Showing papers by "Indian Association for the Cultivation of Science published in 2001"

Effect of alkali treated jute fibres on composite properties

Abstract: Jute fibres were subjected to a 5% alkali (NaOH) solution treatment for 0, 2, 4, 6 and 8 h at 30°C. An improvement in the crystallinity in the jute fibres increased its modulus by 12%, 68% and 79% after 4, 6 and 8 h of treatment respectively. The tenacity of the fibres improved by 46% after 6 and 8 h treatment and the % breaking strain was reduced by 23% after 8 h treatment. For the 35% composites with 4 h treated fibres, the flexural strength improved from 199.1 MPa to 238.9 MPa by 20%, modulus improved from 11.89 GPa to 14.69 GPa by 23% and laminar shear strength increased from 0.238 MPa to 0.2834 MPa by 19%. On plotting the different values of slopes obtained from the rates of improvement of the flexural strength and modulus, against the NaOH treatment time, two different failure modes were apparent before and after 4 h of treatment. In the first region between 0 and 4 h, fibre pull out was predominant whereas in the second region between 6 and 8 h, transverse fracture occurred with a minimum fibre pull out. This observation was well supported by the SEM investigations of the fracture surfaces.

Characterization of alkali-treated jute fibers for physical and mechanical properties

Abstract: Changes occurring in jute fibers when treated with a 5% concentration of a NaOH solution for 0, 2, 4, 6, and 8 h were characterized by weight loss, linear density, tenacity, modulus, FTIR, and X-ray measurements. A 9.63% weight loss was measured during 2 h of treatment with a drop of hemicellulose content from 22 to 12.90%. The linear density value showed no change until 2 h of treatment followed by a decrease from 33.0 to 14.5 denier by 56% after 6 h of treatment. The tenacity and modulus of the fibers improved by 45 and 79%, respectively, and the percent breaking strain was reduced by 23% after 8 h of treatment. X-ray diffractograms showed increase in crystallinity of the fibers only after 6 h of treatment, while FTIR measurements showed much of the changes occurring by 2 h of treatment with an increased amount of OH groups. By measuring the rate of change of the modulus, tenacity, and percent breaking strain with the time of treatment, a clear transition was apparent at 4 h of treatment with the dissolution of hemicellulose, causing a weight loss and drop in the linear density before and development of crystallinity with an improvement in the properties after the transition time. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1013–1020, 2001

The mechanical properties of vinylester resin matrix composites reinforced with alkali-treated jute fibres

Abstract: Jute fibres were subjected to alkali treatment with 5% NaOH solution for 0, 2, 4, 6 and 8 h at 30°C. The modulus of the jute fibres improved by 12, 68 and 79% after 4, 6 and 8 h of treatment, respectively. The tenacity of the fibres improved by 46% after 6 and 8 h treatment and the % breaking strain was reduced by 23% after 8 h treatment. For 35% composites with 4 h-treated fibres, the flexural strength improved from 199.1 to 238.9 MPa by 20%, modulus improved from 11.89 to 14.69 GPa by 23% and laminar shear strength increased from 0.238 to 0.283 MPa by 19%. On plotting different values of slopes obtained from the rates of improvement of flexural strength and modulus, against NaOH treatment time, two different failure modes were apparent before and after 4 h of NaOH treatment. In the first region between 0 and 4 h, fibre pull out was predominant whereas in the second region between 6 and 8 h, transverse fracture occurred with minimum fibre pull out. This observation was well supported by the SEM investigations of the fracture surfaces.

Phase transitions in the quantum Ising and rotor models with a long-range interaction

