Farzana Ahmad

Physical Chemistry, Polymer Chemistry, Analytical Chemistry



  • M. Jamil · Farzana Ahmad · Y.J. Jeon
    Renewable and Sustainable Energy Reviews 07/2015; DOI:10.1016/j.rser.2015.05.087 · 5.90 Impact Factor
  • F. Ahmad · M. Jamil · L.J. Woo · Y.J. Jeon
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    ABSTRACT: In this work the properties of PDLC film based on block copolymer film are presented. The FTIR; phase transition temperature properties are studied in order to see the absorption of block copolymer with the LC. Optical microscopic work showed the increase in droplet size with the increase in block copolymer contents. It is found absorption of block copolymer does not increase linearly with the increase in its contents. Moreover a decrease in refractive index is observed with the increase in block copolymer contents. The decrease in refractive index of block copolymer with temperature is interesting for thermo-optical and electro-optical devices simultaneously.
    MATERIALE PLASTICE 06/2015; 52(2):171-174. · 0.82 Impact Factor
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    ABSTRACT: We prepared silane-coated indium tin oxide (ITO) glass having different surface energies and topologies by using dipping and evaporation methods with the silane solution. The silane-coated ITO glass samples were analysed using contact angles and atomic force microscopy. Liquid crystal (LC) cells with positive and negative dielectric LCs and a mixture of negative dielectric LCs and liquid crystalline monomers were viewed between crossed polarisers. The ITO glass prepared using the dipping method showed a rougher topology and higher surface energy than the ITO glass prepared using the evaporation method. LCs having positive and negative dielectric anisotropy showed vertical alignment on the silane-coated ITO glass samples as viewed between crossed polarisers. However, the mixture of negative dielectric LCs and liquid crystalline monomers showed vertical alignment only for the ITO glass prepared using the evaporation method. The evaporation method was used for fabrication of reverse-mode polymer-dispersed liquid crystals, and the crystals showed well-aligned vertical polymer networks, good reverse operational mode and a double-U-shaped graph around each 40° by the crystal rotation method.
    Liquid Crystals 04/2015; 42(4):473-480. DOI:10.1080/02678292.2015.1006150 · 2.49 Impact Factor
  • M. Jamil · J.T. Rhee · H.G. Kim · Farzana Ahmad · Y.J. Jeon
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    ABSTRACT: In this work, we report the design configuration and the performance of the hybrid Gas Electron Multiplier (GEM) detector. In order to make the detector sensitive to thermal neutrons, the forward electrode of the GEM has been coated with the enriched boron-10 material, which works as a neutron converter. A total of 5 x 5 cm(2) configuration of GEM has been used for thermal neutron studies. The response of the detector has been estimated via using GEANT4 MC code with two different physics lists. Using the QGSP_BIC_HP physics list, the neutron detection efficiency was determined to be about 3%, while with QGSP_BERT_HP physics list the efficiency was around 2.5%, at the incident thermal neutron energies of 25 meV. The higher response of the detector proves that GEM-coated with boron converter improves the efficiency for thermal neutrons detection.
    Applied Radiation and Isotopes 01/2015; 95. DOI:10.1016/j.apradiso.2014.09.023 · 1.23 Impact Factor
  • H.G. Kim · J.T. Rhee · M. Jamil · Farzana Ahmad · Y.J. Jeon
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    ABSTRACT: In the current work, we demonstrate the possibility of using the FLAIR (an advanced user friendly interface) that can be employed for building the radiation simulator via inserting the basic parameters in it. Generally, the FLAIR interface is utilized by the user for FLUKA MC package to assist in the editing of the input files, execution of the simulation code and for the visualization of the output data. The current work describes some of the features of the radiation simulator which a general user has to handle, while using the FLUKA MC code. Further it explores the basic structure of the FLAIR simulator generator. In the last section the results of a simulation test obtained for the thermal neutrons detection via Boron-coated (gas electron multiplier) GEM-detector using the FLUKA-MC code have been described. The detector efficiency ∼4.7% and ∼6.03% has been evaluated for the forward- and backward detector setup, respectively. The current simulation results have been compared with the experimental findings which reveals a close agreement. The obtained results revealed that the GEM-detector can detect the thermal neutrons efficiently.
