DIBUTYLTIN DILAURATE-CATALYZED DIISOCYANATE COUPLING- GRAFTING OF POLY(ETHYLENE GLYCOL) ONTO NANO-SILICA SURFACE THROUGH A ONE-STEP PROCEDURE

Grafting polymer glycols onto nano-silica surface through one-step procedure was investigated. The major characteristic of this procedure is that all the materials and reagents (silica, PEG, TDI, DBTDL, solvent) required for grafting were added simultaneously into the reaction vessel. TDI and DBTDL were used as coupling agent and catalyst, respectively.The products were characterized by FTIR, TGA, elemental analyses and TEM, giving evidence for successful grafting of PEG. Possible mechanism of this grafting was studied and two grafting processes were proposed. The process through which the grafting proceeds depends on the reaction temperature. Effect of molecular weight of PEG on grafting was also investigated.     

First and second coordination spheres in 8-azaxanthinato salts of divalent metal aquacomplexes – Ab initio and DFT study

The hydrogen bonding pattern in complexes of the type [M²⁺(H₂O)₆](dmax)₂ (M = Mn, Ni, Co, Zn, Cd, Hdmax = 1,3-dimethyl-8-azaxanthine), [M²⁺(H₂O)₄(py)₂](dmax)₂ (M = Mn, Co, Zn, Cd, py = pyridine) and [M²⁺(dmax)₂(H₂O)₂(py)₂]·2H₂O (M = Ni, Cu) were studied by ab initio (MP2/LANL2DZ//B3LYP/LANL2DZ) and density functional theory methods (B3LYP/LANL2DZ, B3LYP/6-31G^∗∗ and B3PW91/6-31G^∗∗). The investigation includes a variety of theoretical analyses, which include interaction energy, many body analyses, electron density analysis, topological analysis, Mulliken atomic charges, natural atomic charges and harmonic vibrational analysis. The geometrical parameters and vibrational frequencies of dmax (the mono anion of 1,3-dimethyl-8-azaxanthine), [M²⁺(H₂O)₆] (M = Mn, Ni, Co, Zn, Cd), [M²⁺(H₂O)₄·(py)₂] (M = Mn, Co, Zn, Cd) and the complexes, calculated by the theoretical methods, were compared with the recent X-ray crystallographic results and it was observed that the results are found to agree well with the crystallographic results. The present calculations provide an important physicochemical insight into metal cations with 1,3-dimethyl-8-azaxanthine. The results also reveal the active role of coordinated water molecules in modulating the binding of the cation through a specific network of hydrogen bonds. The topology of the motifs generated by these hydrogen bonds has been characterized, adapting to the second coordination sphere concepts usually applied to the first (monodentate, chelate, and bridge) coordination sphere. The optimized structures of the Cd²⁺, Zn²⁺ and Cu²⁺ complexes further interact among themselves in a less tight fashion to generate three dimensional structures (a tape-like hydrogen bond network). Finally these tape-like hydrogen bond network were optimized using the B3LYP/LANL2DZ basis set.     

Silica gel promoted synthesis of N-sulfonylcyclothioureas in water

N-Sulfonylcyclothioureas were synthesized from N-sulfonyldiamines and CS₂ with moderate to good yields in silica gel-water system. Moreover, the silica gel can be recycled for at least three times.     

In situ deposition behavior of silica-based layers and its effect on thermal degradation of IN713 turbine blades during operation of a micro-gas turbine

