Green Nanosilver as Reinforcing Eco-Friendly Additive to Epoxy Coating for Augmented Anticorrosive and Antimicrobial Behavior

Epoxy resin GY250 representing diglycidyl ethers of bisphenol-A (DGEBA) was reinforced with 1, 3 and 5 wt % of surface functionalized silver nanoparticles (F-AgNPs) which were synthesized using Couroupita guianensis leaves extract with a view of augmenting the corrosion control property of the epoxy resin and also imparting antimicrobial activity to epoxy coatings on mild steel. Corrosion resistance of the coatings was evaluated by EIS, potentiodynamic polarization studies and cross scratch tests. AFM, SEM, HRTEM and EDX were utilized to investigate the surface topography, morphology and elemental composition of the coatings on MS specimens. Results showed that the corrosion resistance, hardness and T-g of the DGEBA/F-AgNPs coatings increased at 1 wt % of F-AgNPs. The DGEBA/F-AgNPs coatings also offered manifold antimicrobial protection to the MS surfaces by inhibiting the growth of biofilm forming bacteria like P. aeruginosa, B. subtilis, the most common human pathogen E. coli and the most virulent human pathogenic yeast C. albicans.

Electromagnetic Shielding Properties of Nano Carbon Filled Silicone Rubber Composites

Electromagnetic shielding has become important for various electrical systems because of the electromagnetic pollution caused by the large scale use of electronic devices operating at different frequencies and power levels. Traditionally used metallic shields lack flexibility and hence may not be the right choice for certain applications. In such situations, filled polymer composites provide a good alternative for electromagnetic shielding applications. Being polymer based, they are easy to manufacture and can be molded into the required geometry and shape. In this study, the shielding properties of multiwalled carbon nanotubes and carbon nanofibers filled silicone rubber are studied. The conductivity and the shielding effectiveness of the composites were measured at different filler loadings. Both the fillers are able to make the base polymer conducting even at very low filler loadings. The conductivity and the shielding effectiveness improved when the filler loading was above the percolation threshold.

Antibacterial Applications of Silver Nanoparticles Synthesized by Aqueous Extract of Azadirachta Indica (Neem) Leaves

Silver nanoparticles are known to have bactericidal effects. A new generation of dressings incorporating antimicrobial agents like silver nanoparticles is being formulated to reduce or prevent infections. The particles can be incorporated in materials and cloth rendering them sterile. Recently, it was found that aqueous silver ions can be reduced by aqueous extract of plant parts to generate extremely stable silver nanoparticles in water. Apart from being environmentally friendly process, use of Neem leaves extract might add synergistic antibacterial effect of Neem leaves to the biosynthesized nanoparticles. With this hypothesis the biosynthetic production of silver nanoparticles by aqueous extract of Neem leaves and its bactericidal effect in cotton cloth against E. Coli were studied in this work. Silver nanoparticles were synthesized by short term (1 day) and long term (21 days) interaction of Neem extract (20% w/v) and 0.01 M AgNO3 solution in 1:4 mixing ratio. The synthesized particles were characterized by UV visible spectroscopy, transmission electron microscopy, and incorporated into cotton disks by (i) centrifuging the disks with liquid broth containing nanoparticles, (ii) in-situ coating process during synthesis, and (iii) coating with dried and purified nanoparticles. The antibacterial property of the nanoparticles coated cotton disks was studied by disk diffusion method. The effect of consecutive washing of the coated disks with distilled water on antibacterial property was also investigated. This work demonstrates the possible use of biologically synthesized silver nanoparticles by its incorporation in cloths leading them to sterilization.

Defect-selective photothermal imaging: a sensitive tool for damage mapping in optical coatings