    Measurement 01/2015; 60. DOI:10.1016/j.measurement.2014.09.076 · 1.48 Impact Factor
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    ABSTRACT: In the reported work the block copolymers are used in the polymer disperse liquid crystal (PDLC) films. The present work has been performed to investigate the effect of block copolymer addition and block ratios on the PDLC characteristics. From our experimental finding, addition of block copolymer in PDLC shows variation in droplet size, electro-optical properties, extent of phase separation, and phase transition temperature. These finding indicate the alteration in solubility parameters of solutions with the addition of block copolymers. Moreover, the tri-block copolymer shows enlarge droplet size, enhancement in the degree of phase separation, and predict improvement in electro-optical properties, as compared to di-block copolymer. Similarly upon such comparison, the study suggests the tri-block copolymer have a relative lower molecular interaction with the liquid crystal molecules.
    Journal of Modern Optics 07/2014; 61(12). DOI:10.1080/09500340.2014.919037 · 1.01 Impact Factor
  • Farzana Ahmad · M. Jamil · Y. J. Jeon
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    ABSTRACT: Reverse-mode polymer dispersed liquid crystals (PDLCs) comprise an important new class of materials for optical device applications. Generally reverse-mode PDLCs are transparent and opaque in the absence and presence of an external field, respectively. Display devices based on reverse-mode PDLC technology are useful for large-area displays; because their fabrication for manufacturing shutters is considered to be easier and faster, they are also employed for automotive technology and smart windows. These devices can be operated at a low voltage, which conserves energy in intelligent-device applications. This work presents a comprehensive review of past research regarding reverse-mode PDLCs and includes the advantageous features, applications, and various fabrication methods of reverse-mode PDLCs and photo-chromic reverse-mode PDLCs. In addition, some new features of this technology that have recently been reported and future investigations by a variety of research groups are presented.
    Electronic Materials Letters 07/2014; 10(4):679-692. DOI:10.1007/s13391-013-3279-8 · 1.98 Impact Factor
  • Wiheeb · Ahmad · Murat · Kim · Othman
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    ABSTRACT: Microporous silica membrane containing hydrotalcite (HT) was prepared successfully without losing the former’s molecular sieving property. The microporous HT-silica membrane (200 nm in thickness) was formed on the surface of mesoporous γ-alumina layer (9 μm in thickness) and supported by macroporous α-alumina substrate (ca. 2 mm in thickness). The pore size of the microporous HT-silica membrane was 8.5Å, slightly larger than the pristine silica membrane (5Å). The composite membrane was found to enhance the permeability of gases and permselectivity of carbon dioxide from gas mixture comprising methane, hydrogen or nitrogen. Microporous HT-silica membrane with 15 vol.% HT displayed the highest permselectivities in the order of CO2/CH4 > CO2/N2 > CO2/H2 and the permselectivities decreased with increasing HT content.
    Separation Science and Technology 06/2014; 49(9). DOI:10.1080/01496395.2014.890629 · 1.17 Impact Factor
  • Lee · Baek · Kim · Choi · Ahmad · Jamil · Jeon
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    ABSTRACT: The vertical alignment of liquid crystals (LCs) on cetyltrimethylammonium bromide-coated (CTAB-coated)indium tin oxide (ITO) glass is the consequence of specific interactions between the LCs, CTAB and ITO surface. The CTAB concentration influences the LC orientation, which changes the ITO surface energy. Changes in the surface energy of CTAB-coated ITO glass are investigated by the Owens–Wendt method. Both polar- and dispersive-component energies on the ITO surface decrease as the CTAB concentration increases, and reach saturation around 0.002% CTAB. The physico-chemical interaction between the LCs and the ITO surface was diminished by the presence of the CTAB layer, which induced the vertical alignment of LCs having positive or negative dielectric anisotropy. Vertical alignment is confirmed using crossed polarisers and the crystal rotation method. The electro-optical properties of fabricated reverse mode polymer dispersed liquid crystal films display transmittance of T on: 29.7%, T off: 85% and a response time of τ on: 33 ms, τ off: 107 ms.
    Liquid Crystals 05/2014; 41(5). DOI:10.1080/02678292.2013.869626 · 2.49 Impact Factor
  • Lee · Kim · Ahmad · Jamil · Jeon
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    ABSTRACT: Polymer-dispersed liquid crystal (PDLC) films block UV light and have been used as smart windows, light shutters and rear screens on buildings. Generally, PDLCs are fabricated by photopolymerisation using photoinitiators (PIs), which may induce film degradation by UV light. In this study, we report the fabrication of thiol–vinyl PDLC films by the polymerisation-induced phase separation method without the addition of PI. The stoichiometric ratio of the thiol and vinyl monomers was optimised based on variations in the FT-IR absorbance intensity. The fabricated films displayed good electro-optical properties. The durability of the PDLC films (with and without PI) was investigated by observation under UV irradiation for 10 days, following which the films were characterised using a spectrophotometer, scanning electron microscope and polarised optical microscope. The thiol–vinyl PDLC film without PI exhibited good physicochemical durability and low haze variation under UV irradiation.
