Dynamic mechanical behavior of high‐density polyethylene/ethylene vinyl acetate copolymer blends: The effects of the blend ratio,reactive compatibilization,and dynamic vulcanization

The effects of the blend ratio, reactive compatibilization, and dynamic vulcanization on the dynamic mechanical properties of high‐density polyethylene (HDPE)/ethylene vinyl acetate (EVA) blends have been analyzed at different temperatures. The storage modulus of the blend decreases with an increase in the EVA content. The loss factor curve shows two peaks, corresponding to the transitions of HDPE and EVA, indicating the incompatibility of the blend system. Attempts have been made to correlate the observed viscoelastic properties of the blends with the blend morphology. Various composite models have been used to predict the dynamic mechanical data. The experimental values are close to those of the Halpin–Tsai model above 50 wt % EVA and close to those of the Coran model up to 50 wt % EVA in the blend. For the Takayanagi model, the theoretical value is in good agreement with the experimental value for a 70/30 HDPE/EVA blend. The area under the loss modulus/temperature curve (LA) has been analyzed with the integration method from the experimental curve and has been compared with that obtained from group contribution analysis. The LA values calculated with group contribution analysis are lower than those calculated with the integration method. The addition of a maleic‐modified polyethylene compatibilizer increases the storage modulus, loss modulus, and loss factor values of the system, and this is due to the finer dispersion of the EVA domains in the HDPE matrix upon compatibilization. For 70/30 and 50/50 blends, the addition of a maleic‐modified polyethylene compatibilizer shifts the relaxation temperature of both HDPE and EVA to a lower temperature, and this indicates increased interdiffusion of the two phases at the interface upon compatibilization. However, for a 30/70 HDPE/EVA blend, the addition of a compatibilizer does not change the relaxation temperature, and this may be due to the cocontinuous morphology of the blends. The dynamic vulcanization of the EVA phase with dicumyl peroxide results in an increase in both the storage and loss moduli of the blends. A significant increase in the relaxation temperature of EVA and a broadening of the relaxation peaks occur during dynamic vulcanization, and this indicates the increased interaction between the two phases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2083–2099, 2003     

Structural and luminescence enhancement properties of Eu3＋/Ag nanocrystallites doped SiO2-TiO2 matrices

We reported here the structural and optical characterisation of silver nanocrystallites/Eu3+ :SiO2-TiO2 matrices synthesised through sol-gel route. Structural characterisations were done by using energy dispersive spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM) and transmission electron microscopy (TEM) measurements and optical characterisations were performed by absorption and emission spectroscopy. The TEM and XRD measurements confirmed the presence of nanocrystals. A broad absorption band was observed due to surface plasmon resonance of silver nanocrystals. The effect of silver nanocrystals on the emission spectrum of Eu3+ doped SiO2-TiO2 matrices was discussed. An attempt was made to explain this fluorescence enhancement by invoking phenomena such as energy transfer, asymmetry ratio, surface plasmon, surface roughness, crystallinity and grain boundary. Our analysis, based on the experimental results, suggested that all the phenomena except crystallinity and grain boundary had favourable effects on fluorescence enhancement. We also estimated the relevant parameters associated with the phenomena that affected the fluorescence emission from the Eu3+ ions in the matrix. It was seen that the theoretical estimate of fluorescence enhancement agreed well with the experimental estimate.     

Effect of phenol end functional switching segments on the shape memory properties of epoxy‐cyanate ester system

