1,721,007 research outputs found
Crystallization behaviour of neodymium doped yttrium silicate nanophosphors
No full textSol-gel technique was used to prepare yttrium silicate powders doped with 0.01Nd(3+). The crystallite sizes were determined to be 23 +/- 0.5 nm from the XRD patterns of the powders annealed at 960 degrees C. The Y(4.67)(SiO(4))(3)O, Y(2)Si(2)O(7) and Y(2)SiO(5) crystalline phases were observed upon heat treatment at 960 degrees C which is much lower than 1500-1650 degrees C are reported before. (C) 2011 Elsevier Ltd. All rights reserved
Viscous Behavior of PS, PP, and ABS in Terms of Temperature and Pressure-Dependent Hole Fraction
No full textWe have developed a zero-shear viscous model in terms of temperature- and pressure-dependent hole fraction computed from Simha-Somcynsky Hole Theory. This model successfully interprets the viscosity data of PS, PP, and ABS as a function of hole fraction for a broad range of temperature and pressure. We have also introduced and discussed a new term: Viscoholibility; the derivative of logarithm of viscosity with respect to hole fraction. When the hole fraction takes highest available value, the viscoholibility approaches asymptotically to a constant value by which the viscosity changes linearly with the hole fraction. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 110-113,201
Structural and spectroscopic properties of Nd3+:Y2Si2O7 phosphors
No full textPhosphors of alpha-Y2Si2O7 doped with Nd3+ ions were prepared using the sol gel technique. Nano-sized crystalline phosphor powders were obtained by annealing the dried gels at 960 degrees C. The crystallization properties of the phosphor powders were determined from their XRD patterns. The alpha-Y2Si2O7 phase was the only phase observed in all compositions. As the amount of amorphous SiO2 in the composition was increased, the crystalline sizes and the widths of the size distribution curves were found to decrease from 17.8 nm to 10.6 nm and from 15.6 nm to 12.2 nm, respectively. The spectroscopic properties of the powders were studied by measuring the luminescence and the decay patterns of the F-4(3/2) -> I-4(9/2) and F-4(3/2) -> I-4(11/2) transitions between 50 K and 310 K. No appreciable effect of the crystallite sizes on the average lifetime of the F-4(3/2) level was observed at temperatures below 100 K. The effect of temperature, however, becomes relevant above 100 K as the size of alpha-Y2Si2O7 nano-crystal becomes smaller. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved
On the Non-Newtonian Viscous Behavior of Polymer Melts in Terms of Temperature and Pressure-Dependent Hole Fraction
Full text linkA new theoretical non-Newtonian viscosity model is developed by taking the fractional series expansion of Eyring's shearing strain rate. A broad range of experimental rheological data of various polymer melts including polyethylenes, polypropylene, polystyrene, poly (methyl methacrylate), and polycarbonate are fitted well using the proposed model. From the model; zero shear, constant shear-stress and constant shear-rate viscosities are derived as a linear function of viscosity related quantity, Y-h, called thermo-occupancy function and their coefficients are discussed in detail. The thermo-occupancy function is expressed in terms of temperature and structural vacancies such as hole fraction computed from the Simha-Somcynsky Hole Theory (SS). In addition, the derivative of the logarithm of viscosities with respect to the hole fraction, named as viscoholibility, is observed decreases with the increasing hole fraction. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40540
The Effect of Hole Fraction on Viscosity in Atactic and Syndiotactic Polystyrenes
No full textThe non-Newtonian viscosity behavior of atactic and syndiotactic polystyrenes (aPS and sPS), at temperatures from to and pressures up to 30 MPa, was studied using the recently proposed Yahsi-Dinc-Tav model, in particular, the Cross-like model. Viscosity data with shear rates of to were taken from literature at ambient pressure and were reproduced from the Cross-Vogel model at elevated pressures. The viscosities were predicted using the Yahsi-Dinc-Tav model with average absolute deviations of 4.37 % at ambient pressure and 9.63 % at high pressures for aPS and 2.54 % at ambient pressure and 4.79 % at high pressures for sPS. We extended this work to relate the zero shear and the constant shear rate viscosities in terms of the temperature- and pressure-dependent hole fraction using the thermo-occupancy function. The hole fraction (h) was computed from Simha-Somcynsky hole theory. Analytical relationships of specific density and hole fraction in terms of scaled temperature and pressure were constructed for practical purposes. The effects of tacticity of polystyrenes were discussed in terms of the thermo-occupancy function in detail. In particular, the derivative of the logarithm of the viscosities (viscoholibility) was found to decrease with an increasing hole fraction
On the Ionic Conductivity of Polymer Electrolytes in Terms of Hole Fraction
No full textA theoretical model to interpret the conductivity of ions through polymer electrolytes is established in terms of the temperature and pressure-dependent hole fraction computed from Simha-Somcynsky hole theory. The model successfully linearizes the logarithm of PPG and PEG conductivity data with NaCF3SO3 in a 20:1 ratio for a broad range of temperature and pressure. The conductivity parameter and transmission coefficient with an additive hole fraction constant are discussed and compared for both species. The derivative of the logarithm of conductivity with respect to the hole fraction decreases inversely with the hole fraction and saturates at about 0.08 and 0.12 hole fractions for PPG and PEG, respectively. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2249-2254, 200
Effect of Free Volume on Curcumin Release from Various Polymer-Based Composite Films Analyzed Using Positron Annihilation Lifetime Spectroscopy
