关键词： Reaction kinetics  

摘要： The reaction kinetics of 1,3-butadiene with Criegee Intermediate (CH2OO, CI) was investigated over T = 200-400 K using the CCSD(T)/aug-cc-pVTZ//B3LYP/6311G (d, p) level of theory. Reaction pathways involving distinguished conformational addition variants of both the reactants proceeds via a 1,3-dipolar cycloaddition to form the SOZ. The effect of temperature suggested that, the contribution by the inner-facing TSs decreases, while outer-facing reaction channels become more significant, as the temperature increases. At low pressures, the effect of pressure was more prominent at temperatures close to 200 K. However, at 760 Torr, the effect was insignificant over the complete temperature range.

关键词： molecular dynamics simulation   pmma/sio(2)   multilayer nanocomposite film   mechanical behavior  

摘要： Poly(methyl methacrylate) (PMMA)/nano-silica (nano-SiO2) nanocom-posite film with 256 layers containing different amounts of nano-SiO2 was manufactured by a new type of micro-nano multilayer co-extrusion technology. The structure, morphology and mechanical properties of PMMA/nano-SiO2 nanocomposite films were investigated through Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and tensile test Besides, molecular dynamics simulation <^>J<^> was adopted to study the dispersion and content effect on mechanical properties of PMMA/nano-SiO2 nanocomposite film. It is demonstrated that the tensile strength and the elongation at break of the composites improved with increasing nano-SiO2 content from 0 to 5 wt%, which was in good agreement with the Molecular Dynamics simulation. And the nanofiller dispersion in the multilayer nanocomposite film was better than that in the single-layer film with equivalent thickness under the effect of torsion lamination. Overall, the best performance was found for the nanocomposites of PMMA with nano-SiO2 content of 3.5 wt%.

关键词： Differential scanning calorimetry  

摘要： This study investigated the effect of polyethylene glycol (PEG) and nanosilica (NS) on the physical-mechanical properties and cure kinetics of diglycidyl ether of bisphenol-A-based epoxy (DGEBA-based EP) resin. For this purpose, tensile and viscometry tests, dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC) were carried out under dynamic conditions. The results showed that adding NS and PEG enhances the maximum cure temperature as well as the heat of cure reaction (Delta H) in EP-NS, while it decreases in EP-PEG and EP-PEG-NS. The cure kinetic parameters of EP-PEG-NS were calculated by Kissinger, Ozawa, and KSA methods and compared with each other. The Ea calculated from the Kissinger method (96.82 kJ/mol) was found to be lower than that of the Ozawa method (98.69 kJ/mol). Also, according to the KAS method, the apparent Ea was approximately constant within the 10-90% conversion range. Tensile strength and modulus increased by adding NS, while tensile strength diminished slightly by adding PEG to EP-NS. The glass transition temperature (Tg) was calculated using DMTA which was increased and decreased by the addition of NS and PEG, respectively. The results of the viscometry test showed that the viscosity increased with the presence of both PEG and NS and it prevented the deposition of solid particles.

关键词： Prednisone acetate   oxidation   degradation kinetics   ozonation products   reaction pathways  

摘要： Prednisone acetate (PNSA) is one of the regular glucocorticoid medicines that have been detected in surface water. In this work, the removal of PNSA by ozone was systematically studied under various conditions, and degradation intermediates and reaction pathways were proposed. The results showed that aqueous ozonation was able to remove PNSA effectively, and low pH favored this reaction. The addition of tertiary butanol did not inhibit the oxidation of PNSA by ozone, suggesting that the degradation was caused mainly by the direct oxidation effect of ozone molecules. Moreover, the presence of carboxylated or hydroxylated multiwalled carbon nanotubes can enhance the removal efficiency of PNSA by ozone. Under neutral and acidic conditions, the degradation of PNSA followed pseudo-first-order reaction. Seven intermediates were detected via liquid chromatography-mass spectrometry, and the degradation pathways were then proposed by considering the relative charge density of the frontier orbitals calculated with the Gaussian program. The electrophilic reaction and the Criegee mechanism were the primary reaction mechanisms in the degradation of PNSA by ozone. Formic acid, acetic acid, and oxalic acid were detected as the final reaction products via ion chromatography. Additionally, the aquatic toxicity of the ozonation products was predicted using ECOSAR method. The biodegradation potentials of the pollutant and the ozonation products were estimated using BIOWINTM, suggesting that O-3 treatment could significantly enhance the biodegradable potentials of PNSA and its transformation intermediates in the biological post-treatment process. This work can provide useful information for the treatment of PNSA-containing wastewaters.

