Nonequilibrium Molecular Dynamics Method Research Articles

Nonequilibrium Molecular Dynamics Method to Generate Poiseuille-Like Flow between Lipid Bilayers.

There are various flows inside and outside cells in vivo. Nonequilibrium molecular dynamics (NEMD) simulation is a useful tool for understanding the effects of these flows on the dynamics of biomolecules. We propose an NEMD method to generate a Poiseuille-like flow between lipid bilayers. We extended the conventional equilibrium MD method to produce a flow by adding constant external force terms to the water molecules. Using the Lagrange multiplier method, the center of mass of the lipid bilayer is constrained so that the flow does not sweep away the lipid bilayer, but the individual lipid molecules fluctuate. The temperature of the system is controlled properly in the solution and membrane by using the Nosé-Hoover thermostat. We found that the flow velocity increases linearly as the applied external force term increases. It is possible to estimate the appropriate value of acceleration to generate a flow with an arbitrary velocity using this proportional relation once a single short MD simulation is performed. We also found that the flow between two lipid bilayers is slower than the analytical solution of the Navier-Stokes equations between rigid parallel plates due to the interactions between water molecules and the membrane. This method can be applied not only to a flow on lipid membranes but also to a flow on soft surfaces generally.

Research on the viscosity characteristics of water glycol hydraulic fluids in deep-sea environment from molecular dynamics

The utilization of water glycol as a working medium represents a significant advancement in the realm of deep-sea hydraulic transmission systems. The viscosity of water glycol is a crucial parameter for hydrodynamic lubrication, yet it is profoundly influenced by the environmental conditions of the deep sea. This study employs the TIP4P/2005 water molecule model in conjunction with the optimized potentials for liquid simulations all-atom force field, and non-equilibrium molecular dynamics method to predict the viscosity of water glycol hydraulic fluids with varying compositions under deep-sea conditions. The simulation values agree well with the experimental results. Furthermore, this study introduces a fitting equation that accounts for the effects of composition, temperature, and pressure, enabling the prediction of the viscosity of water glycol hydraulic fluids within the 0–11 000 m sea water environment.

Molecular Dynamic Simulations of the Physical Properties of Four Ionic Liquids

In this study, the molecular structure models of four ionic liquids were created, the reverse nonequilibrium molecular dynamics simulation (RNEMD) approach was used to predict their densities and viscosities, and their thermal conductivity was simulated using the non-equilibrium molecular dynamic simulation method (NEMD). The calculated results of ionic liquid densities were compared with the data in the literature; most of the variances are around 2.5%, and the maximum relative deviation was less than 6.27%; viscosity values were compared with the experimental data, with a maximum relative deviation of −8.96% and a minimum relative deviation of −2.72%. The simulated thermal conductivity has a good linear relationship with respect to temperature and pressure, which is in good agreement. This study provides a reference for molecular dynamics simulation to measure the physical properties of ionic liquids, which is important for the development of ionic liquids.

Tailoring thermal transport and confinement effect of GaN/Si3N4 nanowires utilizing core–shell architecture

The thermal transport properties of nanowires (NWs) can be significantly influenced by the implementation of a core-shell structure, which introduces interface scattering and phonon localization effects, opening avenues for novel applications. In this paper, we use the method of non-equilibrium molecular dynamics to simulate the effects of system temperature, cross-sectional width, and nanopillar interface on the thermal transport of GaN/Si3N4core-shell NWs. The thermal transport process of phonons in core-shell NWs is studied by calculating the vibrational density of states, phonon participation rate, and dispersion curve. The results show that the core-shell NWs characterized by smooth interfaces exhibit a 17.4% decrease in thermal conductivity (TC) at room temperature when contrasted with pristine GaN NWs. Furthermore, the TC of GaN/Si3N4core-shell NWs can be further reduced by adding nanopillars at the interface. Due to resonance effect, thus effectively regulating the thermal transport. The presence of nanopillars increases phonon-surface scattering intensity at low-frequency and modifies phonon dispersion to decrease the group velocity. In addition, the hybridization of phonon modes between those of the nanopillars and the Si3N4shell gives rise to numerous dispersionless resonance phonon modes that span the entire phonon spectrum. This research delves into the effects of nanopillars and interfaces on thermal transport, providing important guidance for understanding confinement effects and establishing a robust theoretical basis for the regulation of thermal transport.

