Heat and moisture transfer in sol–gel treated cotton fabrics

Cotton fabrics have been treated by sol–gel processes in order to produce an inorganic coating on fibres, able to modify their thermal conductivity under an irradiating flow. To this aim, fabric specimens with different silica content have been tested following the ISO 6942 standard in order to establish the effect of the coating on coupled heat and moisture transfer through the cotton fibres. The collected results have been compared with those obtained by an optimized method using a cone calorimeter as the heating source. By this latter approach, it has been demonstrated that sol–gel cotton treated fabrics with high moisture uptake possess a significantly lower thermal conductivity with respect to cotton alone.     

Sol–gel treatments for enhancing flame retardancy and thermal stability of cotton fabrics: optimisation of the process and evaluation of the durability

Cotton fabrics have been treated by sol–gel processes in order to create a silica compact coating on the fibres to enhance their thermal stability and flame retardancy. The effect of process parameters such as silica precursor:water molar ratio and drying conditions (temperature and time) has been thoroughly investigated, aiming at optimization of target properties. Thermogravimetry and cone calorimetry have been respectively used to assess thermal stability and combustion behaviour of treated fabrics. Coating durability to different washing programmes has been evaluated as well.     

The role of pre-hydrolysis on multi step sol–gel processes for enhancing the flame retardancy of cotton

The flame retardancy properties of cotton have been enhanced by exploiting an optimized multistep sol–gel process, consisting of a pre-hydrolysis step, followed by consecutive depositions of hybrid phosphorus-doped silica layers, using DPTS as precursor of the oxidic phases. Upon optimization, it has been demonstrated that just one phosphorus-doped silica layer is able to strongly reduce the heat release rate (?52 %), and the total smoke release (?56 %) and its rate (?62 %) with respect to the untreated fabric. In addition, the deposition of three layers allows achieving a higher flammability resistance if compared to a single layer, as indicated by the final residue after the flammability tests. As far as flammability resistance is concerned, the new coatings have shown a good durability when subjected up to five washing cycles according to ISO 6330 standard.     

Structural stability and electrochemical properties of Gd-doped ZrO2 nanoparticles prepared by sol–gel

Cubic, tetragonal and monoclinic Gd-doped zirconia nanoparticles with nominal composition Gd_xZr_1?xO₂ in the range 0 ≤ x ≤ 0.2, were prepared by annealing dried gels of Gd-containing zirconia at temperatures over the range between 450 and 1,300 °C. The synthesized zirconia-based nanoparticles with increased gadolinium load were characterized by X-ray powder diffraction, infrared and Raman spectroscopies, and transmission electron microscopy. The stabilization of the crystalline forms of Gd-doped ZrO₂ solid solutions depends on the amount of Gd dopant and the annealing temperature. For low Gd loads in Gd_xZr_1?xO₂ being x < 0.05, the tetragonal form is the single phase up to 1,100 °C, whereas the monoclinic is the crystalline form detected up to 1,300 °C. Within the range of compositions 0.05 ≤ x < 0.1, is the tetragonal the only stabilized zirconia crystalline structure over the whole range of temperature up to 1,300 °C. For higher Gd-contents, in the range 0.1 ≤ x ≤ 0.2, is the cubic zirconia form the only stable phase for the whole range of annealing temperatures. Solid-state electrochemistry of the gadolinium-doped zirconia performed by the voltammetry of microparticles approach allowed distinguishing different electrochemical answers of Gd cation associated with slightly different local coordination surrounding of cations. Enantioselective electrocatalytic effect of monoclinic Gd-doped ZrO₂ on the oxidation of l-(+)-tartaric acid and d-(?)-tartaric was also studied.     

Thermal stability of sol–gel derived methacrylate oligosiloxane-based hybrids for LED encapsulants

Methacrylate oligosiloxane-based hybrid materials (methacrylate hybrimers) were fabricated by curing the methacrylate oligosiloxane resins synthesized by sol–gel condensation reaction of 3-(trimethoxysilyl)propyl methacrylate (MPTS) and diphenylsilanediol (DPSD) for the LED encapsulant application. The fabricated hybrimers are optically transparent and have a high refractive index up to 1.565 depending on the precursor composition. The lower DPSD content hybrimer, which is the more polymerized and heated in a vacuum to remove the non-polymerized methacrylate groups, produces higher optical transmittance and thermal stability. This behavior is interpreted by thermal degradation of methacylate groups in the hybrimers.     

Lactic acid based sol–gel process of Ag nanoparticles and crystalline phase control of Ni particles in aqueous sol–gel process

Nickel and silver particles were prepared by using sol–gel auto-combustion method under N₂ atmosphere where lactic acid was applied as chelating agent. The synthesis of nickel particles was carried out at various pH conditions (2–7), resulting in the face-centered-cubic or hexagonal-close-packed crystalline nickel phase. The morphology and structure of synthesized nickel particles and silver nanoparticles were characterized by X-ray diffraction, transmission electron microscope, energy dispersive X-Ray spectroscopy and differential scanning calorimetry-thermogravimetric analysis. The results show that the spherical Ag nanoparticles with diameters in the range of 18–27 nm and narrow size distribution can be obtained by this sol–gel process.     

