关键词： epoxidation   mechanical properties   nonisothermal crystallization kinetics   poly(butylene terephthalate) (PBT)   polypropylene (PP)  

摘要： The epoxidized ethylene propylene diene rubber (eEPDM) was successfully prepared by the epoxidation of ethylene propylene diene rubber (EPDM) using t-butyl hydroperoxide as the oxidant in association with molybdenum oxide as the catalyst and characterized by Fourier-transform infrared (FTIR) spectrometer and H-1-nuclear magnetic resonance analyses. Then the poly(butylene terephthalate) (PBT)/eEPDM/polypropylene (PP) blends with different eEPDM contents were prepared using a twin-screw extruder, and the effect of eEPDM on nonisothermal crystallization kinetics of PBT/PP blend was investigated by differential scanning calorimetry. Meanwhile, morphological features of samples were observed using scanning electron microscopy. Also, the mechanical properties of samples were evaluated. Analyses of the crystallization data by various macro-kinetic models like Jeziorny modified Avrami and Liu-Mo model demonstrated that PP as diluents accelerated the crystallization of PBT in PBT/PP. Moreover, the addition of eEPDM into PBT/PP further facilitated the crystallization of PBT in PBT/eEPDM/PP. The eEPDM was an effective crystallization promoter for PBT/PP blend. And the presence of eEPDM promoted the uniform dispersion of PP in PBT matrix. When the content of eEPDM was 5 phr, the PBT/eEPDM/PP exhibited the highest notched impact strength and Young's modulus among all the specimens.

关键词： superhard materials   elastic constants   hardness   molecular dynamics   boron-doped diamond  

摘要： In this work molecular dynamics simulations are employed to compare the mechanical properties and hardness of three polytypes of cubic BC3. Firstly, two interatomic Tersoff potentials, with different parameterizations, were identified from the literature for the boron-carbon system. Based on cohesive energies and structural properties from existing ab-initio studies, the suitability of the two potentials for predicting the properties of BC3 was analyzed. Secondly, using the better interatomic potential, more detailed molecular dynamics simulations were conducted to estimate and compare the elastic, yield, post-yield behavior and hardness of the three polytypes. The elastic constants compare well with existing abinitio values and vary by at most by 15% amongst the three polytypes. Response to indentation showed considerable qualitative differences in yield and post-yield response. One of the polytypes showed lower yield strength and seemed more ductile than the other two. The hardness also showed a complex dependence on both the material and the indentation depths. A peculiar, indenter-size dependent pile-up behavior was also seen. Specifically, for lower radii, pile-up was seen on indentation. As the radius of the indenter was increased, pile-up was seen only on retracting the indenter. The higher volume occupied by the indentation-amorphized material was found to be the reason for pile-up on retracting the indenter.

关键词： Thermo-mechanical characteristics   Modified gears   Synthetic stiffness   Elasto-hydrodynamic contacts  

摘要： The thermo-mechanical characteristics of high-speed and heavy-load modified gears in non-Newtonian transient micro thermo-elasto-hydrodynamic contacts are investigated. The synthetic stiffness model is developed from the stiffness of both the oil film and gear pair. Scuffing prediction and mesh efficiency are determined by the total contact temperature and frictional loss ratio respectively. By utilizing the verified numerical procedure, effects of geometric parameters on aforementioned thereto-mechanical characteristics are discussed. The results show that crown modification and the increase of tooth number, module, and pressure angle contribute to vibration and impact reduction of gear drive. Larger tooth number and module are beneficial to scuffing resistance and efficiency improvement. It indicates that gear system can achieve high-performance transmission by rationally matching geometric parameters.

