关键词： 1B2MZ   IPDA   Epoxy groups   Curing kinetics   Mechanical properties  

摘要： The epoxy resin of diglycidyl ether of bisphenol A (DGEBA) diluted with allyl glycidyl ether (AGE) was mainly cured by 1-benzyl-2-methylimidazole (1B2MZ). Then, the effect of isophorone diamine (IPDA) on the properties of DGEBA-AGE-1B2MZ system was investigated. The differential scanning calorimetry (DSC) results revealed that when the content of 1B2MZ was small, the epoxy groups need to be completely cured by imidazole regeneration, which would be unnecessary with the introduction of IPDA thereby alleviating the burden of 1B2MZ. The variations of the activation energy with the degree of curing determined via Ozawa-Flynn-Wall were various for the studied systems. Calculations based on the Cure Index (CI) approved that the cure states of all the composite systems were affected by the heating rate. Finally, the resin of optimal formula could be cured in 20 min at 120 degrees C with the best mechanical properties and the glass transition temperature (T-g) of 100.61 degrees C.

关键词： hPTP1B(1-400)   Dimeric phenalenones   Duclauxin   Talaromyces sp.   Allosteric modulators/inhibitors   Homology modeling  

摘要： A critical biological event that contributes to the appearance and progress of cancer and diabetes is the reversible phosphorylation of proteins, a process controlled by protein tyrosine-kinases (PTKs) and protein tyrosine-phosphatases (PTPs). Within the PTPs, PTP1B has gained significant interest since it is a validated target in drug discovery. Indeed, several PTP1B inhibitors have been developed, from both, synthesis and natural products. However, none have been approved by the FDA, due to their poor selectivity and/or pharmacokinetic properties. One of the most significant challenges to the discovery of PTP1B inhibitors (in vitro or in silico) is the use of truncated structures (PTP1B(1-300)), missing valuable information about the mechanisms of inhibition, and se-lectivity of ligands. The present study describes the biochemical characterization of a full-length PTP1B (hPTP1B(1-400)), as well as the description of phenalenones 1-4 and ursolic acid (5) as allosteric modulators. Compounds 1-5 showed inhibitory potential on hPTP1B(1-400), with IC50 values ranging from 12.7 to 82.1 mu M. Kinetic studies showed that 1 and 5 behave as mixed and non-competitive inhibitors, respectively. Circular dichroism experiments confirmed that 1 and 5 induced conformational changes to hPTP1B(1-400). Further insights into the structure of hPTP1B1(-400) were obtained from a homology model, which pointed out that the C-terminus (residues 301-400) is highly disordered. Molecular docking with the homologated model suggested that com-pounds 1 and 3-5 bind to the C-terminal domain, likely inducing conformational changes on the protein. Docking positions of compounds 1, 4, and 5 were refined with molecular dynamics simulations. Importantly, these simulations confirmed the high flexibility of the C-terminus of hPTP1B(1-400), as well as the changes to its rigidity when bound to 1, 4, and 5.

关键词： Bioactive materials   Non-isothermal crystallization kinetic   Differential thermal analysis (DTA)   TiO2  

摘要： The effects of TiO2 content and thermal parameters on crystallization kinetics and mechanical properties of sodium-calcium-phosphate glass system have been revealed in this study. From the DTA results using for crystallization kinetics study, the activation energies of crystallization and Avrami parameters have been calculated. The glass transition (T-g), crystallization temperature (T-p) and activation energy (E) were found to increase with the increase in the content of TiO2. The major crystalline phases were calcium pyrophosphate and sodium dititanium triphosphate along with rutile as the minor crystalline phase presented as phase separation in the samples. Mechanical properties were obtained from the microhardness measurements for all samples. It was found that the added TiO2 content caused positive effect while heat treatment temperature caused negative effect on Young's modulus, Knoop hardness and Vickers hardness.

关键词： Optical grinding   Spindle   Thermal displacement   Spindle dynamics   FEM  

摘要： Advanced optical systems have brought forward higher requirements for aspheric processing of hard brittle materials, which put forward higher request to the dynamic performances of optical grinding spindles. Due to the integration of the spindle and the tool of optical machine systems, the dynamic behaviors of the spindle system are more complicated than that of other spindles. An integrated model dynamic model of optical grinding motorized spindles which consists of a bearing model, a thermal model and a spindle-tool dynamic model is proposed. The bearing model takes the effect of the thermal displacement into account, and the rotor dynamic model with the effects of the tool and damp is established by the finite element method (FEM). An example calculation on a grinding motorized spindle is preformed and the correlative test is carried out. In the process, the dynamic model is modified by the free excitation test. The mathematical results agree well with the experimental data, which indicates that the proposed model is able to analyse the bearing-spindle-tool assembly dynamics of optical grinding motor-ized spindles. Meanwhile, the influences of the thermo-mechanical coupled factor (TMCF) and the tool on the dynamic behaviors of the system are obtained. The conclusions are available to the dynamic analysis and design of various high speed and precision spindles.

关键词： Epoxy   Amine   Maleimide   Curing kinetics   Thermal properties  

摘要： A new epoxy curing system, combining amine and maleimide functionality into a single molecule, was introduced to broaden current state of the art as regards epoxy, amine and maleimide systems. Curing agent aminomaleimide was tested in the curing process of several aromatic and aliphatic epoxies. Prepared mixtures in different weight (molar) ratios were investigated by nonisothermal differential scanning calorimetry to study and compare curing kinetics of different epoxies. The apparent activation energy was determined by Kissinger method, while Friedman method accompanied by Malek statistical approach was used in confirming the autocatalytic nature of epoxy curing and additional maleimide polymerization at the excess amount of aminomaleimide. Thermo-mechanical properties were determined by dynamic mechanical analysis and the effect of aminomaleimide curing agent compared to curing agent containing only amino functional groups was evaluated. Aminomaleimide showed improvement in the glass transition temperatures and higher char yields due to the involvement of maleimide moiety in the curing process. In overall, aminomaleimide showed the positive onemolecule joint effect of the amino group, behaving as an accelerator, and maleimide group, a mechanical properties enhancer.

