Sol–gel coating of cellulose fibres with antimicrobial and repellent properties

Multifunctional, water and oil repellent and antimicrobial finishes for cotton fibres were prepared from a commercially available fluoroalkylfunctional water-born siloxane (FAS) (Degussa), nanosized silver (Ag) (CHT) and a reactive organic–inorganic binder (RB) (CHT). Two different application procedures were used: firstly, one stage treatment of cotton fabric samples by FAS sol (i), as well as by a sol mixture constituted from all three precursors (Ag–RB–FAS, procedure 1S) (ii), and secondly, two stage treatment of cotton by Ag–RB sol and than by FAS sol (Ag–RB + FAS, procedure 2S) (iii). The hydrophobic and oleophobic properties of cotton fabrics treated by procedures (i)–(iii) before and after consecutive (up to 10) washings were established from contact angle measurements (water, diiodomethane and n-hexadecane) and correlated with infrared and XPS spectroscopic measurements. The results revealed that even after 10 washing cycles cotton treated with Ag–RB + FAS (2S) retained an oleophobicity similar to that of the FAS treated cotton, while the Ag–RB–FAS (1S) cotton fibres exhibited a loss of oleophobicity already after the second washing, even though fluorine and C–F vibrational bands were detected in the corresponding XPS and IR spectra. The antibacterial activity of cotton treated by procedures (i)–(iii) was tested by its reduction of the bacteria Escherichia coli and Staphylococcus aureus following the AATCC 100-1999 standard method and EN ISO 20743:2007 transfer method. The reduction in growth of both bacteria was nearly complete for the unwashed Ag–RB and Ag–RB–FAS (S1), but for the unwashed Ag–RB + FAS (S2) treated cotton no reduction of S. aureus and 43.5 ± 6.9% reduction of E. coli was noted. After the first washing, the latter two finishes exhibited nearly a complete reduction of E. coli but for the Ag–RB treated cotton the reduction dropped to 88.9 ± 3.4. None of the finishes retained antibacterial properties after 10 repetitive washings. The beneficial and long-lasting low surface energy effect of FAS finishes in the absence of Ag nanoparticles, which led to the “passive” antibacterial properties of FAS treated cotton fabrics, was established by applying the EN ISO 20743:2007 transfer method. The results revealed a reduction in bacteria of about 21.9 ± 5.7% (FAS), 13.1 ± 4.8% (Ag–RB–FAS (S1)) and 41.5 ± 3.7% (Ag–Rb + FAS (S2)), while no reduction of the growth of bacteria was observed for cotton treated with Ag nanoparticles after 10 repetitive washings. The physical properties (bending rigidity, breaking strength, air permeability) of finished cotton samples were determined, and showed increased fabric softness and flexibility as compared to the Ag–RB treated cotton, but a slight decrease of breaking strength in the warp and weft directions, while air permeability decreased for all type of finishes.     

Sol–gel preparation of double-layer tri-wavelength antireflective coating

Double-layer tri-wavelength antireflective (AR) coating effective simultaneously at 351, 527 and 1,053?nm has been designed and prepared by the sol?Cgel process. The refractive index and film thickness of bottom layer and up layer are 1.27 and 113?nm, and 1.17 and 245?nm, respectively. The bottom layer with refractive index of 1.27 was prepared from a mixture of acid-catalyzed and base-catalyzed silica sols, and the up layer with refractive index of 1.17 was prepared from polypropylene oxide modified silica sol. It was found that the addition of polypropylene oxide into the sol significantly decreased the refractive index and increased the hydrophobicity of the AR coating. The obtained tri-wavelength AR coating gives very high transmittance of 99.7, 99.1 and 98.0?% at 351, 527 and 1,053?nm, simultaneously.     

Sol–gel derived durable antireflective coating for solar glass

In this paper, we present the design and preparation of a type of high-strength SiO₂/TiO₂ AR coatings used in solar glass by dip coating method. The average transmittance of glass coated in this way is increased by more than 6% in the wavelength from 400 to 800 nm, which fits well with the theoretical expectation. The mechanical performance and atmospheric exposure tests prove that the coatings have scratch resistance, erosion resistance and long-time stability. The AFM morphology shows that the surface of the coating is very smooth with the experimental result of RMS roughness 0.306 nm. These phenomena indicate that the SiO₂/TiO₂ AR coatings have high potential commercialization for low-cost solar glass.     

