Interaction Energy Function Research Articles

Calculating structure factors of protein solutions by atomistic modeling of protein-protein interactions

We present a method, FMAPS(q), for calculating the structure factor, S(q), of a protein solution, by extending our fast Fourier transform-based modeling of atomistic protein-protein interactions (FMAP) approach. The interaction energy consists of steric, nonpolar attractive, and electrostatic terms that are additive among all pairs of atoms between two protein molecules. In the present version, we invoke the free-rotation approximation, such that the structure factor is given by the Fourier transform of the protein center-center distribution function gC(R). At low protein concentrations, gC(R) can be approximated as e−βW(R), where W(R) is the potential of mean force along the center-center distance R. We calculate W(R) using FMAPB2, a member of the FMAP class of methods that is specialized for the second virial coefficient [Qin and Zhou, J Phys Chem B 123 (2019) 8203–8215]. For higher protein concentrations, we obtain S(q) by a modified random-phase approximation, which is a perturbation around the steric-only energy function. Without adjusting any parameters, the calculated structure factors for lysozyme and bovine serum albumin at various ionic strengths, temperatures, and protein concentrations are all in reasonable agreement with those measured by small-angle X-ray or neutron scattering. This initial success motivates further developments, including removing approximations and parameterizing the interaction energy function.

Droplet coalescence in coupled shear and electric fields: A molecular dynamics study

Water droplet coalescence in coupled flow and electric fields is a phenomenon extensively observed in petrochemical, microfluidic, and chemical synthesis processes; however, the existing research in this domain lacks the necessary depth. This paper employs a molecular dynamics approach to elucidate the microscopic mechanisms governing droplet aggregation in water-in-oil emulsions. The investigation spans various shear rates and droplet angles, considering droplet morphology and molecular interactions. The study reveals an interrelation between shear rate and droplet angle effects on droplet coalescence, both seeking to understand the impact of the flow field's shear effect on the electrocoalescence of water droplets. Increasing the shear rate proves advantageous to droplet aggregation up to a certain threshold; however, complete coalescence is hindered beyond the critical shear rate, γ = 7.5 × 109 s−1. Augmenting the droplet angle amplifies the shear force exerted by the flow field on the droplets, while diminishing the radial electric field force. Consequently, an optimal droplet angle of θ = 25° facilitates comprehensive droplet merging. The analysis of the coalescence process, interaction energy, charge density and radial distribution function shows that the approximate process of droplet motion is as follows: the shear effect drives the droplets to approach, and then the directional migration of charge and electrostatic attraction between water molecules drive the coalescence. The existence of a moderate shear effect enables complete droplet coalescence. This study offers theoretical guidance for the exploration of dynamic electrocoalescence technology.

Experimental studies and molecular dynamics simulation of the compatibility between thermoplastic polyurethane elastomer (TPU) and asphalt

Compatibility between polymer and asphalt is an important issue to be considered when the polymer is added to base asphalt as a modifier. It determines the stability of the modified asphalt system. The purpose of this paper is to investigate the effect of shearing temperature and the content of thermoplastic polyurethane elastomer (TPU) on the compatibility between TPU and asphalt by means of experiments and molecular dynamics simulations. Firstly, the molecular models of base asphalt, TPU chain and TPU/asphalt blends were constructed by using Materials Studio 8.0. Based on the rational construction of the model, the effect of shearing temperature on the storage stability of TPU modified asphalt was evaluated by the calculation of solubility parameter (δ) and mean square displacement (MSD). In addition, the effect of different TPU admixtures on the compatibility of TPU with asphalt was characterized by interaction energy and radial distribution function (RDF). The results of molecular dynamics calculation were compared with the results of fluorescence microscopy test (FM) and segregation test. It showed that the minimum difference in solubility parameters between TPU and asphalt occurs when the shearing temperature was 170 °C, at which the diffusion movement of TPU in asphalt was the most active. The interaction energy between TPU and asphalt reached the peak when the content of TPU in asphalt was 17 wt%. Furthermore, the RDF results also indicated that the optimum dispersion effect of TPU in asphalt is achieved at this TPU content. The molecular dynamics simulation results are in agreement with the experimental results.