Abstract: We investigate the zero-temperature and finite-temperature phase transitions of quantum Ising and quantum rotor models. We here assume a long-range (falling off as ${1/r}^{d+\ensuremath{\sigma}},$ where r is the distance between two spins/rotors in units of lattice spacing) ferromagnetic interaction among the spins or rotors. We find that the long-range behavior of the interaction drastically modifies the universal critical behavior of the system. The corresponding upper critical dimension and the hyperscaling relation and exponents associated with the quantum transition are modified and, as expected, they attain values of short-range system when $\ensuremath{\sigma}=2.$ The dynamical exponent varies continuously as the parameter \ensuremath{\sigma} and is unity for $\ensuremath{\sigma}=2.$ The one-dimensional long-range quantum Ising system shows a phase transition at $T=0$ for all values of \ensuremath{\sigma}. The most interesting observation is that the phase diagram for $\ensuremath{\sigma}=d=1$ shows a line of Kosterlitz-Thouless transition at finite temperature even though the $T=0$ transition is a simple order-disorder transition. These finite temperature transitions are studied near the phase boundary using renormalisation group equations and a region with diverging susceptibility is located. We have also studied one-dimensional quantum rotor model which exhibits a rich and interesting transition behavior depending upon the parameter \ensuremath{\sigma}. We explore the phase diagram extending the short-range quantum nonlinear \ensuremath{\sigma} model renormalisation group equations to the present case.

Thermoreversible Gelation of Regioregular Poly(3-hexylthiophene) in Xylene

Abstract: Regioregular poly(3-hexylthiophene) (P3HT) produces thermoreversible gel in xylene. The gel is brownish-red in color. SEM and TEM studies indicate the presence of fibrillar network. WAXS and electron diffraction pattern indicate the presence of P3HT crystallites in the gel. The gels exhibit a first-order phase transition when heated in DSC. A time-dependent UV−vis study indicates that gelation in this system is probably accompanied by two different processes, e.g., (1) coil-to-rod transformation and (2) aggregation of rods to form the crystallites producing the gel. The gelation rate (tgel-1) measured from the test tube tilting method is analyzed using the equation tgel-1 = f(C) f(T), where f(c) = φn, φ being the reduced overlapping concentration and n is an exponent. The average “n” value determined is 0.52, which indicates that three-dimensional percolation is a suitable model for this gelation. The gelation rate is analyzed according to the Flory−Weaver theory of coil-to-helix transition, and the free ...

Solvation dynamics of DCM in human serum albumin

Abstract: Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran (DCM) in aqueous solution of a protein, human serum albumin (HSA), is studied using picosecond time-resolved emission spectroscopy. The solvation dynamics of DCM bound to HSA is found to be biexponential with one component of 600 ± 100 ps (25%) and a very long component of 10 ± 1 ns (75%). This indicates that the motion of the water molecules in the vicinity of the protein is highly constrained.

Excited state photodynamics of 4-N,N-dimethylamino cinnamaldehyde: A solvent dependent competition of TICT and intermolecular hydrogen bonding

Abstract: This paper describes the dual fluorescence of 4-N,N-dimethylamino cinnamaldehyde (DMACA) in various solvents. Based on major findings the first fluorescence band has been assigned to be arising out of delocalized excited state (DE) and the anomalous fluorescence band in polar aprotic solvents has been assigned to twisted intramolecular charge transfer (TICT) state whereas, in protic solvent it is arising out due to hydrogen bonding interaction between hydrogen donor part of the solvent and carbonyl group of the probe molecule. This hydrogen bonding being an efficient fluorescence quenching channel trammels the TICT formation and thus an apparent competition exists between TICT and hydrogen bonding formation in protic solvent. The calculated absorption spectrum generated from CNDO calculations follows nicely the experimental absorption band. The AM1 calculations corroborate the large dipole moment change and the charge transfer in orthogonal position as found from experimental observations.

Fluorescence Anisotropy Decay in Polymer-Surfactant Aggregates

Abstract: The fluorescence anisotropy decay of two dyes merocyanine 540 and oxazine 1 has been studied in a polymer−surfactant aggregate containing poly(vinylpyrrolidone) (PVP) and sodium dodecyl sulfate (SDS). The results are analyzed in terms of the necklace model of the polymer−surfactant aggregate. The rotational motion of the probe is assumed to involve “wobbling-in-cone” along with translational motion along the micellar surface. It is observed that the presence of the polymer chains around the spherical SDS micelles causes significant retardation of both the wobbling motion as well as the translational motion of the two dyes. As a result, the wobbling and translational diffusion of the dyes in the PVP−SDS aggregate are slower than those in SDS micelle.

