Department of Physics
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Item ZnO nanorod incorporated nematic liquid crystal for high multiplexing and high refresh rate displays(Elsevier, 2023-11) Gupta, Raj Kumar; Manjuladevi, V.Zinc oxide nanorods incorporated in nematic liquid crystal matrix (NLC) are observed to improve physical properties of NLC and its device parameters, especially, for displays. In this article, we present the results of effect of incorporation of zinc oxide nanorods of various sizes but similar aspect ratio on physical properties of NLC. Zinc oxide nanorods (ZR) of similar aspect ratio (4–5) but different sizes (diameter: length) abbreviated as., ZR1 (10:50 ), ZR2 (50:200 nm) and ZR3 (1:5 ) are synthesized. Nanocomposites of synthesized nanorods with wide temperature range NLC are prepared. Smaller nanorods (ZR1) are expected to form chain like structures in host NLC matrix leading to softening of order parameter at the isotropic-nematic (I–N) transition. As the size of the nanorods increases the discontinuity of order parameter at I–N transition is observed to increase. Enhancement of dielectric anisotropy as well as birefringence which in turn indicates increase in the order parameter of the system is observed with the incorporation of zinc oxide nanorods. Reduction of threshold voltage, electro-optic response time and bulk ac conductivity and enhanced bend to splay elastic constant ratio of the nanocomposite samples as compared to pure NLC is observed with the incorporation of ZR in host NLC. Observed results show that nanorods of size 50: 200 are the most suitable to be incorporated in NLC for high multiplexing display devices.Item Nematic liquid crystal dispersed with two-dimensional functionalised graphene oxide (fGO): insights on improving the nematic ordering and reducing electro-optic response time(Taylor & Francis, 2024-01) Manjuladevi, V.; Gupta, Raj KumarDoping a nematic liquid crystal (NLC) with nanoparticles (NPs) of varied dimensions and properties to form LC-NP nanocomposites with improved electro-optic and dielectric properties has recently been a much-explored field of work. But still, NLC nanocomposites based on two-dimensional (2D) NPs have not been studied vividly because of the high tendency of 2D NPs to aggregate together. In the present work, we have studied the effect of incorporating hexadecanethiol functionalised graphene oxide (fGO), a 2D NP, in a conventional NLC medium under varying doping concentrations. We found that at a lower doping concentration (⁓10−4 wt.%), the NLC nanocomposite showed a substantial increase in dielectric anisotropy (Δε) and birefringence (Δµ) values as compared to pure NLC sample. A significant decrease (⁓50%) in ionic conductivity as well as reduced electro-optic response time (⁓75%) was also observed in this NLC nanocomposite. As the fGO doping concentration was increased (⁓10−2 wt.%), a reverse trend was observed for Δε, Δµ and response time values, which declined sharply with increasing doping concentration. Hence, the present work highlights two different working mechanisms at low- and high-doping concentrations of 2D NPs.Item Zinc Oleate Nanorod-Induced Vertical Alignment of Nematic Liquid Crystal(ACS, 2022-12) Gupta, Raj Kumar; Manjuladevi, V.Nanocomposite zinc oxide nanorods capped with oleic acid (ZOR) with positive dielectric anisotropy liquid crystal (LC) 4′-octyl-4-biphenylcarbonitrile (8CB) filled in unaligned cells exhibit homeotropic alignment of host LC molecules. Further, systematic investigation of the textural, dielectric, and conductivity properties of nanocomposites filled in planar cells is performed with increasing concentration of nanorods. At a nanorod concentration ≤0.2 wt % in 8CB, the order parameter of nanocomposite samples is found to be increasing and ionic conductivity is found to be decreasing as compared to pure LC. Beyond 0.3 wt % concentration of nanorods in 8CB, vertical alignment (VA) of host LC is observed even in a planar aligned cell. The VA of LC molecules in ZOR nanocomposites is confirmed through attenuated total reflection–Fourier transform infrared absorption spectra studies.Item Effect of shape of ZnO nanoparticle on electro-optic and dielectric properties of nematic liquid crystal(Elsevier, 2023-09) Manjuladevi, V.; Gupta, Raj KumarProperties of liquid crystal incorporated with