Sol-gel Treatment Research Articles

Tuning the surface wettability of carbon nanotube carpets in multiscale hierarchical solids

An attractive approach of increasing functionality of solid surfaces is to create hierarchical multiscale morphology by attaching tailored carpet-like arrays of Carbon nanotubes (CNT) on them. Such surfaces offer fractal morphology along with unprecedented increase in specific surface areas, and significantly boost the potency of porous materials used in surface-active applications. However, full utilization of these structures will require intimate interaction between the solid surface and its environmental fluid. CNT arrays tend to be hydrophobic, which limit their effectiveness in aqueous environments. In this research, we investigated two different surface modifications methods to induce hydrophilic property to CNT nano-carpets on graphitic substrates: dry oxygen plasma treatment and wet sol–gel oxide coating. Structure, morphology, composition and chemistry of these multiscale surfaces have been related to wettability and water flow properties. Plasma oxygen treatments did not alter the surface morphology, but induced temporary wettability, that could be reversed by heat treatment. On the other hand, sol–gel treatment permanently coated the nanotubes with a strongly bonded layer of amorphous SiO2. This coating imparts permanent alterations in surface chemistry, contact angle, wettability and water flow. Porous carbon foams were coated with CNT arrays and their water permeability measured before and after sol–gel silica coating. The hydrophilic coating was seen to increase flow rate and reduce pressure build-up. These results have important implications on all devices that utilize surface activity of porous solids, such as catalytic membranes, antimicrobial filters, and microfluidic sensors.

Preparation, characterization, and in vitro evaluation of antibacterial sol–gel coated cotton textiles with prolonged release of curcumin

The aim of this study was to develop a textile-based sol–gel release system with antibacterial properties intended for medical applications. Curcumin (a herbal compound extracted from Curcuma longa L.) was embedded in an acid-catalyzed silica xerogel coating on cotton textiles. The release of curcumin was found to be diffusion-controlled, as expressed by the Higuchi and the first-order models. Matrix dissolution release was ruled out by the absence of dissolved silica in the release medium. Results from nitrogen sorption analysis confirmed the presence of mesopores in the xerogel coating, and an increase in both the BET surface area from 1.95 to 2.23 m2 g−1 and in the mesopore volume from 0.003 to 0.004 cm3 g−1 after the sol–gel treatment. Thicker xerogel coatings therefore provided greater porosity for curcumin entrapment, leading to retardation of the diffusion processes and consequently extended release profiles. The treated samples showed better antibacterial properties against Staphylococcus aureus (99% reduction) compared with Escherichia coli (37% reduction). Overall, the developed sol–gel coated textiles demonstrate promising potential for use as wound dressing materials.

A comparative study on titanium dioxide sol-gel treatment for protein fabrics, focusing on UV transmittance effects

Sol-gel technology offers a promising route to impart new properties to textile substrates. However, relatively little attention has been paid to the effect of precursor concentration in the sol-gel processing on the inherent properties of sol-gel treated textile substrates. In this study, titanium (IV) isopropoxide (TTIP) was used as the precursor material, and colourless TiO2 sol solutions were prepared at three precursor concentrations. Wool fabrics were coated with as-prepared TiO2 sol solutions via a dip-dry-cure technique. The optical, morphological, tensile properties and washing durability of both untreated or sol-gel treated wool fabrics were then evaluated. The results show that TiO2 sol-gel prepared at a relatively higher precursor concentration resulted in a thicker coating and a better UV protection on the treated wool fabric. TTIP precursor concentration also played an important role in the washing durability of TiO2 sol-gel coatings. Both the tensile strength and elongation at break of the treated wool fabrics were largely improved, however the degree of improvement seemed to be less dependent on the precursor concentrations of as-prepared TiO2 sol-gels.