Observation of Dominant Ferromagnetic Interaction in Fumarate-Bridged 1-D Polymer of Cu(II)

Abstract: The reaction of CuCl2·2H2O and Na2C4H2O4 (disodium fumarate) in dilute ammonia solution produces 1-D polymeric chain [Cu(μ-C4H2O4)(NH3)2]n(H2O)n. The crystal structure of the compound has been solved. The compound crystallizes in the monoclinic system, space group C2/m (No. 12), with chemical formula C4H10N2O5Cu, a = 13.955(5) A, b = 7.330(3) A, c = 8.927(2) A, β = 102.39(3)°, Z = 4. The interesting feature of the complex is that one of the carboxylic acid groups acts as a monodentate coordinating ligand whereas the remaining carboxylate moiety acts as a monoatomic bridging bidentate ligand. This unusual coordination behavior of fumarate anion produces a chain with alternate repetition of 4- and 14-member rings. The magnetic properties of the compound have been studied from room temperature to 4 K, which reveal the existence of a dominant ferromagnetic interaction with exchange coupling parameter values of JF = +12 cm-1 and JAF = −3.8 cm-1, using an alternating ferro- and antiferromagnetic chain model for...

Noise properties of stochastic processes and entropy production.

Abstract: Based on a Fokker-Planck description of external Ornstein-Uhlenbeck noise and cross-correlated noise processes driving a dynamical system we examine the interplay of the properties of noise processes and the dissipative characteristic of the dynamical system in the steady state entropy production and flux. Our analysis is illustrated with appropriate examples.

Dispersion polymerization of aniline using hydroxypropylcellulose as stabilizer: role of rate of polymerization

Abstract: Hydroxypropylcellulose (HPC) has been used as a steric stabilizer for preparing polyaniline dispersions using the route of oxidative dispersion polymerization of aniline. Using strongly acidic conditions (1 mol l−1 HCl), low temperature of about 2 °C and a concentration of aniline as low as 0.5%, ammonium peroxodisulfate at 1.25% and hydroxypropylcellulose concentrations at 0.5–1 g d l−1, unstable dispersions were obtained not only in water but also in aqueous alcohols (ethanol and methanol) up to at least 70 vol% alcohol. In contrast, dispersions that remained stable for at least 72 h were obtained when the alcohol concentration of the medium was as high as about 80 vol%. Kinetic studies of the polymerization systems suggested that success in the latter case was due to a lowering of the rate of polymerization. Transmission electron microscopy studies showed that dispersion particles prepared in 80 vol% alcohol media are spherical in shape and their diameter decreases with increasing stabilizer concentration. However, a change of morphology from spherical to aggregated needle-shaped was observed when the rate was increased by increasing the aniline concentration from 0.5% to 0.75% g d l−1 in the above recipe. The aggregated particles were found to be broken down to spherical nanoparticles when the as-prepared dispersions were sonicated for about 30 min. The sonicated dispersion on drying showed the presence of fractal clusters of polyaniline particles in the dried film. The fractal dimension was determined to be 1.77 which agreed well with the theoretical value determined by computer simulation based on a diffusion limited cluster–cluster aggregation model in three dimensions. © 2001 Society of Chemical Industry

Slow Solvation Dynamics of Dimethylformamide in a Nanocavity. 4-Aminophthalimide in β-Cyclodextrin

Abstract: Solvation dynamics of a nonaqueous solvent, N,N-dimethylformamide (DMF) has been studied for the first time in a β-cyclodextrin (β-CD) cavity using picosecond time dependent fluorescence Stokes' shift and 4-aminophthalimide (4-AP) as a probe. Solvation dynamics of confined DMF molecules within the β-CD cavity is found to be described by a component of 400 ± 50 ps (25%) and a slow component of 8 ± 1 ns (75%). This is substantially slower than the solvation time (∼1 ps) in bulk DMF.

