gel coatings offer lower efficiency and can not be used as protective coatings at high SDS concentrations due to the repulsion between SDS and negatively charged silanolate groups, which results in a highly unstabilized sol–gel structure with a distorted morphology. The proposed surfactant-template sol–gel coatings show excellent operational stability in the corrosive medium for a long time.

Nanopatterning of Perovskite Thin Films for Enhanced and Directional Light Emission.

Lead-halide perovskites offer excellent properties for lighting and display applications. Nanopatterning perovskite films could enable perovskite-based devices with designer properties, increasing their performance and adding novel functionalities. We demonstrate the potential of nanopatterning for achieving light emission of a perovskite film into a specific angular range by introducing periodic sol–gel structures between the injection and emissive layer by using substrate conformal imprint lithography (SCIL). Structural and optical characterization reveals that the emission is funnelled into a well-defined angular range by optical resonances, while the emission wavelength and the structural properties of the perovskite film are preserved. The results demonstrate a flexible and scalable approach to the patterning of perovskite layers, paving the way toward perovskite LEDs with designer angular emission patterns.

Sol‒gel synthesis, structure, ferromagnetism and optical properties of Mn‒doped titania diluted magnetic semiconductors nanoparticles

Sol‒gel synthesis, structure, ferromagnetism and optical properties of Mn‒doped titania diluted magnetic semiconductors nanoparticles

Evaluation of the Composite Mechanism of Nano-Fe2O3/Asphalt Based on Molecular Simulation and Experiments.

Asphalt, as an indispensable binder in road paving, plays an important role in transportation development. However, the mechanism of action between the modifier and asphalt cannot be fully explained by the existing test methods. This paper combines molecular simulations with experiments to provide a research and analysis tool to evaluate the “structure−performance” relationship of asphalt. From the trend of experimental results, the optimal content of Nano-Fe2O3 is 1% to 3%. The AFM micrograph of the asphalt material shows that at 3%, the Nano-Fe2O3 can be effectively dispersed in the asphalt and the unique “ bee structures “ of the asphalt can be adsorbed around the modifier. Molecular dynamics studies and results show that when Nano-Fe2O3 are incorporated into the asphalt and have a strong adsorption force on the colloidal structure of asphalt, the “ bee structures “ can be adsorbed around the Nano-Fe2O3. In the range of 208–543 K, the sol-gel structure of asphalt in the Nano-Fe2O3/asphalt composite system is gradually disrupted.

Optimization of parameters of integrated optical waveguides based on thin-film Sol-gel structures by using mathematical modelling

An algorithm for calculating optical waveguide film parameters was proposed, the use of which makes it possible to reduce the time for processing experimental data. The developed algorithm was tested using experimental data of waveguides samples with a wave-guiding layer of zirconium dioxide sol-gel films. A comparison of the developed algorithm and the Wolfram Mathematica program showed a good agreement of the results, as well as the developed method advantage in terms of using ease and timesaving spent on processing the results.

Reactive extrusion of sol-gel silica as fire retardant synergistic additive in ethylene-vinyl acetate copolymer (EVA) composites

Silica derived from sol-gel approach was used as co-filler in aluminium hydroxide (ATH) or hydromagnesite (HM) ethylene-vinyl acetate (EVA) formulations. In this bottom-up approach, the silica network is formed inside the extruder in a first process step. The 3D silica structure is investigated by solid-state nuclear magnetic resonance (ssNMR) spectroscopy and a combined TGA-FTIR analysis revealing a partially incomplete reaction to form silica particles. In addition, 29Si CPMAS NMR showed the formation of chemical Si–C bonds between EVA and silica networks. The performance enhancement of the fire retardant properties was established by comparing with composites prepared by a top-down approach, i.e by adding preformed silica. It is confirmed that the preformed silica acts as a synergistic agent with both ATH or HM, increasing the flame retardant properties (limiting oxygen index, UL-94 and cone calorimeter tests) of EVA composites, however, the sol-gel silica shows the best performances in reducing both heat release and smoke production. The role of the sol-gel structure was deeply investigated in correlation with combustion test.

