Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

Synthesis of hydroxyl‐terminated poly(ether ether ketone) with pendent tert‐butyl groups and its use as a toughener for epoxy resins

Abstract: Hydroxyl-terminated poly(ether ether ketone) with pendent tert-butyl groups (PEEKTOH) was synthesized by the nucleophilic substitution reaction of 4,4'-difluorobenzophenone with tert-butyl hydroquinone with potassium carbonate as a catalyst and N-methyl-2-pyrrolidone as a solvent. Diglycidyl ether of bisphenol A epoxy resin was toughened with PEEKTOHs having different molecular weights. The melt-mixed binary blends were homogeneous and showed a single composition-dependent glass-transition temperature (T g ). Kelley-Bueche and Gordon-Taylor equations gave good correlation with the experimental Tg. Scanning electron microscopy studies of the cured blends revealed a two-phase morphology. A sea-island morphology in which the thermoplastic was dispersed in a continuous matrix of epoxy resin was observed. Phase separation occurred by a nucleation and growth mechanism. The dynamic mechanical spectrum of the blends gave two peaks corresponding to epoxy-rich and thermoplastic-rich phases. The Tg of the epoxy-rich phase was lower than that of the unmodified epoxy resin, indicating the presence of dissolved PEEKTOH in the epoxy matrix. There was an increase in the tensile strength with the addition of PEEKTOH. The fracture toughness increased by 135% with the addition of high-molecular-weight PEEKTOH. The improvement in the fracture toughness was dependent on the molecular weight and concentration of the oligomers present in the blend. Fracture mechanisms such as crack path deflection, ductile tearing of the thermoplastic, and local plastic deformation of the matrix occurred in the blends. The thermal stability of the blends was not affected by blending with PEEKTOH.

Fourier transform infrared and wide‐angle X‐ray diffraction studies of the thermal cyclization reactions of high‐molar‐mass poly(acrylonitrile‐co‐itaconic acid)

Abstract: The stabilization reactions of a high-molar-mass poly(acrylonitrile-co-itaconic acid) precursor in air at 200, 220, and 240°C were studied with Fourier transform infrared. Principally, the cyclization of nitrile groups leading to the ladder structures of tetrahydropyridine occurred. Evidence for oxidative reactions causing the conversion of the CC structure to CC and generating groups such as OH and CO was also obtained. As the temperature of stabilization was increased, the rate of the reaction increased without causing great changes in the Fourier transform infrared spectral patterns. The maximum nitrile conversion achievable was limited by the temperature of stabilization. Although the reaction stagnated at 40 and 80% at 200 and 220°C, it was practically complete in about an hour at 240°C. Higher temperatures also favored the formation of extended conjugated structures. Wide-angle X-ray diffraction studies of the polymer stabilized at 300 and 400°C in argon confirmed that the aromatization index value and the crystallinity of the polymer increased proportionally to the temperature of pyrolysis. An analysis of the wide-angle X-ray diffraction pattern and the elemental composition of the stabilized polymer implied the formation of the tetrahydropyridine structure at 400°C. The higher pyrolysis temperature favored the formation of the lattice constituted by this group. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3055–3062, 2006

A European aerosol phenomenology - 6: Scattering properties of atmospheric aerosol particles from 28 ACTRIS sites

Abstract: This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (σsp) and hemispheric backscattering (σbsp) coefficients, scattering Angstrom exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of σsp is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, σsp also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intraannual variability. At mountain sites, higher σsp and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher σsp values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low σsp values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high σsp values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of σsp are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of σsp are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe. © Author(s) 2018.

High Performing Biobased Ionic Liquid Crystal Electrolytes for Supercapacitors

Abstract: Production and storage of energy in a highly efficient and environmentally sustainable way is a demand of the current century to meet the growing global energy requirement. Design and development of novel materials and processes that allow precise control over the electrochemical behavior and conductivity of electrolytes is necessary for acquiring such targets. Development of ionic liquid crystals with ordered domains endowed with enhanced ionic conductivity from renewable resources is receiving much interest in this respect. In this paper, we report a unique strategy for the preparation and utilization of ionic liquid crystalline electrolyte derived from a renewable resource: cashew nut shell liquid; an abundantly available waste byproduct from cashew industry. We have prepared imidazolium-based ionic liquid crystal (PMIMP) from cardanol and studied its structure and liquid crystalline phase formation by various techniques. The symmetrical supercapacitor fabricated with mesoporous carbon electrodes emplo...