Molecular dynamics simulation of the interaction between monofluoronitrobenzene and Ti electrode

In the process of degradation of aqueous fluoro-nitrobenzene (FNB) solution by titanium (Ti) electrode, the interaction between aqueous FNB solution and Ti electrode has an important impact on the performance and catalytic performance of electrode materials. The interaction involves complex physical, chemical and physical chemical processes, however, the mechanism of action is still unclear. In this study, Materials Studio software was used to design and construct molecular models of the interactions between aqueous FNB (p-, m-, o-FNB) solutions and Ti electrode, and molecular dynamics (MD) simulation was carried out in the absence of applied electric field and external electric field of 0.02 V/Å, respectively. Density functional theory (DFT) method was used to calculate the frontier molecular orbitals of three FNB molecules. Based on the calculation and analysis of the interaction energy (ΔE), diffusion coefficient (D) and radial distribution function (RDF), the interaction mechanism was discussed. It provides a theoretical basis for further research and development of Ti electrode degradation of fluorine compounds.The results showed that the order of ΔE between the three different aqueous FNB solutions and Ti surface is m-FNB > p-FNB > o-FNB when there is no external electric field. Under electric field of 0.02 V/Å, the order is p-FNB > m-FNB > o-FNB. The substitution position of F has an important effect on the HOMO of the nitro group and the LUMO of C–H in the three FNB molecules, and also affects the chemical reaction activity. In the model system, the diffusivity of different FNB solutions with electric field is less than that without electric field. The presence of an external electric field makes the diffusion of water and FNB molecules more orderly. The analysis results of RDF show that the bonding interactions between different FNB molecules and Ti surface is not much different before 3.5 Å, and all of them are weak. At about 8 Å, FNB molecule forms a non-bond with Ti electrode. ΔE, D and RDF of the model system can be changed by applying a certain external electric field, and the results are in better agreement with the experimental results.

Insight of chitooligosaccharides diffusion within polymeric membranes using molecular dynamic simulation

The membrane separation technology with the advantage of cost-benefit, energy-efficient and ease to scale up, is promising to realize the industrialized separation of chitooligosaccharides (COS) to meet the industrial demands. While COS with different degree of polymerization (DP) have similar molecular size and physicochemical properties which hinders the precise separation of COS by the commercial membranes. Herein, molecular dynamics simulations were performed to explore the diffusion behavior of COS within PEEK, PES, PSF, PVDF and PPTA membranes, to provide a theoretical basis for the screening and development of novel polymeric membrane materials for precise separation of COS. The interaction among the COS, water, and the polymer chains were investigated by calculating diffusion coefficient, interaction energy, hydrogen bonding and radial distribution function. And the diffusion process of the COS within the five polymeric membranes was investigated. Results showed that the diffusion behavior of the COS within the polymeric membranes depended on the interactions among the polymer chain, COS and water, which determined by the DP of COS and the structural properties of the polymer chain. Compared with other four kinds of materials, the interaction between PPTA chain and COS molecules repressed the decline trend of the difference between the diffusion coefficients of COS with adjacent DP as the DP of COS increased, making PPTA the most beneficial to the precise separation of the COS with different DP.

Investigation on the effect of functional groups on the wettability of coal dust: Experiments and theoretical validation