The effect of phenol end functional shape memory oligomers on the shape memory properties of an epoxy‐cyanate ester resin system was examined. The basic resin system consisted of diglycidyl ether of bisphenol A (DGEBA) cured with bisphenol A dicyanate (BADC). For conferring the shape memory properties, the switching segment (SS) components selected are α, ω‐phenol‐terminated poly(tetramethyleneoxide) (PPTMO), poly(ε‐caprolactone) (PPCL), and poly(propylene glycol) (PPPG). Epoxy‐cyanate ester blend of defined composition was analyzed for thermal, mechanical, thermo‐mechanical, and shape memory properties at two concentrations of the three SSs. The transition temperature of heavily SS loaded matrix increased in the order: PPTMO < PPCL < PPPG commensurate with crystallizability of SS segments at ambient. For same reason flexural property showed an increasing trend. This is in league with the increased crystallizability of the shape memory polymer components. The shape fixity, recovery extent, and recovery time followed a reverse order: PPPG < PPCL < PPTMO. In contrast to the alcohol terminated shape memory components, phenol terminal groups were helpful in integrating the shape memory segments into the matrix by way of reaction with both epoxy and cyanate groups. The coreaction was conducive for achieving better shape memory properties and decreasing the transition temperature. A direct relation existed between the modulus ratio and the shape recovery property. Higher concentration of the SSs caused a diminution in transition temperature but enhanced the shape memory properties, though the mechanical properties were adversely affected. The shape recovery increased with increase in temperature. All polymers possessed good mechanical properties and thermal stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41196.     

Polyaniline / carbon nanotube composites: starting with phenylamino functionalized carbon nanotubes

Summary Composites of carbon a nanotube with polymers are a developing and interesting area of research. The dispersion of the nanotube in polymer matrices is an important factor while making its nanocomposites. Even though in-situ polymerization approach offers a better approach for synthesizing homogeneous polymer nanotube composites, the dispersion of the nanotubes in the monomer solution is a problem. In this article we report a new chemical method for dispersing nanotubes in monomer and the preparation of uniform tubular composite of polyaniline (PANI) and multiwalled carbon nanotube (MWNT). For this the oxidized multiwalled nanotube (o-MWNT) was functionalized with p-phenylenediamine, which gave phenylamine functional groups on the surface. This functionalization helped to disperse the nanotubes in acidic solution. The in-situ polymerization of aniline in the presence of these well dispersed nanotubes gave a new tubular composite of carbon nanotube having an ordered uniform encapsulation of doped polyaniline. The phenylamine functional groups on the surface were grown into polyaniline chain so that the composite contains polyaniline functionalized CNT and they were no more an impurity in the final nanocomposite. The microscopic and structural properties of this composite were compared with that of a composite prepared under identical condition using o-MWNT.     

Influence of Ho-Doping on the Electromagnetic Field-Dependent $E$–$J$ Characteristics of (Bi,Pb)-2212 Superconductor

The magnetic field (B ) dependence of electric field versus transport current density (E-J characteristics) of Bi_1.6Pb_0.5Sr_2-xHo_xCa_1.1Cu_2.1O_8+delta superconductor was studied for x from 0.000 to 0.200. The behavior of supercurrent flow under magnetic fields in Ho-doped (Bi,Pb)-2212 is explained using thermally activated flux-creep. The n -value and characteristic pinning energy ( U_c) estimated from E-J characteristics show that at applied fields, the flux-lines in Ho-doped samples are in the glass-state. A correlation is observed between n -index and J_c of doped samples. The highly enhanced critical current density (J_c) and n-index in both self- and applied-fields due to Ho-doping is of great scientific and technological significance.     

Catalytic packed bed non‐thermal plasma reactor for the extraction of hydrogen from hydrogen sulfide

The decomposition of hydrogen sulfide (H₂S) to hydrogen and sulfur with Al₂O₃, MoO_x/Al₂O₃, CoO_x/Al₂O₃ and NiO/Al₂O₃ packed non‐thermal plasma dielectric barrier discharge reactor was studied. The reaction was carried out with 5‐mm discharge gap during the decomposition of 5 vol.% H₂S at 150 ml/min (STP) flow rate. Typical results indicated the conversion of ~50% at a specific input energy of ~0.92 kJ/l H₂S and 10% (in length) packed reactor showed the best conversion. Among the catalysts studied, MoO_x and CoO_x supported on Al₂O₃ showed high performance, which may be caused by synergy between plasma excitation of the carrier gas molecules and catalytic behaviour of MoO_x and CoO_x. Copyright © 2012 John Wiley & Sons, Ltd.     