Thermal conductivity calculation using homogeneous non-equilibrium molecular dynamics simulation with Allegro

In this study, we derive the heat flux formula for the Allegro model, one of machine-learning interatomic potentials using the equivariant deep neural network, to calculate lattice thermal conductivity using the homogeneous non-equilibrium molecular dynamics (HNEMD) method based on the Green-Kubo formula. Allegro can construct more advanced atomic descriptors than conventional ones, and can be applied to multicomponent and large-scale systems, providing a significant advantage in estimating the thermal conductivity of anharmonic materials, such as thermoelectric materials. In addition, the spectral heat current (SHC) method, recently developed for the HNEMD framework (HNEMD-SHC), allows the calculation of not only the total thermal conductivity but also its frequency components. The verification of the heat flux and the demonstration of HNEMD-SHC method are performed for the extremely anharmonic low-temperature phase of Ag2Se.

Geometric Variability‐Aware Thermal Characteristics Modeling of Nanoscale Silicon Gate‐All‐around Nanowire Transistor

Thermal management becomes increasingly important in silicon gate‐all‐around (GAA) field‐effect transistor (FETs) for 3 nm technology node and beyond. The channel thermal conductivity significantly differs from bulk silicon. Precise determination of thermal conductivity is crucial for device evaluation and optimization. This study investigates the thermal conductivity of silicon nanowires, examining the complex interplay between size and channel orientation. The conventional nonequilibrium molecular dynamics (NEMD) method is used with the standard Stillinger–Weber potential at the atomic scale. The results indicate that the thermal conductivity of silicon nanowires along the [100] direction increases monotonically with both length (L) and cross‐sectional side length (D). Conversely, the [110] direction exhibits nonmonotonic variation in thermal conductivity with D, due to increased acoustic–optic phonon scattering. For GAA FET devices with a silicon nanowire channel of L = 20 nm and D = 5 nm, the NEMD calculations yield thermal conductivities of 10.8 W m·K−1 for the [100] direction and 25.3 W m·K−1 for the [110] direction. Subsequently, the self‐heating effect (SHE) in silicon nanowire GAA FETs by technology computer‐aided design with the modified channel conductivity is analyzed. The results suggest that silicon nanowires with the [110] transport direction are more suitable for device design.

Differential study on the thermal–physical properties of metal and its oxide nanoparticle-formed nanofluids: Molecular dynamics simulation investigation of argon-based nanofluids

Abstract The influence of nanoparticle shape, volume fraction, and temperature on the thermal properties of nanofluids plays a pivotal role in engineering applications. However, there remains a considerable lack of systematic research comprehensively considering these factors to study the similarities and differences in the thermal properties of nanofluids composed of metals and their oxides and to conduct in-depth analyses of their internal mechanisms and characteristics. In this study, molecular dynamics simulations were conducted, employing reversing perturbation non-equilibrium molecular dynamics and non-equilibrium molecular dynamics methods. The thermal conductivity and viscosity of Al–Ar and Al2O3–Ar nanofluids were thoroughly investigated under the various influencing factors. Results reveal that under identical conditions, the thermal conductivity of Al–Ar nanofluid surpasses that of Al2O3–Ar nanofluid, exemplified by values such as 0.1832 W/m K (Al–Ar, 1.5%, cylinder, 86 K) versus 0.17745 W/m K (Al2O3–Ar, 1.5%, cylinder, 86 K). Furthermore, the viscosity of Al–Ar nanofluid is lower than that of Al2O3–Ar nanofluid, demonstrated by values such as 0.0004882 Pa S (Al–Ar nanofluid, 86 K, 2.5%, platelets) compared to 0.008975 Pa S (Al2O3–Ar nanofluid, 86 K, 2.5%, platelets). Subsequently, this study analyzed the difference in thermal conductivity between the two nanofluids from the perspective of microscale interface heat conduction by comparing the phonon density of states curves of Al, Ar, and Al2O3 in the two nanofluids for overlap. Subsequently, through radial distribution function analysis, the viscosity difference between Al–Ar and Al2O3–Ar nanofluids is explained based on nanofluid–solid interface and microstructural considerations. This research addresses the comprehensive lack of comparative studies on the thermal properties of nanofluids formed by metals and their oxides. The internal mechanisms underlying the thermal property differences of nanofluids formed by metals and their oxides were revealed from a microscopic perspective, which holds significant implications for the engineering applications of nanofluids.