The interaction between the functional groups of pulverized coal and water molecules is essential to study the wettability of pulverized coal surfaces. Coal dust samples with the same degree of deterioration were modified in this study using appropriate concentrations of nitric acid and hydrogen peroxide. Based on macroscopic experiments such as Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the functional group content and surface wettability changes of coal dust before and after modification were investigated, respectively. Experiments demonstrated that the increase in the percentage of oxygen-containing functional groups (OFGs) before and after the modification of coal samples improved the hydrophilicity of the coal surface, which was mainly dominated by the effect of O = C-O. Eight simulation systems were also constructed by grafting different functional groups with flaky graphene as the substrate in combination with molecular dynamics (MD) theory. The results of simulated contact angle, interaction energy, and radial distribution function were used to analyze the influence law of these groups on the wettability of pulverized coal in detail. Simulations indicate that the diffusion of water molecules on the coal surface is related to the number of hydrogen bonds formed between water and coal. In the simulated system of polar groups, the hydrophilicity of the interface is enhanced due to the strong hydrogen bonding between water molecules and functional groups. However, for the analysis of non-polar groups, the hydrophobic nature is improved due to the increase of carbon chains. The results of the experiments and the simulations correspond to each other, revealing the reasonableness of the simulations. It was finally confirmed that the wetting ability of water molecules for the eight functional groups was in the order of: –COOH > –OH > –CHO > –NH2 > –COC > –CH3 > -C2H5 > -C3H7.

Effect of TiO2 nanoparticles on the mass transfer process of absorption of toluene: Experimental investigation and molecular dynamics simulation

Toluene is a typical representative of aromatic volatile organic compounds, and its elimination makes an important contribution to combating air pollution. In this work, the effect of TiO2 nanoparticles on the mass transfer process during the removal of toluene by deep eutectic solvent (tetraethylammonium chloride and oleic acid) was investigated experimentally and theoretically. First, the removal effect of different nanofluids was evaluated by dynamic bubble absorption experiments. The concentration and particle size of TiO2 nanoparticles have a significant effect on the toluene removal performance of nanofluids. Toluene removal performance was improved with the increase of TiO2 concentration until the concentration increased to 0.1 wt %. However, However, when the concentration of TiO2 nanoparticles increases further to 0.5 wt %, the toluene removal performance is weakened. It was also found that the mass transfer effect decreases as the size of the nanoparticles increases. In addition, the microscopic mechanism of mass transfer of toluene before and after the addition of TiO2 nanoparticles is investigated by molecular dynamics simulations. The interaction energy, radial and spatial distribution functions, and self-diffusion coefficient were calculated to provide molecular insights into the mass transfer mechanism. The results show that TiO2 nanoparticles improve the mass transfer performance of toluene without changing the mechanism of interaction between toluene and deep eutectic solvent. TiO2 nanoparticles increase the area of gas-liquid mass transfer or the diffusion rate of gas in the liquid phase to improve the mass transfer process.

Mechanistic insight into separation of benzene and cyclohexane by extractive distillation using deep eutectic solvent as entrainer

In this work, a technical scheme for separation of benzene and cyclohexane by extractive distillation using deep eutectic solvent (DESs) as entrainer was proposed. Acetic acid (AA) was selected as hydrogen bond donor (HBD), tetraethylammonium bromide (TEAB) and tetraethylammonium chloride (TEAC) were selected as hydrogen bond acceptors (HBA), and two kinds of DESs were successfully prepared (i.e., DES1 is TEAC : AA = 1:3, DES2 is TEAB : AA = 1:3). Vapor liquid equilibrium experiments show that the relative volatility of benzene cyclohexane system can be significantly improved by using DESs as an entrainer, so that the separation of the target system can be achieved by extractive distillation. Further, quantitative calculations and molecular dynamics simulations were performed to explore the separation mechanism at the molecular level. The interaction sites between molecules were revealed by ESP analysis, and the interaction types between molecules were further elaborated by IGMH analysis. The results show that the Br atom of TEAB and the Cl atom of TEAC have hydrogen bonding with benzene, while there is π - π interaction between AA and benzene. The intermolecular interaction energy and spatial distribution function (SDF) further proved that the interaction between DES and benzene was stronger than that with cyclohexane. In conclusion, DES as entrainer for azeotrope separation has broad industrial application prospects.

