Debtosh Kundu

Inorganic–organic hybrid coatings on polycarbonate.: Spectroscopic studies on the simultaneous polymerizations of methacrylate and silica networks

Abstract Hybrid methacrylate–silica coatings derived from 3-(methacryloxypropyl)-trimethoxy silane were deposited on polycarbonate via hydrolysis–condensation reactions followed by UV curing ( λ =253.7 nm). The formation of –Si–O–Si– (inorganic backbone) and polymethacrylate (organic) networks leading to the generation of hybrid structure was monitored by UV and Fourier transform infrared (FTIR) spectroscopies. UV and FTIR spectra showed complete polymerization of methacrylate groups during UV curing of the coatings. The silica network was initially formed through the hydrolysis–condensation reactions of alkoxy groups in the sol as evident from the appearance of FTIR peaks due to –Si–O–Si– vibrations. Further silanol (Si–OH) condensation reactions leading to the generation of more silica network were occurred simultaneously with methacrylate polymerization during UV photo curing of the coating.

Structural control of surfactant-templated hexagonal, cubic, and lamellar mesoporous silicate thin films prepared by spin-casting

Large-area mesoporous silicate thin films are reported to be formed on solid silica substrates by the simple technique of spin-coating. The mesophase of the films can be controlled to be one-dimensional hexagonal, cubic, or lamellar by adjusting the casting solution composition, i.e., mainly the ratio of surfactant to tetraethyl orthosilicate (TEOS). The X-ray diffraction results leading to the assignment of the mesophase types are presented and reasons for the change of phase with solution composition discussed. The films are expected to have applications in catalysis, molecular separation, and sensors.

FTIR studies of gel to glass conversion in TEOS-fumed silica-derived gels

Abstract Hybrid gels, prepared from mixtures of tetraethyl orthosilicate (TEOS) solution and fumed silica (alkoxide: fumed silica = 1 : 1.25) were examined by FTIR at different stages of drying/densification up to glass formation. Transparent, bubble-free glasses containing low hydroxyl were obtained at up to 1525°C under vacuum, oxygen, carbon tetrachloride and helium atmospheres. Spectroscopic investigations revealed a free, isolated silanol stretching (v1) band at around 3740 cm−1 split into two to three overlapping peaks after heat treatment of the gels at 600–950°C. This phenomenon is suggested to be due to either the presence of two types of isolated silanols (single and geminal) and/or an effect of the hybrid microstructure of the gels with widely varying spatial relationships among SiOH groups, leading to closely related, weak interactions.

Silica microspheres from the system tetraethyl orthosilicate-acetic acid-water

Abstract Dense silica microspheres (density 2.11–2.16 g cm−3) were obtained from a range of molar compositions tetraethyl orthosilicate (TEOS):CH3COOH:H2O = 1:(0.5–4.0):(1.5–5.0). FTIR spectroscopic studies of the reaction between TEOS and CH3COOH in the presence and absence of water showed that acetic acid readily attacked TEOS and generated SiOH groups via the formation of SiOOCCH3 groups; (OH)(OH) condensation finally led to the formation of silica particles.

Monolithic zirconia gels from metal-organic solutions

It has recently been shown by Ganguli and Kundu [1] that amorphous and transparent coatings of pure ZrO 2 could be prepared by controlled hydrolysis of zirconium propoxide and subsequent polymerization by using a non-polar solvent like cyclohexane instead of the usual alcoholic solvents employed for preparing coatings and monoliths [2-7]. The non-polar, hydrophobic solvent was used to avoid precipitation caused by the high rate of hydrolysis of Zr(OC3H7)4. The present work is a continuation of the above study, leading to the preparation of pure, transparent and amorphous zirconia gels (including monoliths), using zirconium propoxide and cyclohexane. It was observed during this work that the rate of evolution of the volatiles from the gel-forming compositions could play a vital role in determining the nature of the product. This has also been systematically examined. Technical grade zirconium n-propoxide (Fluka) and Analar grade cyclohexane (BDH) were used for preparing the zirconia gels. The cyclohexane was thoroughly dried before use by repeated contact under stirring with activated silica gel and molecular sieve 4A. Solutions of the propoxide in cyclohexane (in the range 4 to 10 equivalent wt % ZrO2) were prepared in

