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Author: search.filters.author.Manjuladevi, V.Subject: search.filters.subject.Nanocomposites

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    Impact on bulk and interfacial dielectric properties of nematic liquid crystals due to silver nanoparticles
    (AIP, 2021-09) Manjuladevi, V.; Gupta, Raj Kumar
    Doping of nanomaterials into the liquid crystals (LC) can greatly enhance the physical properties of host LC. Since, it is not possible to obtain all the desired parameters of a display device in a single LC, several researchers are trying to optimize the display parameters by using different nanomaterials of different functionalization. In this work, we report the effect of hexane thiol functionalised silver nanoparticles (f-AgNPs) on the dielectric relaxation and electrical properties of nematic liquid crystal 4-trans-pentyal-cyclohexyl cyanobenzene (5PCH) in the homeotropic alignment. The impedance spectroscopy response of pure and f-AgNPs doped nanocomposites of 5PCH are studied in the frequency range of 20Hz - 12MHz. The electrical properties such as bulk capacitance, electrode resistance, double layer capacitance, bulk resistance and Warburg diffusion coefficients were determined by fitting a suitable equivalent electrical circuit model to the experimental data. Temperature dependence of the dielectric relaxation frequency for pure and f-AgNPs doped nanocomposites of 5PCH were also investigated.
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    Studies on Thin Films of Hexa-Alkoxy Triphenylene(HAT5) and Composite of HAT5-TiO2 Nanoparticles
    (American Scientific Publishers, 2014-05) Manjuladevi, V.; Gupta, Raj Kumar
    The studies on discotic liquid crystals are important not only for basic scientific research but also for industrial applications. It can be potentially employed for the fabrication of devices in photovoltaics, organic solar cells and organic LEDs. Hexa-alkoxy triphenylene (HAT5) is one of the commonly studied discotic liquid crystals. We formed Langmuir monolayer of pure HAT5 on ultrapure water subphase. We have studied the effect of doping the monolayer of HAT5 with different concentration of TiO2 nanoparticles on the surface pressure-area isotherms of the Langmuir monolayer. We observed considerable shift in the isotherms towards lower area per molecule on increasing the concentration of TiO2. We deposited the Langmuir-Blodgett (LB) films of pure HAT5 and HAT5+TiO2 (5 and 20% by weight) nanocomposites on the glass substrates. We characterized the films using UV-Vis spectrophotometer and atomic force microscope (AFM). The energy gap is found to decrease with increasing concentration of TiO2 nanoparticles in the HAT5 matrix. It decreases rapidly with increasing the target surface pressure of LB deposition. The AFM images reveal higher density of clusters of TiO2 nanoparticles with the increase in concentration of the nanoparticles in HAT5 monolayer. Such increase in the density may results in reduction in energy gap of the LB films of the nanocomposites.
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    Detection of cadmium ion in water using films of nanocomposite of functionalized carbon nanotubes and anionic polymer
    (AIP, 2018-05) Manjuladevi, V.; Gupta, Raj Kumar
    Presence of cadmium in drinking water is one of the major threats to human health. According to international standards, the maximum permission concentration of cadmium ion in drinking water should be less than 0.002 to 0.010mg/l (2-10 ppb). It is one of the major contaminants in potable water in western part of Indian subcontinent. It is found up to 2.3 to 8.6 mg/l in Rajasthan water. In this article, we report our study on detection of cadmium ion in water employing a sensing layer of nanocomposites of functionalized single walled carbon nanotubes (SWCNTs) and polyacrylic acid (PAA). The film was deposited onto 5 MHz AT-cut quartz crystal of a quartz crystal microbalance (QCM). The response was collected in both static and dynamic mode. We obtained a linear response curve in a given concentration range of cadmium ion indicating the suitability of the functional layer for cadmium ion detection in water. The surface morphology of the functional layer was studied using atomic force microscope before and after sensing.
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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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    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.