Archives-September 2012

Liquid crystals are the soft materials composed of self organized molecules. They are known for their order and mobility which makes them a potential candidate for different applications. Among the different mesophases known, Blue phases are a special type of chiral nematic phases and some of them are optically isotropic. Generally these phases will be exhibited by molecules which possess sufficiently high anisotropy. These blue phases are usually stable for very narrow temperature range between the isotropic and the cholesteric phase. In the present work we will be studying the mesophase behaviour of liquid crystalline compounds doped with some chiral materials in different proportions to induce blue phase mesomorphism. The mesomorphic behaviour of these mixtures will be characterized using POM and DSC. Using ZnS Nanoparticles dispersed in these systems, we aim to widen the temperature range of the blue phase. Recently these nanomaterials stabilized blue phases are shown to have some advantages for display applications and is being actively studied across the world.

Ferromagnetic shape memory alloys (FSMAs) are keenly investigated due to their Shape Memory Effect (SME), high frequency response and large magnetic field-induced strain. Polycrystalline Ni53.2Mn24.6Ga22.1 alloy was synthesized by arc-melting technique. X-ray diffraction revealed that annealed alloy at 1073 K exhibit a well-defined 5M structure .Scanning Electron Microscope image confirms the twinned martensite plate with magnetic domain walls. It is worthy to notice that a high saturation magnetization of 65 (emu/g) and martensitic transformation temperature of TM (334 K) are found by Vibrating Sample Magnetometer and Differential Scanning Calorimetry.

Silver nanoparticles dispersed in water in presence of trisodium citrate have been prepared and characterised. Aqueous solutions of silver nitrate and trisodium citrate were mixed in various proportions and heated at 30oC for 3 hours. The nanoparticles of silver dispersed in water in presence trisodium citrate were characterised by UV-visible absorption spectra, X-ray diffraction, EDX, and SEM. Nano-silver dispersed in water based nanofluids may used to increase thermal conductivity of fluids.

Nano-crystallite LiFePO₄ cathode material has been prepared by polyol technique. The crystalline structure, functional group vibration analyses of the prepared cathode material were characterized by X-ray diffraction (XRD), Fourier transfer infrared spectroscopy (FT-IR) and Raman Studies. The surface morphology of synthesized material has been studied by scanning electron microscopy (SEM) and the compositional analysis has also been carried out through EDX analysis. It is inferred from XRD result that LiFePO₄ powder have an orthorhombic structure with a space group of Pmna. The magnetic properties of the fine particles of LiFePO₄ were examined by vibrating sample magnetometer (VSM) at room temperature, which showed that the prepared sample exhibited a tiny hysteresis loop with the coercivity of 401.81 G.

Binding energy of a donor hydrogenic impurity is computed in a Cd based II-VI semiconducting material taking into account both the effects of phonon and geometrical confinement effects. The former effect is considered with the inclusion of Fröhlich interaction Hamiltonian whereas the latter effect is considered by varying the dot radius. Moreover, lowest binding energy and the donor binding energy are obtained using internal built-in electric fields. All the computations are carried out using Bessel function as an orthonormal basis for different confinement potentials of barrier height considering the internal electric field induced by the spontaneous and piezoelectric polarizations. Since the optical properties of hydrogenic impurity in a quantum dot are strongly affected by the confining potential and the quantum size effect on the changes of refractive index is brought out. It is also observed that the magnitude of the refractive index changes enhances with the inclusion of phonon and geometrical effects.

Composites are currently receiving much attention due to their tuneable chemical and physical properties. ZnO -Al₂O₃ composites attract particular interest because of their possible applications in dye-sensitized solar cells and sensors. Zinc oxide - Aluminum oxide composites were synthesized by hydrothermal method. The precursors used were Zinc Acetate, Aluminum nitrate and Sodium hydroxide. X-ray diffraction (XRD) pattern indicated that the synthesized Al₂O₃ was of hexagonal structure. Thermogravimetric analysis (TGA) was done to determine the thermal properties of the nanopowder UV-Vis spectroscopy and Dielectric analysis were done to determine the optical and dielectric properties of composite.  The results were further discussed.

Co_0.5Mn_0.25Zn_0.25Fe₂O₄ nanoparticles of average size of 61 nm were prepared by chemical co-precipitation method which could be used for ferrofluid preparation. The composition is characterized by X-ray diffraction technique (XRD). XRD study shows formation of single phase homogeneous compound with cubic structure. The crystal size was calculated from XRD data by using Scherrer equation and is confirmed by SEM, which reveals the formation of nanocrystalline ferrite. The dielectric constant and dielectric loss dependence on doping level and frequency at room temperature were described in detail. The leakage current properties of Co_0.5Mn_0.25Zn_0.25Fe₂O₄ nanoparticles were also discussed.

Effect of pressure on the ground state exciton binding energy and the interband emission energy in a wurtzite GaN quantum dot are investigated. The interband emission energy is computed as a function of pressure with a constant geometrical confinement. All the numerical calculations are performed using variational procedure within the single band effective mass approximation. The internal electric fields comprise the spontaneous polarization and piezo electric polarization are included in the Hamiltonian. Our results show that the effects of pressure and the geometrical confinement have great influence on the optical properties of this wide band gap nitride based group-III quantum dots.

Renewable energy sources has drawn attention around the world due to the rapid industrial development and growing population .In order to make the effective use of renewable energy to meet the global energy consumption, it is important to develop high performance, low cost and economically friendly energy storage devices. Since conventional capacitors have some inadequacies such as small energy density (i.e., <0.05 Wh/kg) for many applications which require a large amount of energy storage or delivery,supercapacitors has emerged as new storage device due to their high durability during its long charge – discharge cycles. Supercapacitors are governed by the same fundamental equations as conventional capacitors, but utilize higher surface area low resistance electrodes and thinner dielectrics to achieve greater capacitances. Properties of supercapacitors depend both on the technique used to prepare the electrode and on the current collector structure. Carbon Materials in different forms such as carbon fibers, carbon aerogels, activated carbon, carbon nanotubes and graphene are the attractive electrode materials for supercapacitors. The incorporation of nanomaterials as electrodes help to control the surface area as well as porosity which results in improved performance, greater efficiency and life time of the super capacitors .This recent technology improvement enabled supercapacitors as an alternative to pulsed batteries for applications in industry and telecommunication equipment. This review focuses on the taxonomy of supercapacitors, explores principle and theory of operation, dependence on different electrode materials on supercapacitor output and their application in the present world.

The dye, Grey BL was adsorbed on an absorbent prepared from mature leaves of the Arasu tree (ficus relegosia) leaves powder(ALP). In order to understand the adsorption behavior of Arasu Biomass Carbon, batch type experiments, effect of PH Contact time, Carbon dose are conducted and properly examined. At PH 7 the dye studies could be removed effectively. The Isothermal data fitted with both Langmuir and Freundlich model. The adsorption processes followed the first order rate kinetics. Mathematical Equations have been designed for the wide range of applications. The results in this study indicated that Arasu Leaves Powder was an attractive candidate for removing dye from industrial effluent and waste water.