关键词： cure kinetics   epoxy resin   graphene oxide   hyper branched polyester   mechanical performance  

摘要： In this study, the hyperbranched polyester were successfully grafted onto graphene oxide (GO). The mechanical performance and curing kinetics of epoxy resin (EP), EP/ graphene oxide (EP/GO), and EP/ hyperbranched polyester grafted GO (EP/GO-B) were investigated by means of mechanical tests and differential scanning calorimetry (DSC). Results revealed that the presence of GO lowered the cure temperature and accelerated the curing of EP, and the addition of GO-B exhibited a stronger effect in accelerating the cure of EP compared with GO. Activation energies were calculated using Kissinger approach, and Ozawa approach, respectively. Results revealed lowered activation energy after the addition of GO or GO-B at low degrees of cure, indicating that GO had a large effect on the curing reaction. The presence of GO facilitated the curing reaction, especially the initial epoxy-amine reaction. Moreover, GO-B exhibited better performance. Related mechanism was proposed.

关键词： molecular dynamics   nanocomposites   rubber   swelling  

摘要： Molecular models of pure and 10% and 20% swollen nitrile rubber matrices were developed. Different amounts of carbon nanotubes (CNTs) were incorporated into the swollen nitrile rubber matrices. The effects of the swelling behaviors and introduced CNTs on the mechanical properties of the nitrile rubber matrices were investigated using molecular dynamics simulations. The simulation results show that compared to the pure nitrile-butadiene rubber (NBR) models, the elastic moduli and tensile strengths of the nitrile rubber matrices were reduced by 31.72% and 20.10% (at a swelling ratio of 10%) and 68.28% and 36.82% (at a swelling ratio of 20%), respectively. Compared to those of the swollen NBR models without CNTs, after the introduction of one CNT, the elastic modulus and tensile strength improved by 67.02% and 4.17% (at a swelling ratio of 10%) and 215.27% and 7.00% (at a swelling ratio of 20%), respectively. The mechanical properties of the nitrile rubber matrix improved when the content of CNTs increased. The radial distribution functions of the rubber materials, interfacial energies of the reinforced regions, and mean square displacements and diffusion coefficients of the solutions were analyzed. The introduced CNTs blocked the diffusion of the solute in the nitrile rubber matrix. This study elucidates the swelling behaviors of rubber materials from an atomic perspective and mechanical properties of carbon-nanotube-reinforced swollen rubber matrices.

关键词： Fe-Ti alloys   Mechanical Alloying   Heat treatment   Amorphization   Crystallization kinetics  

摘要： The crystallization behaviors of mechanically alloyed amorphous Fe-Ti alloys were studied. The a-Fe phase formed during annealing as a result of the devitrification of the amorphous phase. According to the Kissinger plot, the crystallization activation energy (E) was obtained as 171 kJ/mol, which is close to the activation energy for the diffusion of Fe in a-Ti. According to the non-isothermal Johnson-Meh l-Avrami (JMA) analysis and obtaining the volume fraction of the crystalline phase from the differential scanning calorimetry (DSC) plots, the average Avrami exponent (n) was determined as 1.61 and 5.67 for low and high heating rates, respectively. Moreover, a method for obtaining the value of E based on the non-isothermal JMA analysis was proposed. The value of E was determined as similar to 185 and 191 kJ/mol respectively for low and high heating rates, which are consistent with the value determined from the Kissinger plot for all heating rates. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

摘要： In a recent paper [J. Mater. Sci. Mater. Electron. 30(6), 15116-15129 (2019)] Akilan et al. have studied the physical properties of the thiosemicarbazide cadmium chloride monohydrate (TSCCCM) single crystals. The approach that has been used to study the optical properties of the specimens is likely to have errors. Consequently, the reported values of the reflectance, refractive index, as well as real and imaginary parts of the third-order susceptibility are most likely to be incorrect.

关键词： Hydrogel   Molecular dynamics   Xyloglucan   Self-assembly   Nanodroplets  

摘要： Indigenous polymers have functional implications in biomedicine due to the presence of an inherent favorable structural architecture that supports hydrogel formation. In this study, we present the molecular level characterization of xyloglucan hydrogels using experimental and molecular simulation methods. We studied supramolecular self-assembly of tamarind seed-derived xyloglucan induced by low molecular weight gelators to form dense networks and rationalized its capabilities as a multifunctional and multiresponsive matrix for holding hydrophobic nanometric oleic acid globules intact for extended periods, preventing coalescence triggered instability using computational methods and imaging. Computational studies using molecular dynamics simulations provided mechanistic evidences of molecular associations supported by strong hydrogen bonding interactions responsible for fundamental gel network formation. Real-time imaging studies revealed that the gel matrix immobilizes intact oleic acid globules within its framework preventing coalescence. Molecular dynamics studies further showed key interactions of xyloglucan with the surfactant polysorbate 60 involved in sustaining oleic acid globules within the gel matrix, which corroborate with FE-SEM results. This study is an interesting approach to understand how molecular level associations in xyloglucan-based hydrogels can control and preserve nanosized hydrophobic oils imparting tenability and long-term droplet stability. The study also brings new insights into the conformational flexibility of xyloglucan around molecules with favorable and unfavorable interactive chemistries. Graphical abstract .