DNA damage by radiation as a function of electron energy and interaction at the atomic level with Monte Carlo simulation

In radiotherapy, X-ray or heavy ion beams target tumors to cause damage to their cell DNA. This damage is mainly induced by secondary low energy electrons. In this paper, we report the DNA molecular breaks at the atomic level as a function of electron energy and types of electron interactions using of Monte Carlo simulation. The number of DNA single and double strand breaks are compared to those from experimental results based on electron energies. In recent years, DNA atomistic models were introduced but still the simulations consider energy deposition in volumes of DNA or water equivalent material. We simulated a model of atomistic B-DNA in vacuum, forming 1122 base pairs of 30 nm in length. Each atom has been represented by a sphere whose radius equals the radius of van der Waals. We repeatedly simulated 10 million electrons for each energy from 4 eV to 500 eV and counted each interaction type with its position x, y, z in the volume of DNA. Based on the number and types of interactions at the atomic level, the number of DNA single and double strand breaks were calculated. We found that the dissociative electron attachment has the dominant effect on DNA strand breaks at energies below 10 eV compared to excitation and ionization. In addition, it is straightforward with our simulation to discriminate the strand and base breaks as a function of radiation interaction type and energy. In conclusion, the knowledge of DNA damage at the atomic level helps design direct internal therapeutic agents of cancer treatment.

Molecular dynamics-assisted process design and multi-objective optimization for efficient production of N-butyl acetate by reactive-extractive distillation/pervaporation

At present, the market demand for methyl acetate (MEOAC) is small and there is the problem of overcapacity. As an important organic solvent, n-butyl acetate (nBuOAC) is widely used in industry. It is very important to explore the efficient transesterification synthesis and separation process of nBuOAC. In this work, the schemes of reactive-extractive distillation (RED), side-line reactive extractive distillation (SLRED) and reactive distillation-pervaporation (RDPV) were proposed for the transesterification of MEOAC and n-butanol (nBuOH) to synthesize nBuOAC and methanol (MEOH). Firstly, according to the relative volatility of MEOAC and MEOH azeotrope systems, and the interaction energy and radial distribution function (RDF) were calculated by molecular dynamics (MD) to complete the screening of extractants. Then the process design is completed based on reaction kinetics, and the established processes with optimal operating conditions were obtained by the multi-objective particle swarm optimization algorithm. Finally, the total annual cost (TAC) and gas emissions are used to assess the economic efficiency and environment performance of these processes and the optimal process was obtained. The calculation results show that among the three proposed processes, the RDPV process performs best economically and environmentally. The TAC of RDPV is 8.17% lower than that of RED and 6.46% lower than that of SLRED. Meanwhile, the TAC of SLRED is 1.83% lower than that of RED. The gas emissions of RDPV is 23.13% lower than that of RED and 23.51% lower than that of SLRED, and there is little difference between RED and SLRED process.

Molecular dynamics simulations of oil recovery from dolomite slit nanopores enhanced by CO2 and N2 injection

Shale oil reservoirs are dominated by micro-and nanopores, which greatly impede the oil recovery rates. CO2 and N2 injection have proven to be highly effective approaches to enhance oil recovery from low-permeability shale reservoirs, and also represent great potential for CO2 sequestration. Therefore, a better understanding of the mechanism of shale oil recovery enhanced by CO2 and N2 is of great importance to achieve maximum shale oil productivity. In this paper, the adsorption behavior of shale oil and the mechanism of enhancing shale oil recovery by CO2 and N2 flooding in dolomite slit pores are investigated by performing nonequilibrium molecular dynamics simulations. Considering the shale oil adsorption behavior, mass density distribution is analyzed and the results indicate that a symmetric density distribution of the oil regarding the center in the slit pore along the x-axis can be obtained. The maximum density of the adsorbed layer nearest to the slit wall is 1.310 g/cm3 for C8H18 , which is about 2.0 times of that for bulk oil density in the middle area of slit pore. The interaction energy and radial distribution functions (between oil and CO2 , and between oil and N2 ) are calculated to display the displacement behavior of CO2 and N2 flooding. It is found that CO2 and N2 play different roles: CO2 has strong solubility, diffusivity and a higher interaction energy with dolomite wall, and the oil displacement efficiency of CO2 reaches 100% after 1 ns of flooding; however, during N2 flooding, the oil displacement efficiency is 87.3% after 4 ns of flooding due to the lower interaction energy between N2 and dolomite and that between N2 and oil. Cited as: Guo, H., Wang, Z., Wang, B., Zhang, Y., Meng, H., Sui, H. Molecular dynamics simulations of oil recovery from dolomite slit nanopores enhanced by CO2 and N2 injection. Advances in Geo-Energy Research, 2022, 6(4): 306-313. https://doi.org/10.46690/ager.2022.04.05