A defect-selective photothermal imaging system for the diagnostics of optical coatings is demonstrated. The instrument has been optimized for pump and probe parameters, detector performance, and signal processing algorithm. The imager is capable of mapping purely optical or thermal defects efficiently in coatings of low damage threshold and low absorbance. Detailed mapping of minor inhomogeneities at low pump power has been achieved through the simultaneous action of a low-noise fiber optic photothermal beam defection sensor and a common-mode-rejection demodulation (CMRD) technique. The linearity and sensitivity of the sensor have been examined theoretically and experimentally, and the signal to noise ratio improvement factor is found to be about 110 compared to a conventional bicell photodiode. The scanner is so designed that mapping of static or shock sensitive samples is possible. In the case of a sample with absolute absorptance of 3.8 x 10(-4), a change in absorptance of about 0.005 x 10(-4) has been detected without ambiguity, ensuring a contrast parameter of 760. This is about 1085% improvement over the conventional approach containing a bicell photodiode, at the same pump power. The merits of the system have been demonstrated by mapping two intentionally created damage sites in a MgF2 coating on fused silica at different excitation powers. Amplitude and phase maps were recorded for thermally thin and thick cases, and the results are compared to demonstrate a case which, in conventional imaging, would lead to a deceptive conclusion regarding the type and location of the damage. Also, a residual damage profile created by long term irradiation with high pump power density has been depicted.

On the cytotoxicity of carbon nanotubes

The cytotoxicity of carbon nanotubes (CNTs) is a major concern today well before its unusual physicochemical, mechanical, and electrical properties are fully exploited for commercial interests and subsequent mass production leading to greater possibilities for its exposure to humans and the environment. Contradictory reports on cytotoxicity of CNTs often appear in the literature and a mechanistic explanation of the reported toxicity remains obscure. We review here the conflicting results to focus categorically on an array of issues in CNT cytotoxicity. They include dispersion, aggregation status, coating or functionalization and immobilization, cellular uptake or internalization, purity in terms of metal catalyst contaminants, size and size distribution, surface area, surface chemistry and surface reactivity, cell types selected for experimentation as well as bioassay of nanotoxicity itself attesting as an issue in cytotoxicity. Recently a general agreement has emerged towards the potential toxicity of CNTs, although various paradigms explaining the mechanisms of CNT cytotoxicity continue to be elusive in the literature. A lack of synergy among various issues while studying cytotoxicity and most developed paradigms for the mechanism of CNT toxicity is highlighted.

Some studies on TiO2 films deposited by sol-gel technique

TiO2 films are extensively used in various applications including optical multi-layers, sensors, photo catalysis, environmental purification, and solar cells etc. These are prepared by both vacuum and non-vacuum methods. In this paper, we present the results on TiO2 thin films prepared by a sol-gel spin coating process in non-aqueous solvent. Titanium isopropoxide is used as TiO2 precursor. The films were annealed at different temperatures up to 3000 C for 5 hours in air. The influence of the various deposition parameters like spinning speed, spinning time and annealing temperature on the thickness of the TiO2 films has been studied. The variation of film thickness with time in ambient atmosphere was also studied. The optical, structural and morphological characteristics were investigated by optical transmittance-reflectance measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The refractive index and extinction coefficient of the films were determined by envelope technique and spectroscopic ellipsometry. TiO2 films exhibited high transparency (92%) in the visible region with a refractive index of 2.04 at 650 nm. The extinction coefficient was found to be negligibly small. The X-ray diffraction analysis showed that the TiO2 film deposited on glass substrate changes from amorphous to crystalline (anatase) phase with annealing temperature above 2500 C. SEM results show that the deposited films are uniform and crack free.

Theoretical Optimization of Metal Para-Normal Silicon Schottky-Barrier Solar-Cell

The theoretical optimization of the design parametersN A ,N D andW P has been done for efficient operation of Au-p-n Si solar cell including thermionic field emission, dependence of lifetime and mobility on impurity concentrations, dependence of absorption coefficient on wavelength, variation of barrier height and hence the optimum thickness ofp region with illumination. The optimized design parametersN D =5×1020 m−3,N A =3×1024 m−3 andW P =11.8 nm yield efficiencyη=17.1% (AM0) andη=19.6% (AM1). These are reduced to 14.9% and 17.1% respectively if the metal layer series resistance and transmittance with ZnS antireflection coating are included. A practical value ofW P =97.0 nm gives an efficiency of 12.2% (AM1).

