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991.
Relationships between molecular structure and thermomechanical properties of bio‐based thermosetting polymers 下载免费PDF全文
Jung Ho Yang Arun Srikanth Changwoon Jang Cameron F. Abrams 《Journal of Polymer Science.Polymer Physics》2017,55(3):285-292
Molecular dynamics simulations are used to study highly cross‐linked epoxy networks comprised of furanyl epoxy monomer, 2,5‐bis[(2‐oxiranylmethoxy)methyl]‐furan (BOF), that is cross‐linked by two furanyl amine hardeners, 5,5'‐methylenedifurfurylamine (DFDA) and 5,5'‐ethylidenedifurfirylamine (CH3‐DFDA). Important properties of these fully furan‐based systems, including room temperature density, glass transition temperature, and Young's modulus are found to agree with previous experimental results. We also compare the simulated and experimental values of four fully furan‐based thermosetting materials to those using the conventional resin diglycidyl ether of bisphenol A (DGEBA) cured with the two furanyl hardeners. Our simulation results predict a slight decrease in density and Young's modulus, but no impact on the glass transition temperature, upon adding the methyl group in DFDA. Detailed analyses of the MD trajectories reveal the underlying mechanisms responsible for the observed structure/property relations, which center on the lack of collinear covalent bonds in the BOF molecular structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 285–292 相似文献
992.
Physical gelation and macromolecular mobility of sustainable polylactide during isothermal crystallization 下载免费PDF全文
Huagao Fang Qizheng Xie Haibing Wei Pei Xu Yunsheng Ding 《Journal of Polymer Science.Polymer Physics》2017,55(16):1235-1244
The mobility of free macromolecular chains is of importance to the growth of crystallites in a crystallizing sustainable polylactide (PLA), which was scarcely explored by rheology. In this study, the time‐resolved rheological properties for PLA during isothermal crystallization were investigated first, showing that the storage and loss modulus experience 2–3 decades of increase. The Avrami analysis reveals that the crystallization kinetics in rheological measurement protocol follows the homogeneous nucleation and three‐dimensional growth mechanism. The linear viscoelastic properties in the vicinity of physical gelation point were then studied at the inverse quenching temperature of 165 °C. The results show that physical gelation occurs when the critical absolute crystallinity reaches 13% as determined by the rheological method. Relaxation time spectra reveal that the interfacial relaxation is greatly retarded but the presence of growing spherulites possesses little constraint on the mobility of free chains in matrix especially before physical gelation point. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1235–1244 相似文献
993.
X-ray analysis and magnetic properties have been studied for the system Co0.6Zn0.4MnxFe2-xO4. The bulk density, X-ray density and porosity were also studied. It was found that the lattice constant decreased with increasing manganese concentration x. The X-ray density, the bulk density and porosity do depend on the manganese content. The magnetic susceptibility and the activation energies were found to be increased with increasing percentage of the manganese ions while the dc conductivity decreased. 相似文献
994.
995.
Various types of wound debridement approaches are currently available in clinical practice such as autolytie, enzymatic. biodebridement, mechanical, and surgical debridemenl techniques. A critical look at these various options can explain their potential but also their limitations. In this study, a novel textile pad, which is composed of polyester filaments on the fleecy side and a bioeompatible coating on the opposite side, was made to provide a safe, inexpensive, easier and especially more efficient debridement process that can be used in all healthcare settings by all healthcare practitioners. Eighteen kinds of samples were prepared with different pile density, ground yarn count and coating amount. Dimensional morphology, stitch density, mass per unit area and mechanical properties were investigated to study the intrinsic relationship of structure and properties of textile pad for wound debridement. Results showed that tensile strength and suturing strength at piped site increased obviously with the increment of ground yarn count, while the amount of coating could also have a slight impact on these two properties. However, compressive load was mainly affected by pile density, with no obvious relation to ground yarn count and coating amount. 相似文献
996.
《Journal of Coordination Chemistry》2012,65(20):3560-3574
A new coordination complex, aqua bis(o-phenanthroline) cadmium(II) sulfate cyanoguanidine pentahydrate, [Cd(o-phen)2(SO4)(H2O)](cnge)?·?5H2O, was synthesized and characterized. The crystal structure was solved by X-ray diffraction methods. It crystallizes in the monoclinic space group P21/n with a?=?13.7650(2) Å, b?=?10.2796(2) Å, c?=?21.4418(3) Å, β?=?90.106(2)°, and Z?=?4 molecules per cell unit. The cadmium(II) is in a distorted octahedral environment coordinated to two nearly planar and mutually perpendicular o-phenanthrolines, one oxygen atom of sulfate, and a water molecule. Non-bonded and planar cyanoguanidine and five crystallization water molecules complete the asymmetric unit. Vibrational (FT-IR and FT-Raman) spectroscopies and thermogravimetric determinations support this structure. Intensity enhancement of the fluorescence spectrum may be a demonstration of the interaction of the metal with phenanthroline. In solution the coordination behavior is rather different, and the speciation studies point to coordination of both cnge and phenanthroline to cadmium. The improvement of the antibacterial activity of cadmium upon complexation has been determined. 相似文献
997.