Preparation of amorphous ZrO2 coatings from metal-organic solutions

Conditions de preparation et proprietes de transmission optique des revetements transparents et amorphes de ZrO 2 des substrats de verres sodocalciques

A study of the structural evolution of the sol-gel derived Sm3+-doped silica glass

Abstract Sm3+-doped silica gels have been prepared by a sol-gel process using tetraethyl orthosilicate, H2O, HCl and Sm(NO3)3 · 6H2O. The structural evolution and densification behaviour of the gels during thermal treatment have been monitored by physical property measurements, visible-NIR, IR and fluorescence spectroscopy. The gels show a continuous densification and strengthening of the silica network with increasing heat-treatment temperatures (60–100 °C). The fluorescence intensity ratio of the 4G 5 2 → 6H 9 2 to 4G 5 2 → 6H 5 2 transition has been used to study the change of Sm3+ environment during gel-glass conversion. Samarium passes through three different environments at different heat-treatment temperatures during gel to glass conversion.

Sol-gel preparation of wavelength-selective reflecting coatings in the system ZrO2SiO2

Multilayer, wavelength-selective reflecting coatings were prepared by alternate stackings of amorphous zirconia and silica by the sol-gel spinning technique; alkoxide-derived, polymeric sols were used. A detuned, i.e. non-λ/4 stacking system was applied. The spectrum showed a transmission minimum (∼ 4%) at a wavelength of 430 nm, with a bandwidth of 72.5 nm after deposition of the 17th layer.

Silver-nanocluster-doped inorganic-organic hybrid coatings on polycarbonate substrates

Abstract Ag-nanocluster doped inorganic–organic hybrid coatings were prepared on polycarbonate (PC) substrates. The sol was prepared by incorporating AgNO 3 in a composite inorganic–organic hybrid sol derived from 3-(glycidoxypropyl)-trimethoxy silane (GLYMO)–tetraethyl orthosilicate–3-(methacryloxypropyl)-trimethoxy silane (MEMO). The hydrolysis–condensation of alkoxy groups and polymerization of epoxy and methacrylate groups formed the composite matrix network. The coating compositions with respect to the equivalent silver metal and silica were 1 mol% Ag–99% SiO 2 and 5 mol% Ag–95% SiO 2 . Thermal annealing (100°C) of former coatings (1 Ag) showed no precipitation of Ag-nanoclusters whereas the latter one (5 Ag) showed Ag precipitation. As a result 5 Ag films showed the characteristic absorption at 412 nm due to the surface plasmon resonance (SPR) of Ag-nanoclusters. When these coated PCs were exposed to UV light, polymerization of the methacrylate groups, strengthening of the silica network, along with formation of Ag-nanoclusters occurred simultaneously. The UV curing induced generation of Ag-nanoclusters in 1 Ag films whereas coarsening of Ag-nanoclusters resulted in the case of 5 Ag films.

Alkoxide-derived amorphous ZrO2 coatings

Pure and transparent ZrO2 coatings on microscopic glass slides, ranging in thickness from 250 to about 1500 A, were prepared from (i) zirconium n-propoxide in dry cyclohexane, and (ii) zirconium n-propoxide in isopropanol with additions of acetic acid and water. A dipping technique was used. A baking temperature of 450°C was chosen for the conversion of as-prepared gel films into the pure oxide state. The coatings were X-ray amorphous. The dependence of coating thickness on lifting speed and concentration of zirconium n-propoxide in solution was examined. The coating profile showed that these films were fairly smooth beyond a “trouble zone” (appearing along the boundary between the coated and non-coated parts of a slide and extending up to about 1 mm) where a relatively high and irregular profile was observed.