关键词： Molecular dynamics   Simulation   SiO2   Glass   Deformation   Voids  

摘要： Molecular dynamics simulations of silica glass have been carried out to investigate the mechanical behavior upon uniaxial tension. Fractions of SiOx (x = 4, 5 and 6) units and OSiy (y = 2, 3 and 4) linkages change with the density. The densified samples of 3.59 and 4.29 g cm(-3) exhibit ductile behavior, at which transition of SiOx units occurs from higher- to lower-fold Si coordination and the Si-O bond lengths are stretched upon deformation. Geometries of SiOx units almost do not distort with increasing strain. The big voids are formed during tension process and the biggest voids belong to O-voids. Clusters of crystalline O atoms in the samples of 4.29 g cm(-3) are maintained and formed upon uniaxial tension, suggesting inhomogeneous elastic-plastic deformation. The sample of 2.35 g cm(-3), consisting of principal SiO4 units, exhibits brittle behavior, at which fraction of SiO4 units is almost maintained and the Si-O bond lengths are stretched with the strain. Si-4-voids and O-voids are mainly big voids (radii > 2.0 angstrom) but O-voids play pivotal roles in the evolution and coalescence of voids causing the crack propagation. The network structure of SiOx units rearranges close to normal state during the fractured free surfaces in the sample.

关键词： glass article   firing   regime   running stresses   residual stresses   mathematical model   dynamics   minorant   majorant   relaxation   container glass   digital modeling  

摘要： Mathematical models of the dynamics of mechanical stress fields in glass articles with complex configuration of the cylindrical-conical and prismatic-cylindrical type were developed. Finite difference equations making possible computer modeling of the process of change of the stress state in a glass article during firing are derived, using the obtained models of the dynamics of temperature fields, on the basis of a relaxation theory of vitrification. The results of a computer experiment on models of the dynamics of the mechanical stress field in glass articles are presented.

关键词： Carbon nanotubes  

摘要： Molecular dynamics (MDs) simulations are carried out to study the mechanical properties of low- and high-density polyethylene (LDPE and HDPE) and their composites filled with carbon nanotubes (CNTs). The influences of the number of polymer chains, CNT type and concentration, and strain rate on the predicted mechanical properties are studied. Two different temperatures of 100 and 300 K are used to represent the glassy and rubbery states of the polymers, respectively. Results indicate that the models typically show four stages of deformation before failure: linear elastic and yield followed by strain softening and strain hardening. Thepristine models simulated at a given temperature exhibit a similar behavior regardless of their density, especially during the linear elastic stage. The HDPE models exhibit fairly similar behaviors in their strain-hardening response regardless of the number of chains, while this factor considerably influences the strain-hardening response of the LDPE models. Strain rate is shown to have a strong influence on different mechanical characteristics of all of polymer models examined (i.e., elastic modulus, yield stress, post-yield strain softening, and strain hardening behavior). In contrast, LDPE and HDPE composites exhibit essentially the same behavior and similar failure characteristics under a given temperature regardless of the strain rate applied. The tensile strength of CNT-filled LDPE and HDPE increases linearly with CNT concentration within the range of concentrations studied (0.79-2.63 wt%) and is inversely proportional to the CNT chirality. The results are thoroughly discussed and the factors contributing to their departure from reference laboratory data are outlined. (C) 2018 Society of Plastics Engineers

关键词： Benzene  

摘要： Natural molecular machines perform important tasks in organisms under a reasonable energy supply strategy: a series of step-by-step biochemical reactions after the intake of a fuel such as glucose. As analogues of biomolecular machines, most artificial molecular machines and shuttles are still powered by two opposite stimuli, such as acid and base or oxidation and reduction. This inconvenient stimulus method for artificial molecular machines and shuttles creates great obstacles for realizing more functions of artificial molecular machines and shuttles owing to low energy utilization efficiency and troublesome operation. In this work, we report a new step-by-step reaction system combining two known reactions: (1) the formation of [bis(trifluoroacetoxy)iodo]benzene from the reaction of iodosylbenzene and trifluoroacetic acid;and (2) the catalytic oxidation of alcohols by [bis(trifluoroacetoxy) iodo] benzene in the presence of TEMPO. Owing to the acid absorption features of the first reaction and the acid releasing characteristics of the second reaction, the new step-by-step reaction obtains a pH oscillation feature. Taking advantage of the pH oscillation feature, the new reaction cycle triggered by iodosylbenzene was coupled with an acid-base switchable helicarene-based molecular shuttle. Benefitting from the reaction rate difference of the two known reactions (the reaction rate of the first reaction is faster than that of the second reaction), the movement of the helicarene on the axle could be controlled automatically by the reaction system through adding iodosylbenzene to a solution of alcohol, TEMPO and protonated rotaxane, and the manual addition of another opposite stimulus could be avoided.