Molecular dynamics simulation of the adsorption properties of graphene oxide/graphene composite for alkali metal ions

As one of the effective methods to remove heavy metals, graphene (G) composite adsorption technology is irreplaceable in water pollution control and water purification, but its adsorption mechanism is not clear. Materials Studio (MS) software was used to simulate the molecular dynamics of the interaction between graphene oxide/graphene (GO/G) composite and alkali metal ion (M+). Based on the calculation of the interaction energy, diffusion coefficient and radial distribution function (RDF), The adsorption law of GO/G on M+ was investigated and its mechanism was revealed. It provides a theoretical basis for the research and development of the adsorption performance of G composite electrode. The calculated results show that the interaction energy between different M+ and GO/G is negative, indicating that the interaction between them is mutual attraction. The energy of GO/G composites and the total energy of M+-GO/G increase with the increase of M+ radius. The larger the hydrated ion radius of M+ is, the larger the diffusion coefficient is. Cs+ diffusion coefficient is slightly lower than rubidium. According to RDF analysis, M+-GO and M+ − O (GO) both have bonding within 3.5 Å and non-bonding after 3.5 Å, and the non-bonding interaction of M+-GO is greater. However, the bonding interaction between M+-O(GO) is larger than the non-bonding interaction, indicating that there are bonding and non-bonding interactions in the system when GO/G composite adsorb M+. The interaction between M+ and GO surface is mainly provided by non-bonding interaction, while the interaction between M+ and O atoms of GO surface is mainly provided by bonding interaction.

A novel in situ transesterification of yellow horn seeds to biodiesel using a dual function switchable solvent

A novel and cyclic in situ transesterification of yellow horn (Xanthoceras sorbifolia Bunge.) seeds to biodiesel using the switchable solvent, N, N-dimethylcyclohexylamine (DMCHA) as both a reusable solvent and catalyst was proposed. An optimizing study for the reaction conditions has been performed through response surface methodology. The maximum yield of fatty acid methyl esters (FAMEs) achieved 96.07% under the best conditions of temperature 63.93 °C, 28.05 min, methanol amount of 10.41 mL/g (v/w of material) and DMCHA amount of 16.42 mL/g. Notably, The results of mechanism study combined with molecular dynamics and quantum chemistry theory showed that DMCHA is compatible with the triglycerides, and the effect of the hydrogen bonds, interaction energy, and radial distribution function on DMCHA performance were investigated for the first time. This new configuration of using switchable solvent for simultaneous extraction and reaction would be an appropriate, efficient and environment-friendly approach for simplify biodiesel production.

Extraction mechanism analysis and energy saving enhancement of extraction separation of methyl tert-butyl ether and methanol by ionic liquid based on molecular dynamics simulation