Sol–gel silica antireflective coating with enhanced abrasion-resistance using polypropylene glycol as porogen

Silica antireflective (AR) coatings with high transmittance and enhanced abrasion-resistance were synthesized by sol–gel process using polypropylene glycol (PPG) as porogen. The effects of molecular weight of PPG and weight ratio of PPG to SiO₂ on the refractive index and abrasion-resistance of the coating were systematically studied and compared with those of polyethylene glycol (PEG). Experimental data showed that the refractive index decreased with increasing the weight ratio to SiO₂ and molecular weight of both PEG and PPG, but PPG was much more effective than PEG. In the case of same molecular weight, PPG modified coating has the higher porosity than PEG modified one. When the weight ratio of PPG to SiO₂ is in a low level, the PPG-containing silica AR coatings exhibit the good abrasion-resistance. PPG is liquid at room temperature and the better solubility than PEG. These effective and economic AR coatings with enhanced abrasion-resistance have potential value in the field of solar thermal collectors.     

Sol–gel titania coating on unmodified and surface-modified polyimide films

Sol–gel coating of metal oxides on polymer substrates is a useful process to fabricate various organic–inorganic hybrid materials under mild conditions. However, this process is hardly applicable to pristine polyimide (PI) films because their surfaces do not display effective functional groups for metal oxide coatings. In this study, we firstly examined direct sol–gel coating of titania thin layers on unmodified PI film surfaces. The results confirmed homogeneous, ultrathin titania layer coating and showed that the thickness and microscopic morphology of the titania layers were affected by titanium alkoxide concentrations in the spin coating solutions. We next investigated titania layer coating on surface-modified PI films that prepared using alkaline hydrolysis, which generated carboxylic acid groups on the film surfaces. Optimal hydrolysis time was determined using FT-IR spectroscopy and contact angle measurements. After sol–gel titania coating on the hydrolyzed PI film surfaces, the Scotch tape test was conducted to evaluate adhesion strength between the titania layers and PI film surfaces. Morphological observations of the sample surfaces after the tests clearly showed that surface modification of PI films increased titania layer adhesions. Effect of hydrothermal treatments on film formability and adhesion strength between titania-PI film interfaces was also evaluated.     

Sol–gel titania coating on NiTi alloy with a porous titania film as interlayer

Porous titania film is prepared by alkali treatment of NiTi alloy followed by soaking treatment in HCl solution. The benefit of this porous titania film as an interlayer to improve adhesion and integrity of the sol–gel titania coating on NiTi alloy substrate is evidenced by surface morphological observations. X-ray diffraction analyses indicate the formation of Ni₄Ti₃ phase in the matrix during heat treatment of the NiTi samples. X-ray photoelectron spectroscopy results indicate that the titania coating with two dip-coating layers has completely covered the NaOH–HCl treated NiTi substrate, and potentiodynamic polarization tests show that this titania coating provides good protection for the treated NiTi substrate in 0.9% NaCl solution. Ultraviolet illumination can increase surface hydrophilicity of the NiTi samples by reducing contact angles from 60–80° to 20–10°.     

Sol–gel synthesis and optical behavior of Mg–Ce–O nano-crystallites

The Mg–Ce–O powder are shown to contain periclase-type MgO and/or fluoride-type cerium oxide (CeO₂) depending upon the composition (x) defined by Ce/(Ce + Mg) atomic ratio. Lattice contraction of pariclase phase of MgO (average crystallite size ~8.8 nm) at Ce content of ‘x’ = 0.20 in comparison to pure MgO (crystallite size ~9.5 nm) has been realized due to oxygen vacancy formation. The optical band gap values of CeO₂ varies (3.0–3.2 eV) due to oxygen vacancy formation in CeO₂ phase, crystallite size and/or Ce³⁺/Ce⁴⁺ ratio. Further, the addition of Ce has shown to reduce the physisorption and chemisorption of water significantly as reflected by (1) suppression of related absorption peaks and (2) absence of magnesium hydroxide, Mg(OH)₂, bands in Fourier transform infrared spectra.     

