Antiwetting silica–gelatin nanohybrid and transparent nano coatings synthesised through an aqueous sol–gel process

Hydrophobic silica-biopolymer hybrid has been synthesised using colloidal silica as the precursor for silica, gelatin as the biopolymer counterpart and vinyltrimethoxysilane as the surface modifier through a sol–gel method. The precursor sol was coated on glass substrates and further investigated for the extent of chemical modification, thermal degradation, hydrophobicity, particle size and transparency in the UV-Visible region. Stereomicrographs clearly indicate the water repellent nature of the hybrid coatings with respect to a water drop. FTIR was used to follow the presence of vinyl groups that impart hydrophobicity to the resultant hybrids. By varying the concentration of functionalizing agent, the extent of hydrophobic property could been tailored. The optimum concentration for effective surface modification of the silica–gelatin hybrid is about 50 wt%. Nearly 100% optical transmittance was obtained for silica–VTMS–gelatin hybrid coatings on glass substrates and this may have potential applications in optical devices and also for transparent biocompatible hydrophobic coatings on biological substrates such as leather.     

Synthesis of mesoporous hydrophobic silica microspheres through a modified sol–emulsion–gel process

Mesoporous silica microspheres were synthesised through a sol–emulsion–gel process using Span 80 as the surfactant in silica sol/n-hexane water in oil emulsion system. Surface modification of the microspheres was done with trimethylchlorosilane to obtain hydrophobic silica microspheres. Various parameters related to the synthesis of microspheres, including concentration of surfactant and viscosities of sol were studied. The hydrophobicity (wettability), thermal stability, porosity, and morphological features were also investigated.     

Silica–titania aerogel monoliths with large pore volume and surface area by ambient pressure drying

Ambient pressure drying has been carried out for the synthesis of silica–titania aerogel monoliths. The prepared aerogels show densities in the range 0.34–0.38 g/cm³. The surface area and pore volume of these mixed oxide aerogels are comparable to those of the supercritically dried ones. The surface area for 5wt% titania aerogel has been found to be as high as 685 m²/g with a pore volume of 2.34 cm³/g and the 10wt% titania aerogel has a surface area of 620 m²/g with a pore volume of 2.36 cm³/g. Some gels were also made hydrophobic by a surface treatment with methyltrimethoxysilane and trimethylchlorosilane. The surface modified aerogels possess high surface areas in the range of 540–640 m²/g, and are thermally stable in terms of retaining hydrophobicity up to a temperature of 520 °C. The pore size distribution of the aerogels clearly indicates the preservation of the aerogel structure. High Resolution Transmission Electron microscopy has been employed to characterise the aerogels and Fourier Transform infrared spectroscopy to study the effect of titania addition to silica and the surface modification. X-ray diffraction patterns were recorded to verify the molecular homogeneity of the aerogel.     

Effect of 3-glycidoxypropyltrimethoxysilane precursor on the properties of ambient pressure dried silica aerogels

The effect of an organically modified precursor, 3-glycidoxypropyltrimethoxysilane in an ambient pressure process involving aging in silane solution for silica aerogels is presented. The effect of increasing trialkoxysilane/tetraalkoxysilane precursor ratio and the influence of water to Si molar ratio on the gelation and adsorption properties were investigated. An optimum water to Si molar ratio (8) gave the fastest gelation for all precursor ratios indicating a balance between the increase in rate of hydrolysis and a decrease in concentration of the monomers. Surface area analysis proved that in the dried gel, the organic groups are largely present on the pore walls and prevent the condensation of the silanol groups during drying. This in turn prevents pore collapse and further increases the total pore volume. The inclusion of the organically functionalised silane in the process further enhances the ambient pressure drying through this effect.     

Synthesis of biocompatible hydrophobic silica-gelatin nano-hybrid by sol-gel process

Silica-biopolymer hybrid has been synthesised using colloidal silica as the precursor for silica and gelatin as the biopolymer counterpart. The surface modification of the hybrid material has been done with methyltrimethoxysilane leading to the formation of biocompatible hydrophobic silica-gelatin hybrid. Here we are reporting hydrophobic silica-gelatin hybrid and coating precursor for the first time. The hybrid gel has been evaluated for chemical modification, thermal degradation, hydrophobicity, particle size, transparency under the UV-visible region and morphology. FTIR spectroscopy has been used to verify the presence of CH(3) groups which introduce hydrophobicity to the SiO2-MTMS-gelatin hybrids. The hydrophobic property has also been tailored by varying the concentration of methyltrimethoxysilane. Contact angle by Wilhelmy plate method of transparent hydrophobic silica-gelatin coatings has been found to be as high as approximately 95 degrees . Oxidation of the organic group which induces the hydrophobic character occurs at 530 degrees C which indicates that the surface hydrophobicity is retained up to that temperature. Optical transmittance of SiO2-MTMS-gelatin hybrid coatings on glass substrates has been found to be close to 100% which will enable the hybrid for possible optical applications and also for preparation of transparent biocompatible hydrophobic coatings on biological substrates such as leather.     

