Study on the temperature-induced sol–gel transition of cellulose/silk fibroin blends in 1-butyl-3-methylimidazolium chloride via rheological behavior

Temperature-induced sol–gel transition of cellulose/silk fibroin/1-butyl-3-methylimidazolium chloride ([BMIM]Cl) was studied from the viscosity and dynamic modulus of the mixtures. The shear thinning behavior of the mixture solution was very obvious with a decrease in temperature. The curves of storage modulus G′ and loss modulus G″ were parallel when the temperature was below 20 °C, indicating that a gel structure exists in the system. The sol–gel transition process was described according to Winter and Chambon’s theory. The gel structure of the mixture system was loosened with the increase of silk fibroin concentration.     

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.     

Effect of pendant group on the second-order optical nonlinearity of sol–gel films

A series of organically modified sol–gel films with various acceptor groups were prepared and characterized. All the chromophores exhibit much larger microscopic optical nonlinearity compared with the classical chromophore DR1 in solvatochromic measurement. Using in situ second harmonic generation (SHG) technique, the optimal poling temperatures (T _opt) for sol–gel films were obtained. The second harmonic coefficients (d ₃₃) of hybrid films at the wavelength of 1,064 nm were in the range of 50.1–70.3 pm/V after corona poling under their T _opt. The NLO stabilities of these poled films were also investigated by tracing the d ₃₃ value as a function of temperature and time. One of the hybrid films, which was prepared from chromophore 2,4-dinitro-4′-(N,N-dihydroxyethyl) aminoazobenzene exhibited a combination of large optical nonlinearity and high NLO stability. Furthermore, the effects of molecular structure on the NLO property and thermal stability of the hybrid films were also discussed.     

Effect of annealing on photoluminescence of blue-emitting ZnO nanoparticles by sol–gel method

In this work, we investigated the influence of annealing on the crystallinity, microstructures, and photoluminescence (PL) properties of ZnO nanoparticles prepared by sol–gel method. The annealing was carried out both in air and vacuum. X-ray powder diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy were used to characterize the crystal structures, diameter, surface morphology, and PL properties of ZnO nanoparticles. It has been found that both the as-grown and annealed ZnO nanoparticles had a hexagonal wurtzite crystal structure, and their average diameter and crystallinity increased with the anneal time and temperature. Pure blue-emitting behavior was observed in all samples. The emission intensity of ZnO nanoparticles was found to be enhanced after annealing, but it was highly dependent on the annealing conditions. Optimal annealing conditions both in air and vacuum were obtained for achieving maximum emission intensity in the ZnO nanoparticles. The dependence of PL properties of the ZnO nanoparticles on the annealing conditions was discussed.     

Effect of hydrophobic and hydrophilic additives on sol–gel transition and release behavior of timolol maleate from polycaprolactone-based hydrogel

The objective of this work was to delineate the effect of hydrophilic and hydrophobic polymeric additives on sol–gel transition and release profile of timolol maleate (TM) from poly (ethylene glycol)–poly (ε-caprolactone)–poly (ethylene glycol) (PEG–PCL–PEG)-based thermosensitive hydrogel. Polycaprolactone (hydrophobic additive) and polyvinyl alcohol (PVA) (hydrophilic additive) reduced critical gel concentration of PEG–PCL–PEG triblock polymer. The effect of PCL on sol–gel transition was more pronounced than PVA. However, with PCL no statistically significant difference in release profile was observed. The effect of PVA on release profile was more pronounced, which reduced the cumulative percentage release of TM from 86.4 ± 0.8% to 73.7 ± 1.8% over 316 h. Moreover, cytotoxicity of the hydrogel was also investigated utilizing rabbit primary corneal epithelial culture cells. No significant cytotoxicity of hydrogel alone or in presence of additives was observed. So, polymeric additive strategy serves as a valuable tool for optimizing TM release kinetics from PEG–PCL–PEG hydrogel matrix.     