Structure and luminescent properties of oxyfluoride glass-ceramics with YF3:Eu3+ nanocrystals derived by sol-gel method

In this paper, the transparent oxyfluoride glass-ceramic materials containing YF3:Eu3+ nanocrystals were fabricated via controlled ceramization of precursor xerogels at relatively low temperature T = 350 °C. The formation of YF3 nanocrystalline phase from Y(CF3COO)3 was verified based on X-ray diffraction (XRD) measurements as well as high-resolution transmittance electron microscopy (HR-TEM). Based on IR-ATR spectroscopy the functional groups inside sol-gel structures were identified. The optical properties of Eu3+ ions in fabricated sol-gel samples were investigated based on photoluminescence excitation and emission spectra as well as luminescence decay analysis of the 5D0 excited level. Upon excitation at near-UV illumination, λexc = 393 nm, the series of 4f6-4f6 photoluminescence bands of Eu3+ ions in reddish-orange light area were recorded. The Stark splitting of photoluminescence bands, double-exponential character of decay curves and long-lived emission for fabricated glass-ceramic samples clearly evidenced the partial substitution of Y3+ by optically active Eu3+ ions in precipitated YF3 nanocrystals. Indeed, it was identified that applied annealing conditions resulted in significant, almost 34-fold prolongation of luminescence lifetime from 0.24 ms (Eu3+ ions in xerogel host) up to 8.14 ms (Eu3+ ions incorporated into YF3 nanocrystals). It was also observed a clear correlation between identified phonon energies from IR measurements and luminescence behavior of Eu3+ ions.

Investigation on the polarization resistance of steel embedded in highly resistive cementitious systems – An attempt and challenges

Concretes with fly ash, slag, limestone calcined clay, etc. exhibiting high resistivity are being used to enhance the chloride resistance of structures – to achieve durability. Prior to use, the engineers need to determine the chloride threshold (Clth) of such highly resistive steel cementitious (S-C) systems (a key parameter to estimate service life). Most Clth tests involve repeated measurements of polarization resistance (Rp) and detection of corrosion initiation of steel embedded in hardened cementitious system (a sol-gel structure with partially filled pores). The high resistivity of such systems should be considered while interpreting the electrochemical response to determine Rp. This paper experimentally evaluates the suitability of LPR and EIS techniques for assessing Rp of steel embedded in highly resistive systems. Experiments were conducted with lollipop type specimens (steel reinforcement embedded in mortar cylinders). The following three types of mortar having various resistivities were prepared: (i) ordinary portland cement (OPC), (ii) OPC + fly ash, and (iii) limestone calcined clay cement. Experimental observations on how the following three factors affect the electrochemical response in highly resistive S-C systems are provided: (i) resistivity of concrete covering the embedded steel, (ii) electrode configuration, and (iii) electrochemical test parameters. It was found that electrochemical impedance spectroscopy (EIS) can detect corrosion initiation in highly resistive systems at earlier stages than the linear polarization resistance (LPR) technique. Also, the guidelines on how to use EIS technique to determine the Rp of steel embedded in highly resistive S-C systems are provided.

The effect of the sol–gel structure on the catalysis performance of l-proline

Two sol–gel materials based on tetraethylorthosilicate (TEOS) and a combination of methacryloxypropyltrimethoxysilane and zirconium propoxide were developed and used as host matrices for the organic catalyst (l-proline) and iron oxide nanoparticles with the objective of formulating a magnetic sol–gel catalyst. In order to investigate the effect of the sol–gel condensation process on the catalyst recyclability and the effect of the dopants on the structure of the sol–gel matrices, iron oxide nanoparticles and l-proline were introduced in the sol–gel matrices either during the sol–gel synthesis or at the end of the sol–gel synthesis. While both systems were successfully recycled three times when applied to the Aldol reaction, the TEOS based sol–gel material with the dopants introduced at the end of the sol–gel synthesis showed excellent reaction efficiency and recyclability with 99% conversion. In parallel, the zirconium sol–gel-based material did not enable any conversion. Remarkably, it is demonstrated that the process of introducing the dopants strongly effects the condensation of the inorganic networks of the sol–gel matrix by involving the organic catalyst in the catalysis of the condensation of the inorganic moieties. Furthermore, this condensation process is shown to play a major role in the mobility of the organic catalyst and therefore on its ability to be recycled. This study is, to our knowledge, the first that investigates the effect of the morphology and structure of sol–gel matrices on the catalytic performance of an organic catalyst.

