关键词： Joint action   Group dynamics   Social coordination   Physical interaction   Perceptual coupling  

摘要： Although most research on interpersonal coordination focuses on perceptual forms of interaction, many interpersonal actions also involve interactions of mechanical nature. We examined the effect of mechanical coupling in a rowing task from a coupled oscillator perspective: 16 pairs of rowers rowed on ergometers that were physically connected through slides (mechanical coupling condition) or on separate ergometers (no mechanical coupling condition). They rowed in two patterns (in- and antiphase) and at two movement frequencies (20 and 30 strokes per minute). Seven out of sixteen pairs showed one or more coordinative breakdowns, which only occurred in the antiphase condition. The occurrence of these breakdowns was not affected by mechanical coupling, nor by movement frequency. For the other nine pairs, variability of steady state coordination was substantially lower in the mechanical coupling condition. Together, these results show that the increase in coupling strength through mechanical coupling stabilizes coordination, even more so for antiphase coordination.

关键词： Amorphization   Molecular dynamics   Nanoporous gold   Porous materials   Thermal treatment  

摘要： The amorphization causes significant changes in the mechanical behavior of a structure and the consequences of this phenomenon are yet to be investigated for nanoporous metals. In this paper, the thermally induced amorphization of a nanoporous gold structure is investigated in the aspects of morphological evolution and mechanical performance by utilizing classical molecular dynamics simulations. For this purpose, two different heat treatment profiles with varied heating/cooling rates and durations are applied to the nanoporous gold. During the heat treatment, the morphology of the nanoporous gold evolves through merging and thickening of the ligaments while local amorphous regions are formed and preserved by controlling the parameters (i.e. temperature, rate and duration). Additionally, the mechanical behavior of the thermally treated nanoporous gold is examined by applying tensile and compressive loadings to the structure. The results of the thermally treated nanoporous gold are compared with the non-treated structure to determine the alterations in mechanical behavior.

关键词： CeMg12 alloy   Activation energy   Mechanical ball-milling   Hydrogen storage dynamics  

摘要： An attempt that effectively advances the quantity of hydrogen storage for CeMg12-type alloys was adopting a method of partial substitution of Mg in alloy by Ni. It is also employing mechanical ball-milling technology to prepare the nanocrystalline and amorphous CeMg11Ni + x wt.% Ni (x = 100, 200) alloys. And these two factors, Ni content after replacement as well as ball grinding time, affecting the structures and hydrogen storage dynamics belonging experimental alloys were studied systematically. Thereinto, characterization analysis on structures was using XRD, SEM and HRTEM. Then, the WA of gaseous hydrogen storage performance was carried out through Sievert device as well as differential scanning calorimeter (DSC) that connected with H-2 detector. Besides, Arrhenius and Kissinger equations were served as a convenient method for calculating the hydrogen desorption activation energy of alloys. Finally, it can adopt the automatic galvanostatic system to measure the electrochemical hydrogen storage performance. It is shown that, for experimental alloys, the more Ni content shows beneficial on the formation of glass, meanwhile, it also strikingly ameliorates both gaseous and electrochemical hydrogen storage dynamics properties. In addition, milling time varying brings a very large impact upon hydrogen storage properties of alloys. When the ball-grinding time is constantly changing, the gaseous hydrogen absorption capacity, gaseous hydriding rate as well as high-rate discharge ability (HRD) of alloys are able to appear the maximum values respectively. However, following the prolongation of milling time, both electrochemical discharge capacity and gaseous dehydrogenating rate raise all the time. The increase in Ni content and the prolongation of milling time can both enhance the gaseous hydrogen storage dynamics of alloys, inferring that their essence all can be attributed to the reduction of the activation energy of hydrogen desorption.

关键词： Chemical structure   Clay   Layered materials   Layers   Polymers  

摘要： In this work, we studied the structural, dynamical, and mechanical properties of the interfacial region I of a ternary montmorillonite-MT2EtOH-polyamide-6 nanocomposite using molecular dynamics modeling. Through analysis of structural parameters, including the density, bond orientation, and vector to the second-neighbor orientation, we demonstrated that, in this nanocomposite, the polymer has a laminate structure and estimated the Young modulus of its different regions. The region closest to the clay surface was the hardest with an elastic modulus of more than twice that of the pure polyamide;the other regions did not exhibit as high an elastic modulus. Closest to the clay surface, the polymer chains were aligned in the direction parallel to the platelet, which appears to explain the hardening of this region. In addition, the atomic mobility was shown to differ significantly for atoms located in the interfacial space and far away from filler particles. Therefore, we can conclude that atoms near the interface are strongly constrained, whereas those far from the interface exhibit the same mobility as that of the pure polymer. All of these analyses enabled us to estimate the thickness of the interfacial region, which did not exceed 15 angstrom.

