Showing papers by "Indian Association for the Cultivation of Science published in 1996"
TL;DR: In this paper, the solution properties of the surfactants dodecyl, tetradecyl-, and hexadecyl(cetyl)trimethylammonium bromide (DTAB, TTAB and CTAB), as well as hexadecylpyridinium chloride (CPC) in pure and mixed states (binary and ternary combinations) were studied.
Abstract: The solution properties of the surfactants dodecyl-, tetradecyl-, and hexadecyl(cetyl)trimethylammonium bromide (DTAB, TTAB, and CTAB, respectively) as well as hexadecylpyridinium chloride (CPC) in pure and mixed states (binary and ternary combinations) have been studied. The critical micelle concentration (cmc), counterion binding, aggregation number, polarity, thermodynamics of micellization, interfacial adsorption, etc., have been quantitatively estimated by surface tension, conductance, spectrophotometry, fluorescence, and calorimetric methods. The micellar compositions, activities of the components in the micelle, and their mutual interactions have been estimated from Rubingh's theory. The surfactant mixtures have been found to be nonideal, with a lower degree of counterion association compared to pure states, but possess more or less comparable micellar polarity and energetic parameters.
352 citations
TL;DR: In this paper, the Stokes shift of the laser dye coumarin 480 (I) was studied in Aerosol OT-heptane reverse micelles at various concentrations of water.
Abstract: The picosecond time-resolved Stokes shift of the laser dye coumarin 480 (I) is studied in Aerosol OT-heptane reverse micelles at various concentrations of water. On addition of water to a n-heptane solution of I containing 0.09 M AOT, the emission spectrum of I exhibits a prominent shoulder at 480 nm which is ascribed to the dye molecules in the water pool of the reverse micelles. In n-heptane, the fluorescence decays of I at short and long wavelengths are identical, which rules out any time-resolved Stokes shift. On addition of water to the AOT/heptane system, the decay at long wavelengths exhibit a distinct growth on the nanosecond time scale. This and the time-dependent Stokes shift indicate that the water molecules in the water pool of the AOT reverse micelles undergo slow relaxation on the nanosecond time scale.
264 citations
TL;DR: In this paper, an analogue calorimetry for blends of poly(vinyl ester)s and polyacrylates has been studied, and it is found that isomeric esters differing only in the orientation of the COO group mix with only small heat change, which can be positive or negative.
Abstract: Analogue calorimetry for blends of poly(vinyl ester)s and polyacrylates has been studied. Hydrogenated monomers were used as analogues of the corresponding polymers. It is found that isomeric esters differing only in the orientation of the COO group mix with only small heat change, which can be positive or negative. The values of the interaction energy density, B12 (in cal/cm3), are −0.045, 0.031, and −0.076, respectively, for the following binary mixtures; ethyl acetate + methyl propionate, n-propyl propionate + ethyl butyrate, and phenyl propionate + ethyl benzoate. The negative heat of mixing for the two pairs of very similar liquids, although unexpected, explains why the corresponding polymers are miscible. The small positive heat of mixing for the other pair is sufficient to predict demixing of the corresponding polymers, viz., poly(n-propyl acrylate) and poly(vinyl butyrate), which contradicts the observation of their homogeneous mixing. This suggests that hydrogenated monomers are not always the pr...
248 citations
TL;DR: In this paper, it was shown that propionitrile, the hydrogenated monomer of polyacrylonitrile (PAN), is very unsuitable as an analogue of the latter.
246 citations
TL;DR: In this paper, the Stokes shift of the laser dye coumarin 480 (I) is studied in neutral (Triton X-100, TX), cationic (cetyltrimethylammonium bromide, CTAB), and anionic (sodium dodecyl sulfate, SDS) micelles.
Abstract: The picosecond time-resolved Stokes shift of the laser dye, coumarin 480 (I) is studied in neutral (Triton X-100, TX), cationic (cetyltrimethylammonium bromide, CTAB), and anionic (sodium dodecyl sulfate, SDS) micelles. Above critical micellar concentration (cmc) for all three micelles I exhibits wavelength dependent fluorescence decays and a distinct growth at the long wavelengths. The time dependent Stokes shift studies indicate that the water molecules in the Stern layer of the micelles relax on the time scale 180−550 ps, which is slower than the subpicosecond relaxation dynamics observed in ordinary bulk water.
235 citations
TL;DR: The behavior of binary mixtures of aqueous solutions of surfactants has been analyzed in the light of Rubingh's approach based on regular solution theory, the method of excess thermodynamic quantities of Motomura et al., and (c) the molecular thermodynamic theory of Sarmoria et al..