Fabrication and electrical characterization of transparent NiO/ZnO p–n junction by the sol–gel spin coating method

Sol–gel spin technique was used to fabricate transparent p–n junction between NiO and ZnO semiconductors. Atomic force microscopy studies indicated that ZnO film had a fibrous structure, while NiO film showed very smooth surface morphology. The optical transmittance of these films was about 75 %. The optical band gaps of ZnO and NiO films were obtained to be 3.25 and 3.89 eV, respectively. The current–voltage characteristics of NiO/ZnO junction showed a good rectifying behavior. The junction parameters such as ideality factor and barrier height were calculated using thermionic emission model. The barrier height and ideality factor values of the diode were obtained to be 0.48 and 2.91 eV, respectively. The variation of photocurrent with wavelength indicates that this device had high efficiency in wavelength range of 450–475 nm.     

Structural and optical properties of Na doped ZnO nanocrystalline thin films synthesized using sol–gel spin coating technique

Sodium (Na) doped Zinc oxide (ZnO) thin films have been deposited on a glass substrate by the sol–gel spin coating method. Effect of doping with various percentages of Na at a particular annealing temperature of 500 °C is studied. The samples were characterized by X-ray diffraction (XRD), micro-photoluminescence, Raman and Polarized Raman spectroscopy. The X-ray diffraction and micro-Raman spectroscopy confirmed the presence of Na substitution in zinc oxide and the wurtzite structure of the lattice is retained. An enhancement of resonant Raman scattering processes as well as longitudinal optical phonon overtones up to the fifth order were observed in the micro Raman spectra. The similar values of depolarization ratios obtained from Polarized Raman studies recommend no change in the symmetry. Photoluminescence showed a strong emission peak in the near UV at 3.2 eV and negligible visible emission.     

Proteins conjugation with ZnO sol–gel nanopowders

The conjugation between probe biomolecules and inorganic nanoparticles has been studied. Three different and biologically relevant proteins, bovine serum albumin (BSA), lysozyme (LSZ) and Ribonuclease A (RNAseA), have been selected as model systems because of their difference in size and isoelectric point. Zinc oxide nanoparticles, synthesized via sol–gel, have been thoroughly characterized by X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and X-ray Diffraction, and subsequently used as platforms for immobilization of the biomolecules. The interaction of the three proteins with the ZnO surface was performed in phosphate buffer solutions at pH 7.2 in order to mimic physiological fluids and was investigated through fluorescence experiments. The obtained results indicate that conjugation of BSA, LZS and RNAseA on the oxide nanoparticles was mostly dictated by the overall charge of the different proteins. Electrostatic bonds dominate the formation of the protein/ZnO conjugates, whereas the size of the proteins seems to play a negligible role under the adopted experimental conditions.     

Sol–gel behavior of a novel nanodroplet biomaterial for drug delivery

Nanodroplets can be considered as those nano/microemulsions in which the oil itself forms the active agent and the droplet size ambits in the nanometer range. Eugenol is an anti-inflammatory agent and its nanodroplet gel (NDG) has immense potential for topical use. Topical gels oblige some rheological characteristics to nail down the demands of proper application, stability and storage. Thus, the purpose of our study was to comprehend the effect of eugenol on the sol–gel tranisition properties of its NDGs. Towards this goal nanodroplets of eugenol were prepared and evaluated and the three selected nanodroplet formulations with 5, 10 and 5% v/v eugenol were converted into topical gel formulation using 1% w/w Carbopol 940. The NDGs were characterized using frequency sweep, creep recovery and thixotropy. All these tests pointed out that eugenol concentration has significant effect on the sol–gel behavior of NDGs. The NDGs exhibited more viscous (sol) properties than elastic (gel) properties as observed from the frequency sweep studies. The thixotropy of the NDGs was found to decrease with increase in eugenol concentration. Efforts have been made to explain the study results using mechanistic approach. The outcomes of our research studies could be of great use in future endeavors towards development of a topical NDG of eugenol with tailored sol–gel behavior.     

