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Yasuda I, Kobayashi Y, Endo K, Hayakawa Y, Fujiwara K, Yajima K, Arai N, Yasuoka K. Combining Molecular Dynamics and Machine Learning to Analyze Shear Thinning for Alkane and Globular Lubricants in the Low Shear Regime. ACS APPLIED MATERIALS & INTERFACES 2023; 15:8567-8578. [PMID: 36715349 DOI: 10.1021/acsami.2c16366] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Lubricants with desirable frictional properties are important in achieving an energy-saving society. Lubricants at the interfaces of mechanical components are confined under high shear rates and pressures and behave quite differently from the bulk material. Computational approaches such as nonequilibrium molecular dynamics (NEMD) simulations have been performed to probe the molecular behavior of lubricants. However, the low-shear-velocity regions of the materials have rarely been simulated owing to the expensive calculations necessary to do so, and the molecular dynamics under shear velocities comparable with that in the experiments are not clearly understood. In this study, we performed NEMD simulations of extremely confined lubricants, i.e., two molecular layers for four types of lubricants confined in mica walls, under shear velocities from 0.001 to 1 m/s. While we confirmed shear thinning, the velocity profiles could not show the flow behavior when the shear velocity was much slower than thermal fluctuations. Therefore, we used an unsupervised machine learning approach to detect molecular movements that contribute to shear thinning. First, we extracted the simple features of molecular movements from large amounts of MD data, which were found to correlate with the effective viscosity. Subsequently, the extracted features were interpreted by examining the trajectories contributing to these features. The magnitude of diffusion corresponded to the viscosity, and the location of slips that varied depending on the spherical and chain lubricants was irrelevant. Finally, we attempted to apply a modified Stokes-Einstein relation at equilibrium to the nonequilibrium and confined systems. While systems with low shear rates obeyed the relation sufficiently, large deviations were observed under large shear rates.
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Affiliation(s)
- Ikki Yasuda
- Department of Mechanical Engineering, Keio University, Yokohama, Kanagawa223-8522, Japan
| | - Yusei Kobayashi
- Department of Mechanical Engineering, Keio University, Yokohama, Kanagawa223-8522, Japan
| | - Katsuhiro Endo
- Department of Mechanical Engineering, Keio University, Yokohama, Kanagawa223-8522, Japan
| | - Yoshihiro Hayakawa
- Department of General Engineering, National Institute of Technology, Sendai College, Sendai, Miyagi989-3128, Japan
| | - Kazuhiko Fujiwara
- Department of General Engineering, National Institute of Technology, Sendai College, Sendai, Miyagi989-3128, Japan
| | - Kuniaki Yajima
- Department of General Engineering, National Institute of Technology, Sendai College, Sendai, Miyagi989-3128, Japan
| | - Noriyoshi Arai
- Department of Mechanical Engineering, Keio University, Yokohama, Kanagawa223-8522, Japan
| | - Kenji Yasuoka
- Department of Mechanical Engineering, Keio University, Yokohama, Kanagawa223-8522, Japan
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Yu L, Huang D, Wang X, Yu W, Yue Y. Tuning thermal and electrical properties of MXenes via dehydration. Phys Chem Chem Phys 2022; 24:25969-25978. [PMID: 36263720 DOI: 10.1039/d2cp03619c] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Recently, MXenes (a class of two-dimensional transition metal carbides) have attracted great attention in various applications such as humidity sensors, owing to their unique electrical and thermal properties. However, previous studies of MXenes mostly focus on their humidity-sensing characteristics such as the mechanical response, and only few reports on their electrical and thermal response are available. Herein, we present novel transient electrothermal experiments to demonstrate that a transition from a negative to a positive resistance-temperature relationship can take place when the MXene sample becomes fully dehydrated. This surprising and unusual phenomenon was elucidated through non-equilibrium molecular dynamics simulations and attributed to water absorption/desorption onto the chemically active MXene surface. A linear relationship was also found between electrical/thermal properties and environmental humidity, which could be related to water adsorption on the surface of the MXene sensor. We further decomposed the total measured thermal conductivity and found that phonons were the dominant thermal carriers in the MXene sample. The main breakthrough of this work is the discovery of the unusual resistance-temperature relationship, which should be applicable to the design of MXene-based sensors for various applications.