    Liquid Crystals 03/2014; 41(8). DOI:10.1080/02678292.2014.904013 · 2.49 Impact Factor
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    Farzana Ahmad · Muhammad Jamil · Young Jae Jeon
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    ABSTRACT: Polymer dispersed liquid crystal (PDLC) films morphologies and electro-optical properties have been mostly investigated on the method of polymerization, rate of reaction, the relative amount, characteristic, and temperature of the LC/monomer mixtures; in chorus with the molecular associations existing among the LC, monomer molecules and with the glass. In this effort the molecular associations of polymer matrix having hydrophilic and hydrophobic characteristics are considered with the LC. Here the hydrophilic/hydrophobic interactions of material are deduced equally accountable for change in the morphology, electro-optical properties and phase separation of PDLC films. For such investigations the spectroscopic techniques such as Fourier transform infrared (FTIR) spectroscopy, polarized optical microscopy (POM) and phase transitions temperatures have been implemented which appreciably elucidate the subsequent studies.
    Arabian Journal of Chemistry 02/2014; 58. DOI:10.1016/j.arabjc.2014.01.022 · 3.73 Impact Factor
  • Farzana Ahmad · Muhammad Jamil · Jin Woo Lee · Young Jae Jeon
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    ABSTRACT: We propose a simple methodology to vertically align nematic liquid crystal (LC) molecules by a single-step process. This is achieved by dispersing a small amount of ferromagnetic particles in LCs under a weak magnetic field. For this purpose, a magnetic field of 0.1T is applied for 5 min. The resulting vertical arrangement of LC molecules was confirmed by a cross-polarised optical microscope, Fourier transform infrared analysis and the optical transmittance of polymer-dispersed liquid crystal films.
    Liquid Crystals 01/2014; 42(2):233-239. DOI:10.1080/02678292.2014.981603 · 2.49 Impact Factor
  • J. T. Rhee · H. G. Kim · Farzana Ahmad · Y. J. Jeon · M. Jamil
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    ABSTRACT: In this work, we demonstrate the feasibility and characteristics of a single-gap parallel plate avalanche counter (PPAC) as a low energy neutron detector, based on Gd-converter coating. Upon falling on the Gd-converter surface, the incident low energy neutrons produce internal conversion electrons which are evaluated and detected. For estimating the performance of the Gd-based PPAC, a simulation study has been performed using GEANT4 Monte Carlo (MC) code. The detector response as a function of incident neutron energies in the range of 25-100 meV has been evaluated with two different physics lists. Using the QGSP_BIC_HP physics list and assuming 5μm converter thickness, 11.8%, 18.48%, and 30.28% detection efficiencies have been achieved for the forward-, the backward-, and the total response of the converter-based PPAC. On the other hand, considering the same converter thickness and detector configuration, with the QGSP_BERT_HP physics list efficiencies of 12.19%, 18.62%, and 30.81%, respectively, were obtained. These simulation results are briefly discussed.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 12/2013; 732:233-236. DOI:10.1016/j.nima.2013.06.036 · 1.22 Impact Factor
  • Farzana Ahmad
    Electronic Materials Letters 11/2013; · 1.98 Impact Factor
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    ABSTRACT: Drought stress is one of the major yield constraints for cereal crops. Traditionally, for developing drought tolerant cultivars, selection either direct or indirect is practiced. Although this approach is effective, yet time consuming and labour intensive. Identification of drought related quantitative trait loci (QTLs) coupled with marker assisted selection has shown some positive results. Transgenic and "omics" technologies promise to make progress in breeding for drought tolerance through a more fundamental understanding of underlying mechanisms of drought tolerance and identifying potential candidate genes. These new approaches provide opportunities to direct the continued breeding of genotypes giving stable yields under drought stress.
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    ABSTRACT: The addition of dichroic dye to liquid crystal (LC) display makes an optical shutter easily without polarizer. However, the dichroic dye induces one significant problem an inadequate contrast. The general reason for this is the less available UV light for polymerization due to absorption of UV light by trapped dye molecules in polymer matrix. This problem results into accumulation of residual pre-polymer molecules and induces slow polymerization that produces larger droplet size for LCs. This in turns produces insignificant electro-optical properties for dye-PDLC display. Our strategy proposed a new way to overcome this difficulty by adjusting the some factors, e.g., pre-polymer, initiator contents and curing time.
