Publications

  • H.G. Kim, J.T. Rhee, M. Jamil, Farzana Ahmad, Y.J. Jeon
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    ABSTRACT: We report the possibility of using the FLAIR interface that can be used as the radiation simulator.•It reports the features of the radiation simulator that a user has to handle on using the FLUKA code.•The results of thermal neutrons found with Boron-coated GEM-detector are described.•The detector efficiency ∼4.7% and ∼6.03% has been found via the forward- and backward detector setup.•The results revealed that GEM-detector can detect the thermal neutrons efficiently.
    Measurement. 01/2015; 60.
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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). · 1.16 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; · 2.27 Impact Factor
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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; · 1.14 Impact Factor
  • Farzana Ahmad
    Electronic Materials Letters 11/2013; · 1.87 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). · 1.40 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 01/2012; · 1.96 Impact Factor
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    ABSTRACT: This article deals with the study of polymer-dispersed liquid crystal (PDLC) films that consisted of microdroplets of liquid crystals (LCs) dispersed in a polymer matrix. The PDLC films were fabricated by the photoinduced phase separation method under room-temperature conditions. To determine the extent of the effects of the molecular structures and their physical properties of different mixtures of monomers and LCs on the morphology and electrooptical properties of the PDLC films, various mixtures were used. A detailed discussion of the obtained results is given. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
    Journal of Applied Polymer Science 03/2011; 121(3):1424 - 1430. · 1.40 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 01/2011; 34(1):256-260. · 2.08 Impact Factor
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    ABSTRACT: The micellization behavior of cetyltrimethylammonium bromide (CTAB) is investigated in the absence and presence of poly(ethylene oxide) employing surface tension, light scattering, and viscosity and conductance measurement. It has been concluded that the critical micellization concentration (CMC) of CTAB in the presence of polymer increases with the increase in polymer concentration. The three ranges of interaction among the polymer and CTAB with respect to concentration of CTAB are identified at surface tension plot and noted to depend upon polymer concentration. The effect of temperature over these interactions and CMC of CTAB has been investigated. It is observed that the CMC, ΔH, and flow activation energy of the system increases with the increase in polymer concentration whereas CMC of CTAB decreases with the temperature. RH and Rg/RH values determined by light scattering also indicate such type of behavior. The CMC values have also been obtained by viscosity and conductivity measurement. The results and conclusions drawn through all the techniques were consistent. New methodology has also been introduced to interpret the data obtained by surface tension, viscosity, and conductance measurement, and get information about the point of interaction and saturation of polymer with surfactant, which was noted to be very useful and informative. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
    Journal of Applied Polymer Science 01/2010; 116(4):2133 - 2142. · 1.40 Impact Factor
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    ABSTRACT: The recent studies deal with a diblock copolymer, polystyrene–poly(ethylene oxide). Infrared spectroscopy, proton resonance spectroscopy (1H-NMR), and laser light scattering techniques have been used to characterize the polymer. It has been concluded that the sample investigated is diblock copolymer polystyrene–poly(ethylene oxide) having molecular mass 1.656 × 104 g/mol and blocks ratio 1 : 2. The micellization behavior is explored through 1H-NMR, laser light scattering, light absorption, surface tension, and conductance and viscosity measurements. The results conclude that the critical micelles concentration of copolymer is 0.0951 g/dL at 25°C. It has been observed that the surface tension of solution decreases with the temperature and its impact is maxima in dilute concentration region. In addition, new methodologies have been introduced to get accurate critical micelles concentration and critical micelles temperature. © 2010 Wiley Periodicals, Inc., J Appl Polym Sci, 2010
    Journal of Applied Polymer Science 01/2010; · 1.40 Impact Factor
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    ABSTRACT: Micellization behavior of sodium dodecyl sulfate (SDS) and its mixture with polyethylene oxide (PEO) are investigated using surface tension and light scattering techniques. The data are presented and interpreted in a novel way, which provides more and reliable information about the interaction of the components. The concentration of SDS corresponding to the initiation of interaction with PEO (T1) and the saturation point (T3) are well identified in this way. It has been observed that the concentration span between T1 and T3 is not much affected by the amount of PEO added. The detail investigation of data concludes that SDS and PEO interactions are in one to one ratio at molecular level and CMC decreases with the addition of salt to the system and the micelles become more compact. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
    Journal of Applied Polymer Science 01/2009; 114(3):1444-1448. · 1.40 Impact Factor
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    ABSTRACT: This paper presents the directly obtained rotational viscosity values of E7, which includes pentylcyanobiphenol, heptylcyanobiphenol, 4-cyano-4′ -n-octyloxy-1,1′ -biphenyl, and 4-cyano-4-n-pentyl-1,1′,1-terphenyl, at various temperatures using molecular dynamics computer simulation. The director mean squared displacement was achieved from the squared displacement of the mean director using the concept of the mean director of various nematic liquid crystals. The calculated values were compared with the experiment results that predicted a good agreement. Additional points that must be considered for further study are also discussed.
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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 35(2). · 0.58 Impact Factor
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    ABSTRACT: Acrylic polyethylene glycol(PEG)-based polymer-dispersed liquid crystal (PDLC) films have been fabricated to investigate the effect of intermolecular interactions on PDLC performance. For this purpose, the amphiphilic liquid crystal and polymers are selected as PDLC composite materials. The acrylic PEG contents are varied from 0 to 66.66 mol wt.% in order to understand the effects of different levels of additions on the microstructure and electro-optical properties of the PDLC films. For this intention, polarized optical microscopy and UV–vis spectroscopy are used. The extent of phase separation and anchoring energy are also examined using Fourier transform infrared (FTIR) spectroscopy and contact angle measurements in consequence of acrylic PEG addition. The contrast ratio, threshold voltage, as well as saturation voltage, tended to increase with the addition of acrylic PEG. The molecular affinity involved in the polymer matrix and LC molecules affected the phase separation which is responsible for the formation of domain size; this accordingly changed the electro-optical properties of PDLC film.
    Colloid and Polymer Science 290(7). · 2.16 Impact Factor

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