关键词： DMA   TGA   kinetic analysis   Coats-Redfern model   EVA   conductive PPy   polymer nanocomposite  

摘要： Pure ethylene-co-vinyl acetate (EVA) and its conductive blend-nanocomposite with polypyrrole (PPy)/carbon black (CB) were prepared using a melt mixing process. Dynamic mechanical analysis and non-isothermal thermal gravimetrical analysis were performed on the samples. The storage modulus, loss modulus, and damping factor of the EVA/PPy/CB nanocomposites were significantly affected by the incorporation of PPy/CB. Two thermal decomposition stages were detected for pure and blended nanocomposite samples. Peak analysis was used to deconvolve the first complex decomposition stage. The Coats-Redfern method was used to determine the kinetic parameters. Improving the thermal and mechanical properties of the EVA co-polymer will enable the three-phase blend/nanocomposites to be used in several industrial applications.

关键词： Composites   Silica   Molecular dynamics   Nanocomposites   Polyimides  

摘要： A continuing challenge in polymer nanocomposites (PNCs) is to control nanoparticle (NP) dispersion and understand its role in property enhancements. Previous studies have been focused on the flexible polymer chain systems. In this study, we report the structure, glass transition behavior, segmental dynamics, and mechanical properties of polyimide (PI) nanocomposites that consisted of either bare or PI-grafted silica NPs to discriminate the role of grafted rigid chains in polymer-NP interactions and dynamic response of such hybrids. Silica NPs are well dispersed in the poly(amic acid) (the precursor of PI) nanocomposites. After thermal imidization, the aggregate structure and self-assembled small clusters of NPs are observed in ungrafted and grafted silica NP-filled PI composites, respectively. The glass transition temperature (T-g) shifts to high temperature by the addition of silica NPs resulting from strong polymer-NP interactions and steric hindrance, and T-g deviation is more visible with increasing the molecular weight of grafted PI chains. The alpha-relaxation dynamics are suppressed in PI nanocomposites, but there is no interfacial layer relaxation detected because of the rigid chain characteristic of PI. The accelerated Maxwell-Wagner-Sillars polarization process is noted in the presence of PI-grafted silica NPs with high molecular weight. PI-grafted silica NPs are effective in improving polymer-NP interfacial adhesion, resulting in superior mechanical properties to those of the bare silica NP-filled composites. Moreover, high molecular weight grafted PI chains are beneficial in the mechanical enhancement of the resulting PI nanocomposites. These findings provide new insight into the fundamental understanding of chain packing and relaxation dynamics of PNCs with rigid polymer chains and therefore provide guidance in designing such materials with desired macroscopic properties.

关键词： Density functional theory   Homogeneous catalysis   Ionic liquids   Esterification mechanism   Reaction kinetics  

摘要： The thermodynamic and kinetic aspects of the mechanism of butyl acetate synthesis catalyzed by the diprotic ionic liquid pyridinium hydrogen sulfate ([H-Pyr](+)[HSO4](-)) were investigated using density functional theory (DFT) at B3LYP/6-311 + G(d,p) level of calculation. Electronic structure and geometry for individual molecules (substrate, catalyst) were clarified using molecular electrostatic potential surface, natural bond orbital analysis and atoms in molecules theory. The DFT results elucidated the catalytic cycle, which involved the formation of a transition state via substrate-BAIL interaction. Hydrogen bond interactions were found to exist throughout the process of the catalytic cycle, which are of special importance for stabilizing the transition state. Thus, a mechanism involving cooperative hydrogen bonding for BAIL catalyzed butyl acetate synthesis was established. Based on the above mechanism, the calculated thermodynamic parameters were validated by the subsequent kinetic study. Such results may provide fundamental insights into the design of ionic liquid-based homogeneous catalysts for esters production. (C) 2019 Elsevier B.V. All rights reserved.

关键词： Chromatography   Deformation   Phase transitions   Order   Polymers  

摘要： Cross-linked liquid crystalline polymers (CLCPs) incorporated with photochromic azobenzene moieties can exhibit large and reversible deformations under the exposure of actinic lights. To practically utilize CLCPs in applications such as flexible photoresponsive actuators and soft robots, the user-defined diverse deformation modes have been demonstrated by controlling the liquid crystalline phases and polymer architectures. However, conventional all-atom molecular dynamics (AA MD) simulation is unsuitable for modeling complicated phases and conducting a parametric study of the photomechanical effect in terms of the polymer morphology due to its excessive computational cost. Therefore, a multiscale analysis framework based on coarse-grained molecular dynamics (CG MD) simulations is developed in this study. The mesoscale CLCP network model is constructed to satisfy the structural and thermodynamic properties of the full-atomistic reference. Also, the photoisomerization process is operated by integrating multiscale phenomena as follows. The AA MD reference describes the quantum events by implementing reactive rotational potential for trans-to-cis conversion, and corresponding CG potential sets are derived based on the associated structural changes. Because the mesoscale photoswitching potential is transferable to a wide range of cis-concentrations, the light-induced sequential-smectic-nematic-isotropic phase transition is realized. The results show that corruptions of the smectic layer and nematic orientational order reversely influence the overall shape of the network, which causes different photodeformation modes under each transition. Furthermore, the light-induced disordering behaviors are combined with the mechanical deformations of the polymer according to various light and temperature conditions. We expect the presented work contributes to the precise prediction and design of the optomechanical behaviors of photoresponsive devices.