• The ILs extractant is screened by quantum chemistry and MD simulation. • The process flow of applying ILs in the production of MTBE was designed. • The sequential iterative optimization integrating reaction conditions is proposed. • The TAC in MTBE production was reduced by 26.77% when applying ILs. Methyl tert-butyl ether as an excellent gasoline additive has been widely used. There are a lot of mixtures of Methyl tert-butyl ether and methanol in the process of Methyl tert-butyl ether production. In this work, the interaction between different ionic liquids and methyl tert butyl ether / methanol was studied by the combination of quantum chemistry and molecular dynamics. In addition, there is little difference between the experimental data and the MD simulation results, indicating that the extraction performance can be predicted by MD simulation even without the phase equilibrium data. The interaction energy, radial and spatial distribution functions, and self-diffusion coefficients are calculated based on the molecular dynamics simulation results. It is proved that anions play a key role in the extraction process. The process of synthesis of methyl tert-butyl ether with ionic liquid extraction as separation unit was studied and the optimum process parameters were determined. Methyl tert-butyl ether with mole fraction greater than 99.9% could be obtained by ionic liquid extraction, and the use of Ionic liquids liquid-liquid extraction can save 26.77% of total annual cost than extractive distillation using conventional solvents. It plays a guiding role in the selection of green solvent ionic liquids extractant and the energy saving of liquid-liquid extraction.

Interaction mechanism between metal hydrides and energetic compounds: an extensive literature survey

The existing results show that the combustion heat, energy level and some other performance indices of system could be improved effectively, while opportune percentages of metal hydrides (MHs) are added in solid propellants or explosives. Despite huge potentials exist for the addition of MHs in energetic materials (EMs), some practical difficulties hinder the widespread application of them. For example, the compatibility between metal hydrides materials and other components in EMs is one of the key concerns. The synergy of energy release between MHs and EMs will be limited if the interaction mechanism between them are not clear. Combustion, thermal and microscopic interaction between MHs and EMs were summarized in this paper. From our point of view, laser ignition is the most effective and convenient method to study the combustion interaction between metal hydrides and energetic compounds, the research on such mechanism should start with quantum chemical computation (QCC) and molecular dynamics simulation (MDS), in which the interaction energy (binding energy, adsorption energy) and radial distribution function (RDF) are identified as key characteristic parameters to estimate the nature of the interaction.

Experimental determination of the interaction potential between a helium atom and the interior surface of a C60 fullerene molecule.

The interactions between atoms and molecules may be described by a potential energy function of the nuclear coordinates. Nonbonded interactions between neutral atoms or molecules are dominated by repulsive forces at a short range and attractive dispersion forces at a medium range. Experimental data on the detailed interaction potentials for nonbonded interatomic and intermolecular forces are scarce. Here, we use terahertz spectroscopy and inelastic neutron scattering to determine the potential energy function for the nonbonded interaction between single He atoms and encapsulating C60 fullerene cages in the helium endofullerenes 3He@C60 and 4He@C60, synthesized by molecular surgery techniques. The experimentally derived potential is compared to estimates from quantum chemistry calculations and from sums of empirical two-body potentials.

Adaptive CPG-Based Gait Planning With Learning-Based Torque Estimation and Control for Exoskeletons

In this letter, a new adaptable gait trajectory shaping method is proposed for lower-limb exoskeletons by defining central pattern generators (CPGs). These CPGs are synchronized across different joints and updated online in response to the human users' physical behavior to enhance their safety and comfort. In this CPG structure of a high-level control scheme, an overall locomotion frequency is defined for all joint motions that can be modulated as a function of the human-robot interaction (HRI) energy. The amplitude and equilibrium position of oscillation for each joint can be adjusted in real-time based on the HRI torque. Logarithmic barrier functions are also formulated for these connected CPGs to avoid exceeding safe bounds of the joints' motion. A supervised learning algorithm is employed to identify the exoskeleton-limb dynamics and estimate the active HRI torque on different joints based on an autoregressive network with exogenous inputs (NARX) model. In order to track the reference trajectories generated by CPGs, a proportional derivative (PD) controller with torque compensation is designed. In the experimental evaluation of this intelligent control strategy, an able-bodied person wearing the Indego exoskeleton could amend and personalize the gait features considerably over a short period of time by applying active torques on different joints. In these experiments, the user increased the motion amplitude of the hip and knee joints up to 14% and made more than 200% variation in the gait frequency, which implies a considerable level of flexibility in locomotion planning for further user studies.

