Indian Association for the Cultivation of Science

About: Indian Association for the Cultivation of Science is a education organization based out in Kolkata, India. It is known for research contribution in the topics: Excited state & Catalysis. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Ionic conductivity and relaxation dynamics in lithium tellurite glasses

Abstract: The ionic conductivity and relaxation in the lithium tellurite glasses with varying Li 2 O content have been investigated in the frequency range 10 Hz to 2 MHz and in the temperature range from 373 K to just below the glass transition temperature. The composition dependences of the dc conductivity and the activation energy of these glasses have been compared with those of other glasses formed with traditional network formers such as B 2 O 3 , P 2 O 5 , and SiO 2 containing the same Li + ions as modifiers and explained in terms of composition dependent network structure of these glasses. The frequency-dependent electrical data have been analyzed in the framework of the conductivity and modulus formalisms. Both these formalisms have provided for qualitative similarities in the compositional variation of the relaxation times, interaction between the cations, and the dc conductivity. The finite frequency window has been suggested as the reason for the difference between the numerical values of the stretched exponent β obtained from the odulus formalism and the values of (1-n) obtained from the conductivity formalism.

Dispersion of functionalized silver nanoparticles in polymer matrices: Stability, characterization, and physical properties

Abstract: Three types of silver/polymer nanocomposite films were prepared: (1) silver/polymethyl methacrylate, (2) silver/polystyrene, and (3) silver/polyt-butyl methacrylate by mixing colloidal solution of functionalized Ag nanoparticles with solution of pre-made polymers. The nanoparticles are randomly dispersed into the matrices. The desired surface functionality of Ag nanoparticle was achieved by using specific amphiphilic block copolymer (specific hydrophobic block part) as stabilizer. The stability of nanoparticles in these host hydrophobic polymer matrices was determined after annealing the nanocomposite films at high temperature. The nanoparticles remained stable and no agglomeration occurred upon annealing up to 120°C. Up to 20 wt% of block copolymer stabilized Ag nanoparticles (11% Ag) was successfully loaded in the polymer matrix. Such a dispersion of Ag nanoparticles into a hydrophobic polymer matrix significantly enhances the mechanical properties of the nanocomposite films. The storage and loss modulus increase with increasing Ag nanoparticles content. Compared with a polymer matrix, the polymer/Ag nanocomposites film (containing 0.65% of Ag) prepared by this method displayed storage modulus that are up to 130% higher. This is attributed to the high surface area of the polymer coated Ag nanoparticles in the polymer matrix and van der Waal's attraction force between surface of Ag nanoparticles (polymer brush) and host polymer matrix. Comparison of thermal properties of polymer and polymer/Ag nanocomposite films showed that the thermal stability of nanocomposites increases by about 20°C. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Time sensitive, temperature and pH responsive photoluminescence behaviour of a melamine containing bicomponent hydrogel

Abstract: Melamine (M) produces supramolecular complexes MQ31, MQ11 and MQ13 with 6,7-dimethoxy-2,4[1H,3H]-quinazolinedione (Q) (numbers indicate respective molar ratios of components) and they produce thermoreversible hydrogels [≥0.1% (w/v)] at 30 °C. Optical microscopy shows fibrillar network morphology and on irradiation with 300 nm light, the fibrils emit blue light. DSC results indicate a thermoreversible first order phase transition and the storage modulus (G′) is invariant with frequency supporting the formation of thermoreversible hydrogel. The magnitude of G′ follows the order MQ11 > MQ13 > MQ31 and a probable cause is attributed to number of H-bonds, which follows the same order in the nanofibers. FTIR-spectra suggest H-bonding interaction between components and WAXS results indicate a different crystalline structure of the complexes. The UV-vis spectra of the MQ systems shows red shift of both π–π* and n–π* bands and a maximum red shift is observed for the MQ13 system. The PL intensity decreases with increase in M concentration and lifetime data indicates PL quenching due to the formation of less fluorescent complexes. The PL property of the gel depends on aging time. A gradual development of a new emission peak at the expanse of an initial peak suggests the formation of an initial metastable state, which transforms into the stable state after 24 h of aging. The gel is stable in the pH range 6–9, above or below which the gel breaks down showing a significant PL-quenching and a blue shift of the emission peak. With increase of temperature, the emission peak intensity increases at first up to 45 °C, followed by an abrupt decrease at ≥55 °C. Possible reasons are attributed to the gradual disassembly of the complexes converting thinner fibers and finally melting.

Giant multicaloric response of bulk Fe 49 Rh 51

Abstract: We report on the multicaloric response of the ${\mathrm{Fe}}_{49}{\mathrm{Rh}}_{51}$ alloy under the combined application of hydrostatic pressure and magnetic field. Experimental data are complemented by a mean field model that takes into account the interplay between structural and magnetic degrees of freedom. A large multicaloric strength has been found for this alloy, and it is shown that a suitable combination of pressure and magnetic field enables the sign of the entropy change to be reversed and thus the multicaloric effect can be tuned from conventional to inverse. It is also shown that an extended temperature window for the multicaloric effect can be achieved by taking advantage of the coupling between structure and magnetism which enables a cross response of the alloy under the application of different external fields. Mean field calculations remarkably reproduce experimental results.