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Samui A.B.,Indian Defence Institute of Advanced Technology | Pandey S.,Polymer Science and Technology Center | Mishra S.P.,Polymer Science and Technology Center
RSC Advances | Year: 2015

Liquid crystalline siloxane azo polymers were synthesized through hydrosilylation reaction between diallyl azo monomer and siloxane dihydride. The molecular weights of the polymers ranged from 3000-4000 g mol-1. The polymers were found to be soluble in chloroform, THF, DMF, DMSO, and DCM respectively. The photoresponsive behavior was studied during exposure of the polymers to UV radiation. The trans-cis photoisomerisation rate constants were also determined. The thermotropic behavior of the polymers was studied by using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The polymers exhibited liquid crystalline texture of nematic droplets in POM images existing at room temperature and extending over broad temperature range up to 155 °C. The DSC thermogram also supported the characteristic liquid crystalline transitions. © The Royal Society of Chemistry 2015.

Palai A.K.,Polymer Science and Technology Center | Palai A.K.,Konkuk University | Kumar A.,National Physical Laboratory India | Kumar A.,Konkuk University | And 2 more authors.
Journal of Materials Science | Year: 2014

The synthesis and characterization of a series of polyalkylthiophenes- containing electron-rich thienothiophene (donor heteroaromatic bicycle) and electron-deficient benzothiadiazole (acceptor heteroaromatic bicycle) block have been reported. The polymers are synthesized by Stille cross-coupling reaction and are found to be having high molecular weight with number-average molecular weight in the range of 7.1 × 104-5.7 × 104. The photo-physical, electro-chemical, and electroluminescent (EL) properties of the polymers are investigated in detail. The optical band gap of the polymers is found to be in the range of 1.53-1.54 eV. These new polymers are luminescent in nature and showed red photoluminescence in chloroform solution (722-740 nm) as well as in thin film (781-786 nm). Ionization potential for these polymers is calculated and falling in the range of 5.23-5.33 eV. Polymer light emitting diodes with configuration ITO/PDOT:PSS/polymer/BCP/Alq3/LiF/Al have been fabricated, and a deep red emission is observed. The EL maxima of polymers are found to be in the range of 750-760 nm with threshold voltages around 4.0-5.5 V. The fabricated devices show luminescence around 40 cd/m2 at current density of 100 mA/cm2 with maximum value of 580-810 cd/m2 at 11 V. Graphical abstract: [Figure not available: see fulltext.] © 2013 Springer Science+Business Media New York.

Kolli B.,Polymer Science and Technology Center | Mishra S.P.,Polymer Science and Technology Center | Joshi M.P.,Raja Ramanna Center for Advanced Technology | Raj Mohan S.,Raja Ramanna Center for Advanced Technology | And 2 more authors.
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2012

Four linear polymers containing pendant azo moiety were synthesized through click chemistry for second-order nonlinear optical study. The polymers were found soluble in most of the polar organic solvents such as tetrahydrofuran (THF), chloroform, and dimethyl formamide (DMF). The polymers showed thermal stability up to 300 °C and glass transition temperatures (T g) in the range of 120-140 °C. The molecular weights (M w) of these polymers (measured by gel permeation chromatography) were in the range 37,900-55,000 g/mol. The polymers were found to form optically transparent films by solution casting from THF solution. Order parameters were calculated from UV-vis absorption spectra. The morphology changes in the films after poling were characterized by atomic force microscopy. The angular dependence, temperature dependence, and time dependence of second harmonic generation (SHG) intensity were obtained by using 1064 nm Nd:YAG laser. The SHG intensity remained unchanged up to 95 °C. At room temperature, it remained stable up to 8 days after initial drop of about 14%. © 2012 Wiley Periodicals, Inc.

Jagtap S.B.,Polymer Science and Technology Center | Kushwaha R.K.,Polymer Science and Technology Center | Ratna D.,Polymer Science and Technology Center
RSC Advances | Year: 2015

Nanocomposites of poly (ethylene oxide) (PEO) and graphene were made in aqueous solution using an organic salt containing a carboxylate ion and a carboxylic acid group. The cation corresponding to the carboxylate ion interacts with the π electron clouds of graphene through cation-π interaction and promotes the exfoliation of graphene sheets. The carboxylic acid group of the modifier forms H-bonds with the PEO and thereby improves interfacial adhesion. The effect of the number of carbon atoms present in the modifier on its dispersing ability was investigated. It was observed that there exists an optimum number of carbon atoms present in the modifier with respect to the level of dispersion of graphene in the related nanocomposites as examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanical properties of the nanocomposites having various concentrations of graphene were evaluated and compared with the theoretical values using the Halpin-Tsai model. The crystallization behavior of the PEO upon incorporation of modified graphene was studied by temperature modulated differential scanning colorimetry (MDSC) and discussed as well. The dispersion process used here is green as it does not require any toxic solvent or hazardous material for modification of graphene. This journal is © The Royal Society of Chemistry 2015.

Ghorpade T.K.,Polymer Science and Technology Center | Patri M.,Polymer Science and Technology Center | Mishra S.P.,Polymer Science and Technology Center
Sensors and Actuators, B: Chemical | Year: 2016

Four novel deeply coloured and highly fluorescent anion sensors have been developed by coupling calix[4]pyrrole with two different diketopyrrolopyrroles. The sensors showed both colorimetric and fluorometric sensitization by selective anions. Complexation properties of the receptors with anions like halides, acetate, phosphate, sulphate, hydrogen sulphate, perchlorate and cyanide were investigated by UV-vis spectroscopy and fluorescence spectroscopy. Sharp visual colour changes as well as complete fluorescence quenching was observed in the presence of selective anions like fluoride, acetate, phosphate and cyanide. Visual detection of sensing properties was achievable up to anion concentration of 1.15 ppm for detection in visible light and 0.025 ppm under UV light. One of the sensor, namely S1, showed a dramatic colour change in the presence of CN- ion. Furthermore, a cheap and highly efficient procedure for bulk scale synthesis of monoiodo-octamethylcalix[4]pyrrole, which is one of the main building blocks for the design of calix[4]pyrrole based sensors has been developed. © 2015 Elsevier B.V. All rights reserved.

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