An investigation on sol–gel treatment to aramid yarn to increase inter-yarn friction

Inter-yarn friction helps to increase energy absorption in ballistic fabrics. This paper reports on the results of sol–gel treatment on aramid yarns to increase the inter-yarn friction. Two types of TiO2/ZnO hydrosols (submicro-sized and nano-sized) prepared using hydrolysis and peptization methods were used to treat aramid yarns with and without curing. SEM was used to characterize the change in morphology. FTIR and EDX analyses were applied to identify the coating substance. The inter-yarn friction was tested using Capstan method. Images from SEM showed that the surface of the yarn treated with TiO2/ZnO submicro-sized hydrosol was covered with lump-like coating whilst in the case of TiO2/ZnO nano-sized sol treatment, the coating on the fibres was more film-like. The substance in the coating was confirmed as titanium dioxide and zinc oxide by FTIR and EDX analyses. The test results for coefficient of friction revealed that the coefficient of friction between the yarns treated by submicro-sized hydrosol was 54% higher than the non-treated, and the nano-sized hydrosol was associated to a 10% increase. However, the curing process had little effect on the coefficient of friction between yarns. The study also showed that the tensile properties of the treated yarns and the weight add-on were not significantly affected.

Preparation of nanocomposites by swelling of a UV cured cycloaliphatic epoxy film in a silica precursor

In this work, nano composites were prepared from a UV cured cycloaliphatic epoxy resin by swelling the cured film in tetramethoxysilane (TMOS) followed by exposure to humid atmosphere at an elevated temperature. The flexibility of the resin was tuned by using different modifiers, namely hexanediol-diglycidylether (HDGE) and a diglycidoxy terminated polydimethylsiloxane (GTMQ). Glycidoxypropyl trimethoxysilane (GPTS) was also added to the UV-curable mixture in order to promote the swelling of the cured films in TMOS, thus obtaining the silica phases through a sol–gel approach. The swelling was performed at different temperatures (40 and 80 °C); the subsequent hydrolysis and condensation reactions were carried out in dry and humid atmospheres at 80 °C. The obtained films were investigated through DSC and TGA analyses; their submicro- nano- morphology was assessed by SEM. The UV-cured films showed silica rich surfaces, the morphology of which was related to the presence of GPTS and of the reactive comonomers and to the experimental conditions adopted for the sol–gel process. The TMOS absorption and hence the subsequent hydrolysis-condensation processes seem to occur at the surfaces of the films probably due to the selective migration of the silicone chains towards the air interface. The pencil scratch hardness values too were found to increase after the sol–gel treatment on the films.

Formation of Hydroxyapatite Produced by Microarc Oxidation Coupled with Sol-gel Technology

Bioactive composite coatings containing hydroxyapatite on magnesium alloy AZ91D are prepared successfully by microarc oxidation (MAO) coupled with sol-gel treatment. The morphologies of the composite coatings formed by MAO treatment at 0.5 A · cm−2 current density coupled with sol-gel treatment appear to be much denser and smoother than the coatings produced at 1.0 A · cm−2. The Ca/P ratio (1.70) of the composite coatings produced at 0.5 A · cm−2 is slightly higher than the ratio of the sol prepared (1.67), due to the substitute groups in apatite lattice according to the Fourier transform infrared spectroscopy test. Moreover, electrochemical tests illustrate that the composite coatings (0.5 A · cm−2) have higher open-circuit potential, corrosion potential, and corrosion resistance than the composite coatings at 1.0 A · cm−2. Immersion tests have been performed showing an enhanced bioactivity and apatite-forming ability. Consequently, combining the MAO and sol-gel treatments provides a promising candidate for further investigation.

Alteration of Porous Media Wettability to Gas-Wetting by Sol-Gel and Fluorochemical Surfactant

Gas well productivity is affected by liquid blockage of the wellbore region, and if the wettability of porous media shifts to gas-wetting, then deliverability in gas condensate reservoirs will increase. In this article, a sol-gel process and modification of perfluoroalkyl methacrylic copolymer (Zonyl 8740) were employed to alter the wettability of rock core surfaces. Contact angle analysis and a spontaneous imbibition test suggested that wettability of the core could be altered to gas-wetting by sol-gel deposition and treatment with Zonyl 8740. Consequently, the rough surfaces made by sol-gel, which were modified by Zonyl 8740, resulted in wettability reversal to gas-wetting of porous media.