Catalytic activity and stability of laccase entrapped in sol–gel silica with additives

This study investigated the effects of different additives and precursors on the catalytic activity of laccase entrapped in sol–gel silica. It was found that the laccase catalytic activity and stability of sol–gel laccase could be enhanced if the entrapment was performed in the presence of additives such as PVA, PEG and APTS. The use of TEOS as a precursor showed slightly higher laccase catalytic activity compared to TMOS. The PVA as an additive showed a better catalytic activity enhancement compared to the PEG and APTMS with the optimum PVA concentration of 0.03 mg/mL. The optimal temperatures of sol–gel laccase without and with additives were found to be at 40 and 27°C, respectively. After 70 days of storage at 27°C, the catalytic activity of the immobilized sol–gel laccase with additives maintained its catalytic activity compared to only 30% of its original catalytic activity for the sol–gel laccase without additives.     

Cobalt ferrite nanoparticles synthesis by sol–gel auto-combustion method in the presence of agarose: a non-isothermal kinetic analysis

Journal of Thermal Analysis and Calorimetry - In this study, cobalt ferrite (CoFe2O4) nanoparticles were synthesized by sol–gel auto-combustion technique in the presence of agarose as a...     

High water solubility and sol–gel transition behavior of titania nanoparticles obtained by an in situ functionalization sol–gel process

Herein, addition reaction occurred between glycidol and partially hydrolyzed Ti⁴⁺ complexes provides a opportunity to obtain dry anatase nanopowder with high redispersity in water. This property is considered to be originated from the two OH groups located in the two ends of glycidol resulted chlorinated propandiol molecules. In aqueous solution, the two OH groups are respectively connected with particle surface and external free water by the formation of hydrogen bonds, resulting in high water redispersity of nanoparticles. Due to the much less amount of chlorinated propandiol molecules than adsorbed molecule water on particle, the wide space between organic molecules facilitates the mutual physical surface touch of individual particles to form hydrogen bond between them. A novel property is then obtained for surface modified titania nanoparticles, which is the gelation of redispered nanoparticles in aqueous solution.     

Non-aqueous sol–gel preparation of carbon-supported nickel nanoparticles

This work addresses the novel non-aqueous sol–gel process preparation of carbon-supported nickel nanoparticles. In the sol–gel process, ethanol, nickel nitrate or nickel (П) acetylacetonate, and citric acid were used as solvent, source of metallic element, and chelating agent, respectively. Hexadecylamine (HDA), oleic acid and oleylamine were used as surfactants. The calcination process was performed under protecting Ar or N₂ flowing. Carbon supported nickel nanoparticles can be prepared by this sol–gel process. Moreover, no grain growth occurs in a temperature range of 200 K, meaning that the grain size of the nickel nanoparticles can be controlled in this sol–gel process. The nickel nanoparticles can display typical superparamagnetic behavior at room temperature when HDA has been used. This novel method is expected to have wide applications in the field of metallic nanoparticles.     

Investigation on the thermal decomposition and flame retardancy of wood treated with a series of molybdates by TG–MS

A flame-retardant wood was prepared using a series of insoluble molybdates through the double bath technique. The flame retardancy of the wood samples was studied with the limiting oxygen index (LOI) method. The relationships between the flame-retardant performance and the thermal property of wood were studied by the thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), scanning electron microscopy (SEM), and the thermogravimetry–mass spectrometry (TG–MS) analysis methods. The results showed that the insoluble molybdates, which were precipitated into the wood by the double bath technique, can obviously improve the flame retardancy of wood. Similarly, the transition metal molybdates showed higher flame-retardant efficiency than the main group metal molybdates do, which probably due to the thermal barrier effect that Fe₂(MoO₄)₃ acts during the combustion of the samples. At the same time, Fe₂(MoO₄)₃ catalyzed the dehydration and carbonization reactions of wood, and caused an increase in the amount of char produced, and an improvement of the stability of the char residue. Moreover, the mass spectrometry results indicated that the excess transition metal ions speed up the deep decomposition of the char residue, and resulting in the smoldering of wood.     

Strategy to enhance catalytic activity and stability of sol–gel oxidoreductases

Journal of Sol-Gel Science and Technology - Oxidoreductases are widely recognized for their capability to degrade phenolic pollutants and versatile. However, the lack of enzyme stability makes this...     