On the Sol-Gel Synthesis and Structure, Electronic and Ionic Conductivities and Impedance Behavior of Y, Fe Co-Doped SrTiO<sub>3</sub> Mixed Conductor

A single phase perovskite, YxSr1−xTi0.6Fe0.4O3-δ(x=0.06-0.09), was fabricated at 1350°C in air by sol-gel method. The effects of Y-and Fe-doping into SrTiO3on phase structure, electrical conductivity, ionic conductivity and its impedance behavior were investigated. The optimized Y0.07Sr0.93Fe0.4Ti0.6O3-δsample exhibits an electrical conductivity of 0.135 S·cm-1at 800 °C. Y-doping decreases the migration energy for oxygen ions, leading to a significant increase in ionic conductivity. The ionic conductivity of Y0.09Sr0.91Ti0.6Fe0.4O3-δsample varies from 0.0052 S· cm-1at 600°C to 0.02 S·cm-1at 800°C. Impedance characteristics over a wide frequency range of 0.01Hz-100 KHz reveal that the resistance of ionic conduction is predominantly influenced by grain boundary, the relaxation time of which decreases with increase of Y-doping amount.

Sol-gel preparation and in vitro cytotoxic activity of nanohybrid structures based on multi-walled carbon nanotubes and silicate

ABSTRACTThis work deals with the influence of silicate precursors such as tetraethyl orthosilicate and/or Citrus aurantium L. extract on the structure and cellular uptake of multi-walled carbon nanotubes-based hybrid nanomaterials. The sol-gel synthesis and structure formation have been investigated using X-ray diffraction patterns, Fourier transform infrared spectroscopy, and scanning and transmission electron microscopes. In addition, the particle size distribution and zeta potential measurements were carried out.The cytotoxicity was examined and evaluated by sulforhodamine B (SRB) assay using different human cell lines (normal melanocytes, and carcinoma of breast and liver) in comparison with standard doxorubicin.

Synthesis and dissolution behaviour of CaO/SrO-containing sol–gel-derived 58S glasses

The effect of the substitution of strontium for calcium in the tertiary the SiO2–CaO–P2O5 sol–gel bioactive glass 58S (60SiO2·36CaO·4P2O5, mol%) on its structure and its chemical durability on soaking in simulated body fluids was investigated. 58S was selected as a starting composition, and substitution for calcium was carried out from 0 to 100% with an increment of 25%. A novel phosphate source of diethylphosphatoethyltriethoxysilane, which consists of Si and P connected with ethylene group, was used in this work. XRD and FTIR showed that the gels obtained following drying at 130 °C had a typical sol–gel structure, where a continuous amorphous silica gel network and surface bound mineral salts of Ca(NO3)2 and Sr(NO3)2. Once the gels were heat stabilised to decompose nitrates and incorporate the cations into the network, samples containing Sr formed a strontium silicate crystalline phase. With increasing levels of Sr in the composition, the overall crystallinity of the glass–ceramic increased, while, at the maximum substitution of 100% SrO, macroscopic phase separation was observed, characterised by needle-like crystals of strontium apatite (Sr5(PO4)3OH) and strontium silicate (Sr2SiO4) phases in addition to amorphous regions. Dissolution experiments in Tris-buffered solution showed Sr successfully released into the media even though it existed as a crystalline phase in the glass–ceramic. Further, the glass–ceramics induced nucleation and growth of carbonated hydroxyapatite (HA) on their surface suggesting potential bioactivity of the materials. At higher substitutions (75 and 100% SrO for CaO), HA nucleation was not found to occur this may have been due to low amount of phosphate released from the original glass–ceramic as a result of it being locked up in the strontium apatite phase.