Abstract: The behavior of binary mixtures of aqueous solutions of surfactants has been analyzed in the light of (a) Rubingh's approach based on regular solution theory, (b) the method of excess thermodynamic quantities of Motomura et al., and (c) the molecular thermodynamic theory of Sarmoria et al. and Puvvada et al. The binary combinations of anionic−nonionic, anionic−cationic, anionic−anionic, cationic−cationic, and nonionic−nonionic surfactant systems including a number of bile salts and several synthetic ionic and nonionic surfactants have been tested. The theoretical approaches are found to be most successful in describing the mixed micellar properties of anionic−nonionic surfactant solutions. The anionic−cationic combinations of bile salts and cetyltrimethylammonium bromide exhibit striking behaviors. The scope and limitations of the treatments in describing and also predicting the behaviors of different types of mixed micellar entities have been discussed.
172 citations
TL;DR: In this article, the ortho-carbon atom of the pendant phenyl ring of each pyridine ring was selectively thiolated, and the crystal structure and spectra of compound 3 were reported.
Abstract: ctc-Ru(L)2(Cl)2, 1 [L = pyridine-2-azobenzene], reacts with EtOCS2K to give an unusual product, 3, where the ortho-carbon atom of the pendant phenyl ring of each L is selectively thiolated. Crystal structure and spectra of compound 3 are reported.
97 citations
TL;DR: In this paper, the molecular structures of [Zn(mmpcd)]ClO4 (1b) and [Cu(mpcd]ClO 4 (2b) were refined to final R = 0.042 for 1b and 0.049 for 2b.
Abstract: Zinc(II) and copper(II) complexes of two new potentially pentadentate ligands based on methyl 2-aminocyclopent-1-ene-1-dithiocarboxylate with pendent pyrazolyl groups (Me2pzCH2)2NC2H3RNHC5H6CSSCH3 (R = H, Hmmecd, and R = CH3, Hmmpcd, both having N4S donor atoms set) have been reported. The molecular structures of [Zn(mmpcd)]ClO4 (1b) and [Cu(mmpcd)]ClO4 (2b) show a distorted trigonal bipyramidal geometry for the Zn(II) ion and a square pyramidal geometry for the Cu(II) ion. 1b crystallizes in the triclinic space group P1, a = 9.900(3) A, b = 15.379(5) A, c = 8.858(2) A, α = 99.93(2)°, β = 93.62(2)°, γ = 100.38(2)°, V = 1300.5(7) A3, and Z = 2; while 2b crystallizes in the monoclinic space group P21/n, a = 12.859(6) A, b = 12.642(3) A, c = 16.503(2) A, β = 102.67(2)°, V = 2617(1) A3, and Z = 4. The structures were refined to final R = 0.042 for 1b and 0.049 for 2b. The EPR and electronic spectroscopic studies showed that the copper(II) species doped into zinc(II) complex adopts the zinc(II) trigonal bipyr...
77 citations
TL;DR: A series of heterobimetallic complexes of the type [Fe(III)M(II)L(&mgr;-OAc)(OAc))(H(2)O)](ClO(4)).nH( 2)O (2-5) and [{Fe( III)Co(III]L(& mgr;)-OAc(OAc)}(2)(&mGr;- O)]( ClO( 4))(2).
Abstract: A series of heterobimetallic complexes of the type [FeIIIMIIL(μ-OAc)(OAc)(H2O)](ClO4)·nH2O (2−5) and [{FeIIICoIIIL(μ-OAc)(OAc)}2(μ-O)](ClO4)2·3H2O (6) where H2L is a tetraaminodiphenol macrocyclic ligand and MII = Zn(2), Ni(3), Co(4), and Mn(5) have been synthesized and characterized. The 1H NMR spectrum of 6 exhibits all the resonances between 1 and 12 ppm. The IR and UV−vis spectra of 2−5 indicate that in all the cases the metal ions have similar coordination environments. A disordered crystal structure determined for 3 reveals the presence of a (μ-acetate)bis(μ-phenoxide)−NiIIFeIII core, in which the two metal ions have 6-fold coordination geometry and each have two amino nitrogens and two phenolate oxygens as the in-plane donors; aside from the axial bridging acetate, the sixth coordination site of nickel(II) is occupied by the unidentate acetate and that of iron(III) by a water molecule. The crystal structure determination of 6 shows that the two heterobinuclear CoIIIFeIII units are bound by an Fe−O−...