Molecular Dynamics Study on the Leaching of Zinc-Bearing Dust Sludge by Choline Chloride-Malonic Acid

Molecular dynamics of the interaction between four metal oxides (ZnO, Fe2O3, Al2O3, and CaO) present in zinc-bearing dust sludge and choline chloride (ChCl)-malonic acid (MA)(1:2) was studied in this work using Materials Studio software. The interaction mechanism was revealed by analyzing the interaction energy and radial distribution function from the perspective of quantum mechanics, and the simulation results were verified by single factor leaching experiments. The calculation results show that the complete cleavage surface of the four metal oxides is the (001) surface, and ChCl-2MA forms a stable structure with multiple intermolecular hydrogen bonds centered on the chlorine atom. The dynamic simulation of the interaction model shows that strength of interaction between ChCl-2MA and the four metal oxides follows the order: ZnO > Fe2O3 > Al2O3 > CaO. ChCl-2MA mainly interacts with ZnO by chemical adsorption, while ChCl-2MA mainly interacts with Fe2O3, Al2O3, and CaO by physical adsorption. The radial distribution function shows that Cl in ChCl-2MA and C=O in MA form chemical bonds with Zn in ZnO, and the choline cation (Ch+) forms C-H···O with ZnO. Among these bonds, the Cl-Zn bond energy is stronger. During the interaction between ChCl-2MA and Fe2O3 and Al2O3, O-H···O and C-H···O are formed and interact with CaO by van der Waals force. Single factor leaching experiments show that, under the same leaching conditions, the leaching rate of ZnO by ChCl-2MA is greater than 90%, while the leaching rate of Fe2O3, Al2O3, and CaO is about 10%. These results indicate good selectivity of ChCl-2MA for ZnO in the zinc-bearing dust sludge. The above conclusions have important theoretical significance and provide an in-depth understanding of the leaching mechanisms of zinc-bearing dust sludge in deep eutectic solvents.

Mechanical performance analysis of polyurethane‐modified asphalt using molecular dynamics method

AbstractIn this study, the mechanical performance of polyurethane (PU)‐modified asphalt was investigated. To this end, the molecular dynamics method was adopted to study the influence of the PU modifier on the compatibility, mechanical properties, and structure of asphalt. Using the Materials Studio software, a four‐component molecular model of asphalt, a PU molecular model, and an asphalt–PU mixed system model were constructed, and the molecular density and glass transition temperature () were used to verify the performance of the aforementioned models. Molecular dynamics simulations of the three molecular models were conducted under different temperatures, and the solubility parameter (), interaction energy, mechanical properties, and radial distribution functions (RDFs) were obtained. The results showed that at 413.15 K (140°C), the difference between the solubility parameters of the asphalt and PU molecules () is the smallest, and their interaction reaches the most optimal phase state. The effects of the PU modifier on the Young's modulus, bulk modulus, and shear modulus of asphalt were studied. Finally, the RDF analysis showed that the PU modifier has a direct effect on the degree of swelling and dispersion between the aromatic–aromatic and saturate–saturate components in the asphalt, reducing the aggregation of both molecules. This verifies the PU modification effect.

Tribological Behavior of Poly(tetrafluoroethylene) and Its Composites Reinforced by Carbon Nanotubes and Graphene Sheets: Molecular Dynamics Simulation

Low‐dimensional fillers play an important role in improving the tribological properties of poly(tetrafluoroethylene) (PTFE) composites. However, the reinforcement mechanism is not fully understood, since few in situ experiments are able to capture the dynamics evolution and interfacial behavior of fillers. Herein, the tribological behavior of PTFE composites filled with graphene (Gr) sheets and carbon nanotubes (CNT) at the nanoscale is investigated. The results demonstrate that the composites filled with the CNT and Gr fillers have much better wear resistance than that of the pure PTFE, and the wear amounts are reduced by 76.2% and 85.7%, respectively. The relative bond and angle energy of PTFE indicate less deformation in the reinforced composite matrices. The calculations of interfacial interaction energy and radial distribution function reveal that the Gr fillers have better reinforcements than CNT due to stronger interactions at the Gr/PTFE interfaces.