Structure-property correlation in BaO-TiO2-B2O3 glasses: glass stability, optical, hydrophobic, and dielectric properties

Glasses in the x(BaO-TiO2)-B2O3 (x = 0.25, 0.5, 0.75, and 1 mol.) system were fabricated via the conventional melt-quenching technique. Thermal stability and glass-forming ability as determined by differential thermal analysis (DTA) were found to increase with increasing BaO-TiO2 (BT) content. However, there was no noticeable change in the glass transition temperature (T-g). This was attributed to the active participation of TiO2 in the network formation especially at higher BT contents via the conversion of the TiO6 structural units into TiO4 units, which increased the connectivity and resulted in an increase in crystallization temperature. Dielectric and optical properties at room temperature were studied for all the glasses under investigation. Interestingly, these glasses were found to be hydrophobic. The results obtained were correlated with different structural units and their connectivity in the glasses.

Low loss waveguide on chalcogenide glass using ultrafast laser at low repetition rate

In this work, we synthesized bulk amorphous GeGaS glass by conventional melt quenching technique. Amorphous nature of the glass is confirmed using X-ray diffraction. We fabricated the channel waveguides on this glass using the ultrafast laser inscription technique. The waveguides are written on this glass 100 mu m below the surface of the glass with a separation of 50 ae m by focusing the laser beam into the material using 0.67 NA lens. The laser parameters are set to 350 fs pulse duration at 100 KHz repetition rate. A range of writing energies with translation speeds 1 mm/s, 2 mm/s, 3 mm/s and 4 mm/s were investigated. After fabrication the waveguides facets were ground and polished to the optical quality to remove any tapering of the waveguide close to the edges. We characterized the loss measurement by butt coupling method and the mode field image of the waveguides has been captured to compare with the mode field image of fibers. Also we compared the asymmetry in the shape of the waveguide and its photo structural change using Raman spectra.

Photo-thermal modifications in ultrafast laser inscribed chalcogenide glass waveguides

We report here, a finite difference thermal diffusion (FDTD) model for controlling the cross-section and the guiding nature of the buried channel waveguides fabricated on GeGaS bulk glasses using the direct laser writing technique. Optimization of the laser parameters for guiding at wavelength 1550 nm is done experimentally and compared with the theoretical values estimated by FDTD model. The mode field diameter (MFD) between 5.294 mu m and 24.706 mu m were attained by suitable selection of writing speed (1mm/s to 4 mm/s) and pulse energy (623 nJ to 806 nJ) of the laser at a fixed repletion rate of 100 kHz. Transition from single-mode to multi-mode waveguide is observed at pulse energy 806nJ as a consequence of heat accumulation. The thermal diffusion model fits well for single-mode waveguides with the exception of multi-mode waveguides.

Gold nanoparticles anchored reduced graphene oxide as catalyst for oxygen electrode of rechargeable Li-O-2 cells

Gold nanoparticles decorated reduced graphene oxide (Au-RGO) catalyst for O-2 electrode is prepared by in situ reduction of Au3+ ions and graphene oxide dispersed in water. The Au nanoparticles are uniformly distributed on the two-dimensional RGO layers. Li-O-2 cells assembled in a non-aqueous electrolyte using Au-RGO catalyst exhibit an initial discharge capacity as high as 5.89 mA h cm-(2) (5230 mA h g(-1))at a current density of 0.1 mA cm(-2). The voltage gap between the charge and discharge curves is less for Li-O-2(Au-RGO) cell in comparison with Li-O-2(RGO) cell. The Li-O-2(Au-RGO) cells are cycled over about 120 charge-discharge cycles. The results suggest that Au-RGO is a promising catalyst for rechargeable Li-O-2 cells.

Effect of Net-Fluence on waveguide formation in ultrafast laser inscribed chalcogenide glass

Waveguides were fabricated on GeGaSEr chalcogenide glass using ultrafast laser inscription method. The thermal diffusion model is discussed for understanding the light matter interaction and shown the effect of net-fluence in waveguide formation on chalcogenide glass. (C) 2012 Optical Society of America

Early osseointegration of a strontium containing glass ceramic in a rabbit model

The most important property of a bone cement or a bone substitute in load bearing orthopaedic implants is good integration with host bone with reduced bone resorption and increased bone regeneration at the implant interface. Long term implantation of metal-based joint replacements often results in corrosion and particle release, initiating chronic inflammation leading onto osteoporosis of host bone. An alternative solution is the coating of metal implants with hydroxyapatite (HA) or bioglass or the use of bulk bioglass or HA-based composites. In the above perspective, the present study reports the in vivo biocompatibility and bone healing of the strontium (Sr)-stabilized bulk glass ceramics with the nominal composition of 4.5SiO(2)-3Al(2)O(3)-1.5P(2)O(5)-3SrO-2SrF(2) during short term implantation of up to 12 weeks in rabbit animal model. The progression of healing and bone regeneration was qualitatively and quantitatively assessed using fluorescence microscopy, histological analysis and micro-computed tomography. The overall assessment of the present study establishes that the investigated glass ceramic is biocompatible in vivo with regards to local effects after short term implantation in rabbit animal model. Excellent healing was observed, which is comparable to that seen in response to a commercially available implant of HA-based bioglass alone. (C) 2013 Elsevier Ltd. All rights reserved.