E. Pollatos E. Logakis P. Chatzigeorgiou V. Peoglos I. Zuburtikudis M. Gjoka 《Journal of Macromolecular Science: Physics》2013,52(5):1044-1056
In this work, syndiotactic polypropylene/multiwalled carbon nanotubes (MWCNT) nanocomposites, in various concentrations, were produced using melt mixing. The influence of the addition of MWCNT on the morphology, crystalline form, and the thermal and electrical properties of the polymer matrix was studied. To that aim, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, and dielectric relaxation spectroscopy were employed. Significant alterations of both the crystallization behavior and the thermal properties of the matrix were found on addition of the carbon nanotubes: conversion of the disordered crystalline form I to the ordered one, increase of the crystallization temperature and the degree of crystallinity, and decrease of the glass transition temperature and the heat capacity jump. Finally, the electrical percolation threshold was found between 2.5–3.0 wt.% MWCNT. For comparison purposes, the results of the system studied here are also correlated with the findings from a previous work on the isotactic polypropylene/MWCNT system. 相似文献
998.
A novel one-step synthesis process was used to prepare CdTe:Cu2+/TiO2 nanotube arrays (TNTAs). X-ray powder diffraction and high-resolution transmission electron microscopy analyses confirmed that the obtained CdTe:Cu2+ quantum dots (QDs) possess cubic structures, which are approximately spherical, and a small particle size (2.95 nm). The photoluminescent and UV–visible absorption spectra of CdTe:Cu2+ QDs also display an obvious redshift, which was attributed to the replacement of Cd2+ with Cu2+. Compared with that of the TNTAs and CdTe/TNTAs, the photoelectric conversion efficiency of CdTe:5% Cu2+/TNTAs increased by 785.7% and 103.3%, respectively. The incident photo-to-current conversion efficiency of CdTe:5% Cu2+/TNTAs was 50.6%, which indicated the potential use of QDs in photochemical solar cells. 相似文献
999.
Ce doped ZnTiO3 as a novel catalyst with highly efficient and stable sonocatalytic activity was synthesized via an ultrasound-assisted sol–gel method using non-ionic surfactant Pluronic F127 as structure directing agent. Synthesized samples were characterized by using various techniques, such as XRD, TEM, SEM, EDX, XRF, BET, DRS, and PL, and their sonocatalytic activity studied toward degradation of p-Nitrophenol as a model organic compound. The synthesized mesoporous Ce/ZnTiO3 had mixed cubic–hexagonal phase with large surface area (118.2 m2 g–1) and narrow pore size distribution (4.9 nm). The effects of cerium concentration, calcination temperature, and calcination time on the structure and the sonocatalytic activity of Ce/ZnTiO3 were studied in detail. XRD results were suggested that the relation between the phase structure and the catalytic activity is considerable. Significant decrease in band-gap and PL intensity was observed with increasing the cerium concentration in the ZnTiO3. It became clear that the Ce/ZnTiO3 (0.81 mol%) shows high sonocatalytic activity compared with pure ZnTiO3 and other Ce/ZnTiO3 samples as well as commercial TiO2-P25. The possible mechanism for the enhanced sonocatalytic activity of Ce/ZnTiO3 was discussed in details. The electrical energy consumption was also considered during sonocatalytic experiments. 相似文献
1000.
Magnetically separable CoFe2O4/CoxFey/activated carbon composites for Cd(II) removal from wastewater
《应用有机金属化学》2017,31(8)
CoFe2O4 and Cox Fey were anchored into activated carbon (AC) to synthesize CoFe2O4/Cox Fey /AC composites using the sol–gel method for Cd(II) adsorption from wastewater. The results indicated that CoFe2O4 and Cox Fey nanoparticles existed in the pores of AC. The magnetic properties of CoFe2O4/Cox Fey /AC indicated it could be separated and retrieved easily using an external magnet after Cd(II) adsorption. The effects of solution pH, temperature and initial Cd(II) concentration on the Cd(II) adsorption of AC and CoFe2O4/Cox Fey /AC were investigated. The standard free energy, enthalpy change and entropy change were evaluated. The kinetic parameters of Langmuir and Freundlich isothermal equation were analyzed, and the Freundlich kinetic model was feasible for describing the Cd(II) adsorption process of CoFe2O4/Cox Fey /AC composites. 相似文献