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Affiliation(s)
- Litao Yu
- School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei, 430072, P. R. China.
| | - Dezhao Huang
- School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei, 430072, P. R. China.
| | - Xuezi Wang
- School of Environmental and Materials Engineering, College of Engineering, Shanghai Second Polytechnic University, Shanghai 201209, China.
| | - Wei Yu
- School of Environmental and Materials Engineering, College of Engineering, Shanghai Second Polytechnic University, Shanghai 201209, China.
- Research Center of Resource Recycling Science and Engineering, Shanghai Polytechnic University, Shanghai 201209, China
| | - Yanan Yue
- School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei, 430072, P. R. China.
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Traction behavior and mechanism of molecular level with effects of molecular structure and sliding velocity in boundary lubrication regime: A molecular dynamics study. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.118844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Wang R, Chai J, Luo B, Liu X, Zhang J, Wu M, Wei M, Ma Z. A review on slip boundary conditions at the nanoscale: recent development and applications. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2021; 12:1237-1251. [PMID: 34868800 PMCID: PMC8609245 DOI: 10.3762/bjnano.12.91] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Accepted: 11/01/2021] [Indexed: 06/13/2023]
Abstract
The slip boundary condition for nanoflows is a key component of nanohydrodynamics theory, and can play a significant role in the design and fabrication of nanofluidic devices. In this review, focused on the slip boundary conditions for nanoconfined liquid flows, we firstly summarize some basic concepts about slip length including its definition and categories. Then, the effects of different interfacial properties on slip length are analyzed. On strong hydrophilic surfaces, a negative slip length exists and varies with the external driving force. In addition, depending on whether there is a true slip length, the amplitude of surface roughness has different influences on the effective slip length. The composition of surface textures, including isotropic and anisotropic textures, can also affect the effective slip length. Finally, potential applications of nanofluidics with a tunable slip length are discussed and future directions related to slip boundary conditions for nanoscale flow systems are addressed.
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Affiliation(s)
- Ruifei Wang
- Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, College of Petroleum Engineering, Xi’an Shiyou University, 710065, China
| | - Jin Chai
- Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, College of Petroleum Engineering, Xi’an Shiyou University, 710065, China
| | - Bobo Luo
- Research Institute of Exploration and Development, Zhongyuan Oilfield Company, SINOPEC, Puyang 457001, China
| | - Xiong Liu
- Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, College of Petroleum Engineering, Xi’an Shiyou University, 710065, China
| | - Jianting Zhang
- Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, College of Petroleum Engineering, Xi’an Shiyou University, 710065, China
| | - Min Wu
- Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, College of Petroleum Engineering, Xi’an Shiyou University, 710065, China
| | - Mingdan Wei
- Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, College of Petroleum Engineering, Xi’an Shiyou University, 710065, China
| | - Zhuanyue Ma
- Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, College of Petroleum Engineering, Xi’an Shiyou University, 710065, China
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Schiffbauer J, Ganchenko G, Nikitin N, Alekseev M, Demekhin E. Novel electroosmotic micromixer configuration based on ion-selective microsphere. Electrophoresis 2021; 42:2511-2518. [PMID: 34553795 DOI: 10.1002/elps.202100040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 06/18/2021] [Accepted: 09/11/2021] [Indexed: 11/07/2022]
Abstract
In this paper, a micromixer of a new configuration is presented, consisting of a spherical chamber in the center of which an ion-selective microsphere is placed. Stratified liquid is introduced through the chamber via inlet and outlet holes under an external pressure gradient and an external electric field is directed in such a way that the resulting electroosmotic flow is directed against the pressure-driven flow, resulting in mixing. The investigation is carried out by direct numerical simulation on a super-computer. Optimal values of the applied electric field are determined to yield strong mixing. Above this optimal mixing regime, a number of instabilities and bifurcations are realized, which qualitatively coincide with those occurring during electrophoresis of an ion-selective microgranule. As shown by our calculation, these instabilities do not lead to an enhanced mixing. The resulting electroconvective vortices remain confined near the surface of the microgranule, and do not sufficiently perturb the stratified fluid flow further from the granule. On the other hand, another type of instability caused by the salt concentration gradient can generate sufficiently strong oscillations to enhance mixing. However, this only occurs when the external electric field is sufficiently high that the electroosmotic flow is comparable to the pressure-driven flow. This ultimately leads to creation of reverse flows of the liquid and cessation of the device operation. Thus, it was shown that the best mixing occurs in the absence of electrokinetic instability. Based on the data obtained, it is possible to select the necessary geometric characteristics of the micromixer to achieve the optimal mixing mode for a given set of liquids, which may be ten times more effective than passive mixers at the same flow rates. A comparison with the experimental data of the other authors confirms the effectiveness of this device and its other capabilities. Furthermore, the basic device design can be operated in other modes, for example, an electrohydrodynamic pump, a streaming current generator, or even a micro-reactor, depending on the system parameters and choice of an ion-selective granule.
