Browsing by Author "R. Dhar"

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Dielectric relaxation studies in N-(4-octyloxy-2-hydroxybenzylidene)-4- carbethoxyaniline
(2004) R. Dhar; Meenal Gupta; V.K. Agrawal; M.K. Singh; B. Singh
Temperature dependent dielectric spectroscopy of a newly synthesized compound N-(4-octyloxy-2-hydroxybenzylidene)-4-carbethoxyaniline, having a wide temperature range (∼70°C) Smectic A (SmA) phase has been carried out in the frequency range 100Hz-10MHz. Dielectric permittivity and loss in the homeotropic (ε′∥and ε″∥) and planar (ε′⊥ andε″⊥) alignments of the molecules have been determined. Relaxation frequencies corresponding to the rotation of the molecules about their short axes have been found to lie below 1 MHz and exhibit Arrhenius behaviour. Relaxation frequencies corresponding to the rotation of the molecules about their long axes are expected to lie above 10 MHz. Dielectric anisotropy (Δε′ = ε′∥ - ε′⊥) has been found to be negative throughout the range of the SmA phase.
Enhanced Hole transport in polyfluorene polymer by using hole injection layer
(Springer Science and Business Media Deutschland GmbH, 2014) Manisha Bajpai; Ritu Srivastava; R.S. Tiwari; R. Dhar
Hole transport in poly(9,9-dioctylfluorene) (PFO) are measured by performing current density- voltage (J-V) measurements as a function of temperatures. For the J-V measurements, F4TCNQ is used as hole injection layer (HIL). Two different devices of PFO polymer are fabricated F4TCNQ having device configuration ITO/PFO/Au (with interface modification) and ITO/PFO/F4TCNQ/Au (with interface modification) respectively. Since, F4TCNQ is evaporated on the top of PFO film so that the contacts are taken from Au. © Springer International Publishing Switzerland 2014.
Synthesis, characterization and mesomorphic behaviour of lanthanide (III) 4-alkoxybenzoates
(2005) Madan K. Singh; B. Singh; R. Dhar; V.K. Agrawal
The lanthanide (III) 4-alkoxybenzoates [Ln(CnH2n+1 OC6H4CO2)3, Ln = La (III), Pr (III), Nd (III), Eu (III), Gd (III), Tb (III) and Dy (III) and n = 6, 8, 10, 12 and 16] have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, and IR and electronic spectroscopy. Hot-stage polarizing optical microscopy and differential scanning calorimetry have been used to investigate the mesomorphic behaviour. The chain length influences the structure and hence the thermal behaviour of these compounds. All the lanthanide complexes except decyloxy derivatives exhibit smectic A mesophase. The decyloxycontaining complexes are non-mesomorphic. The differential scanning calorimeter traces do not display the exothermic peak for all the compounds except for the hexadecyloxy derivatives, which exhibit enantiotropic smectic A phase. The influence of the lanthanide ions on the phase transition has also been clearly demonstrated. © 2005 Taylor & Francis Group Ltd.
Synthesis, characterization and mesomorphic properties of n-(4-n-alkoxy-2-hydroxybenzylidene)-4-carbethoxyaniline and their copper complexes
(2004) B. Singh; M.K. Singh; R. Dhar; A.K. Srivastava
New homologous series of N-(4-n-alkoxy-2-hydroxybenzylidene)-4-carbethoxy- aniline, H2n + 1 CnOC6H3(OH)C(H) = NC6COOC2H5 (n = 6, 8, 10, 12, 16) have been synthesized. These compounds were reacted with copper acetate to get the metal complexes. All these compounds have been characterized by elemental analysis, FT-IR and NMR spectroscopy. Mesomorphic properties of these compounds were studied by differential scanning calorimeter and polarizing microscope. These compounds exhibit wide range enantiotropic SmA phase as confirmed by their typical optical, texture under polarizing microscope. In the heating cycle, all the members of the series (hexyl to hexadecyl) show SmA phase in the range of 70 to 115°C and 115°C and this range is almost independent of the alkoxy chain (except in decyl). All the members show supercooling effect and the range of SmA phase in increased in the cooling cycle in comparison to the corresponding heating cycle. The copper (II) complexes of the series also show enantiotropic SmA phase but at higher temperatures (above 140°C) with decreased temperature range of existence in comparison to organic compounds.