Journal of Sol-Gel Science and Technology

Thermally curable interpenetrating networks employing short and long chain components were successfully prepared via the sol-gel route. Their mechanical properties were assessed and correlated to their composition and structure. The role of the organic cross-links was found to be a larger determinant of the mechanical properties than the inorganic network. Their low frequency dielectric properties were investigated and found to be comparable to those of conventional encapsulation materials. Observed mass losses at 523 K ranged between 3–5% after 1000 minutes, the suspected mechanism being the development of organic cross-links.

In this research, tribological properties of Fe3O4/TiO2 composites were investigated. To improve the tribological properties and dispersion of Fe3O4 nano-lubricant additives, the nanoparticles were modified via the Stöber method, then TiO2 shells were successfully coated on the Fe3O4 surface with chemical techniques. The results showed that the average particle size of Fe3O4/TiO2 nanostructures was about 360–420 nm. The TiO2 shell with a thickness of about 36 nm is deposited on the surface of Fe3O4. The tribological performance of base oil including Fe3O4/TiO2 nanostructures were determined by a ball-on-disk tribometer. Results of friction tests showed that the Fe3O4/TiO2 nanostructures can reduce the friction coefficient by 7.78% compared to base oil. The average wear volume and wear scar width of base oil with 0.25 wt% Fe3O4/TiO2 additive compared to pure base oil decreased by 44.47% and 11.02%, respectively, which can be correlated to the synergistic effect of TiO2 and Fe3O4 from the Fe3O4/TiO2 composites.

A unique photochemical sol–gel route was employed to prepare La-doped Bi4Ti3O12 film (BLT) using bismuth nitrate, lanthanum nitrate, and titanium tetra-n-butoxide as starting materials. Through complex reaction between benzoyl acetone and Ti4+ ions, the synthesized La-doped Bi4Ti3O12 sol and gel films exhibited photosensitivity. Micro-patterned BLT film was obtained by a photoresist-free micro-patterning technique. The phase microstructures, electrical and ferroelectric properties of the as-prepared BLT film were characterized. By doping Lanthanum, the strong (00l)-oriented BT phase was transformed to randomly-oriented orthorhombic phase, resulting in the enhanced remanent polarization and improved fatigue properties. The obtained BLT film showed good ferroelectric properties with a long fatigue cycles over 1010 cycles.

Hydroxyapatite coatings can be readily deposited on metal substrates by electrophoretic deposition. However, subsequent sintering is highly problematic owing to the fact that temperatures in excess of 1100°C are required for commercial hydroxyapatite powders to achieve high density. Such temperatures damage the metal and induce metal-catalysed decomposition of the hydroxyapatite. Furthermore, the firing shrinkage of the hydroxyapatite coating on a constraining metal substrate leads to severe cracking. The present study has overcome these problems using a novel approach: the use of aged nanoparticulate hydroxyapatite sols (lower sintering temperature) and a dual coating strategy that overcomes the cracking problem. Dual layers of uncalcined hydroxyapatite (HAp) powder were electrophoretically coated on Ti, Ti6Al4V and 316L stainless steel metal substrates, sintered at 875–1000°C, and characterised by SEM and XRD, and interfacial shear strength measurement. Dual coatings on stainless steel had an average high bond strength (about 23 MPa), and dual coatings on titanium and titanium alloy had moderate strengths (about 14 and 11 MPa, respectively), in comparison with the measured shear strength of bone (35 MPa). SEM and XRD demonstrated that the second layer blended seamlessly with the first and filled the cracks in the first. The superior result on stainless steel is attributed to a more appropriate thermal expansion match with hydroxyapatite, the thinner oxide layer, or a combination of these factors.

SiO2 sols were prepared by hydrolysis and condensation reactions of tetraethyl orthosilicate through a one step acid or a two step acid + base catalysis process, in the presence of nitric acid and four different base catalyzers, namely trimethylamine, triethylamine, tripropylamine and tributylamine. Hydrolysis of TEOS was followed by FT-IR analyses. Particle size distributions of the sols were evaluated after predetermined durations in 1–22 days. Particle growth was seen to be faster in amine catalyzed systems than in one step acid catalyzed system. The highest rate of growth was in triethylamine catalyzed system. Glass substrates were dip coated with the prepared SiO2 sols. Effect of sol aging duration on film thickness and on light transmittance properties of the films was investigated with respect to type of base catalyst. Thicknesses of the films which were measured to be in the range of 100–400 nm, were seen to increase with aging duration of the sols. Triethylamine catalyzed system presented the highest film thickness. Films obtained from one step acid catalyzed system presented an increase of 4.8%; whereas acid + base catalyzed films provided an increase in the light transmittance of 5.7% in the first 4 days of aging. Surfaces of films were examined by FESEM and AFM. The antireflective character of the films was verified by diffuse reflectance analyses.

Magnetic thrombolytic composites are a promising and rapidly developing class of nanostructured bioactive materials with plausible applications in cardiovascular diseases treatment. This class of nanoformulations can be applied to enhance the efficiency of thrombolytic agent delivery in occluded vessels. The main trends in this topic are aimed at the simplification of the composition, enhancement of specific activity, and completeness of action of the formulations. Herein we describe four thrombolytic systems prepared using urokinase-type plasminogen activator (uPA) conjugated to a magnetite core via polyelectrolyte molecules, namely heparin, enoxaparin, polyacrylic acid (PAA) and polystyrene sulfonate (PSS). All systems, except PSS-based, demonstrated close thrombolytic activities when taken in equivalent quantities, while the heparin based system demonstrated 30% greater activity at early stages of clot lysis. Both heparin and enoxaparin-based systems showed moderate anticoagulant activities which prolonged thrombin time from 13 to 17 s that is 3.1 and 1.5-folds lower than for equal amounts of free anticoagulants. The enoxaparin-based formulation inhibited the intrinsic coagulation pathway by 30%, while all other composites were ineffective for this purpose. These findings can be further applied for development of magnetically controlled nanomedicines with dual anticoagulant and thrombolytic properties.

Sol-gel-derived silica films were fabricated by dip-coating onto planar and optical fibre substrates. The films were pre-doped with the oxygen-sensitive ruthenium complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)], whose fluorescence is quenched in the presence of oxygen. The structure and behaviour of sol-gel films is related to the fabrication parameters. In order to optimise the films for oxygen sensing in gaseous and in aqueous media, the quenching behaviour was monitored as a function of dip-speed and water : precursor ratio. By adjusting the above parameters, film properties can be tailored to optimise oxygen quenching in particular concentration ranges and environments.