Sol–gel derived ZnO/porous silicon composites for tunable photoluminescence

ZnO/porous silicon nanocomposites were fabricated by spin-coating the sol?Cgels of zinc acetate onto the top surface of porous silicon films. The photoluminescent properties of ZnO/porous silicon nanocomposites were investigated as a function of the concentration of zinc cations in the sol?Cgels. Characterizations with scanning electron microscopy, X-ray diffractometry and photospectroscopy indicated that ZnO nanocrystals were embedded into the spongy nanostructures of porous silicon after heat treatment at 245?°C for 20?min in air. The recorded photoluminescence exhibited that orange to green?Cblue emissions were achieved for the ZnO/porous silicon nanocomposites as the concentration of zinc cations in the sol?Cgels increased from 4 to 260?mM. The mechanisms on the tunability of the photoluminescence were discussed for the ZnO/porous silicon nanocomposites. Our results have demonstrated that the incorporation of green?Cblue phosphors into the porous matrix of porous silicon represents one endeavor to tune the photoluminescence of porous silicon across the visible spectral region.     

Nano ZnO thin films synthesis by sol–gel spin coating method as a transparent layer for solar cell applications

Zinc oxide nano-structured thin films have been synthesized by low-temperature and cost-effective sol–gel spin coating method. Zinc oxide films with good adherence have been deposited on soda lime glass substrates with two thicknesses 250.15 and 311.32?nm. High transmission (>95%) zinc oxide films with proper interference fringes in the visible and near infrared region have been obtained. Film thickness, optical constants and dispersion parameters have been calculated accurately by using Swanepoel method, which basely depends on the interference fringes of the transmission spectra. Zinc oxide films have direct optical band gap, its values slightly change with the annealing temperatures and film thickness. The X-ray diffraction studies indicated the hexagonal wurtzite structure for zinc oxide films with preferred orientation along (002) plane. Raman spectroscopy confirmed the hexagonal structure for the films. The average particle size is in the nano-scale and the crystallinity level increases with the annealing temperatures and film thickness.

     

Preparation of thick and hard coating films via sol–gel process with a low temperature treatment

SiO₂-polymer hybrid thick and hard coating films were successfully obtained via sol–gel process with a heat treatment at 200 °C. The films were achieved by control of hydrolysis and poly-condensation reaction of silica species. Key parameters were pH, water content and additional polymer in the coating solution. No-cracking and highly transparent films were formed with polymer content in a range from 28 to 42 mass% [vs. SiO₂]. Their thickness was varied from 2.6 to 3.5 μm with an increase in the polymer content. The haze values of the films after Taber abrasion were very low in a range from 1.3 to 2.7%, and the pencil hardness was over 9H. Moreover, no-damage was observed on the surface after steel wool abrasion with 4 kg loaded. These high mechanical strengths were come up to that of float glass, so that the coating films prepared by this process have a great potential for application to architectural and automotive window glass.     

Room temperature ferromagnetism in sol–gel deposited un-doped ZnO films

Dilute magnetic semiconductors are fast emerging spintronic materials where advantage of magnetic properties of semiconductor materials (usually doped with small quantities of magnetic ions) is being explored. Sol–gel technique, being low-cost simple and application oriented method, has been used in the present case. ZnO films of <150 nm thickness have been deposited by spin coating onto single crystal p-type Si substrates. The optimized sol is of paramagnetic nature, whereas, mixed para- dia-magnetic phase is observed for the as-prepared films. A complete ferromagnetic phase transition has been observed after heating the films in vacuum at a temperature of 300 °C. These sol–gel prepared films exhibit hexagonal wurtzite structure as observed by X-ray diffraction. After the magnetic field annealing in vacuum the films showed strengthened magnetic as well as structural properties. This work presents a clear evidence of ferromagnetic behavior of the un-doped ZnO films deposited by sol–gel at room temperature. It is also pointed out that Zn vacancies rather than oxygen deficiency are responsible for ferromagnetism in these sol–gel deposited ZnO thin films, whereas, the experimental evidence has been substantiated with the theoretical calculations using density functional theory.     

Sol–gel synthesis and thermal behavior of bioactive ferrous citrate–silica hybrid materials

Journal of Thermal Analysis and Calorimetry - Imbalance of the iron level in the body causes several diseases. In particular, the low level of iron, during pregnancy, is responsible for the iron...