various shapes of a nanomaterial are expected to show multifaceted behaviour as properties of nanomaterial are extremely dependent on its size and shape. In view of this, we have investigated the effect of shape of ZnO nanoparticle on electro-optic and dielectric properties of nematic liquid crystal (NLC), PCH5. Nanocomposites of 0.01 wt% ZnO nano- sphere, rods, and wires in NLC are prepared. The addition of ZnO nanoparticles to NLC leads to increase in the order parameter and reduction in threshold voltage, response time as well as ionic conductivity as compared to the pure NLC host. Dielectric permittivity measurements indicate nanoparticle induces short range order in isotropic phase. Dielectric measurements also show increase in order parameter in nanocomposites with 1D nanoparticles whereas negligible change is observed in nanocomposites with spherical nanoparticles in NLC in deep nematic range. The ATR-FTIR measurements support the enhancement in parallel correlation of dipole moments in ZnO nanocomposites as compared to pure NLC.Item Investigation on physical properties of silver nanorod doped nematic liquid crystal(AIP, 2021-09) Manjuladevi, V.; Gupta, Raj KumarImprovement in the physical properties of nematic liquid crystals plays an important role in the performance of display devices. In the present study, the physical properties of silver nanorod (AgNR) doped nematic liquid crystal is investigated. The negligible change is observed in the value of birefringence for the lower doping concentration of AgNR in NLC. The parallel and perpendicular components of dielectric permittivity at T-TIN = −15 ° C increase with the addition of lower concentration (≤ 0.5 wt%) of silver nanorods to the NLC host. The ac conductivity decreases with the increase in the dopant concentration because of the trapping of ionic impurities of NLCItem Dielectric spectroscopy studies of silver nanorod doped nematic liquid crystal(Elsevier, 2022) Manjuladevi, V.; Gupta, Raj KumarDielectric spectroscopy provides information on molecular dynamics as well as on important material parameters such as the static dielectric permittivity (ε) and DC electrical conductivity (σ) of the bulk as well as at the interfaces. In this study, we present the dielectric spectroscopy results of silver nanorod doped nematic liquid crystal (NLC) in the frequency range of 20 Hz to 10 MHz. The relaxation frequencies tend to increase owing to the availability of free volume due to addition of nanorods. However, the conductivity (at 1 kHz) is observed to decrease with the increase in the nanorod concentration until aggregation of nanorods is observed in the NLC host. Dielectric strength of doped NLC samples also increases with increasing concentration of nanorods.Item Frequency dependence of dielectric permittivity and conductivity of functionalized carbon nanotube-nematic liquid crystal nanocomposite(Elsevier, 2022-03) Manjuladevi, V.; Gupta, Raj KumarThe addition of carbon nanotubes (CNTs) to nematic liquid crystal (NLC) medium is known to enhance the orientational order along with the enhancement in electro-optical and dielectric properties of the liquid crystal (LC). The studies on the dielectric behavior of LC-nanocomposites at wide range frequencies are essential for optimizing the LC based device performances. The nanocomposites of octadecylamine functionalized single-walled carbon nanotubes (ODA-SWCNTs) with NLC are studied with the aid of dielectric spectroscopy. The important parameters of LCs relevant to display related applications such as dielectric permittivity, relaxation frequency, threshold voltage, and conductivity are investigated over a wide range of frequency and temperatures in planar as well as homeotropic configurations. The doping of ODA-SWCNTs into the NLC increases the local orientational order in the nematic matrix due to the strong interaction between LC and CNT molecules. The optimum doping decreases threshold voltage due to enhancement of dielectric anisotropy and decrease in splay elastic constant. The experimental data obtained from impedance spectroscopy measurements are fitted with a suitable equivalent electric circuit model, and the estimated electrical components are studied as a function of temperature. Investigation on interfacial and bulk properties of pure and ODA-SWCNT nanocomposites of 7CB NLC are also discussed.