Polymer template-assisted microemulsion synthesis of large surface area, porous Li2MnO3 and its characterization as a positive electrode material of Li-ion cells

Lithium-rich manganese oxide (Li2MnO3) is prepared by reverse microemulsion method employing Pluronic acid (P123) as a soft template and studied as a positive electrode material. The as-prepared sample possesses good crystalline structure with a broadly distributed mesoporosity but low surface area. As expected, cyclic voltammetry and charge-discharge data indicate poor electrochemical activity. However, the sample gains surface area with narrowly distributed mesoporosity and also electrochemical activity after treating in 4 M H2SO4. A discharge capacity of about 160 mAh g(-1) is obtained. When the acid-treated sample is heated at 300 A degrees C, the resulting porous sample with a large surface area and dual porosity provides a discharge capacity of 240 mAh g(-1). The rate capability study suggests that the sample provides about 150 mAh g(-1) at a specific discharge current of 1.25 A g(-1). Although the cycling stability is poor, the high rate capability is attributed to porous nature of the material.

Synthesis, characterisation and application of an exfoliated graphite-diamond composite electrode in the electrochemical degradation of trichloroethylene

A composite electrode made up of exfoliated graphite (EG) and diamond was prepared for the electrochemical oxidation of trichloroethylene (TCE). The SEM images of the EG-diamond material showed that diamond powders were dispersed on the surface of EG materials. The N-2 adsorption-desorption isotherm of EG-diamond material resulted in a poor adsorption capability due to the insertion of diamond powders into the porous matrix of EG. Raman spectroscopy revealed the presence of characteristic sp(3) bands of diamond confirming good interaction of diamond with EG. Electrochemical characterisation of EG-diamond in 0.1 M Na2SO4 resulted in an enhanced working potential window. The EG-diamond electrode was employed for the electrochemical oxidation of trichloroethylene (0.2 mM) in a Na2SO4 supporting electrolyte. The EG-diamond, in comparison to the pristine EG electrode, exhibited a higher removal efficiency of 94% (EG was 57%) and faster degradation kinetics of 25.3 x 10(-3) min(-1) showing pseudo first order kinetic behaviour. Under the optimised conditions, 73% total organic content (TOC) removal was achieved after 4 h of electrolysis. The degradation of TCE was also monitored with gas chromatography-mass spectrometry. Dichloroacetic acid (DCAA) was identified as a major intermediate product during the electrochemical oxidation of TCE. The electrochemical degradation of TCE at the EG-diamond electrode represents a cost effective method due to the ease of preparation of EG-diamond composite material without the necessity of diamond activation which is normally achieved through doping.

Studies on thin film based flexible gold electrode arrays for resistivity imaging in electrical impedance tomography

Practical phantoms are essential to assess the electrical impedance tomography (EIT) systems for their validation, calibration and comparison purposes. Metal surface electrodes are generally used in practical phantoms which reduce the SNR of the boundary data due to their design and development errors. Novel flexible and biocompatible gold electrode arrays of high geometric precision are proposed to improve the boundary data quality in EIT. The flexible gold electrode arrays are developed on flexible FR4 sheets using thin film technology and practical gold electrode phantoms are developed with different configurations. Injecting a constant current to the phantom boundary the surface potentials are measured by a LabVIEW based data acquisition system and the resistivity images are reconstructed in EIDORS. Boundary data profile and the resistivity images obtained from the gold electrode phantoms are compared with identical phantoms developed with stainless steel electrodes. Surface profilometry, microscopy and the impedance spectroscopy show that the gold electrode arrays are smooth, geometrically precised and less resistive. Results show that the boundary data accuracy and image quality are improved with gold electrode arrays. Results show that the diametric resistivity plot (DRP), contrast to noise ratio (CNR), percentage of contrast recovery (PCR) and coefficient of contrast (COC) of reconstructed images are improved in gold electrode phantoms. (C) 2013 Elsevier Ltd. All rights reserved.

Evidence of an intermediate phase in a quaternary Ag bearing telluride glass system using alternating DSC

Alternating Differential Scanning Calorimetric (ADSC) studies on quaternary Ge15Te80-xIn5Agx glasses show the non-reversing enthalpy (Delta H-NR) at T-g to exhibit a broad global minimum in the 8% <= x <= 16% range of Ag, an observation that is taken evidence for existence of an Intermediate Phase (IP) in that range. Glasses at x < 8% are in the flexible phase while those at x > 16% in the stressed-rigid phase. The nature of crystalline phases formed upon crystallization of bulk glasses are elucidated by XRD studies, and reveal presence of Te, GeTe, Ag8GeTe6, AgTe, In2Te3 and In4Te3 phases. These experiments also reveal that the fraction of Ag- bearing phases increases while those of Te- bearing ones decreases with increasing x, suggesting progressive replacement of Te-Te bonds by Ag-Te bonds. (C) 2013 Elsevier Ltd. All rights reserved.