No full textThis work reports the effects of free volume on curcumin release in various polymer-based composite films. Curcumin-reinforced biocomposite films were fabricated with natural biopolymers (carrageenan and chitosan) and bioplastics (poly(lactide) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT)) via the solvent casting method. The curcumin release test was performed using an aqueous medium, and it was found that it was released the fastest in the carrageenan film, followed by the chitosan, PLA, and PBAT films, presumably owing to the dissimilarity of the polymer matrix. The free volume of the polymer films was determined using positron annihilation lifetime spectroscopy (PALS) to understand the release phenomena of curcumin. The free volume fraction was varied and reliant on the type of polymer, with the highest in the PBAT-based film followed by the PLA-, chitosan-, and carrageenan-based films. The free volume method helps analyze the release of bioactive compounds in a polymer matrix and may help to achieve a better understanding of the release of bioactive compounds.</p>
A detailed survey for determination of the grafted semifluorinated acrylic compound effect on thermal, microstructural, free volume, mechanical and morphological features of HDPE
No full textThis study mainly aims to investigate the role of grafted semifluorinated acrylic compound in the crucial characteristic properties of high density polyethylene (HDPE). Graft copolymerization of the semifluorinated acrylic compound, 3,3,4,4,5,5,6,6,7,7,8,8,8-dodecafluoro-5-methyloctyl-4-(acryloyloxy) benzoate (ABCF13) onto HDPE within the different content levels of ABCF13 (5, 10, 15, 20, 30 and 40 %) was performed by bulk-melt polymerization method. The changes in the thermal, microstructural and free volume characteristics of graft coproducts with extent of grafting were investigated in detail by means of DSC, powder X-ray diffraction and PALS techniques, respectively. The experimental findings showed that the melting temperature of crystalline domains and crystallinity ofHDPE reached the maxima at the 15 % and 40 % ABCF13 contents, respectively. The grafting of ABCF13 onto HDPE also gave rise to significant expansion and contraction in lateral dimensions of orthorhombic unit cell parameters in the crystalline domains of HDPE. Moreover, PALS analyses depicted that the size of the free volumes increased almost linearly with the grafting percentage. As for mechanical behaviours of the graft products, remarkable improvements were achieved in especially tensile strength (from 18.75 MPa to 43.75 MPa) and impact strength (from 19.30 Mpa to 38.72 MPa). The morphological properties of the fractured surfaces obtained from tensile and impact tests of products were also examined by SEM analysis. The samples possessed completely homogeneous structure without any phase separation. A gradual transition from ductile behaviour to brittle nature was observed as the grafting level increased in the products
Relaxation time of polypropylene glycol and polypropylene glycol dimethylether-like polymers in terms of fluid-phase temperature and pressure dependent hole fraction
No full textWe present a model explaining relaxation time of PPG (polypropylene glycol) and PPGM (polypropylene glycol dimethylether) as representative compounds, with different molecular weights, PPG2 (M-w = 2 kg mol(-1)), PPG3 (M-w = 3 kg mol(-1)), PPGM1 (M-w = 1 kg mol(-1)), and PPGM2 (M-w = 2 kg mol(-1)), as a function of hole fraction at various fluid phase temperatures and high pressures. Proposed model based on the structural relaxation behavior of chain molecules given by thermo-occupancy function in terms of temperature and tempetature-pressure dependent hole fraction is discussed and compared with the free volume model. The former is the most universal behavior than the latter in terms of temperature and pressure. We discuss activation energy parameter and transmission coefficient for the species in terms of chain length and end groups such as dimethylether. Scaling relaxation time parameter in the proposed model has similar trend with relaxation time parameter of Adam-Gibbs theory. (C) 2015 Elsevier Ltd. All rights reserved
Dielectric properties and conductivity of PVdF-co-HFP/LiClO4 polymer electrolytes
No full textIn this study, it was aimed to prepare a series of PVdF-co-HFP based electrolytes with different LiClO4 loadings and to investigate their chemical and electrical properties in detail. For this purpose, PVdF-co-HFP based electrolytes with different LiClO4 loadings (1-20 weight %) were prepared using solution casting method. X-ray diffraction (XRD), differential scanning calorimetry, and thermogravimetric (TGA)-differential thermal and dielectric spectroscopy analysis of PVdF-co-HFP/LiClO4 were performed to characterize their structural, thermal, and dielectric properties, respectively. XRD results showed that the diffraction peaks of PVdF-co-HFP/LiClO4 electrolytes broadened and decreased with LiClO4. TGA patterns exhibited that PVdF-co-HFP/LiClO4 electrolytes with 20 wt % of LiClO4 had the lowest thermal stability and it degraded above 473 K, which is highly applicable for solid polymer electrolytes. Dielectric constant, dielectric loss, and conductivities were calculated by measuring capacitance and dielectric loss factor of PVdF-co-HFP/LiClO4 in the range from 10 mHz to 20 MHz frequencies at room temperature. In consequence, conductivities of PVdF-co-HFP/LiClO4 increased significantly with frequency for low loading of LiClO4 while they only slightly changed with higher LiClO4 addition. On the other hand, dielectric constant values of PVdF-co-HFP/LiClO4 films decreased with frequency whereas they rose with LiClO4 addition. The dielectric studies showed an increase in dielectric constant and dielectric loss with decreasing frequency. This result was attributed to high contribution of charge accumulation at the electrode-electrolyte interface. The electrolyte showed the maximum conductivity of 8 x 10(-2) S/cm at room temperature
- …