Accelerated Multistress Aging of Outdoor Polymeric Insulators

Multistress aging of outdoor composite polymeric insulators continues to be a topic of interest for power transmission research community. Aging due to dry conditions alone at elevated temperatures and electric stress in the presence of UV radiation environment probably has not been explored. This paper deals with long-term accelerated multistress aging under the above conditions on full-scale 11 kV distribution class composite silicone rubber insulators. To evaluate the long-term synergistic effect of electric stress, temperature and UV radiation on insulators, they were subjected to accelerated aging in a specially designed multistress-aging chamber for 12000 hours. Chemical, physical and electrical changes due to degradation have been assessed using various techniques. It has been found that the content of low molecular weight molecules and hydrophobicity reduced significantly. Also, due to oxidation and aging there is appreciable increase in surface roughness and weight percentage of oxygen. Study is under progress and only intermediate results are presented in this paper.

Ultrafine powders of SrTiO3 from the hydrothermal preparation and their catalytic activity in the photolysis of water

Ultrafine powders of SrTiO3 are prepared at 100–150°C by the hydrothermal method, starting from TiO2·xH2O gel and Sr(OH)2 and H2O-isopropanol mixed solvent as the medium, The X-ray diffractograms of the powder show line broadening. The minimum crystallite size obtained ranges from 5 to 20nm with 20% H2O-80% C3H7OH as the reaction medium, as estimated from X-ray half-peak widths and TEM studies. The electron diffraction results indicate high concentration of lattice defects in these crystallites. The optical spectra of the particle suspensions in water show that the absorption around the band gap is considerably broadened, together with the appearance of maxima in the far ultraviolet. Aqueous suspensions of SrTiO3 powders, as such, do not produce H2 or O2 on UV irradiation. After coating with rhodium, H2 and O2 are evolved on illumination. However, the turn over number of O2 is lower than the stoichiometrically expected values from the corresponding values of H2. No correlation of the photocatalytic activity with surface area is observed. The activity of Rh-SrTiO3 slowly deteriorates with extended period of irradiation.

Pulsed laser surface treatment of magnesium alloy: Correlation between thermal model and experimental observations

The effect of deposition of Al +Al2O3 on MRI 153 M Mg alloy processed using a pulsed Nd:YAG laser is presented in this study. A composite coating with metallurgical joint to the substrate was formed. The microstructure and phase constituents were characterized and correlated with the thermal predictions. The laser scan speed had an effect on the average melt depth and the amount of retained and/or reconstituted alumina in the final coating. The coating consisted of alumina particles and highly refined dendrites formed due to the extremely high cooling rates (of the order of 10(8) K/s). The microhardness of the coating was higher and several fold improvement of wear resistance compared to the substrate was observed for the coatings. These microstructural features and physical properties were correlated with the effects predicted by a thermal model.

Nanostructured Peptide Fibrils Formed at the Organic-Aqueous Interface and Their Use as Templates To Prepare Inorganic Nanostructures

Formation of fibril-type nanostructures of the Alzheimer's beta-amyloid diphenylalanine (L-Phe-L-Phe, FF) at the organic-aqueous interface and the factors affecting their structures have been investigated. Such nanostructures are also formed by bovine serum albumin and bovine pancreas insulin. The concentration of the precursor taken in the aqueous layer plays an important role in determining the morphology of the nanostructures, The addition of curcumin to the organic layer changes the structure of the self-assembled one-dimensional aggregates of diphenylalanine. By coating the diphenylalanine dipeptide fibrils with appropriate precursors followed by calcination in air, it has been possible to obtain one-dimensional nanostructures of inorganic materials.

Synthesis and Characterization of Carbon-Coated LiNi1/3Co1/3Mn1/3O2 in a Single Step by an Inverse Microemulsion Route

Layered LiNi1/3Co1/3Mn1/3O2, which is isostructural to LiCoO2, is considered as a potential cathode material. A layer of carbon coated on the particles improves the electrode performance, Which is attributed to an increase of the grain connectivity and also to protection of metal oxide from chemical reaction. The present work involves in situ synthesis of carbon-coated submicrometer-sized particles of LiNi1/3Co1/3Mn1/3O2 in an inverse microemulsion medium in the presence of glucose. The precursor obtained from the reaction is heated in air at 900 degrees C for 6 h to get crystalline LiNi1/3Co1/3Mn1/3O2. The carbon coating is found to impart porosity as well as higher surface area in relation to bare samples of the compound. The electrochemical characterization studies provide that carbon-coated LiNi1/3Co1/3Mn1/3O2 samples exhibit improved rate capability and cycling performance. The carbon coatings are shown to suppress the capacity fade, which is normally observed for the bare compound. Impedance spectroscopy data provide additional evidence for the beneficial effect of a carbon coating on LiNi1/3Co1/3Mn1/3O2 particles.