Effect of hydrophobicity on the stability of sol–gel silica coatings in vacuum and their laser damage threshold

Silica antireflective coatings modified by hexamethyldisilazane (HMDS) were deposited on clean substrates (silicon wafer or K9 glass blanks) by sol–gel processing. The effects of HMDS on the contamination resistant capability and laser-induced damage threshold (LIDT) of coatings were investigated. Transmission electron microscopy revealed that a stable sol with uniformly distributed silica particles with an average particle size of about 15 nm was acquired by adding appropriate amount of HMDS into the standard SiO₂ sol. With the modified sol the resultant coatings were hydrophobic and the contact angle for water increased with increasing amount of HMDS in the reaction mixture. Such increase in hydrophobicity was not the result of surface roughness. The antireflective properties were retained after HMDS-treatment and the maximum transmission values were above 99 %. The introduction of HMDS into silica sols had also increased the LIDT of coatings from 24.3 to 37.0 J cm^?2 when the molar ratio of HMDS to tetraethoxysilane was 0.05:1. The increase in LIDT was attributed to the decrease of nodular defect and uniform microstructures of coatings as an effect of the HMDS modification. After some of the hydroxyl groups on the surface of the SiO₂ particle were replaced by methyl groups, from which the SiO₂ particle gained a water-repellent surface, the stability of coatings in vacuum was increased. The maximum transmission values of modified coatings decreased by only 0.25 % after storage under vacuum for 168 h. In contrast, the standard sol–gel silica coatings decreased about 2 % under similar conditions. The LIDT of modified coatings remained as high as 30.8 J cm^?2, more than that of standard coatings stored for the same duration in air.     

Preparation of hydrophobic and conductive cotton fabrics using multi-wall carbon nanotubes by the sol–gel method

Journal of Sol-Gel Science and Technology - In this paper, a simple method is presented for making a conductive and hydrophobic cotton fabric using a multi-walled carbon nanotube (MWCNT). The...     

Effect of sol–gel hydrophobicity on the distribution and structure of different proteins in organically modified sol–gel thin films

Although the use of silica sol–gels for protein entrapment has been studied extensively our understanding of the interactions between the immobilization matrix and the entrapped biomolecules is still relatively poor. Non-invasive in situ spectroscopic characterization is a promising approach to gain a better understanding of the fundamentals governing sol–gel immobilization of biomolecules. This work describes the application of Fourier transform infrared (FTIR) microscopy to determine the influence of modifying the sol–gel hydrophobicity, by varying the content of the organically modified precursor propyltrimethoxysilane (PTMS), on the distribution and structure of three model proteins (lysozyme [EC 3.2.1.17], lipase [EC 3.1.1.3] and bovine serum albumin (BSA)) in silica sol–gel thin films. FTIR analysis of the overall immobilized protein positional distribution showed a Gaussian type distribution. FTIR microscopic mapping however, revealed that the spatial distribution of proteins was heterogeneous in the sol–gel thin films. When this positional information provided by FTIR microscopy was taken into account, areas of high protein concentration (clusters) were found and were not found to be homogeneously distributed. The shape of these clusters was found to depend on the type of protein entrapped, and in some cases on the composition of the sol–gel. Positional analysis of the distribution of the organically modified precursor PTMS in relation to the protein distribution was also conducted. The localized concentration of PTMS was found to positively correlate with the protein concentration in the case of lipase and negatively correlate in the case of lysozyme and BSA. These results indicate that lysozyme and BSA concentration was higher in areas of low hydrophobicity, while lipase concentration was higher in areas of high hydrophobicity within the sol–gel. Additionally, as determined by peak shape analysis of the amide I peak a higher PTMS content appeared to conserve protein structure in high concentration clusters for lipase. In contrast, lysozyme and BSA, appeared to retain their structure in high concentration clusters better at lower PTMS contents. A hypothesis speculating on the nature of the hydrophobic/hydrophilic interactions between the proteins and the sol–gel domains as the reason for these differences is presented.     

Surface properties of sol–gel treated thermally modified wood

The application of inorganic sol coating agents is a versatile method for wood surface functionalisation. However, the use of sols for the surface finishing of thermally modified wood (TMT) so far has not been investigated thoroughly. This paper reports on the surface properties of TMT treated with modified silica sols. The silica sols are modified with the inorganic colour pigment iron oxide red. Pigment distribution and height profiles of sol treated TMT are characterised by optical microscopy in 3D mode and by scanning electron microscopy. Selected evaluations are also repeated after artificial weathering of the coated wood specimens. Hydrophobic surface properties are determined using contact angle measurements. The coloration can be adjusted by the degree of pigmentation of the applied nanosol. Moreover, the water repellency of TMT is significantly enhanced by the sol treatment. Therefore, the application of pigment modified nanosols could lead to TMT with improved weathering stability and a wider coloration spectrum.     

Nucleation and fractal growth of zirconium oxo-alkoxy nanoparticles at the induction stage of sol–gel process

Monodispersed zirconium oxo-alkoxy nanoparticles are synthesized via a sol?Cgel method in a rapid micromixing reactor with in situ particle size measurements. The nucleated nanoparticles of 4.7?nm diameter are free from impurities and conserve high chemical activity. They can be associated in 1D fractals. These nanoparticles can form high optical-quality coatings on hydrophilic substrates.