Molecular dynamics study on the thermal properties of DGEBA/DETA/Ag/SWCNT-Ag composite materials.

Traditional conductive adhesives based on epoxy resin system often encounter problems such as high brittleness and low heat resistance. Therefore, it is particularly important to improve the thermal and mechanical properties of the conductive adhesive. In this study, the effects of SWCNT-Ag and SWCNT fillers on the thermal properties of DGEBA/DETA/Ag conductive adhesive system were studied by using molecular dynamics to construct different cross-linking models. The final results show that the addition of SWCNT and SWCNT-Ag can significantly improve the thermal properties of the conductive adhesive. However, the nanosilver particles on the surface of SWCNT-Ag act as a bridge for the connection between SWCNT and Ag in the conductive adhesive. Therefore, SWCNT-Ag has a more positive impact on the thermal properties of DGEBA/DETA/Ag conductive adhesive system. In this paper, the influence of SWCNT-Ag on the thermal properties of traditional DGEBA/DETA/Ag conductive adhesive system was studied by using Materials Studio software. The volume shrinkage, glass transition temperature, thermal expansion coefficient, and thermal conductivity of the material were calculated based on COMPASS force field. The thermal conductivity is calculated by using reverse non-equilibrium molecular dynamics method. Finally, it is found that SWCNT-Ag has a positive effect on the thermal properties of the conductive adhesive system by comparing several groups of calculation data.

Non-equilibrium molecular dynamics study of heat transfer parameters in two-dimensional Yukawa systems under uniform magnetic field

The present study explores the effect of a magnetic field on the thermal conductivity of two-dimensional (2D) Yukawa systems in a wide range of system parameters using the non-equilibrium molecular dynamic method (NEMD). We consider an external magnetic field with Ω=ωc/ωp≤1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega =\\omega _c/\\omega _p\\le 1$$\\end{document} (with Ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega$$\\end{document} being the ratio of the cyclotron frequency to plasma frequency) and the coupling parameter values in the range 1≤Γ≤100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1\\le \\Gamma \\le 100$$\\end{document} (with Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma$$\\end{document} being the ratio of the Coulomb interaction energy at mean inter-particle distance to the thermal energy of particles). The results show that an external uniform magnetic field results in the reduction of the thermal conductivity at the considered values of the coupling parameter Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma$$\\end{document}. Additionally, we found that the effect of the magnetic field on thermal conduction is weaker at larger values of the system coupling parameter. To ensure that calculated results for the thermal conductivity are accurate and reliable, we performed a detailed investigation of the convergence of the results with respect to simulation parameters in NEMD with a strong external magnetic field. We believe that the presented results will serve as useful benchmark data for the theoretical models of (2D) Yukawa systems.

Effect of radiation defects on grain boundary evolution under shock loading

Grain boundary (GB) failure in tungsten under shock loading after irradiation is a key factor to estimate the performance of tungsten as a plasma facing material in nuclear fusion reactors and as a target in spallation neutron sources. In this work, GB evolution after absorption of different radiation defect clusters under shock loading has been investigated at atomic scale through non-equilibrium molecular dynamics (NEMD) method. Different to the cases without radiation defects, after absorption of interstitial dislocation loops and voids, two mechanisms have been identified for the decrease of critical shock velocity (vc) and the related GB failure. The direct void growth accompanied by appearance of disordered structure around void, from the remaining vacancy cluster which could not be annihilated by compressive stress wave, is the 1st mechanism. In the 2nd mechanism, activation of slip systems, dislocation formation, motion and multiplication, void nucleation and growth dominate the failure process. The higher potential energy and local stress concentration around a defect absorption region in GB are recognized for atomic motion deviations from shock loading direction, resulting in formation of disordered structure, activation of slip system and dislocation multiplication with lower vc under coupling effects of radiation damage and shock loading. These results indicate that under a high dose of radiation damage, GB failure induced by shock loading should be considered seriously in order to estimate the lifetime of tungsten-based plasma facing materials and spallation target materials.

