Samar Kumar Medda

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.

Synthesis of Au nanoparticle doped SiO2–TiO2 films: tuning of Au surface plasmon band position through controlling the refractive index

The position of the surface plasmon resonance (SPR) band of Au nanoparticles was tailored by controlling the refractive indices (n) of the embedding matrices, to develop different coloured coatings on glass substrates. Five sets of Au nanoparticle doped coatings were prepared from sols derived from tetraethyl orthosilicate–3-(glycidoxypropyl)trimethoxysilane–titanium tetraethoxide containing gold chloride, following a sol-gel dip-coating method. The film samples of nominal formula (SiO2)x(TiO2)0.97−xAu0.03 (x = 0.97, 0.679, 0.485, 0.388 and 0.242) were prepared after heat treatment at 500 °C in air. The Au SPR peak, in the case of a SiO2 host (SiO2 : TiO2 = 1 : 0, n = 1.411), observed at 542 nm, gradually red-shifted to 600 nm upon increasing the TiO2 content (SiO2 : TiO2 = 1 : 3, n = 1.939). As a consequence, a systematic change of the Au SPR position yielded pink, magenta, violet, royal and blue coloured coatings on ordinary sheet glasses. The formation of Au nanoparticles in the above gel and glassy coating matrices was monitored by UV–visible and FTIR spectroscopy, X-ray diffraction and transmission electron microscopy.

Superhydrophobic films on glass surface derived from trimethylsilanized silica gel nanoparticles.

The paper deals with the fabrication of sol-gel-derived superhydrophobic films on glass based on the macroscopic silica network with surface modification. The fabricated transparent films were composed of a hybrid -Si(CH(3))(3)-functionalized SiO(2) nanospheres exhibiting the desired micro/nanostructure, water repellency, and antireflection (AR) property. The wavelength selective AR property can be tuned by controlling the physical thickness of the films. Small-angle X-ray scattering (SAXS) studies revealed the existence of SiO(2) nanoparticles of average size ∼9.4 nm in the sols. TEM studies showed presence of interconnected SiO(2) NPs of ∼10 nm in size. The films were formed with uniformly packed SiO(2) aggregates as observed by FESEM of film surface. FTIR of the films confirmed presence of glasslike Si-O-Si bonding and methyl functionalization. The hydrophobicity of the surface was depended on the thickness of the deposited films. A critical film thickness (>115 nm) was necessary to obtain the air push effect for superhydrophobicity. Trimethylsilyl functionalization of SiO(2) and the surface roughness (rms ≈30 nm as observed by AFM) of the films were also contributed toward the high water contact angle (WCA). The coated glass surface showed WCA value of the droplet as high as 168 ± 3° with 6 μL of water. These superhydrophobic films were found to be stable up to about 230-240 °C as confirmed by TG/DTA studies, and WCA measurements of the films with respect to the heat-treatment temperatures. These high water repellant films can be deposited on relatively large glass surfaces to remove water droplets immediately without any mechanical assistance.

Ag−TiO2 Nanoparticle Codoped SiO2 Films on ZrO2 Barrier-Coated Glass Substrates with Antibacterial Activity in Ambient Condition

Anatase TiO2 and Ag nanoparticles (NPs) codoped SiO2 films were prepared by the sol-gel method. Proportionate amounts of 3-(glycidoxypropyl)trimethoxysilane (GLYMO), tetraethylorthosilicate (TEOS) and 3-(methacryloxypropyl)trimethoxysilane (MEMO) derived inorganic-organic silica sol, commercially available dispersed anatase TiO2 NPs, and AgNO3 were used to prepare the sols. The films were prepared on ZrO2 (cubic) precoated soda-lime glass substrates by a single-dipping technique and heat-treated at 450 °C in air and H2/Ar atmosphere to obtain hard, relatively porous, and transparent coatings of thickness>600 nm. The ZrO2 barrier layer was previously applied on soda-lime glass to restrict the diffusion of Ag into the substrate. The Ag-TiO2 NPs incorporated SiO2 films were intense yellow in color and found to be fairly stable at ambient condition for several days under fluorescent light. These films show a considerable growth inhibition on contact with the gram negative bacteria E. coli.