Adiabatic and non-adiabatic small-polaron hopping conduction in La1−xPbxMnO3+δ (0.0 ≤ x ≤ 0.5)-type oxides above the metal–semiconductor transition

Abstract: Above the semiconductor-to-metallic transition (SMT) temperature (Tp), transport properties of the La1−xPbxMnO3+δ (0 ≤ x ≤ 0.5)-type mixed valence oxides with Tp between 230 and 275 K (depending on x) have been thoroughly examined for a small-polaron hopping conduction mechanism of the carriers. Although the variable range hopping (VRH) model was used earlier to fit the entire conductivity data above SMT, we noticed two distinct regions (above and below θD/2; θD is the Debye temperature) where different types of conduction mechanisms are followed. The high temperature (T > θD/2) conductivity data of all the Pb-doped samples follow the adiabatic hopping conduction mechanism, while those of LaMnO3 (x = 0) showing no SMT follow the non-adiabatic hopping conduction mechanism of Mott or Emin with reasonable values of polaron radius, hopping distance, polaron binding energy, activation energy, etc being different for different systems. The VRH model, however, fits the corresponding low temperature (T < θD/2) data of all the samples. Both resistivity ρ(T) and thermoelectric power S(T) follow a similar microscopic theory above Tp supporting the small-polaron hopping mechanism. Thermoelectric power also showed appreciable magnetic field dependence around SMT.

Effects of moisture on the mechanical properties of glass fibre reinforced vinylester resin composites

Abstract: Glass fibre reinforced vinylester resin composites incorporating varying amounts of fibres (63.5, 55.75, 48.48, 38.63 and 27.48 wt%) were characterized for their mechanical properties both as prepared and after treatment with boiling water for 2, 4, 6, 8 and 24 h. Weights of the samples were found to increase to a saturation at about 8 h with boiling water treatment. In keeping with the composite principle, the mechanical properties improved with fibre loading. However, the properties were relatively inferior when treated with boiling water for longer hours attributing to ingress of moisture by capillary action through the interface between the fibre and the resin matrix. Considering the rates of moisture absorption and correlating with the mechanical properties, it was observed that the deteriorating effects were predominant up to 4 h treatment with boiling water. Estimation of defect concentrations for 63.5 wt% of nascent fibre reinforced composites as well as those composites treated with boiling water for 24 h were 56.93% and 64.16% respectively. Similarly, 27.48 wt% nascent fibre reinforced composites and those composites with boiling water treatment showed the estimation of defect concentrations of 39.94% and 50.55% respectively. SEM study of the fractured surfaces showed heavy fibre pull-out in the tensile zone whilst shear fracture of the fibre bundles was predominant at the compressive zone of the samples tested for flexural strength properties.

Dispersed Molecular Aggregates.

Abstract: Colloidal dispersions of tungstic acid (H2WO4) have been prepared in water/(TX-100+alkanol)/n-heptane water-in-oil microemulsion media by reacting Na2WO4 with HCl. The effects of alkanol chain length, TX-100/alkanol mass ratio, temperature, and dilution at different [water]/[TX-100] mole ratios (ω) have been studied by the dynamic light scattering technique. The formation of H2WO4 in the microwater pool has been established by FT-IR measurements. The particle sizes and shapes in microemulsion media and in isolated states have been measured by TEM and SEM techniques. The enthalpy of formation of H2WO4 in the water pool of the microemulsions has also been determined microcalorimetrically.

Ultrasonic characterisation of ferroelectric BaTiO3 doped lead bismuth oxide semiconducting glasses

Abstract: Ferroelectric BaTiO3 doped lead bismuth xPbO–(100−x)Bi2O3–5BaTiO3 semiconducting oxide glasses with different PbO contents (x=20,30,40 and 50 wt%) have been prepared by the rapid quenching method. The ultrasonic velocity and attenuation measurements have been made at room temperature (298 K) at frequencies 2.25–10 MHz. From the measured density and ultrasonic velocity data, elastic moduli, Debye temperature, Poisson's ratio and other related physical parameters have been determined. At lower PbO content ( PbO wt %) , a monotonic decrease in velocity, elastic moduli and Debye temperature was noted. A further increase in PbO content ( PbO >40 wt %) lead to an increase in all the above parameters, after showing a minimum at 40 wt% of PbO. In addition, the effect of ultrasonic frequency on velocity and attenuation has also been studied in these glasses. The observed results have been explained in terms of the change in the structure and physical properties of the glass network with change in PbO content.