Van der Waals heterojunctions comprising double/single-walled carbon nanotubes: Insights into heat flux and thermal rectification

Van der Waals (vdWs) heterojunctions constructed from double/single-walled carbon nanotubes (DSCNTs) demonstrate exceptional thermal rectification (TR) ratios, coupled with a straightforward fabrication process, making them highly suitable for thermal rectifier applications. In this study, we employed a Nonequilibrium Molecular Dynamics method to investigate the heat flux and TR across DSCNTs with varying interlayer spacings. Our findings reveal that at smaller interlayer spacings, high temperatures readily overcome vdWs interactions. Conversely, increasing the interlayer spacing initially impedes this effect, though elevated temperatures can surmount this barrier. Significantly, at specific combinations of temperature and interlayer spacing, the left side in DSCNTs establishes interlayer phonons transport channels, facilitating forward heat flux but impeding the backward. This mechanism results in an exceptionally high TR ratio, reaching up to 757 %. Additionally, altering the chiral configurations of the CNTs in the inner and outer layers, while preserving interlayer spacing, further enhances the TR ratio and reduces the temperature threshold required to achieve peak TR ratio. Our findings contribute valuable insights into the phonon transport mechanisms within one-dimensional vdWs heterojunctions.

A Reverse Nonequilibrium Molecular Dynamics Algorithm for Coupled Mass and Heat Transport in Mixtures.

We present a new method for introducing stable nonequilibrium concentration gradients in molecular dynamics simulations of mixtures. This method extends earlier reverse nonequilibrium molecular dynamics (RNEMD) methods, which use kinetic energy scaling moves to create temperature or velocity gradients. In the new scaled particle flux (SPF-RNEMD) algorithm, energies and forces are computed simultaneously for a molecule existing in two nonadjacent regions of a simulation box, and the system evolves under a linear combination of these interactions. A continuously increasing particle scaling variable is responsible for the migration of the molecule between the regions as the simulation progresses, allowing for simulations under an applied particle flux. To test the method, we investigate diffusivity in mixtures of identical but distinguishable particles and in a simple mixture of multiple Lennard-Jones particles. The resulting concentration gradients provide Fick diffusion constants for mixtures. We also discuss using the new method to obtain coupled transport properties using simultaneous particle and thermal fluxes to compute the temperature dependence of the diffusion coefficient and activation energies for diffusion from a single simulation. Lastly, we demonstrate the use of this new method in interfacial systems by computing the diffusive permeability of a molecular fluid moving through a nanoporous graphene membrane.

Effect of shear flow on the transverse thermal conductivity of polymer melts.

The effect of shear flows on the thermal conductivity of polymer melts is investigated using a reversed nonequilibrium molecular-dynamics (RNEMD) method. We extended the original RNEMD method to simultaneously produce spatial gradients of temperature and flow velocity in a single direction. This method enables accurate measurement of the thermal conductivity in the direction transverse to shear flow. The Weissenberg number defined with the shear rate and the relaxation time of the polymer conformation can uniformly differentiate the occurrence of shear rate dependence of the thermal conductivity across different chain lengths. The stress-thermal rule (STR) (i.e., the linear relationship between anisotropic parts of the stress tensor and the thermal conductivity tensor) holds for entangled polymer melts even under shear flows but not for unentangled polymer melts. Furthermore, once entanglements form in polymer chains, the stress-thermal coefficient in the STR remains independent of the polymer chain length. These observations align with the theoretical foundation of the STR, which focuses on energy transmission along the network structure of entangled polymer chains [B. van den Brule, Rheol. Acta 28, 257 (1989)0035-451110.1007/BF01329335]. However, under driven shear flows, the stress-thermal coefficient is notably smaller than that measured in the literature for a quasiquiescent state without external forces. Although the mechanism of the STR in shear flows has yet to be fully elucidated, our study confirmed the validity of the STR in shear flows. This allows us to use the STR as a constitutive equationfor computational thermofluid dynamics of polymer melts, thus having broad engineering applications.

