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Molecular dynamics simulation study on the structure and properties of polyimide/silica hybrid materials
摘要： A type of polyimide/silica (PI/SiO2) copolymer model was established through the dehydration of tetraethyl orthosilicate molecules (TEOS) and bonding to a silane coupling agent. The content of SiO2 was controlled by adjusting the number of molecules which bound to the TEOS. Finally, the silica was formed into a hybrid model (hybrid PI/SiO2) with a small molecule embedded in the PI. The model was optimized by geometric and molecular dynamics and the changes in the model structure, Young’s modulus, shear modulus, and glass-transition temperature (Tg) were analyzed. The results showed that the density and cohesive energy density of the composites could be improved by doping SiO2 in PI. Young’s modulus and shear modulus of PI/SiO2 hybrid materials were higher than undoped PI. The tensile strength reached 568.15 MPa when the doping content was 9%. Therefore, the structure design and content control of SiO2 was an effective way to improve the performance of a PI/SiO2 composite. The variation of Tg and tensile strength of PI/SiO2 hybrid composites is consistent with that of PI/SiO2 composite synthesized in real experiment, which will be a convenient method for new material design and performance prediction. ? 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 136, 47335.
关键词： molecular dynamics,shear modulus,Young’s modulus,polyimide/silica,glass-transition temperature
更新于2025-09-23 15:23:52
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Atomistic modeling of resistivity evolution of copper nanoparticle in intense pulsed light sintering process
摘要： In this work, the intense pulsed light (IPL) sintering process of copper nanoparticle ink is simulated using molecular dynamics (MD) method. First, the neck size growth between the two copper nanoparticles during the IPL sintering process is computed. The resultant electrical resistivity is then calculated by substituting the neck size into the Reimann-Weber formula. Overall, a rapid decrease of electric resistivity is observed in the beginning of the sintering, which is caused by quick neck size growth, followed by a gradually decrease of resistivity. In addition, the correlation of the simulated temperature dependent resistivity is similar to that of the experimentally measured resistivity. The MD model is an effective tool for designers to optimize the IPL sintering process.
关键词： Molecular dynamics,Nanoparticle,Electrical resistivity,Intense pulsed light,Copper
更新于2025-09-23 15:23:52
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Treatment of disorder effects in X-ray absorption spectra beyond the conventional approach
摘要： The contribution of static and thermal disorder is one of the largest challenges for the accurate determination of the atomic structure from the extended X-ray absorption fine structure (EXAFS). Although there are a number of generally accepted approaches to solve this problem, which are widely used in the EXAFS data analysis, they often provide less accurate results when applied to outer coordination shells around the absorbing atom. In this case, the advanced techniques based on the molecular dynamics and reverse Monte Carlo simulations are known to be more appropriate: their strengths and weaknesses are reviewed here.
关键词： Reverse Monte Carlo,Extended X-ray absorption fine structure (EXAFS),Molecular dynamics,Static and thermal disorder,X-ray absorption spectroscopy
更新于2025-09-23 15:23:52
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Topology and polarity of dislocation cores dictate the mechanical strength of monolayer MoS2
摘要： In contrast to homoelemental graphene showing common dislocation dipole with pentagon-heptagon (5|7) core, heteroelemental MoS2 is observed to contain diverse dislocation cores that tune the chemical and physical properties. Yet, how the inevitable dislocation cores in MoS2 affect the mechanical behaviours remains virtually unexplored. Herein, we report direct atomistic simulations of mechanical characteristics of isolated dislocation-embedded MoS2 monolayers under tensile load. All isolated dislocation cores in MoS2 monolayer rise polar stress-concentration, while those with larger Burgers vector are less energetically-favorable configurations but show local wrinkling behaviour. It is revealed that the intrinsic tensile strength of MoS2 is dictated by topology and polarity of dislocation cores. There is a strong inverse correlation between the maximum residual stresses induced by the dislocation cores and the strength of MoS2 monolayers. Mechanical failure initiates from the bond at dislocation polygon on which side there is a missing atomic chain. Armchair-oriented 4|8 dislocation exhibits sole brittle failure, however, dual brittle/ductile fractures occur in zigzag-oriented dislocations; Mo-S-Mo angle-oriented crack is brittle, while the S-Mo-S angle-oriented crack becomes ductile. Our findings shed sights on mechanical design of heteroelemental 2D materials via dislocation engineering for practical application.