关键词： Liposomes  

摘要： In specific conditions, co-incubation of polymer nanoparticles and phospholipid vesicles leads to the formation of lipid bilayer coated nanoparticles usable as biocompatible drug delivery systems for co-encapsulation of two drugs. In this work, we focused on the preparation and characterization of liponanoparticles obtained by co-incubation of poly(d,l, lactic acid) (PDLLA) and neutral (POPC) or cationic (POPC/DOTAP) liposomes. The comparison of the behavior of the various studied vesicles co-incubated with nanoparticles highlighted the role of electrostatic interactions. Although the bilayer adsorbed at the surface of polymer nanoparticles was not visible by cryoTEM, zeta-potential measurements and fluorescence confocal microscopy showed evidence of the formation of hybrid nanoparticles in the presence of cationic vesicles. Using silicon dioxide and Langmuir-Schaefer transferred polymer layer-coated surfaces, a thorough analysis of the process of formation of a phospholipid bilayer at the surface of a PDLLA film was performed by combining QCM-D and AFM experiments, taking into account the nature and properties of the support, and the concentration and charge of the lipids. Contrarily to POPC vesicles, cationic ones formed a bilayer on the PDLLA layer in water, but their fast rupture on the soft material did not allow complete nanoparticle surface coverage. This work demonstrates the role of charges and polymer mechanical stiffness in the mechanism and kinetics of formation of PDLLA liponanoparticles in pure water.

关键词： exchange bias   ferromagnetic resonance   spin dynamics   flexible spintronics   strain  

摘要： As a key effect in spintronic devices, exchange bias has attracted tremendous attention. Various approaches have been attempted for optimizing this effect, among which the application of strain in flexible exchange-biased systems is promising, but little significant improvement has been reported. Here, we demonstrate encouraging progress in this field. With a pure mechanical compressive strain of -6.26%o applied to the flexible polyimide (PI) substrate, distinct enhancement of similar to 900% in the bias field (from 20 to 200 Oe) is achieved for the exchange-biased (FeCo/IrMn)(3)/Ta multilayers grown on top of a flexible PI substrate, accompanied by a notable decrease in the Gilbert damping parameter from 0.02 to 0.008, signifying an improved exchange bias effect as well as a potentially reduced switching current density. The underlying mechanism is investigated by a systematic ferromagnetic resonance study, suggesting that the angle between the unidirectional and uniaxial magnetic easy axes plays an important role, which may be controlled by adjusting the layer number. This work offers an efficient strategy for tuning the exchange bias effect via applying appropriate mechanical strain on a multiperiodic exchange bias multilayered system, opening up an avenue for tailoring the magnetic properties of flexible spintronic devices.

关键词： Crystals   Plastics   Crystal structure   Deformation   Alkyls  

摘要： Distinct macroscopic mechanical responses of the three crystals of naphthalene diimide derivatives, 1Me, 1Et, and 1nPr, studied here are very intriguing because their molecular structures are very similar, with the difference only in the alkyl chain length. Among the three crystals examined, 1Me shows highly plastic bending nature, 1Et shows elastic flexibility, and 1nPr is brittle. A detailed investigation by nanoindentation and molecular dynamics (MD) simulations allowed us to correlate their distinct mechanical responses with the way the weak interactions pack in crystal structures. The elastic modulus (E) of 1Me is nearly an order of magnitude lower than that of 1Et, whereas hardness (H) is less than half. The low values of E and H of 1Me indicate that these crystals are highly compliant and offer a low resistance to plastic flow. As the knowledge of hardness and elastic modulus of molecular crystals alone is insufficient to capture their macroscopic mechanical deformation nature, that is, elastic, brittle, or plastic, we have employed three-point bending tests using the nanoindentation technique. This allowed a quantitative evaluation of flexibility of the three mechanically distinct semiconducting molecular crystals, which is important for designing larger-scale applications;these were complemented with detailed MD simulations. The elastic 1Et crystals showed remarkable flexibility even after 1000 cycles. The results emphasize that the alkyl side chains in functional organic crystals may be exploited for tuning their self-assembly as well as their mechanical properties. Hence, the study has broad implications, for example, in crystal engineering of various flexible, ordered molecular materials.