70 citations
TL;DR: Methyl cellulose has been used as a stabilizer in the oxidative dispersion polymerization of aniline using ammonium persulfate oxidant in aqueous alcohol media as discussed by the authors.
Abstract: Methyl cellulose has been used as a stabilizer in the oxidative dispersion polymerization of aniline using ammonium persulfate oxidant The dispersion polymerization is unsuccessful in water but successfully effected in aqueous alcohol media Evidence has been presented that the stabilizer incorporation in polyaniline is increasingly facilitated as the alcohol concentration of the medium is increased Particle morphology changes from long needle-shaped to oblong (doublets of spheres) or spherical as the alcohol concentration is increased from 30% to 70%
66 citations
TL;DR: In this paper, the authors present a review of the literature on the dealkylation of ETHERS and their application in the field of organic preparation and procedures. But they do not discuss their own work.
TL;DR: In this article, bismuth-substituted nickel-zinc ferrites have been synthesized by a solution route in the composition range Ni 0.5 Zn 0.4 Bi x Fe 2.0− x O 4, with 0 ≤ x ≤ 0.2.
TL;DR: In this article, nonamphiphilic pyrene molecules mixed with a fatty acid have been incorporated in Langmuir−Blodgett (LB) films and the surface pressure versus area per molecule isotherms show that the average area per molecules at first increases and then decreases with increasing mole fraction of pyrene in mixtures of Pyrene and stearic acid.
Abstract: Nonamphiphilic pyrene molecules mixed with a fatty acid have been incorporated in Langmuir−Blodgett (LB) films. The surface pressure versus area per molecule isotherms show that the average area per molecule at first increases and then decreases with increasing mole fraction of pyrene in mixtures of pyrene and stearic acid (SA), which indicates that the pyrene molecules are very likely squeezed out of the air−water interface in between the fatty acid chains and are on the surface of the monolayer. A positive deviation from the additivity rule has been observed in the plot of the average area per molecule versus the mole fraction of pyrene, which suggests a repulsive type of interaction between the pyrene and the fatty acid molecules. Spectroscopic studies reveal the formation of I-aggregates. The emission spectra of mixed films of pyrene and stearic acid show a single broad band at 420 nm which has been assigned to a partial excimeric emission band originating from an incomplete or partial overlap of the ...
TL;DR: In this paper, Cordierite ceramics were synthesized by sol-gel processing using alkoxides and acetate with an aim to use the material as substrate and packaging material.
Abstract: Cordierite ceramics were synthesized by sol-gel processing using alkoxides and acetate with an aim to use the material as substrate and packaging material. Preparation conditions were optimized by varying the amount and pH of water added and the amount of acetic acid as chelating agent. The powders were characterized by different analytical techniques such as thermogravimetric analysis, differential thermal analysis, surface area by BET, X-ray diffraction, transmission and scanning electron microscopies and infrared spectroscopy. The best product was obtained using 19.6 mol water and 0.34 mol acetic acid with respect to silicon ethoxide. The pH of the water added did not make any significant difference. Sintered materials were characterized by measuring different physical properties such as density, electrical and dielectric properties, thermal expansion, microstructure and composition. Well-sintered bodies could be achieved at 1000 °C in air with a soaking time of 2 h having a density of ∼ 99% theoretical, electrical resistivity of ∼1014 Ωcm, dielectric constant of 5, dielectric loss ∼0.008 and thermal expansion coefficient of 28.5 × 10−7 °C−1, 25–200 °C. X-ray diffraction studies show the phase evolution in these materials is predominantly μ-cordierite (hexagonal high cordierite) and some β-quartz. SEM reveals a uniformly dense microstructure with crystals of granular habit. X-ray photoelectron spectroscopy indicates that the surface composition of the sintered material is slightly enriched with aluminium and deficient in silicon.
TL;DR: In this article, an interpenetrating polymer network composites of polypyrrole (PPy) with poly(methyl acrylate) (PMA) and poly(styrene- co-butyl acryyl acylate)(SBA) were prepared using FeCl 3 -impregnated matrix polymer films and dipping them into a solution of pyrrole in water using a pyrdrug concentration of 67 mmol/dm 3 and above No polymerization occurs in solution outside the films Polymerization occurs rapidly, about 90% of Pyr
TL;DR: In this article, X-ray diffraction, ellipsometry and absorption spectroscopy of hexagonal CdS films were carried out by XRD and optical spectra of the samples; it was assumed that the below bandgap optical absorption in the films is due to the structural imperfections present.