Sol-Gel Synthesis, Crystal Structure, Electronic and Magnetic Properties of AlxTi1-xBiO3 (0.0 ≤x≤ 0.33) Oxides

Synthesis of AlxTi1-xBiO3 (0.0 ≤x≤ 0.33) (S1-S4: x = 0.0, 0.11, 0.22, 0.33) oxides is performed by sol-gel method via nitrate-citrate route. Analysis of the powder X-ray diffraction (XRD) patterns show tetragonal unit cell with lattice parameters: a = 6.6377, 6.6398, 6.6370, 6.6366 Å; c = 6.5445, 6.5391, 6.5259, 6.6583 Å, respectively in S1-S4, with space group P42/mnm and Z=4. Average crystallite sizes determined by Scherrer relation are found to be in the range ~16-36, 18-50, 19-48 and 19-41 nm in S1-S4, respectively. On Rietveld refinement of unit cell structures the agreement factors are lowered to: Rp= 98.28, 97.65, 98.85, 94.29 %; Rwp= 97.11, 96.76, 97.92, 95.73 %; Rexp= 0.09, 0.09, 0.09, 0.09 % in S1-S4, respectively. Fourier electron density mapping show irregular contours around Bi3+, Ti3+ and O2- ions due to significant ionic character in Ti-O and Bi-O bonds in the materials. Presence of hysteresis loops in the range -6 kG to +6 kG at 300 K with magnetic susceptibility values in the range 5.926 x 10-8 - 6.461 x 10-8 emu/gG in S1-S4 show soft ferromagnetic nature of the oxides. Density functional theory (DFT) calculations using CASTEP (Cambridge Serial Total Energy Package) programme package show energy band gap, Eg, ~ 0.01-0.02 eV indicating weak semiconducting nature of the oxides. The valence band (VB) predominantly comprises O 2p, Ti 3d, Al 3p and Bi 6p orbitals, and the conduction band (CB) comprises mostly O 2p, Al 3p and Bi 6p orbitals with extension of band tails narrowing the energy band gap.

Influence of n-alkyl ester groups on efficiency of crosslinking for methacrylate monomers copolymerized with EGDMA: Experiments and Monte Carlo simulations of reaction kinetics and sol–gel structure

We present the results of applying a computationally efficient Monte Carlo (MC) method to simulate the reaction kinetics and molecular architecture development during free-radical, bulk copolymerizations of a homologous series of methacrylate monomers with ethylene glycol dimethacrylate. The overall objective of the work was to determine the extent to which the ester side chains of the methacrylate monomers hinder chain-end radical propagation reactions through the pendent vinyl groups of the crosslinking monomer. We have determined that this steric hindrance is quite significant and increases with ester side chain length. This is expressed by a reduced reactivity parameter, ΨC,X, that is different for each monomer–crosslinker pair. With this single kinetic parameter adjustment, the MC model was able to effectively predict the reaction kinetics, gel points, and sol−gel fractions throughout the entire reactions, including, to a limited extent, the solvent swelling ratio of the gel for two different levels of crosslinker.

Characterization of Optical Fiber Dissolved Oxygen Sensor for Aquaculture Sensing and Monitoring

Optical fiber sensor using sol gel membrane incorporated RTV silicon rubber was fabricated and developed for the characterization of dissolved oxygen in aqueous solution. The sol gel materials used consists of Tetraethylorthosilicate (TEOS) and Triethoxyoctylsilane (Octyl-triEOS) as the precursor compound for the preparation of the sol gel structures, while tris-BP Ruthenium (II) chloride as the fluorescent lifetime of the oxygen indicator. Dip coating techniques is utilized to position the sol gel technology at the distal end of the optical fiber. Dissolved oxygen gas sensor characterizations include a study on the sensitivity, temperature effects and drift rate of the sensor performance when measured in 40ppt salt water. Potential applications of the optical fiber sensor are including aquaculture, river monitoring and environment sector.