Ambient pressure drying: a successful approach for the preparation of silica and silica based mixed oxide aerogels

Silica aerogels have received much attention in recent years as it has got a wide range of properties like high surface area, low density, high porosity, low dielectric constant, low thermal conductivity. Recently to make aerogels for commercial application ambient pressure drying has been preferred and also a cheap precursor like sodium silicate has been employed as the starting material instead of the alkoxides. In this review, attention will be given to the synthesis adopted for the preparation of silica and silica based mixed oxide/composite aerogels through ambient pressure drying. The properties of the prepared aerogels are also discussed in detail.     

Synthesis of lanthanum oxide doped photocatalytic nano titanium oxide through aqueous sol–gel method for titania multifunctional ultrafiltration membrane

An all aqueous sol gel route has been demonstrated for the synthesis of titania multifunctional ultrafiltration membrane on porous alumina substrate. Doping with lanthana was used to increase the thermal stability of anatase phase. This resulted in a nanoporous membrane with considerable percentage of anatase phase even after consolidation at 800°C. The highly homogeneous membranes with a thickness of ~4–5 μm could be observed in SEM. The presence of anatase phase ensured higher photoactivity for the doped membrane compared to the undoped one. The performance of the membrane was tested based on molecular weight cut off and a very high (>90%) filtration efficiency was observed on Bovine Serum Albumin of molecular weight 66 kD. Rejection of 11 nm sized particles points to the uniform nanoporous nature of these highly efficient membranes.     

Functionalized Ultrabright Fluorescent Mesoporous Silica Nanoparticles

The problem of functionalization of recently reported ultrabright fluorescent mesoporous silica nanoparticles while preserving their fluorescent brightness is solved. This is a serious issue because of the open geometry of mesoporous channels and physical encapsulation of fluorescent dye inside those channels. Amine modification of mesoporous nanoparticles is described to preserve the brightness comparable to that of earlier reported ultrabright silica nanoparticles. Scaling to 40 nm sized particles, amine‐functionalized nanoparticle have fluorescent brightness equivalent to the one of 630 free rhodamine 6G (R6G) dye molecules in water. To demonstrate further most challenging functionalization, which relies on using organic‐solvent‐based chemistry, folic acid conjugation is developed. Two different methods are used to conjugate folites to the amine functionalities. Both methods result in a decrease of fluorescence intensity, which can nonetheless still be called ultrabright. The brightness can drop to either 310 or 80 R6G dye molecules per particle of nominal diameter of 40 nm.     

$\mathcal{PT}$-Symmetric Quantum Electrodynamics—$\mathcal{PT}$QED

The construction of PT\mathcal{PT}-symmetric quantum electrodynamics is reviewed. In particular, the massless version of the theory in 1+1 dimensions (the Schwinger model) is solved. Difficulties with unitarity of the S-matrix are discussed.     

Non-supercritically dried silica–silica composite aerogel and its possible application for confining simulated nuclear wastes

The simpler non-supercritical drying approach has been used for the first time for the preparation of silica–silica composite aerogels (CA) and the efficiency of the process being demonstrated by testing the use of the aerogels for simulated high level nuclear waste confinement. Compositions of 5, 10, 20, 30, 40 and 50 wt% of silica (aerosil® 380) in silica–aerogel were prepared by introducing pyrogenic silica in to silica sol derived by hydrolysis of Tetraethoxy silane (TEOS). The silica–silica composite aerogels (CA) possessed very high surface area and low bulk densities. The effectiveness of the prepared composite aerogels as precursor for high level nuclear waste immobilized glass is also presented. Neodymium nitrate dissolved in isopropanol is used to simulate +3 valent actinides. The stability of neodymium in the glass matrix has been found to be extremely high. Transmission electron microscopy (TEM) has been used to characterise the aerogels as well as neodymium incorporated sintered gels. X-ray diffraction (XRD) studies of the sintered samples reveal the formation of neodymium silicates.