Thermal conductivity of irregularly shaped nanoparticles from equilibrium molecular dynamics

The computation of thermal conductivity for finite nanoparticulate systems, particularly those of irregular shapes, poses significant challenges. The nonequilibrium molecular dynamics (NEMD) methods has been extensively utilized in numerous prior studies for the computation of thermal conductivity of nanoparticles. One of our recent works (Dong et al 2021 Phys. Rev. B 103 035417) proposed that equilibrium molecular dynamics (EMD) methods can be used for the simulation of thermal conductivity of finite-scale systems and demonstrated their equivalence to NEMD methods. In this study, we investigated the application of the (EMD) approach for the computation of thermal conductivity in zero-dimensional nanoparticles. In our initial step, we merged both methodologies to substantiate the equivalence in thermal conductivity calculation for cube and cylinder nanoparticles. After filtering the data, we confirmed the usefulness of EMD for evaluating the thermal conductivity of zero-dimensional materials. The NEMD method faces challenges in accurately predicting thermal conductivity in nanoparticle systems with a varying cross-sectional area along the transport direction, whereas EMD methods can be utilized to estimate thermal conductivity when the volume is known. In a subsequent study, we used the state-of-the-art machine learning potential to calculate the thermal conductivity of spherical nanoparticles and compared the results with those obtained using the classical Tersoff potential. Ultimately, we predicted the thermal conductivity of nanoparticles with various geometries in all directions. Our findings collectively demonstrate the simplicity and effectiveness of employing EMD methods for calculating thermal conductivity in nanoparticle systems, thereby opening up new avenues for investigating thermal transport properties in particle systems as well as nanopders.

Elastic and inelastic phonon scattering effects on thermal conductance across Au/graphene/Au interface

Heat dissipation from graphene devices is predominantly limited by heat conduction across the metal contacts with complex phonon scattering. In this work, the effects of elastic and inelastic phonon scattering on the interfacial thermal conductance (ITC) across the Au/graphene/Au interface are studied using both atomistic Green's function (AGF) and reverse non-equilibrium molecular dynamics methods. The results show that the contribution of inelastic phonon scattering to the ITC increases with the enhancement of interfacial bonding strength. Moreover, the overlap of the vibrational density of states across the interface shows that the coupling between the Au layer (adjacent to the Au/graphene interface) and graphene's out-of-plane modes plays the dominant role in ITC across the Au/graphene interface. By comparing the transmission functions calculated with AGF and spectral heat current decomposition methods, the inelastic phonon scattering process facilitates phonon transmission in the lower and higher frequency range but hinders phonon transmission in the intermediate frequency range. It is expected that this study can contribute to a better understanding of the thermal conduction mechanism across the metal/graphene interface, providing guidance for thermal management and heat conduction optimization of graphene in microelectronic devices.

Molecular dynamics study of the rheology of benzene-based nanofluids with metal particles

The purpose of this paper is to study the rheology of the nanofluids with ordinary spherical particles. The rheology of benzene and benzene-based nanofluids with copper and aluminium particles of 3 and 6 nm diameter been studied by the nonequilibrium molecular dynamics method. The maximum volume concentration of the nanoparticles was 6.11 %. It has been shown that all fluids considered, including benzene and benzene-based nanofluids, exhibit Newtonian behavior at low shear rates. However, with increasing shear rate, both benzene and nanofluids become pseudoplastic. The mechanisms of the rheology change of simple liquid and nanofluids have studied. This change in their rheology is a threshold phenomenon, in which the critical shear rate depends on the concentration, size, and material of the nanoparticles. The critical shear rate increases with increasing particle size and decreases with increasing particle concentration. Correlations describing the critical shear rates at which the rheology of nanofluids changes are obtained. It is shown that the rheology change is due to a change in the structure of both the base fluid and the nanofluid. In all cases, the change in rheology results from the weakening of the short-range order in these fluids. As the shear rate increases, the difference between viscosity of the base fluid and all studied nanofluids decreases monotonically.

Effect of the electric field orientation on the thermal resistance of the solid–liquid interface

ABSTRACT With the rapid development of nanotechnology, using the applied electric field to regulate interfacial heat transfer has become increasingly important. In the present work, the relationship between the thermal resistance of Kapitza and the direction of the applied electric field is explored with nonequilibrium molecular dynamics method at a solid–liquid interface consisting of CU (0, 0, 1) and liquid water. It found that the electric field orientation induces the ordering of water molecules near the solid, which affects the magnitude of the Kapitza thermal resistance. In addition, the electric field orientation affects the degree of mismatch between solid and liquid vibrational dynamical density (VDOS), which affects the phonon transport at the solid–liquid interface, and ultimately affects the process of interfacial heat transfer. Furthermore, it’s found that there is a weak correlation between the interfacial thermal resistance and the dimension of the copper-water model.