Covalently functionalized reduced graphene oxide by organically modified silica: a facile synthesis of electrically conducting black coatings on glass

The fabrication of black and electrically conducting films on glass substrate derived from covalently functionalized reduced graphene oxide (FRGO) has been reported in this work. Graphene oxide (GO) was first prepared following the Hummers method and then functionalized using an organically modified silicon alkoxide, 3-glycidoxypropyltrimethoxysilane (GLYMO) in an ordered fashion. Catalyst (aluminium acetylacetonate) induced selective polymerization of the epoxy groups of GO and GLYMO was found to occur via the formation of ethereal (–C–O–C–) linkages. The formation of such linkages was confirmed by IR, Raman, TGA, X-Ray diffraction and TEM studies. Finally the functionalized graphene oxide (FGO) films were subjected to thermal reduction in an inert (N2) atmosphere to obtain FRGO films. These hard FRGO films are electrically conducting and appeared as black coatings on glass. By varying the loading (20–30 wt%) of GO with the covalently bonded organically modified silica, the sheet resistance values can be tuned in a linear way from 0.8 × 106 to 1.4 × 103 Ω □−1. The uniform current–voltage (I–V) characteristics of the films can be nicely correlated with the sheet resistance values.

Durable superhydrophobic ZnO–SiO2 films: a new approach to enhance the abrasion resistant property of trimethylsilyl functionalized SiO2 nanoparticles on glass

Although trimethylsilyl functionalized SiO2 derived films show excellent superhydrophobicity, their adhesion and abrasion resistant properties are extremely poor. In this study, a new approach has been shown to improve the adhesion and abrasion properties of such films. A neutral and relatively hydrophobic [Zn(CH3OO)2(H2O)2] complex solution has been used to interact with the superhydrophobic silica gel nanoparticle dispersion. After dip-coating, the composite sol yielded films of a zinc acetate/superhydrophobic silica composite network while the hydrophilic part (bonded water) associated with Zn helps in binding the hydroxyl groups (silanols) present on the glass surface. The composite films were heat-treated at 300–400 °C in a nitrogen atmosphere in order to obtain transparent and superhydrophobic ZnO–SiO2 nanocomposite films. The decomposition of zinc acetate formed ZnO nanocrystallites and remained attached with the hybrid silica matrix. These films showed excellent water repellency (water contact angle, CA ≈ 158 ± 7°; hysteresis ≈ 4°) with good adhesion and abrasion resistant properties. XRD, Raman and TEM studies confirm the existence of ZnO nanocrystallites in the composite films. Owing to the stability of hydrophobic methyl groups attached with silicon at relatively high temperature in a nitrogen atmosphere, these ZnO–SiO2 nanocomposite films remain superhydrophobic even after a heat-treatment at 400 °C.

Refractive Index Controlled Plasmon Tuning of Au Nanoparticles in SiO 2 -ZrO 2 Film Matrices

Au-plasmon tuning has been accomplished by controlling the refractive index (n) of the embedding film matrix. The refractive index of the film matrices were controlled by changing the molar ratios of low (SiO2) and high index (ZrO2) components following sol-gel reactions. Thus, Au nanoparticles doped films were prepared from SiO2-ZrO2 inorganic-organic hybrid sols of variable molar ratios containing HAuCl4 following the dip-coating method. The film samples deposited on glass substrates were obtained after drying, UV-treatment, and subsequent heat-treatment at 500 degrees C in air. The nominal mol ratios of SiO2:ZrO2 were 1:0, 1:1, 1:2.3, and 1:4. 3 equivalent mol% Au-97% total oxide (SiO2 + ZrO2) was maintained in the final heat-treated films. FTIR studies confirmed good homogeneity of Si-Zr network in the Zr-containing films. The UV-treatment has been introduced to facilitate the decomposition of HAuCl4 in the hybrid matrix prior to the heat-treatment step. The main Au-plasmon peak, in the case of a SiO2 host (SiO2:ZrO2 = 1:0, n = 1.410), observed at about 546 nm, gradually red-shifted to 592 nm upon increasing the ZrO2 content (SiO2:ZrO2 = 1:4, n = 1.847). Transmission electron microscopy of the final heat-treated (500 degrees C) films showed existence of plate-like (triangular and hexagonal) Au nanoparticles (25-50 nm) along with relatively smaller nanoparticles of about 10 nm in size. X-ray diffraction patterns reveal that the Au nanoparticles have a (111) orientation.

Metal nanoparticle-doped coloured films on glass and polycarbonate substrates

In a program on the development of metal (e.g. Au, Ag, Cu and their alloy) nanoparticles in sol-gel derived films, attempts were made to synthesize different coloured coatings on glasses and plastics. The absorption position of surface plasmon resonance (SPR) band arising from the embedded metal nanoparticles was tailored by controlling the refractive index of the matrix for the development of different colours. Thus different coloured (pink to blue) coatings on ordinary sheet glasses were prepared by generating Au nanoparticles in mixed SiO2-TiO2 matrices having refractive index values ranging from about 1.41 to 1.93. In another development,in situ generation of Ag nanoparticles in the inorganic-organic hybrid host leads to the formation of different abrasion resistant coloured coatings (yellow to pink) on polycarbonate substrates after curing. As expected, the SPR peak of Ag or Au is gradually red-shifted due to the increase of refractive index of the coating matrices causing a systematic change of colour