TL;DR: The first azo-imine chelate system, Pd(N(H)C(R)NNPh)(2) (Pd(RA)(2), has been isolated in the form of diamagnetic solids by the 6e(-)-6H(+) reduction of bis(phenylazooximato)palladium(II), Pd
Abstract: The first azo−imine chelate system, Pd(N(H)C(R)NNPh)2 (Pd(RA)2), has been isolated in the form of diamagnetic solids by the 6e-−6H+ reduction of bis(phenylazooximato)palladium(II), Pd(N(O)C(R)NNPh)2 (abbreviated Pd(RB)2), with ascorbic acid in a mixed solvent (R = Ph, α-naphthyl) Selected spectral features are described The X-ray structures of Pd(PhA)2 and Pd(PhB)2 have revealed trans-planar geometry consistent with metal oxidation state of +2 Bond length trends within the chelate rings are rationalized in terms of steric and electronic factors In Pd(PhA)2 a total of 10 ligand π electrons are present, each formally monoanionic ligand contributing five Model EHMO studies have revealed that the filled HOMO (au) in Pd(RA)2 is a bonding combination of two ligand π* orbitals with large azo contributions The LUMO (bg) is roughly the corresponding antibonding combination The outer π-electron configuration of Pd(RA)2 is (au)2(bg)0 Four successive voltammetric responses, two oxidative and two reductive, ar
TL;DR: In this article, a new type of hydrogenated amorphous silicon film having variable bandgap (1.7 − 1.5 eV) has been developed in an rf powered plasma enhanced chemical vapor deposition system using a mixture of silane and helium at a subtrate temperature of 210°C.
Abstract: A new type of hydrogenated amorphous silicon film having variable bandgap (1.7–1.5 eV) has been developed in an rf powered plasma enhanced chemical vapor deposition system using a mixture of silane and helium at a subtrate temperature of 210°C. The deposition conditions were chosen so that the rf glow discharge occurs in the γ regime, usually avoided because of powder formation. The influence of the chamber pressure, on the optical gap, the hydrogen content and the electronic properties is presented. Increasing the pressure up to 1.8 Torr is found to decrease the optical gap down to 1.5 eV. The densities of states of these films were measured by electron spin resonance, constant and modulated photocurrent techniques. The density of states above the Fermi level is found to be two orders of magnitude less than that of standard amorphous silicon. Moreover, unusually fast kinetics of degradation are observed. This new material could be a good alternative to amorphous silicon germanium alloys.
TL;DR: In this article, a quasi-reversible one-electron cyclic voltammetric couple (E 1/2 = 0.50-0.70 V) was obtained for the Schiff bases of 2,6-diformyl-4-methylphenol with M(PPh 3 ) 3 X 2 in ethanol.
TL;DR: Two enzymes, one NADPH-dependent and another NADH-dependent which catalyze the reduction of methylglyoxal to acetol have been isolated and substantially purified from crude extracts of Escherichia coli K12 cells and are shown to be identical with an aldehyde reductase and alcohol dehydrogenase.
Abstract: Two enzymes, one NADPH-dependent and another NADH-dependent which catalyze the reduction of methylglyoxal to acetol have been isolated and substantially purified from crude extracts of Escherichia coli K12 cells. Substrate specificity and formation of acetol as the reaction product by both the enzymes, reversibility of NADH-dependent enzyme with alcohols as substrates and inhibitor study with NADPH-dependent enzyme indicate that NADPH-dependent and NADH-dependent enzymes are identical with an aldehyde reductase (EC 1.1.1.2) and alcohol dehydrogenase (EC 1.1.1.1) respectively. The Km for methylglyoxal have been determined to be 0.77 mM for NADPH-dependent and 3.8 mM for NADH-dependent enzyme. Stoichiometrically equimolar amount of acetol is formed from methylglyoxal by both NADPH- and NADH-dependent enzymes. In phosphate buffer, both the enzymes are active in the pH range of 5.8–6.6 with no sharp pH optimum. Molecular weight of both the enzymes were found to be 100,000 ± 3,000 by gel filtration on a Sephacryl S-200 column. Both NADPH- and NADH-dependent enzymes are sensitive to sulfhydryl group reagents.
TL;DR: In this paper, a cycloaddition of 1,3-diketones to cinnamic esters in high yield was performed by ceric ammonium nitrate mediated oxidative [3+2] cycloadding.