This study examined the in situ deposition behavior of silica-based layers on IN713 turbine blades during the operation of a 13 kgf-class gas turbine at a rotation speed of 20,000/min as well as its effect on the degradation of the metallic substrate. Tetraethylorthosilicate (TEOS) was mixed with the fuel (liquid petroleum gas, LPG) and burned to generate silica-based coating precursors for deposition from the flame. Two deposition conditions were adopted. For condition 1 (C1), the silicon-to-carbon ratio in the mixed fuel was set at 0.1 mol% for the first 5 min and at zero mol% for the final 95 min in a 100-min operation. For condition 2 (C2), the ratio was set at 0.005 mol% during the entire 100 min operation. The total TEOS feed was the same under both conditions. C1 resulted in a rather uniform and thicker (5-10 μm on the pressure side) porous silica-based coating on the blade than C2. The in situ deposited layer of C1 was well preserved on the blade and protected the underlying metallic substrate from oxidation during the entire 100 min operation. The layer on the C2 blades was ∼5 μm thick at the region near to root, but was too thin in the other areas on the blade to be protective. The early build-up of a porous layer to an effective thickness on the blades produced a thermal barrier toward the substrate as well as a diffusion barrier toward the oxidizing elements during operation.     

Three-bridge links with infinitely many three-bridge spheres

We construct infinitely many three-bridge links each of which admits infinitely many three-bridge spheres up to isotopy.     

Improvement of water and oil repellency on wood substrates by using fluorinated silica nanocoating

We have investigated a one-step fabrication of fluoro-containing silica coating on wooden substrates, showing multi-functions including super repellency toward water and sunflower oil, low sliding angles, good durability, and low adsorption capacity of moisture. The repellent slurry, consisting of well-mixing silica nanospheres and perfluoroalkyl methacrylic copolymer, is simply prepared and subsequently sprayed over wooden substrates with good adhesion. It has shown that the decoration of silica nanospheres on microscaled wooden texture acts as a crucial role in improving the repellency toward water and sunflower oil droplets. The maximal contact angles can reach as high as 168.3° and 153.6° for water and sunflower oil drops, respectively. These analyses of wetted fraction and work of adhesion also demonstrate the improved repellency due to the addition of silica. This improvement of the repellencies is ascribed to the fact that the drops partially sit on F-coated silica spheres, leaving a layer of air underneath the droplet (i.e., Cassie state). On the basis of the results, the multi-functional coating on wooden substrates delivers a promising commercial feasibility on a variety of woodworks.     

Synthesis and characterization of submicron-sized mesoporous aluminosilicate spheres

Mesoporous aluminosilicate spheres of 0.3–0.4 Μm diameter, with different Si/Al ratios, have been prepared by surfactant templating. Surface area of these materials is in the 510–970 m² g^-1 range and pore diameter in the 15–20 ? range.     

Finite-Difference Time-Domain Analysis of the Interaction of Gaussian Evanescent Light with a Single Dielectric Sphere or Ordered Dielectric Spheres

The interaction of gaussian evanescent light with a single dielectric sphere or ordered dielectric spheres in an attenuated total reflection (ATR) geometry was analyzed by the finite-difference time-domain method. Various aspects of this interaction were investigated in terms of spatial visualizations of light intensity, reflectance vs. wavelength characteristics, the transient behavior of reflectances, and so forth. In the case of a single sphere, it was evident that the whispering gallery mode can be excited in ATR geometries, but such excitation cannot be easily confirmed only through the observation of wavelength-scanned ATR spectra. In the case of a closely packed two-dimensional array of dielectric spheres, it was found that an easy axis and also a difficult axis for light propagation exist.This paper was originally presented at the 5th International Conference on NEAR FIELD OPTICS and RELATED TECHNOLOGIES (NFO-5), which was held on December 6–10, 1998 at Coganoi Bay Hotel, Shirahama, Japan, in cooperation with the Japan Society of Applied Phisics and Mombusho Grantin Aid for Scientific Research on Priority Areas “Near-field Nano-optics” Project, sponsored by Japan Society for the Promotion of Science.     

Functionalisation of mesoporous silica nanoparticles with 3-isocynatopropyltrichlorosilane

The functionalisation of Mesoporous Silica Nanoparticles (MSN) with the isocyanate group was carried out. The excellent reactivity of 3-isocynanatopropyltrichlorosilane allowed its grafting on the surface of MSN in mild conditions. Further reaction with different nucleophiles bearing primary amino groups led to the formation of a urea linkage and thus the covalent grafting of the nucleophiles to the MSN surface.