Thermal transports of 2D phosphorous carbides by machine learning molecular dynamics simulations

Carbon phosphide is a newly discovered two-dimensional semiconductor material which wrinkles and has a significant carrier mobility. Due to lack an accurate force field, the use of molecular dynamics to study its phonon-dominated thermal conductivity which lead to inaccurate results. At present, the use of machine learning to construct a high-precision force field has become the mainstream research method to solve this problem. The main work of this study is to construct a comprehensive training sets for Phosphorus-Doped Graphene (PCn) (n = 3, 5, 6) and to use the fitted potential to calculate the related thermal properties. The research found that (PC5) exhibited anisotropic behavior, with a thermal conductivity of 106.6 Wm−1K−1 in the y-direction and 63.6 Wm−1K−1 in the x-direction. In comparison, (PC6) and (PC3) showed isotropic behavior, with thermal conductivity of approximately 104 Wm−1K−1 and 76.83 Wm−1K−1, respectively. Compared to monolayer graphene, the lower thermal conductivity of PCn is mainly attributed to phonon-phonon scattering effects, which are limited by the regular wrinkled structure. Additionally, low-frequency phonon have been found to have a significant impact on the thermal performance of PCn. Furthermore, we investigated the influence of uniaxial strain on the PC6 and observed an increase in the thermal conductivity with increasing strain. This study used key computational and analytical techniques, including phonon dispersion relations, homogeneous nonequilibrium molecular dynamics method, spectral thermal conductivity analysis. These findings provide a theoretical basis for understanding the thermal transport properties of PCn and will guide its potential applications value.

Effects of Topological Parameters on Thermal Properties of Carbon Nanotubes via Molecular Dynamics Simulation

Due to their unique properties, carbon nanotubes (CNTs) are finding a growing number of applications across multiple industrial sectors. These properties of CNTs are subject to influence by numerous factors, including the specific chiral structure, length, type of CNTs used, diameter, and temperature. In this topic, the effects of chirality, diameter, and length of single-walled carbon nanotubes (SWNTs) on the thermal properties were studied using the reverse non-equilibrium molecular dynamics (RNEMD) method and the Tersoff interatomic potential of carbon–carbon based on the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). For the shorter SWNTs, the effect of chirality on the thermal conductivity is more obvious than for longer SWNTs. Thermal conductivity increases with increasing chiral angle, and armchair SWNTs have higher thermal conductivity than that of zigzag SWNTs. As the tube length becomes longer, the thermal conductivity increases while the effect of chirality on the thermal conductivity decreases. Furthermore, for SWNTs with longer lengths, the thermal conductivity of zigzag SWNTs is higher than that of the armchair SWNTs. Thermal resistance at the nanotube–nanotube interfaces, particularly the effect of CNT overlap length on thermal resistance, was studied. The simulation results were compared with and in agreement with the experimental and simulation results from the literature. The presented approach could be applied to investigate the properties of other advanced materials.

Molecular dynamics simulation of viscosity and rheology of nanofluids with single wall carbon nanotubes

The purpose of this work is to study the dependence of the viscosity and rheology of benzene-based nanofluids with carbon nanotubes on their length. The problem is solved by the method of nonequilibrium molecular dynamics; the rheology of nanofluids with single-walled carbon nanotubes with a length from 1.45 to 14.96 nm has been studied. The volume concentration of nanotubes was 2 %. It was established that at low shear rates nanofluids are Newtonian. Their viscosity significantly exceeds the viscosity of benzene, and this excess is not described by classical theories for coarse liquids. In addition, the viscosity of nanofluids significantly depends on the length of the carbon tubes and increases with their growth. Starting from a certain shear rate, nanofluids change rheology and become pseudoplastic. Thus, the change in rheology is a threshold phenomenon and the corresponding critical shear rates depend on the length of the nanotubes. At high shear rates, the differences between the viscosities of nanofluids with different nanotube lengths decrease monotonically. A correlation has been obtained that makes it possible to predict the viscosity of the nanofluid and the trend of its change depending on the shear rate and the length of the nanotubes.