关键词： Renewable polymer   Poly(propylene furanoate)   Polymer nanocomposites   Crystallization   Graphene   Molecular dynamics  

摘要： Poly(propylene furanoate), PPF, is a new bio-based polyester produced from renewable resources and belongs in a class of materials expected to replace their fossil-based homologues. Envisaging its future applications, critical is the optimization of the material properties such as the mechanical performance. The latter is strongly connected with the degree of polymer crystallinity, CF, which in the case of PPF is rather slow. As in previous work in semicrystalline polymers, in order to facilitate crystallization we introduce here graphene nanoplatelets at the amounts of 0.5, 1.0 and 2.5 wt% as fillers into the PPF matrix. The study involves measurements by calorimetry (DSC), X-ray diffraction (XRD), nanoindentation testing and dielectric spectroscopy (BDS) on samples in the amorphous (melt quenched) and semicrystalline (annealed) states. DSC confirmed the aimed facilitation of crystallinity, as the crystallization time of PPF at the relatively mild temperature of 100 degrees C is significantly reduced in the nanocomposites. In next, we were able to estimate the rigid amorphous fraction, RAF, in the two polymer states, i.e. the interfacial polymer due to the fillers and around the formed crystals. The filler addition results in direct improvement of the mechanical performance of the amorphous samples (increase in the elastic modulus and hardness);whereas, upon the additional involvement of crystallization the mechanical properties are improved further. Interestingly, these improvements were found to correlate quite well with the amounts of formed RAF and CF. In addition, we proceed with the exploration of molecular dynamics (local beta and segmental alpha relaxations) of PPF in the bulk and in the presence of the nanofillers, of polymer crystals as well as of introduced water traces. The severe effects on molecular dynamics were found, as expected, to arise from crystallization rather than by the fillers themselves. Results on segmental mobility (calorimetric and die

关键词： Molecular dynamics   Lithium silicate   Glass   Mechanical   Deformation  

摘要： Molecular dynamics (MD) simulations have been carried out to study the structural and mechanical properties of densified (Li2O)(0.2)(SiO2)(0.8) glasses under uniaxial tension. Fractions of SiOx (x = 4 -6) and LiOy(y = 3 - 8) units change with the density. There is a relationship between the changes in Q(n) species and in SiOx unit with increasing density. The sample of 2.28 g cm(-3) exhibits brittle behavior, at which fraction of SiO4 units is almost maintained and the breakages of Li-O bonds cause the transformation of LiOy units from higher- to lower- fold Li coordination. Big-voids are formed during the tension process. Li-O voids play important roles in the evolution and coalescence of voids causing the crack propagation. The densified samples of 2.96 and 3.81 g cm(-3) exhibit ductile behavior, at which the transformations of SiOx and LiOy occur. Shear transformation zones (STZs) and shear bands (SBs) are formed during plastic deformation.

关键词： Molecular dynamics   Nanocomposite   Tobermorite   Graphene   Interface   Molecular friction   Mechanical properties  

摘要： The tensile and shear properties of tobermorite 14 angstrom-based structures reinforced with a single graphene sheet (GS) interfacing with either the surface water, octahedral calcium, or tetrahedral silicate layer were investigated using molecular dynamics simulations. The GS contributed to a significant increase in the XY-plane tensile (180%-360%) and shear (90%-225%) strengths, stiffness, and toughness while degrading the out-of-plane properties of the tobermorite structures. The water interface promoted molecular friction (intermolecular forces) and resulted in greater in-plane fracture tensile strength and toughness but a lower shear toughness than when the GS interfaced with the dry solid surfaces. (C) 2019 Elsevier Ltd. All rights reserved.