TL;DR: In this article, a first principles computer model for simulating the performance of amorphous-silicon-based solar cells has been applied to study the effect on solar cell performance of using an emitter layer with band gap larger than that of the intrinsic absorber.
Abstract: A first principles computer model for simulating the performance of amorphous‐silicon‐based solar cells has been applied to study the effect on solar cell performance of using an emitter layer with band gap larger than that of the intrinsic absorber. We surprisingly find that if the transparent conducting oxide/p‐layer contact barrier height φb0 is held constant, the effect of increasing the band gap of the emitter layer Eμ(p) is to depress the open‐circuit voltage Voc, fill factor (FF), and cell efficiency η, although the short‐circuit current Jsc increases as expected. The main reason for the decrease of Voc, FF, and η at constant φb0 is that as Eμ(p) expands, the field corresponding to the gradient in the electron affinity at the p/i interface increases also, leading more and more to a collapse of the field over the intrinsic absorber layer. Considering the effect of φb0, we find that Jsc in these structures is practically independent of this parameter. However, φb0 exerts considerable influence on Voc...
TL;DR: In this paper, the magnetocrystalline anisotropy constant of Ni0.5Zn0.4 was found to be an order of magnitude higher than that for the bulk material.
TL;DR: In this paper, β-diketones and β-ketoesters were treated with ceric ammonium nitrate and sodium hydrogen carbonate in acetonitrile to create intermediates which add efficiently to cyclic enol ethers to furnish fused acetals in good yields.
TL;DR: In this paper, the dynamics of solvation of coumarin 480 guest molecule in supercages of a faujasite zeolite 13X was studied using picosecond time-resolved emission spectroscopy.
TL;DR: In this article, a facile synthesis of conjugated acetylenic ketones was reported, involving Copper(I) catalysed acylation of terminal alkynes with acyl halides.
13 May 1996
TL;DR: An international intercomparison of photovoltaic (PV) performance measurements and calibrations showed much larger differences among laboratories.
Abstract: This paper presents the results of an international intercomparison of photovoltaic (PV) performance measurements and calibrations. The intercomparison, which was organized and operated by a group of experts representing national laboratories from across the globe (i.e., the authors of this paper), was accomplished by circulating two sample sets. One set consisted of twenty silicon reference cells that would, hopefully, form the basis of an international PV reference scale. A qualification procedure applied to the calibration results gave average calibration numbers with an overall standard deviation of less than 2% for the entire set. The second set was assembled from a wide range of newer technologies that present unique problems for PV measurements. As might be expected, these results showed much larger differences among laboratories. Methods were then identified that should be used to measure such devices, along with problems to avoid.
TL;DR: In this article, the authors measured the dc conductivity and thermoelectric power of the as-quenched and annealed glasses at 500 and 840 degrees, respectively.
Abstract: Electrical conductivity and thermoelectric power (TEP) of the as-quenched and annealed (at 500{degree}C for 10 h and 840{degree}C for 24 h) Bi{sub 4{minus}{ital n}}Pb{sub {ital n}}Sr{sub 3}Ca{sub 3}Cu{sub 4}O{sub {ital x}} ({ital x} = 0{endash}1.0) glasses have been measured. The dc conductivity data of the as-quenched and the partially annealed (at 500{degree}C) glasses can be explained by considering the small-polaron hopping conduction mechanism which is found to change from the nonadiabatic to the adiabatic regime with annealing the glasses at 500{degree}C. This change over is due to the presence of microcrystals in the partially annealed glasses as observed from x-ray-diffraction and scanning electron microscopic studies. This adiabatic behavior is also visualized even for some as-quenched glasses having a very small amount of the more conducting microcrystalline phase. All the 840{degree}C annealed glasses are superconductors with {ital T}{sub {ital c}} between 110 and 115 K. The Seebeck coefficient ({ital S}) of the partially annealed glass system is found to be positive and increases linearly with temperature. The {ital S} values of the corresponding glass-ceramic superconductors showing broad peaks around {ital T}{sub {ital c}}. A change over in the values of {ital S} from positive (below {approximately}290 K) to negative (above {approximately}290more » K) indicates the coexistence of both electrons and holes in these superconductors. The TEP data can be fitted with both the two-band model of Forro {ital et} {ital al}. [Solid State Commun. {bold 73}, 501 (1990)] and the Nagaosa-Lee model [Phys. Rev. Lett. {bold 64}, 2450 (1990)]. Therefore, the bosonic contribution in the transport properties of these superconductors, as suggested by the Nagaosa-Lee model, is supported. {copyright} {ital 1996 The American Physical Society.}« less