Effect of the condensation of hybrid organic–inorganic sol–gel materials on the optical properties of tripan blue

The work reported in this paper highlights the effect of sol–gel structures on the optical properties of a typical organic dye (Trypan Blue, TB). Three transition-metal-based hybrid sol–gel materials with different structures and morphologies were developed and characterised by TEM. The optical properties of TB were investigated by incorporating it in the different sol–gel materials and the UV–Visible spectra recorded in both liquid and solid state, in thin-coatings cured at temperatures in the range 100–150°C. These studies revealed two relevant results. First, the sol–gel morphology plays a critical role in the optical properties of the dye. The effect of the sol–gel host matrix on the optical properties of the dye is attributed to the steric hindrance of the nanostructures, themselves intimately dependant on the reactivity of the transition metal. For instance, the less condensed system showed the highest reactivity with the dye, while the more condensed system exhibited limited interaction with the dye, symbolised by a significant change or quasi-unchanged UV–Visible spectra, respectively. It is also shown that the increase of the condensation degree of the sol–gel coatings by heat-curing can dramatically alter the optical properties of the dye especially for the most condensed sol–gel systems. This has been attributed to proximity effects enabled by the further increase of the materials densities.The results reported here aim to provide a better understanding of how material formulations can influence the optical properties of organic dyes and suggest that the structure of the host matrix along with the applied curing process have to be fully considered and assessed in the choice of organic dyes for a given application.

Straightforward Micropatterning of Oligonucleotides in Microfluidics by Novel Spin-On ZrO₂ Surfaces.

DNA biochip assays often require immobilization of bioactive molecules on solid surfaces. A simple biofunctionalization protocol and precise spatial binding represent the two major challenges in order to obtain localized region specific biopatterns into lab-on-a-chip (LOC) systems. In this work, a simple strategy to anchor oligonucleotides on microstructured areas and integrate the biomolecules patterns within microfluidic channels is reported. A photosensitive ZrO2 system is proposed as an advanced platform and versatile interface for specific positioning and oriented immobilization of phosphorylated DNA. ZrO2 sol-gel structures were easily produced on fused silica by direct UV lithography, allowing a simple and fast patterning process with different geometries. A thermal treatment at 800 °C was performed to crystallize the structures and maximize the affinity of DNA to ZrO2. Fluorescent DNA strands were selectively immobilized on the crystalline patterns inside polydimethylsiloxane (PDMS) microchannels, allowing high specificity and rapid hybridization kinetics. Hybridization tests confirmed the correct probe anchoring and the bioactivity retention, while denaturation experiments demonstrated the possibility of regenerating the surface.

Preparation of the modified limestone possessing higher permeability of gas well based on fluorinated silica: Effect of catalyst

Abstract During natural gas production from gas condensate reservoirs, due to drops in bottom hole pressure below the dew point, liquids drop out and form condensate blockage which results in significant loss of gas and condensate productivity. A new method for stimulating gas–condensate wells is changing the rock wettability in near well-bore regions by chemical treatments. The aim of this study was to employ two comparative methods of chemical treatments for altering the rock wettability from strong liquid-wetting to intermediate gas-wetting. First the surface of rocks was modified by using sol–gel process under acid- and/or base-catalyzed conditions. Then the effects of two different chemical treatments were examined by various experimental tests such as Fourier transform infrared (FTIR), thermogravimetric analyses (TGA), electron dispersive analysis of X-ray (EDX) and scanning electron microscopy (SEM) followed by static contact angle, coreflood test and porosity measurements. The results showed that, such methods could alter the wettability significantly. It was noticed that there were some differences in the experimental results related to sol–gel structure. Compared to a base-catalyzed process which showed higher contact angle value, an acid-catalyzed process tended to produce more linear branched-polymeric networks with fewer cross-linkages and could penetrate into the limestone core easier. The final evaluation of the coatings in terms of their effectiveness by coreflood test showed that the improvement factors were 0.78 and 0.56 for the acid- and base-catalyzed treatments, respectively.