    Journal of Computational and Theoretical Nanoscience 11/2012; 18(1):225-229. DOI:10.1166/asl.2012.4643 · 1.34 Impact Factor
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    ABSTRACT: In this paper, multidirectional light-control reflective (LCR) films are developed in order to create an active reflective structure that will enhance the image brightness and contrast ratio of reflective dye-doped polymer-dispersed liquid crystal (D-PDLC) displays at lower viewing angles. Advantages of LCR films are that their production is low cost and they require a simple photolithographic fabrication method. The optimum design prism-type light-control reflective film succeeded in minimising the surface scattering effect; thus, the contrast ratio is much enhanced. The symmetric and asymmetric LCR films produced multidirectional scattering that enhances the reflectance at lower viewing angles, which has importance in future display applications. In particular, the prism LCR film has been found to be more influential on the reflectance of D-PDLC films due to multidirectional scattering of light by non-symmetric arrays. The improvement in contrast ratio has been confirmed by the enhancement of optical properties for reflective D-PDLC displays at lower viewing angles below 30°.
    Liquid Crystals 11/2012; 39(11):1-6. DOI:10.1080/02678292.2012.715688 · 2.49 Impact Factor
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    ABSTRACT: The enhancement of electro-optical properties in reflective-type dye polymer dispersed liquid crystal (PDLC) has been achieved by applying an additional white PDLC layer along with dye PDLC layer. This newly modified structure that consists of white PDLC layer and scattering reflector acts as an active reflector. In this practice, an additional arrangement of a polymer barrier layer is made-up over white PDLC layer, to block the absorption of any solution from dye PDLC. The contrast ratio of this new configuration is almost doubled with low driving voltage and high ON reflectance. Simultaneously, the “off” state has been observed darker than single layer dye PDLC structure. This new configuration can be potentially significant for various display applications such as E-paper, outdoor billboard, and flexible display. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
    Journal of Applied Polymer Science 04/2012; 124(1). DOI:10.1002/app.35011 · 1.77 Impact Factor
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    ABSTRACT: Sudan black B (SBB) was used to investigate as the nonionic diazo dye-doped in polymer dispersed liquid crystal (PDLC) display, by polymerization-induced phase separation (PIPS) method. The maximum absorbance, contrast ratio, dichroic ratio and the order parameter of nonionic diazo dye in nemetic host (TL203) were investigated using UV–Vis polarized spectroscopy. The orientation of the dye molecules was controlled by electric field, which enabled the contrast ratio of the dye to be obtained by electrically switching. The change occurring on droplet morphologies and electro-optical properties of PDLC film with the change in contents of Sudan black dye and liquid crystals (LC) contents was investigated. We found an increase in LC droplet sizes with the increase of diazo dye and LC contents. Moreover the addition of small amount of nonionic diazo dye reduced the threshold voltage (V $_{\boldsymbol{\rm th}})$ , increased off-state transmittance, enhanced the contrast ratio and decreased the response time of dye-doped PDLC. Additionally the change in transition temperature of LC and changes in LC droplet morphologies with the addition of dye were also observed. Such changes were observed with the images taken by polarized optical microscope (POM). The detail discussions on such behaviours were also made.
    Bulletin of Materials Science 04/2012; 35(2). DOI:10.1007/s12034-012-0286-6 · 1.02 Impact Factor
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    ABSTRACT: Dye-doped PDLC has a high probability to be used as reflective optical shutter due to its good reflectance compared to normal PDLC or LC shutter structures. The black state can be significantly enhanced by the minimized surface scattering between polymer and LC surface, which makes a harmful result to the contrast ratio, one of most important factors for optical shutter. To remove this scattering effect, we have developed new combinational structure, consisted of guest dye-doped LC (DLC) and dye-doped PDLC (DPDLC). In the newly fabricated dye-doped PDLC structure, the front location of dye-doped LC layer can remove the light scattering effect of the surface of single dye PDLC structure. The proposed process can also remove the randomly distributed dyes in polymer area of dye PDLC. This technique enhances the reflectance as well as the contrast ratio.
    Optical Materials 11/2011; 34(1):256-260. DOI:10.1016/j.optmat.2011.08.027 · 1.98 Impact Factor

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