关键词： Mechanical strength,Fracture characteristics,Monolayer MoS2,Molecular dynamics simulations,Dislocation cores
更新于2025-09-23 15:23:52
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Investigation of the graphene thermal motion by rainbow scattering
摘要： The thermal motion of graphene atoms was investigated using angular distributions of transmitted protons. The static proton-graphene interaction potential was constructed applying the Doyle-Turner’s expression for the proton-carbon interaction potential. The effects of atom thermal motion were incorporated by averaging the static proton-graphene interaction potential over the distribution of atom displacements. The covariance matrix of graphene displacements was modeled according to the Debye theory, and calculated using Molecular Dynamics approach. Proton trajectories were used for construction of angular yields. We have found that there are lines, called rainbows, along which the angular yield is very large. Their evolution in respect to different sample orientation was examined in detail. Further we found that atom thermal motion has negligible influence on rainbows generated by protons experiencing distant collisions with the carbon atoms forming the graphene hexagon. On the other hand, rainbows generated by protons experiencing close collisions with the carbon atoms can be modeled by ellipses whose parameters are very sensitive to the structure of the covariance matrix. Numerical procedure was developed for extraction of the covariance matrix from the corresponding rainbow patterns in the general case, when atoms perform fully anisotropic and correlated motion.
关键词： thermal motion,graphene nanoribbon,molecular dynamics,graphene,rainbow scattering
更新于2025-09-23 15:23:52
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High-Performance Chromatographic Characterization of Surface Chemical Heterogeneities of Fluorescent Organic–Inorganic Hybrid Core–Shell Silica Nanoparticles
摘要： In contrast to small-molar-mass compounds, detailed structural investigations of inorganic core–organic ligand shell hybrid nanoparticles remain challenging. The assessment of batch-reaction-induced heterogeneities of surface chemical properties and their correlation with particle size has been a particularly long-standing issue. Applying a combination of high-performance liquid chromatography (HPLC) and gel permeation chromatography (GPC) to ultra-small (<10 nm diameter) poly(ethylene glycol)-coated (PEGylated) fluorescent core–shell silica nanoparticles, we elucidate here previously unknown surface heterogeneities resulting from varying dye conjugation to nanoparticle silica cores and surfaces. Heterogeneities are predominantly governed by dye charge, as corroborated by molecular dynamics simulations. We demonstrate that this insight enables the development of synthesis protocols to achieve PEGylated and targeting ligand-functionalized PEGylated silica nanoparticles with dramatically improved surface chemical homogeneity, as evidenced by single-peak HPLC chromatograms. Because surface chemical properties are key to all nanoparticle interactions, we expect these methods and fundamental insights to become relevant to a number of systems for applications, including bioimaging and nanomedicine.
关键词： surface chemistry heterogeneity,high-performance liquid chromatography,nanoparticle characterization,nanoparticle surface functionalization,fluorescence correlation spectroscopy,molecular dynamics,nanoparticle heterogeneity
更新于2025-09-23 15:23:52
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Ultrafast dynamics of solvated electrons at anatase TiO<sub>2</sub>/H<sub>2</sub>O interface
摘要： Solvated electrons are known to be the lowest energy charge transfer pathways at oxide/aqueous interface and the understanding of the electron transfer dynamics at the interface is fundamental for photochemical and photocatalytic processes. Taking anatase TiO2/H2O interface as a prototypical system, we perform time-dependent ab initio nonadiabatic molecular dynamics (NAMD) calculations to study the charge transfer dynamics of solvated electrons. For the static electronic properties, we find that the dangling H atoms can stabilize solvated electrons. A solvated electron band can be formed with one monolayer H2O adsorption. The energies of the solvated electron band minimum decrease when H2O adsorbs dissociatively. Moreover, the surface oxygen vacancies are also helpful for stabilizing the solvated electron band. For the dynamics behaviour, we find that the ultrafast charge transfer from solvated electron band minimum to anatase TiO2(101) surface at 100 K is mainly contributed by nonadiabatic mechanism. Comparing with rutile TiO2(110) surface, the lifetime of solvated electron on anatase TiO2 (101) surface is longer, suggesting a better photocatalytic properties. Our results provide essential insights into the understanding of the charge transfer dynamics and the possible photocatalytic mechanism at oxide/aqueous interface.