Intermediate gel coating on macroporous Al2O3 substrate for fabrication of thin carbon membranes

To fabricate carbon membranes based on a low-cost macroporous Al2O3 substrate, a pretreatment called “intermediate gel coating” on the substrate was introduced. It can be carried out simply by coating the substrate with an AlOOH sol and drying to form a gel layer. The PFA (polyfurfuryl alcohol) was synthesized and coated on the gel-modified Al2O3 substrate, and the carbon membranes were obtained after a carbonization treatment. Scanning electron microscopy (SEM), thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and pore-size analysis were conducted in material characterization, and the permeation performances of the carbon membranes were tested with H2, N2, O2 and CO2. Upon the substrate surface modification for fabrication of carbon membranes, such an intermediate gel coating method is superior to the traditional sol–gel treatment because the intermediate gel layer effectively prevented the PFA from penetrating into the macroporous substrate during coating and carbonization treatments so that a thin and uniform carbon layer can be created. The resulting carbon membranes exhibited promising gas permeability and permselectivity.

Preparation of durable insecticide cotton fabrics through sol–gel treatment with permethrin

This paper presents the development of an industrially viable procedure for the fabrication of durable insecticide textiles based on the sol–gel technique. Permethrin was incorporated on cotton fabrics by a silicon oxide nanocoating applied by conventional padding followed by curing. The effect of the sol–gel process parameters, such as silica solid content and the permethrin/tetraethyl orthosilicate (TEOS) ratio on the insecticide activity and on the textile properties of the resulting fabrics was evaluated. The application of the nanosol coating results in textiles with a high anti-mosquito effect without altering their flexibility and softness. Moreover, this method allows the insecticide content to be controlled by simply adding the proper amount of it to the coating bath. The washing fastness was assessed on a textile with a permethrin loading close to 500mg/m2 of fabric showing a good insecticide effect even after 50 washing cycles.

Silane based field level surface treatment methods for aluminium, titanium and steel bonding

Grit blast silane and AC-130 sol–gel treatments were tested to assess their performance in aluminium, titanium and stainless steel structural epoxy bonding. Static single lap shear and static double lap shear specimens were tested as dry and wet at room temperature. Wedge tests were performed in a hot and wet exposure and in hot fresh water and salt water immersions. Acceptable field level methods were found for unclad and clad 7075 aluminium bonding without primers. With titanium and stainless steel, the use of a BR 6747-1 primer was found to be necessary for durable adhesion. In a case study, AC-130 sol–gel without a primer on naval grade 5083 aluminium provided good results also when immersed in Baltic Sea water.

Review on the Unbroken Three-Dimensional Network Modification Methods of Waste Rubber Powder

Waste rubber powder (WRP) is global concern, with the development of rubber industry. However, WRP with three-dimensional structure is insoluble and nonmelting and doesnt blend with raw rubber very well. Before added into raw rubber, WRP should be modified. In this paper ,the modification methods of WRP which contain grafting, sol-gel and reactive gas treatment method,through the unbroken three-dimensional network are described.

Preparation and magnetic properties of lanthanum- and cobalt-codoped M-type strontium ferrite nanofibres

(x = 0.12) nanofibres have been successfully prepared by sol-gel method, electrospinning and subsequent heat treatment. The prepared nanofibres were characterised via X-ray diffraction (XRD), transmission electron micrograph (TEM) and superconducting quantum interference device (SQUID). The XRD revealed that the crystal structure of samples was hexagonal magnetoplumbite structure at calcination temperature from 900 °C to 1100 °C. The TEM showed that the ferrite nanofibres had a smooth morphology and a bamboo joint structure, and the diameter of nanofibres increased with the increase of sintering temperature. The SQUID revealed that there were some intriguing changes in magnetic properties with the variation of sintering temperature or altering calcination time, and the optimised magnetic property of samples was Ms 70.76 emu/g, Mr 36.35 emu/g and Hc 6.26 kOe at 950 °C for 2 h, the corresponding grain size was 39.30 nm. Meanwhile, the nanofibres display more significant improvements in the magnetic properties than the nanoparticles obtained by the sol-gel process, which was probably due to the anisotropic morphology and the cylindrical magnetic domain of ferrite nanofibres.