D-A-D-structured conducting polymer-modified electrodes for detection of lead(II) ions in water

Donor-acceptor-donor-structured thiophene derivative-based conducting polymer poly(7,9-dithiophene-2yl-8H-cyclopentaa]acenaphthalene-8-one) was chemically synthesized. This polymer was used to modify both glassy-carbon and carbon-paste electrode, which was used to detect lead(II) ions present in water in the range of 1 mM to 0.1 mu M. Cyclic voltammetry confirms the formation of the co-ordination complex between the soft segment of polymer and the dissolved lead ion. Anodic stripping voltammetry was carried out by the modified electrode to determine the lower limit of detection of dissolved lead(II) species in the solution. Differential adsorptive stripping and impedance measurements were also conducted to find the lowest possible response of the as-synthesized polymer to lead(II) ion in water. The electrochemical performance of the modified electrodes at different pH (4, 7 and 9) environments was carried out by stripping voltammetry, to get optimum sensitivity and stability under these conditions. Finally, interference analysis was carried out to detect the modified electrode's sensitivity towards lead ion affinity in water.

Organic device electrode fabricated by aluminum in nanopowder and bulk form and effect on device properties

Schottky barrier devices of metal/semiconductor/metal structure were fabricated using organic semiconductor polyaniline (PANI) and aluminium thin film cathode. Aluminium contacts were made by thermal evaporation technique using two different forms of metals (bulk and nanopowder). The structure and surface morphology of these films were investigated by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. Grain size of the as-deposited films obtained by Scherrer's method, modified Williamson-Hall method, and SEM were found to be different. Current-voltage (I-V) characteristic of Schottky barrier device structure indicates that the calculated current density (J) for device fabricated from aluminium nanopowder is more than that from aluminium in bulk form.

Efficacious Anticancer Drug Delivery Mediated by a pH-Sensitive Self-Assembly of a Conserved Tripeptide Derived from Tyrosine Kinase NGF Receptor

We present herein a short tripeptide sequence (Lys-Phe-Gly or KFG) that is situated in the juxtamembrane region of the tyrosine kinase nerve growth factor (Trk NGF) receptors. KFG self-assembles in water and shows a reversible and concentration-dependent switching of nanostructures from nanospheres (vesicles) to nanotubes, as evidenced by dynamic light scattering, transmission electron microscopy, and atomic force microscopy. The morphology change was associated with a transition in the secondary structure. The tripeptide vesicles have inner aqueous compartments and are stable at pH7.4 but rupture rapidly at pH approximate to 6. The pH-sensitive response of the vesicles was exploited for the delivery of a chemotherapeutic anticancer drug, doxorubicin, which resulted in enhanced cytotoxicity for both drug-sensitive and drug-resistant cells. Efficient intracellular release of the drug was confirmed by fluorescence-activated cell sorting analysis, fluorescence microscopy, and confocal microscopy.

Mechanical properties of glasses and TiO2 nanocrystal glass composites in BaO-TiO2-B2O3 system

Glasses and glass-nanocrystal (anatase TiO2) composites in BaO-TiO2-B2O3 system were fabricated by conventional melt-quenching technique and controlled heat treatment respectively. Poisson's ratio and Young's moduli were predicted through Makishima-Mackenzie theoretical equation for the as-quenched glasses by taking the four and three coordinated borons into account. Mechanical properties of the glasses and glass-nanocrystal composites were investigated in detail through nanoindentation and microindentation studies. Predicted Young's moduli of glasses were found to be in reasonable agreement with nanoindentation Measurements. Hardness and Young's modulus were enhanced with increasing volume fraction of nanocrystallites of TiO2 in glass matrix whereas fracture toughness was found susceptible to the surface features. The results were correlated to the structural units and nanocrystals present in the glasses. (C) 2013 Elsevier B.V. All rights reserved.

pH sensing by single and multi-layer hydrogel coated Fiber Bragg Grating

In this paper we show a novel chemo-mechanical-optical sensing mechanism in single and multi-layer hydrogel coated Fiber Bragg Grating (FBG) and demonstrate specific application in pH activated processes. The sensing device is based on the ionizable monomers inside the hydrogel which reversibly dissociates as a function of the pH and consequently resulting in osmotic pressure difference between the gel and the solution. This pressure gradient causes the hydrogel to deform which in turn induces secondary strain on the FBG sensor resulting in shift in the Bragg wavelength. We also report on the sensitivity factor of single and multilayer hydrogel coated FBG at various different pH.