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Author: search.filters.author.Gupta, Raj KumarSubject: search.filters.subject.Carbon nanotubes (CNTs)

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    Transparent Indium Tin Oxide Films for Liquid Crystal Display Application
    (American Scientific Publishers, 2013-12) Manjuladevi, V.; Gupta, Raj Kumar
    In this modern era, most of the device applications involve displays as one of the main components of the system. There are multi-dimensional technological advancements with the invention of liquid crystal display (LCD) devices. Indium tin oxide (ITO) deposited substrates has proved to be efficient transparent electrodes for the fabrication of the display devices. The properties of LCD are governed by the ITO, liquid crystal (LC) materials and the interfacial phenomena between the ITO and LC materials. In this article we discuss the role of ITO and LC materials on the performance of LC cells. We also discuss the interfacial properties of LC-functionalized carbon nanotubes composites on the treated ITO substrates.
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    Superior electro-optical switching properties in polymer dispersed liquid crystals prepared with functionalized carbon nanotube nanocomposites of LC for switchable window applications
    (Elsevier, 2023-03) Manjuladevi, V.; Gupta, Raj Kumar
    In this work, we are reporting the results on electro-optical switching properties of polymer dispersed liquid crystal (PDLC) devices for switchable window related applications. The PDLC cells are prepared by mixing octadecylamine functionalized single-walled carbon nanotubes (ODA-SWCNT) nanocomposites of liquid crystals (LC) and acrylate-based monomer by polymerization induced phase separation method. The important switchable device parameters such as threshold voltage, switching voltage, response time, contrast ratio and effective refractive index are investigated. The PDLC cells prepared with 0.05 wt% ODA-SWCNT nanocomposites of the LC, 7CB show almost zero threshold field and 36% less driving field compared to PDLC prepared with pure 7CB. A distinct optical response (frequency doubling) phenomenon is observed for PDLC prepared with 0.03 and 0.05 wt% ODA-SWCNT nanocomposites of 7CB compared to PDLC cells prepared with pure 7CB and lower concentrations (<0.03 wt%) of ODA-SWCNT. The relaxation of optical transmittance is observed at low frequency even when the applied electric field () is ON which is due to the strong induced internal electric field (due to free ions) which nullifies the . The physical mechanism of this unique optical behavior is discussed in detail. The PDLC prepared with 0.01 wt% ODA-SWCNT show 84% faster response time compared to PDLC prepared with pure 7CB. The working of prototype PDLC devices for use in switchable window related applications is reported. The results indicate that, the PDLC prepared with 0.05 wt% ODA-SWCNT nanocomposites of 7CB show high ON state clarity and high OFF state opacity compared to PDLC prepared with pure LC and lower concentrations of ODA-SWCNT.
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    Supramolecular assembly of single-walled carbon nanotubes at air-solid interface
    (Springer, 2014-07) Manjuladevi, V.; Gupta, Raj Kumar
    We formed a stable and reversible Langmuir film (LF) of bundles of unfunctionalized single-walled carbon nanotubes (SWCNTs) at the air–water interface. The film exhibits gas-like and liquid-like phases. The Raman spectrograph of Langmuir–Blodgett (LB) film of single layer of SWCNTs on Si/SiO2 substrate shows the characteristic G, D, and radial breathing mode frequencies of the single-walled carbon nanotubes. Using atomic force microscope (AFM) in spreading resistance imaging mode, we obtained a dependence of target surface pressure on the assembly of SWCNTs in the LB films. The film deposited at very low surface pressure (0.5 mN/m) exhibited an assembly wherein the long axis of the nanotube bundles aligned in the direction of deposition. The LB films deposited in the liquid-like phase of the SWCNTs exhibited supramolecular donut structure. The average width of the SWCNTs was around 30 nm. The current–voltage characterization of the local structures of the LB films using the conducting AFM probe indicates semi-metallic and metallic nature of the donut and the hole in the donut (nanopore), respectively. Such supramolecular assembly of the SWCNTs can find application in the fabrication of the devices like sensors, photochemical cells, batteries, etc.
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    Faster switching polymer dispersed liquid crystal devices incorporated with functionalized SWCNTs
    (Elsevier, 2022-05) Manjuladevi, V.; Gupta, Raj Kumar
    Polymer dispersed liquid crystals (PDLCs) were fabricated using acrylate-based UV curable monomer and a low birefringent nematic liquid crystal, 5PCH, by polymerization induced phase separation method. The effect of ODA-SWCNT dispersion on electro-optical properties of PDLC was investigated and compared with the undoped PDLC. The total response time reduces by 70%, and threshold voltage decreases by 42% in PDLC prepared with 0.015 wt% ODA-SWCNT nanocomposites of 5PCH, compared to the PDLC prepared with pure 5PCH. The optical transparency and sharpness of the image in ON-state was found to be remarkably better in the ODA-SWCNT incorporated PDLC as compared to the PDLC prepared with pure 5PCH.