关键词： nonadiabatic molecular dynamics,solvated electron,oxide/aqueous interface
更新于2025-09-23 15:23:52
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Wetting Transition from the Cassie–Baxter State to the Wenzel State on Regularly Nanostructured Surfaces Induced by an Electric Field
摘要： When droplets are placed on hydrophobic textured surfaces, different wetting state Cassie-Baxter (CB) state or Wenzel (W) state may occur depending on materials and structures of surfaces, types and sizes of droplets, thermal fluctuations, and external stimuli. The wetting transition from the CB to the W state and the opposite process have attracted a great deal of attention due to their primary importance for designing and fabricating textured surfaces. In this work, molecular dynamics (MD) simulations are employed to understand the mechanism behind the CB-to-W transition for a nanoscale water film placed on a surface decorated with a single nanogroove when an external electric field is applied. The free energy variation during the transition process is computed on the basis of the restrained MD simulations. Water intrusion into the groove is observed by simulation snapshots, which provides a direct evidence for the electric-field-induced CB-to-W transition. In the previous experiments, however, only a sharp reduction in the apparent contact angle is employed to judge whether the transition takes place. The free energy curves reveal that there are two energy barriers separating the CB and W states (?E1) as well as separating the W and CB states (?E2). Owing to the presence of ?E1, although the CB state has a higher free energy than the W state, it cannot spontaneously convert to the W state. When the external energy input exceeds ?E1, the CB-to-W transition can be triggered, otherwise the transition will stop, and the water film will return to the CB state. Moreover, it is found that the maximum of free energy always occurs after the film touches the groove bottom. Thus, the requirement of the film touching the groove bottom is responsible for the presence of the energy barrier ?E1. Finally, the dependences of the two energy barriers on the electric field strength, groove aspect ratio, and intrinsic contact angle of the groove are also discussed.
关键词： Cassie-Baxter state,wetting transition,Wenzel state,energy barrier,free energy,molecular dynamics simulations.
更新于2025-09-23 15:23:52
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Structure/Function/Dynamics of Photosystem II Plastoquinone Binding Sites
摘要： Photosystem II (PSII) continuously attracts the attention of researchers aiming to unravel the riddle of its functioning and efficiency fundamental for all life on Earth. Besides, an increasing number of biotechnological applications have been envisaged exploiting and mimicking the unique properties of this macromolecular pigment-protein complex. The PSII organization and working principles have inspired the design of electrochemical water splitting schemes and charge separating triads in energy storage systems as well as biochips and sensors for environmental, agricultural and industrial screening of toxic compounds. An intriguing opportunity is the development of sensor devices, exploiting native or manipulated PSII complexes or ad hoc synthesized polypeptides mimicking the PSII reaction centre proteins as biosensing elements. This review offers a concise overview of the recent improvements in the understanding of structure and function of PSII donor side, with focus on the interactions of the plastoquinone cofactors with the surrounding environment and operational features. Furthermore, studies focused on photosynthetic proteins structure/function/dynamics and computational analyses aimed at rational design of high-quality bio-recognition elements in biosensor devices are discussed.
关键词： plastoquinone binding site,molecular dynamics simulations,plastoquinone,Molecular docking,protein dynamics,Photosystem II
更新于2025-09-23 15:22:29
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Efficient separation of photo-generated charges in a ferroelectric molecular wire: nonadiabatic dynamics study on 3,5-dicyano-1,7-dimethylopyrrolo[3,2-f]indole trimer
摘要： In this work we propose and verify computationally a novel idea of spontaneous separation of charges photo-generated in a highly polar molecular 'wire'. The nuclear and electronic structure of the investigated system, so as the evolution of charge carriers, are characterized at the semi-empirical OM2/MRCI level of theory. Results point to the conclusion that 90% of optically prepared excitons break into charge carriers (holes and electrons) localized on the opposite monomeric units of the trimer on the time scale of 30 fs. Our findings can be helpful in design of photoactive and conducting components for molecular photovoltaic applications.
关键词： ferroelectric polymers,nonadiabatic molecular dynamics,molecular photovoltaics,photo-generated charge separation,molecular wire
更新于2025-09-23 15:22:29