AC conductivity of nanostructured nickel oxide

AC conductivity of consolidated nanoparticles of NiO, having different average particle sizes (2.5 nm–17 nm) was measured in the temperature range 313 K to 413 K and over the frequency range 50 Hz to 3 MHz. The ac conductivity of the samples was found to be enhanced by six to eight orders of magnitude over that of NiO single crystals reported in the literature. This large enhancement in conductivity is attributed to the high density of Ni²⁺ vacancies in the nanoparticles. The variation of ac conductivity with frequency of the applied signal and temperature is discussed on the basis of the Correlated Barrier Hopping (CBH) Model. The observed spread in activation energy and slope of the log _ac Vs log plots is attributed to the distribution of the charge carrier hopping distance and localization energies in the nanoparticle samples. The effect of the interfacial region on the electrical conductivity of the samples is analyzed by taking into account the contributions due to grain boundaries and triple junctions. The observed variation of measured ac conductivity with average particle size is semi-quantitatively explained based on the reasoning that the role of the triple junctions is to reduce the conductivity.     

Structural and superconducting properties of Bi1.7Pb0.4Sr2 − xYbxCa1.1Cu2.1Oy system

The structural, electrical and superconducting properties of Bi_1.7Pb_0.4Sr_2 − xYb_xCa_1.1Cu_2.1O_y system has been studied for different Yb concentrations. The samples are prepared by solid state synthesis in the polycrystalline bulk form. Structural analysis by X-ray diffraction, microstructural examination by SEM and measurements of electrical and superconducting properties have been conducted to study the effects of Yb substitution at Sr site. The critical temperature (T_C) and critical current density (J_C) are found to increase drastically with Yb substitution. Maximum values of T_C and J_C are observed for x = 0.3 and x = 0.2 respectively. The increase in T_C and J_C is explained due to the substitution effect of Yb³⁺ in place of Sr²⁺ and consequent change in the hole concentration in the CuO₂ planes. Above the optimum levels T_C and J_C begin to reduce due to secondary phase formation. A metal-insulator transition originating from the change of carrier concentration is found to occur at higher doping level (x > 0.5).     

Correlating Photoluminescence and Photocatalytic Activity of Mixed-phase Nanocrystalline Titania

Mixed-phase nanocrystalline titania with varying rutile-content has been synthesized via solvent mixing and calcination treatment of sol–gel derived nanocrystalline anatase and rutile precursors. The mixed-phase nanocrystalline titania has been characterized using different analytical techniques for analyzing their phase contents, nanocrystallite size distribution, band-gap, and photoluminescence. The photocatalytic activity of mixed-phase nanocrystalline titania has been studied by monitoring the degradation of methylene blue dye in an aqueous solution under ultraviolet-radiation exposure. A strong correlation between photoluminescence and photocatalytic activity has been demonstrated for the mixed-phase nanocrystalline titania.     

Structural and Spectroscopic Studies of Sm3+/CdS Nanocrystallites in Sol–Gel TiO2-ZrO2 Matrix

A sol–gel method was used to prepare titania-zirconia matrices doped with Sm³⁺/CdS nanocrystallites. The structural properties of the matrices were characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier-transform infrared spectroscopy studies. The thermal stability of the material was determined by TGA/DTA analysis. The absorption spectrum shows the characteristic peaks of the Sm³⁺ ions and the absorption peak corresponding to the CdS nanocrystallites. The optical bandgap and size of the CdS nanoparticles were calculated from the absorption spectrum. From TEM, the interplanar distance (d) was estimated to be 3.533 Å, which matches with the (1 0 0) plane of bulk CdS. The measurements yield a nanocrystallite size of around 7.8 nm. The optical absorption and emission spectra confirmed the formation of CdS nanoparticles along with samarium ions in the titania-zirconia matrices. The fluorescence intensity of the samarium ions was found to be greatly enhanced by codoping with CdS nanocrystallites.