• PANKAJ KUMAR

Articles written in Bulletin of Materials Science

• Morphological control and polarization switching in polymer dispersed liquid crystal materials and devices

Liquid crystals dispersed in polymer systems constitute novel class of optical materials. The precise control of the liquid crystal droplet morphology in the polymer matrix is essentially required to meet the prerequisites of display device. Experiments have been carried out to investigate and identify the material properties and processing conditions required for the precise control of the droplet morphology of the dispersed liquid crystal systems. Polarization switching has been studied. Aligned liquid crystal dispersed systems showed higher polarization over unaligned ones.

• Synthesis and characterization of CuO nanoparticles using strong base electrolyte through electrochemical discharge process

In the present study, cupric oxide (CuO) nanoparticles were synthesized by electrochemical discharge process using strong base electrolytes. The experiments were carried out separately using NaOH and KOH electrolytes.The mass output rate and the crystal size were obtained with variation of the rotation speed of magnetic stirrer for both types of electrolytes. The mass output rate of CuO nanoparticles increased with the increase in the speed of rotation, and, after an optimum speed, it started decreasing. However, the size of the particles reduced with the increase of the rotation speed. The crystal plane of the obtained CuO nanoparticles was similar for both the electrolytes whereas the yield of nanoparticles was higher in KOH as compared with NaOH under the sameexperiment conditions. In this set of experiments, the maximum output rates obtained were 21.66 mg h$^{−1}$ for NaOH and 24.66 mg h$^{−1}$ for KOH at 200 rpm for a single discharge arrangement. The average crystal size of CuO particles obtained was in the range of 13–18 nm for KOH electrolyte and 15–20 nm for NaOH electrolyte. Scanning electron microscopy images revealed that flower-like and caddice clew-shaped CuO nanocrystalline particles weresynthesized by the electrochemical discharge process. Fourier transform infrared spectrum showed that the CuO nanoparticles have a pure and monolithic phase. UV–vis–NIR spectroscopy was used to monitor oxidation course of Cu→CuO and the band gap energy was measured as 2 and 2.6 eV for CuO nanoparticle synthesized in NaOH and KOH solutions, respectively.

• Luminescence properties of ZnO/TiO$_2$ nanocomposite activated by Eu$^{3+}$ and their spectroscopic analysis

A new type of novel orange-red emitting Eu-doped ZnO/TiO$_2$ nanocomposite phosphors have been synthesized by simple low temperature co-precipitation route. Structure and morphology of the prepared sample havebeen investigated using X-ray diffraction and field emission scanning electron microscopy (FESEM) techniques. XRD pattern confirmed the presence of both phases of ZnO and TiO$_2$ simultaneously. The luminescence properties, such as photoluminescence (PL) excitation and emission spectra, Judd–Ofelt parameters, CIE colour coordinates and the dependence of luminescence intensity on the doping level were investigated. The luminescence spectrumcharacteristics of Eu$^{3+}$ ions have a strong dependence on Eu$^{3+}$ doping levels as well as ZnO/TiO$_2$ ratio variations. The photoluminescence results indicate that these phosphors could be efficiently excited by near-ultraviolet radiation, which causes emissions in orange–red regions.

• Improvement in electro-optical and dielectric characteristics of ZnO nanoparticles dispersed in a nematic liquid crystal mixture

Reported herein is the effect of dispersion of a ﬁxed amount of 0.5% (wt/wt) ZnO nanoparticles (NPs) in a nematic (E7) liquid crystal (LC) mixture. Dispersion of ZnO NPs results in a signiﬁcant improvement in electro-optical and dielectric parameters of the nematic mixture. Comparative analysis of undoped and NP-dispersed samples shows a reduced threshold voltage with better transmittance without compromising dielectric permittivity characteristics. In addition, an increase in the contrast ratio, birefringence, alternating-current conductivity and band gap was observed after dispersion of ZnO NPs in LCs. A polarized optical microscopic study of the NP-dispersed sample substantiates a slight increase in nematic–isotropic phase transition temperature of LCs.

• Interdependency among electro-optic characteristics and absorption coefficient of homeotropically aligned liquid crystal considering Beer’s law theory

In the present study, interdependency among electro-optic (E-O) characteristics and absorption coefficient of homeotropically aligned liquid crystal (HALC) considering Beer’s law theory has been studied. Specifically, HALC cellswere prepared using uniform dispersion of ZnO nanoparticles into the nematic liquid crystal without applying any surface treatment to the substrates. Then azo dichroic dye (orange) was added in a fixed concentration to the prepared nanoparticles dispersed LC mixture. The morphological and absorption characteristics of prepared HALC cells were found to be improved with the addition of azo dichroic dye. The optical textures observed at macroscopic and microscopic levels are in correspondence with each other and showed excellent OFF/ON switching with magnificently dark and bright views. Moreover, HALC cells doped with azo dichroic dye exhibited a higher value of absorption coefficient with an improved contrast ratio. Thus, a good consistency was observed among experimentally observed E-O characteristics and theoretically measured absorption coefficient.

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020

Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
Physical Sciences 2020

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Posted on July 25, 2019

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