Insoluble anode of porous lead dioxide for electrosynthesis: preparation and characterization

Preparation of a novel type of titanium-substrate lead dioxide anode with enhanced electrocatalytic activity for electrosynthesis is described. It has been demonstrated that in the presence of a suitable surfactant in the coating solution, an adherent and mainly tetragonal form of lead dioxide is deposited on a platinized titanium surface such that the solution side of the coating is porous while the substrate side is compact. By an analysis of anodic charging curves and steady-state Tafel plots with such porous electrodes in contact with sodium sulphate solution, it has been proved that the electrochemically active area of these anodes is higher by more than an order of magnitude when compared to the area of conventional titanium-substrate lead dioxide anodes. The electrocatalytic activity is also thereby enhanced to a significant degree.

Self-Assembly of Molecular Prisms via Pt-3 Organometallic Acceptors and a Pt-2 Organometallic Clip

The design and two-component [2 + 3] self-assembly of a series of new organometallic molecular prisms (3a-d) are described. Assemblies 3a,b incorporate 4,4',4'-tris[ethynyl-trans-Pt(PEt3)(2)]triphenylamine (1a) containing a Pt-ethynyl functionality as tritopic planar acceptor and organic ``clips'' 2a and 2b, respectively [where 2a = 1,3-bis(3-pyridyl)isophthalic amide; 2b= 1,3-bis(ethynyl-3-pyridyl)benzene]. In a complementary approach all organic tritopic planar donor ligand 2c [2c 4,4',4'-tris(4-pyridylethynyl)triphenylamine] was assembled with all organometallic ``clip'', 1,8-bis[{trans-Pt(PEt3) (2)(NO3)}ethynyl]anthracene (1b), to obtain prism 3c. A organometallic carbon-centered acceptor, 1,1,1- tris[4-{trans-Pt(PEt3)(2)(NO3)}ethynylphenyl]ethane (1c), has been prepared, and its prism derivative (3d) using an organic `clip'' is prepared. Assemblies (3a-d) were characterized by multinuclear NMR spectroscopy, electrospray ionization mass spectroscopy, and elemental analysis. 3a-d showed fluorescence behavior in solution, and quenching of fluorescence intensity (3a,3c-d) was noticed upon addition of TNT (2,4,6-trinitrotoluene), a common constituent of many commercial explosives. A thin film of the assembly 3d made by spin coating of a solution of 3 x 10(-5) M in DMF on it 1 cm(2) quartz plate showed fluorescence response to the vapor of TNT.

Stable Dispersions of Metal Oxide Nanowires and Nanoparticles in Water, Dimethylformamide and Toluene

In view of the important need to generate well-dispersed inorganic nanostructures in various solvents, we have explored the dispersion of nanostructures of metal oxides such as TiO2, Fe3O4 and ZnO in solvents of differing polarity in the presence of several surfactants. The solvents used are water, dimethylformamide (DMF) and toluene. The surfactant-solvent combinations yielding the best dispersions are reported alongwith some of the characteristics of the nanostructures in the dispersions. The surfactants which dispersed TiO2 nanowires in water were polyethylene oxide (PEO), Triton X-100 (TX-100), polyvinyl alcohol (PVA) and sodium bis(2-ethylhexyl) sulphosuccinate (AOT). TiO2 nanoparticles could also be dispersed with AOT and PEO in water, and with AOT in toluene. In DMF, PVA, PEO and TX-100 were found to be effective, while in toluene, only AOT gave good dispersions. Fe3O4 nanoparticles were held for long periods of time in water by PEO, AOT, PVA and polyethylene glycol (PEG), and by AOT in toluene. In the case of ZnO nanowires, the best surfactant-solvent combinations were found to be, PEO, sodium dodecyl sulphate (SIDS) and AOT in water and AOT, PEG, PVA, PEO and TX-100 in DMF In toluene, stable dispersions of ZnO nanowires were obtained with PEO. We have also been able to disperse oxide nanostructures in non-polar solvents by employing a hydrophobic silane coating on the surface.