Effect of glycerol on the optical and physical properties of sol–gel glass matrices

Glass samples are prepared with different amount of glycerol as drying control chemical additive (DCCA) via acid catalysed sol–gel method. These samples are given solvent treatment namely rinse and dip with methanol while drying of the sample. In rinse treatment solid sample is rinsed with small amount of methanol while in dip treatment sample is dipped for 5 h in methanol. Comparative studies of these treated samples containing varied DCCA concentration are carried out by measuring optical transmission, mechanical strength and bulk density. Various instrumental techniques used for analysis are FTIR, DTA-TGA, XRD, SEM and TEM. The untreated samples take long time to dry up and to come out of the cuvette and show very less transmission in UV region which is much enhanced by solvent treatment. On the basis of this study, the solvent treated glass samples with DCCA amount 8 ml in the composition used are found to have the maximum UV transmission, good mechanical strength and may be useful as silica gel host matrices for solid state dye lasers and other applications. The UV transmission reported in the present studies is 90% in 337 nm region, which is the wavelength of N₂ laser pumping.     

Fluorescence studies of the sol–gel transition in deoxygenated conditions

The results of steady-state and time-resolved fluorescence studies of the sol-gel transition initiated by acidic hydrolysis of silane sols of pH 1.8–5.9 are presented. The gelation process was carried out in an oxygen-free atmosphere using pyrene as a fluorescence probe at concentrations of 1×10 ^-5–1×10 ^-2 M. The silica gels were prepared from sols consisting of tetraethylorthosilicate, ethanol and water in a molar ratio of 1:6:6. The steady-state spectra recorded during gelation allowed the polarity to be determined in the microenvironment of the probe for different pH and pyrene concentration. The investigation of the kinetics of fluorescence decay permitted us to discuss the formation of pyrene aggregates due to variations occurring in the gel net.     

Effect of strontium substitution on the composition and microstructure of sol–gel derived calcium phosphates

Sr-doped calcium phosphates have been prepared by sol–gel chemistry. All samples exhibit two phases: hydroxyapatite (HAp) and tricalcium phosphate (β-TCP). With respect to undoped sample, the Sr-doped samples exhibit higher proportion of β-TCP phase but the quantity appears to be quite independent of the doping level. To explain the mismatch with the nominal stoichiometry, the presence of amorphous CaO and SrO compounds have been postulated and their proportions evaluated. The insertion of Sr²⁺ ions in the two crystalline phases HAp and β-TCP is almost total for low doping levels but quite incomplete for the highest doping level. The majority of the inserted Sr²⁺ ions are in the β-TCP phase. Considering the acknowledged beneficial effect of Sr²⁺ on the bone regeneration process, the effective partial substitution of Sr in biphasic calcium phosphate makes these materials very interesting for clinical applications. The Sr-substituted HAp and β-TCP cell parameters agree fairly well with the Vegard’s law and Sr²⁺ ions substitute preferentially for Ca²⁺ in the Ca2 site for hydroxyapatite and in the Ca4 site for β-TCP. The microstructural parameters confirm the previous observation and give a new evidence of clear stabilizing effect of Sr²⁺ ions towards the β-TCP structure.     

Effect of microstructure and surface roughness on the wettability of superhydrophobic sol–gel nanocomposite coatings

Sol–gel nanocomposite coatings were fabricated by spraying precursor mixtures containing hydrophobically modified silica (HMS) nanoparticles dispersed in sol–gel matrices prepared with acid-catalyzed tetraethoxysilane (TEOS), and methyltriethoxysilane (MTEOS). The hydrophobicity of the coatings increased with increase in the concentration of HMS nanoparticles. Superhydrophobic coatings with water contact angle (WCA) of 166° and roll-off angle <2° were obtained by optimizing the sol–gel processing parameters and the concentration of silica nanoparticles in the coating. FESEM studies have shown that surface has a micro-nano binary structure composed of microscale bumps and craters with protrusions of nanospheres. The properties of composite coatings fabricated by spin coating and spray coating methods were compared. It was found that the microstructure and the wettability were also dependent on the method of application of the coating.     

Photo-assisted electrodeposition of sol–gel films on p-type semiconductors

A new approach for the deposition of sol–gel films on semiconducting substrate using photo-electrochemical technique is presented. The deposition is based on accelerating sol–gel condensation reaction by the catalyzing effect of electrochemically generated OH⁻ ions when applying both negative potentials and light irradiation onto p-type semiconductors. Results show that both the negative shift in potential and the increase in light intensity facilitate the deposition kinetics of silica sol–gel films. Surface patterning is further achieved with the assistance of a laser.     