A novel sol-gel multi-layer approach for cotton fabric finishing by tetraethoxysilane precursor

The way of producing functional textile finishings by the sol-gel process using a multistep approach, consisting of consecutive depositions of sol layers on cotton fabric, for obtaining architectures with a different number of layers (namely, 1, 3 or 6 layers) is discussed. To this aim, tetraethoxysilane (TEOS) has been used as a precursor and the role of such architectures has been deeply investigated and correlated with the sol concentration and with the presence of the condensation catalyst DBTA (Dibutyltindiacetate). The multi-layer coatings were applied by padding using sols containing appropriate molar ratios of the precursor, anhydrous ethanol, catalyst and hydrochloric acid. The effects of the catalyst during the alkoxide reaction and the silica amount applied by sol-gel treatment on the thermo-oxidative behavior of the treated fabrics were deeply studied. FT-IR ATR spectroscopy, SEM analysis, thermal and thermo-oxidative stability, washing fastness, flammability and mechanical properties of the sol-gel treated cotton fabrics have been also investigated. The results obtained should be interpreted according to the properties investigated. The higher the concentration and the number of layers of the inorganic matrix, the higher the heat protection of textile samples. However, the resulting coating was so rigid that it modified the mechanical properties and particularly it decreased the wear resistance according to Martindale test. To improve the mechanical properties the best results were obtained by modulating a lower concentration of the matrix using a layered approach. In all cases, high adhesion of the coating to the textile fabrics was observed.

Thermal stability and flame retardancy of polyester fabrics sol–gel treated in the presence of boehmite nanoparticles

Polyester fabrics have been treated with hybrid organic-inorganic sols containing aluminium hydroxide, namely a synthetic boehmite. The treated fabrics have been thoroughly investigated by infrared spectroscopy, scanning electron microscopy coupled to elemental analysis and thermogravimetry. Furthermore, the flammability of the coated fabrics has been assessed and compared with that achieved by applying the two components separately. More specifically, flammability tests have shown that the sol–gel treatment in the presence of boehmite nanoparticles is able to suppress the dripping phenomenon, which represents the main issue to fulfil for polyester fabrics.

Effect of Tetraethoxysilane (hybrid sol) on chemical and abrasion resistance, and dyeability of nano polyamide mat

This work deals with the application of inorganic–organic sol–gel layer on polyamide nanofabrics to protect nanofibres against chemical and mechanical damages. To this aim, fabric specimens with different silica concentration (1, 5, 10, 20 and 40 %) have been prepared. Layers were deposited on polyamide nanofabrics by pad-dry-cure technique. Permeability was defined as the rate of airflow perpendicular to a test sample under specified conditions for the test area, pressure gradient, and time according to DIN EN ISO 9237. Abrasion resistance testing was performed for determining the weight loss of samples before and after sol–gel treatment. For chemical resistant measurement, Formic Acid was used. Infrared spectroscopy was also used for investigation of the chemical structure of the treated polyamide nano mats. The morphology of the fabrics was observed using a Scanning Electron Microscope. Also both untreated and sol–gel treated samples were dyed using cationic dyestuff and dyeability of polyamide nanomats after treating by hybrid sol were compared with untreated one. The results indicate that the K/S value of CI. Basic Red 46 are enhanced by increasing the concentration of Tetraethoxysilane based sol, respectively. Also by increasing the concentration of sol–gel to 50 %, the greatest resistance to formic acid was achieved.