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Affiliation(s)
- Jarrod Schiffbauer
- Department of Physical and Environmental Sciences, Colorado Mesa University, Grand Junction, CO, USA
| | - Georgy Ganchenko
- Laboratory of Micro- and Nanoscale Electro- and Hydrodynamics, Financial University, Krasnodar, Russia
| | - Nikolay Nikitin
- Laboratory of General Aeromechanics, Institute of Mechanics, Moscow State University, Moscow, Russia
| | | | - Evgeny Demekhin
- Laboratory of Micro- and Nanoscale Electro- and Hydrodynamics, Financial University, Krasnodar, Russia.,Laboratory of General Aeromechanics, Institute of Mechanics, Moscow State University, Moscow, Russia.,Department of Mathematics and Computer Science, Financial University, Krasnodar, Russia
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Nazari M, Davoodabadi A, Huang D, Luo T, Ghasemi H. Transport Phenomena in Nano/Molecular Confinements. ACS NANO 2020; 14:16348-16391. [PMID: 33253531 DOI: 10.1021/acsnano.0c07372] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The transport of fluid and ions in nano/molecular confinements is the governing physics of a myriad of embodiments in nature and technology including human physiology, plants, energy modules, water collection and treatment systems, chemical processes, materials synthesis, and medicine. At nano/molecular scales, the confinement dimension approaches the molecular size and the transport characteristics deviates significantly from that at macro/micro scales. A thorough understanding of physics of transport at these scales and associated fluid properties is undoubtedly critical for future technologies. This compressive review provides an elaborate picture on the promising future applications of nano/molecular transport, highlights experimental and simulation metrologies to probe and comprehend this transport phenomenon, discusses the physics of fluid transport, tunable flow by orders of magnitude, and gating mechanisms at these scales, and lists the advancement in the fabrication methodologies to turn these transport concepts into reality. Properties such as chain-like liquid transport, confined gas transport, surface charge-driven ion transport, physical/chemical ion gates, and ion diodes will provide avenues to devise technologies with enhanced performance inaccessible through macro/micro systems. This review aims to provide a consolidated body of knowledge to accelerate innovation and breakthrough in the above fields.
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Affiliation(s)
- Masoumeh Nazari
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Road, Houston, Texas 77204, United States
| | - Ali Davoodabadi
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Road, Houston, Texas 77204, United States
| | - Dezhao Huang
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Tengfei Luo
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Hadi Ghasemi
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Road, Houston, Texas 77204, United States
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Kong XX, Chen WD, Cui FC, Li YQ. Conformational and Dynamical Evolution of Block Copolymers in Shear Flow. CHINESE JOURNAL OF POLYMER SCIENCE 2020. [DOI: 10.1007/s10118-021-2523-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Nazari M, Davoodabadi A, Huang D, Luo T, Ghasemi H. On interfacial viscosity in nanochannels. NANOSCALE 2020; 12:14626-14635. [PMID: 32614001 DOI: 10.1039/d0nr02294b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Capillary driven transport of liquids in nanoscopic channels is an omnipresent phenomenon in nature and technology including fluid flow in the human body and plants, drug delivery, nanofluidic devices, and energy/water systems. However, the kinetics of this mass transport mechanism remains in question as the well-known Lucas-Washburn (LW) model predicts significantly faster flow rates compared to the experimental observations. We here showed the role of interfacial viscosity in capillary motion slowdown in nanochannels through a combination of experimental, analytical and molecular dynamics techniques. We showed that the slower liquid flow is due to the formation of a thin liquid layer adjacent to the channel walls with a viscosity substantially greater than the bulk liquid. By incorporating the effect of the interfacial layer, we presented a theoretical model that accurately predicts the capillarity kinetics in nanochannels of different heights. Non-equilibrium molecular dynamics simulation confirmed the obtained interfacial viscosities. The viscosities of isopropanol and ethanol within the interfacial layer were 9.048 mPa s and 4.405 mPa s, respectively (i.e. 279% and 276% greater than their bulk values). We also showed that the interfacial layers are 6.4 nm- and 5.3 nm-thick for isopropanol and ethanol, respectively.
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Affiliation(s)
- Masoumeh Nazari
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Rd, Houston, Texas 77204, USA.
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