Effect of silver incorporation on crystallization and microstructural properties of sol–gel derived titania thin films on glass

Titanium dioxide (TiO₂) thin films, with and without silver (Ag), were prepared on float glass via sol–gel processing. The float glass substrates were pre-coated with a silica-barrier layer prior to the deposition of TiO₂-based thin films. Silver nanoparticle incorporation into the TiO₂ matrix was achieved by thermal reduction of Ag ions dissolved in a titanium-n-butoxide (Ti[O(CH₂)₃CH₃]₄) based sol during calcination in air at 250, 450 and 650 °C. Thin films were characterized using glancing incidence X-ray diffraction, UV–visible spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The effects of Ag concentration and calcination temperature on microstructure and on chemical and physical properties of the thin films have been reported. The size and chemical state of Ag particles, as well as the phase characteristics of the titania matrix were strongly influenced by Ag concentration and calcination temperature. Results from this study can be utilized in both processing and structure-functional property optimization of sol–gel based Ag-TiO₂ thin films by aqueous routes.     

Effect of nickel and cobalt ions on low temperature synthesis of mullite by sol–gel technique

Synthesis of mullite has been achieved at a low temperature of 600 °C by sol–gel technique in presence of nickel and cobalt ions. Samples were characterized by DTA, XRD, FESEM and FTIR spectroscopy. Mullite formation was found to depend on the concentration of the ions to a certain extent. Highly crystalline spherical mullite particles of dimension 35 nm were obtained at 0.02 M nickel or cobalt concentration.     

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.     

Evidence of ZrO2 sol–gel transition by gelation time and viscosity

Journal of Sol-Gel Science and Technology - Sol–gel transition is a stage of the sol that evolves towards the formation of a gel-like network and that exhibits gradually a mobility loss....     

Effect of CaO additive on sintering and crystallization behavior of cordierite glass–ceramic prepared by sol–gel method

In the present work, cordierite glass–ceramic was prepared via sol–gel method using TEOS, AlCl₃·6H₂O, MgCl₂·6H₂O as starting materials. Different steps of phase transformations to cordierite have been studied by DSC and XRD. Various phases have been formed at different heat-treatment temperatures. Addition of CaO led to an increase in both the formation rate and the intensity of α-cordierite. Sinterability of the samples was determined too. The results showed that high content of CaO improved sintering. Morphology of hexagonal prism for α-cordierite was displayed by SEM.     

Effect of annealing temperature on the quality of Al-doped ZnO thin films prepared by sol–gel method

The different thermal expansion coefficients and lattice mismatch between ZnO and Al may produce residual stress in Al-ZnO (AZO) thin films. Annealing processes can be applied to modulate this residual stress. In this study, three different rapid thermal annealing (RTA) temperatures (350, 450, and 600 °C) were applied to an AZO thin film, prepared using sol–gel method. The mechanical properties, optical properties, and structure of the AZO thin film were investigated experimentally. The results show that increasing the RTA temperature increased the Young’s modulus and hardness of the films. The grain size of the films also increased with increasing RTA temperature. However, the film thickness and shear stress component decreased with increasing RTA temperature. Both compressive and tensile stress decreased gradually with increasing film thickness after RTA treatment. It was demonstrated that the use of a relatively high RTA temperature can effectively relax the residual stress in AZO thin films.     

Effect of post-treatment (gel aging) on the properties of methyltrimethoxysilane based silica aerogels prepared by two-step sol–gel process

The properties of silica aerogels are highly dependent on the post-treatment steps like gel washing, gel aging and gel drying. The experimental results of the studies on one of the post-treatment steps i.e. gel aging effect on the physical and microstructural properties of methyltrimethoxysilane (MTMS) based silica aerogels, are reported. These hybrid aerogels were prepared by two step sol–gel process followed by supercritical drying. The molar ratio of MeOH/MTMS (M) was varied from 7 to 35 by keeping the H₂O/MTMS (W) molar ratio constant at 4. The as prepared alcogels of different molar ratios were aged from 0 to 5 days. It was observed that 2 days of gel aging period is the optimum gel aging period for good quality aerogels in terms of low density, less volume shrinkage and high porosity. The well tailored network matrix with low density (0.04 g/cm³), less volume shrinkage (4.5%), low thermal conductivity (0.05 W/mK) and high porosity (98.84 %) was obtained for 2 days of gel aging period of M = 35. Further, the gelation time varied from 8 to 1 h depending on the M values. The gelation time was being more for lesser M values. The aerogels were characterized by bulk density, porosity, volume shrinkage, thermal conductivity, Scanning Electron Microscopy and the Fourier Transform Infrared spectroscopy.