Department of Physics

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Author: search.filters.author.Gupta, Raj KumarSubject: search.filters.subject.Nanoparticles

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Now showing 1 - 7 of 7
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    Monolayer of amphiphilic functionalized gold nanoparticles at an air-water interface
    (APS, 2008-09) Gupta, Raj Kumar
    Langmuir films at the air-water interface exhibit a variety of surface phases which arise primarily due to the molecular interaction governed by intermolecular separation. We have studied the thermodynamical aspects of Langmuir monolayers of amphiphilic functionalized gold nanoparticles (AGNs) at the air-water (A−W) interface. Interestingly, the AGN monolayer exhibits phases like gas, a low-ordered liquid (L1), a high-ordered liquid (L2), and a collapsed state. We find that the first-order phase transition between L1 and L2 vanishes above a critical temperature of 28.4°C. Surprisingly, for a range of higher temperatures (⩾29.4°C and ⩽36.3°C), the L1 phase undergoes a transition to a bilayer of the L2 phase before entering into the collapsed state.
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    Periodic array of nanoparticles on gold substrate
    (AIP, 2013-06) Gupta, Raj Kumar; Manjuladevi, V.
    The thin films of nanoparticles of titanium dioxide were deposited on gold deposited substrates by drop cast method. The films were characterized employing the atomic force microscope in contact mode. We obtained a high degree of orderness among the nanoparticles. The orderness are different in different direction.
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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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    Langmuir monolayer assisted formation of cadmium sulfide nanoparticles at the air–water interface and their role in the alignment of bulk liquid crystals
    (RSC, 2016-04) Manjuladevi, V.; Gupta, Raj Kumar
    Metal-sulfide nanoparticles can be fabricated by a one-step synthetic route by forming a Langmuir monolayer of long chain fatty acids over a subphase possessing metal ions and H2S gas in an air medium. Due to an interfacial reaction, the metal-sulfide nanoparticles are fabricated. The one-step synthesis can be further simplified by the appropriate choice of the amphiphilic molecules. The Langmuir monolayer of octadecanethiol (ODT) was reported to be stable over an ultrapure ion-free water subphase and can be perturbed significantly due to the presence of metal ions in the subphase. In this paper, we report the Langmuir monolayer assisted formation of CdS nanoparticles due to the interfacial interaction between the organosulfur compound, ODT and cadmium ions in the aqueous subphase. The films of nanoparticles were deposited on a hydrophilic quartz substrate by the Langmuir–Blodgett (LB) technique. UV-VIS spectra of the LB films of CdS nanoparticles at different target surface pressures and different Cd2+ ion concentrations depicted the signature of CdS nanoparticles. X-ray diffraction (XRD) measurements confirmed the crystalline structure of the CdS nanoparticles to be cubic. The average size of the CdS nanoparticles was estimated using field emission scanning electron microscopy, atomic force microscopy and XRD results and it was found to be in the range of 22–25 nm. We also incorporated CdS nanoparticles in the monolayer matrix of rod shaped liquid crystal (4-n-octyl-cyanobiphenyl, 8CB) molecules at an A/W interface, and transferred the film to solid substrates by the LB technique. Such LB films were employed as the alignment layer during the fabrication of liquid crystal cells and the alignment of bulk liquid crystal molecules in a nematic phase was studied using polarizing optical microscopy. The presence of CdS nanoparticles in the 8CB monolayer matrix reduces the surface anchoring of the liquid crystal molecule and thereby enhances the planar alignment of the bulk liquid crystal molecules.
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    Morphological transformation in the supramolecular assembly of discotic liquid crystal molecules using silver nanoparticles and its sensing application
    (IOP, 2020-06) Manjuladevi, V.; Gupta, Raj Kumar
    Triphenylene based discotic liquid crystal (TP) molecules are rich in π-electrons which facilitate π-stacking interaction of the molcules leading to formation of one dimensional nanowires. These nanowires can assemble to form nanoribbons due to a lateral cohesive force among the nanowires. The flat nanoribons undergo a morphological transformation due to incorporation of silver nanoparticles (SNP) into the matrix of TP molecules. The presence of SNP induces a chiral twisting to the nanoribbons and therefore the flat nanoribbons transform into a helical nanoribbon structure. The global chiral structure exhibited by the composition of achiral constituents is due to the creation of topological defects like disclination and dislocation. These defects can lead to a geometrical frustration in the nanoribbons which relaxes with the formation of twisted helical nanoribbons. A minor change in morphology of the supramolecular assembly can have a remarkable effect on the physicochemical properties of the nanoribbons. In this article, we demonstrate that even a minor change in the geometry of aliphatic chains on the surface of nanoribbons can be employed for sensing organic solvents such as acetone and ethanol. The sensing was performed at room temperature. Relative humidity has no effect on the sensing response.
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    Ultrathin Films of TiO2 Nanoparticles at Interfaces
    (ACS, 2015-01) Gupta, Raj Kumar; Manjuladevi, V.; Hazra, Arnab
    The properties of a material change remarkably as a result of the scaling dimensions. The Langmuir–Blodgett (LB) film deposition technique is known to offer precise control over the film thickness and the interparticle separation. To form a well-ordered LB film, it is essential to form a stable Langmuir film at the air–water interface. Here, we report our studies on ultrathin films of TiO2 nanoparticles at air–water and air–solid interfaces. The Langmuir film of TiO2 nanoparticles at the air–water interface was found to be very stable, and it exhibits loose-packing and close-packing phases. The LB films were transferred onto solid substrates for characterization and application. The surface morphology of the LB film was obtained by a field emission scanning electron microscope. The optical and electronic properties of the LB films of TiO2 nanoparticles were studied using UV–vis spectroscopy and current–voltage measurements, respectively. The LB film of TiO2 nanoparticles was employed for ethanol gas sensing, and the sensing performance was compared to that of bulk material. Because of the enormous gain in the surface to volume ratio and the increase in crystalline defect density in the ultrathin LB film of TiO2 nanoparticles, the LB film is found to be a potential functional layer for ethanol sensing as compared to the bulk material.