Nanocrystalline Ho3+-doped WO3: a promising material for acetone detection

In this article, we describe how Ho3+-doped WO3 nanoparticles have been synthesised by sol–gel treatment from the precursors of W, H2O2, Ho2O3 and HNO3 at room temperature, followed by calcinations at 500°C for 1 h. The samples were characterised by X-ray diffraction, scanning electronic microscopy and X-ray photoelectron spectroscopy. Obtained results indicated that the as-synthesised particle diameter is ∼60 nm under different Ho2O3-doped concentrations. In comparison with pure WO3 sensor, all of the Ho3+-doped sensors showed better sensing performance in respect of sensitivity, selectivity and optimum operating temperature. The effects of Ho2O3 content, acetone vapour concentration and operating temperature on the sensing characteristics of the Ho3+-doped WO3 sensors were also investigated. The sensor containing 3.0 mol% Ho2O3 exhibited the maximum sensitivity to acetone vapour at 200°C. A possible mechanism for the influence of Ho2O3 on the acetone-sensing properties of Ho2O3-doped WO3 sensors was proposed.

Size dependent structural and magnetic behaviour of CaFe2O4

CaFe2O4 nanocrystalline powders were synthesized through sol–gel treatment in which the stoichiometric mixing of various nitrates involving calcium and iron in presence of citric acid was performed. Subsequently, the as prepared sample was annealed at various temperatures in order to obtain the fine distribution of size including the bulk counterpart. The samples were then characterized using powder X-ray diffraction followed by 57Fe Mössbauer spectroscopy, SQUID as well as vibrating sample magnetometry. The results of spectroanalyses revealed that the samples were formed in single phase cubic spinel structure and exhibits room temperature superparamagnetism, except the bulk one, which crystallizes in characteristic orthorhombic structure of CaFe2O4 and displays trivial coercivity and remanent magnetization at room temperature.

Sol-Gel Preparation and Infrared Radiation Property of Zinc-Substituted Cordierite Ceramics

The sol-gel process is a useful technique with good control over final amount of compositions which can decrease the temperature of sintering in the melting procedure. A cordierite infrared radiation ceramic with a nominal composition of Mg2(1-x)Zn2xAl4Si5O18（x=0、0.05、0.10、0.15、0.20）was prepared using the powders by sol-gel method and heat treatment at 1523K for 2 hours. The results indicate that the sol-gel method can effectively decrease the sintered temperature and the substitution of Zn2+ to Mg2+ can let structural change and improve the infrared radiation properties. The specimen of x=0.20 attained a relatively high infrared emissivity of 0.91 in the whole band.

Wettability alteration of gas condensate reservoir rocks to gas wetness by sol–gel process using fluoroalkylsilane

AbstractNatural gas is becoming a very important energy source in recent years. A sharp reduction has been observed in gas deliverability in many low permeability gas reservoirs due to bottom‐hole pressure drops below the dew point pressure. It is an established fact that altering the wettability of reservoir rocks from liquid wetness to gas wetness could improve the gas deliverability. In this study, a new polymeric surfactant coating for altering the wettability of Sarkhun reservoir rocks was prepared by using a sol–gel process. Perfluorodecylsilane (PFDS) and triethoxysilane (TEOS) were used to obtain an inorganic‐organic network via hydrolysis and polycondensation reactions. The effect of this method was examined by various characterization tests such as FTIR, SEM, and EDX, static contact angle and imbibition tests for wettability alteration. The experimental results revealed that, the prepared polymeric network including the terminal fluorine groups were effective and provided sufficient repelling characteristics towards oil and water. Static contact angles were raised from 30 to 130° for water, and from <5 to 60° for condensate after sol–gel treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Effects of Sol-Gel Treatment and Plating on the Electrical Properties of Multilayer Filters

The effects of sol-gel treatment and plating on the electrical properties of multilayer filters were investigated. The results showed that the sol-gel treatment process can effectively lower the apparent porosity of multilayer filters, preventing the penetration of electroplate liquid into the filters. The mean insertion loss rise for the sol-gel-treated components was 0.171 dB, which increased up to 0.811 dB for the filters without sol-gel seal treatment. Microstructural studies revealed that the sol-gel seal treatment is an effective preplating treatment to diminish the insertion loss of multilayer filters.