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Smith ER, Theodorakis PE. Multiscale simulation of fluids: coupling molecular and continuum. Phys Chem Chem Phys 2024; 26:724-744. [PMID: 38113114 DOI: 10.1039/d3cp03579d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
Computer simulation is an important tool for scientific progress, especially when lab experiments are either extremely costly and difficult or lack the required resolution. However, all of the simulation methods come with limitations. In molecular dynamics (MD) simulation, the length and time scales that can be captured are limited, while computational fluid dynamics (CFD) methods are built on a range of assumptions, from the continuum hypothesis itself, to a variety of closure assumptions. To address these issues, the coupling of different methodologies provides a way to retain the best of both methods. Here, we provide a perspective on multiscale simulation based on the coupling of MD and CFD with each a distinct part of the same simulation domain. This style of coupling allows molecular detail to be present only where it is needed, so CFD can model larger scales than possible with MD alone. We present a unified perspective of the literature, showing the links between the two main types of coupling, state and flux, and discuss the varying assumptions in their use. A unique challenge in such coupled simulation is obtaining averages and constraining local parts of a molecular simulation. We highlight that incorrect localisation has resulted in an error in the literature. We then finish with some applications, focused on the simulation of fluids. Thus, we hope to motivate further research in this exciting area with applications across the spectrum of scientific disciplines.
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Affiliation(s)
- Edward R Smith
- Department of Mechanical and Aerospace Engineering, Brunel University London, Uxbridge, Middlesex UB8 3PH, UK.
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Tian S, Chen X, Yuan Q. Shape optimization of a meniscus-adherent nanotip. NANOSCALE 2023. [PMID: 37337766 DOI: 10.1039/d3nr00857f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2023]
Abstract
A soluble tip can dissolve into a tip with curvature when partially immersed in a liquid. This process has been used in the manufacture of sophisticated tips. However, it is difficult to observe the dissolution process in the laboratory, and the dissolution mechanisms at the nanoscale still need to be better understood. Here we utilize molecular dynamics simulations to study the dissolution process of a meniscus-adherent nanotip. The tip apex curvature radius reaches its minimum in the intermediate state. The shape of this state is defined as the optimized shape, which can be used as the termination criterion in applications. In addition, the shape of one optimized tip can be well-fitted to a double-Boltzmann function. The upper Boltzmann curve of this function forms via the competition between the chemical potential influence and the intermolecular forces, while the formation of the lower Boltzmann curve is controlled by the chemical potential influence. The parameters of the double-Boltzmann function are strongly correlated with the nanotip's initial configuration and dissolubility. A shape factor ξ is proposed to characterize the sharpness of optimized tips. Theory and simulations show that optimized tips possess a greater ability to shield the capillary effect than common tips. Our findings elucidate the meniscus-adherent nanotip's dissolution process and provide theoretical support for nano-instrument manufacture.
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Affiliation(s)
- Shihao Tian
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China.
| | - Xudong Chen
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China.
| | - Quanzi Yuan
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China.
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Smith ER, Theodorakis PE, Craster RV, Matar OK. Moving Contact Lines: Linking Molecular Dynamics and Continuum-Scale Modeling. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:12501-12518. [PMID: 29727189 DOI: 10.1021/acs.langmuir.8b00466] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Despite decades of research, the modeling of moving contact lines has remained a formidable challenge in fluid dynamics whose resolution will impact numerous industrial, biological, and daily life applications. On the one hand, molecular dynamics (MD) simulation has the ability to provide unique insight into the microscopic details that determine the dynamic behavior of the contact line, which is not possible with either continuum-scale simulations or experiments. On the other hand, continuum-based models provide a link to the macroscopic description of the system. In this Feature Article, we explore the complex range of physical factors, including the presence of surfactants, which governs the contact line motion through MD simulations. We also discuss links between continuum- and molecular-scale modeling and highlight the opportunities for future developments in this area.
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Agius Anastasi A, Ritos K, Cassar G, Borg MK. Mechanical properties of pristine and nanoporous graphene. MOLECULAR SIMULATION 2016. [DOI: 10.1080/08927022.2016.1209753] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Ritos K, Borg MK, Mottram NJ, Reese JM. Electric fields can control the transport of water in carbon nanotubes. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2016; 374:rsta.2015.0025. [PMID: 26712640 PMCID: PMC4696074 DOI: 10.1098/rsta.2015.0025] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 10/12/2015] [Indexed: 06/05/2023]
Abstract
The properties of water confined inside nanotubes are of considerable scientific and technological interest. We use molecular dynamics to investigate the structure and average orientation of water flowing within a carbon nanotube. We find that water exhibits biaxial paranematic liquid crystal ordering both within the nanotube and close to its ends. This preferred molecular ordering is enhanced when an axial electric field is applied, affecting the water flow rate through the nanotube. A spatially patterned electric field can minimize nanotube entrance effects and significantly increase the flow rate.
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Affiliation(s)
- Konstantinos Ritos
- Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ, UK
| | - Matthew K Borg
- School of Engineering, University of Edinburgh, Edinburgh EH9 3FB, UK
| | - Nigel J Mottram
- Department of Mathematics and Statistics, University of Strathclyde, Glasgow G1 1XH, UK
| | - Jason M Reese
- School of Engineering, University of Edinburgh, Edinburgh EH9 3FB, UK
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Zhang J, Borg MK, Sefiane K, Reese JM. Wetting and evaporation of salt-water nanodroplets: A molecular dynamics investigation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:052403. [PMID: 26651708 DOI: 10.1103/physreve.92.052403] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Indexed: 06/05/2023]
Abstract
We employ molecular dynamics simulations to study the wetting and evaporation of salt-water nanodroplets on platinum surfaces. Our results show that the contact angle of the droplets increases with the salt concentration. To verify this, a second simulation system of a thin salt-water film on a platinum surface is used to calculate the various surface tensions. We find that both the solid-liquid and liquid-vapor surface tensions increase with salt concentration and as a result these cause an increase in the contact angle. However, the evaporation rate of salt-water droplets decreases as the salt concentration increases, due to the hydration of salt ions. When the water molecules have all evaporated from the droplet, two forms of salt crystals are deposited, clump and ringlike, depending on the solid-liquid interaction strength and the evaporation rate. To form salt crystals in a ring, it is crucial that there is a pinned stage in the evaporation process, during which salt ions can move from the center to the rim of the droplets. With a stronger solid-liquid interaction strength, a slower evaporation rate, and a higher salt concentration, a complete salt crystal ring can be deposited on the surface.
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Affiliation(s)
- Jun Zhang
- James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ, United Kingdom
| | - Matthew K Borg
- School of Engineering, University of Edinburgh, Edinburgh EH9 3FB, United Kingdom
| | - Khellil Sefiane
- School of Engineering, University of Edinburgh, Edinburgh EH9 3FB, United Kingdom
- Tianjin Key Laboratory of Refrigeration Technology, Tianjin University of Commerce, Tianjin, China
| | - Jason M Reese
- School of Engineering, University of Edinburgh, Edinburgh EH9 3FB, United Kingdom
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Smith ER, Heyes DM, Dini D, Zaki TA. A localized momentum constraint for non-equilibrium molecular dynamics simulations. J Chem Phys 2015; 142:074110. [DOI: 10.1063/1.4907880] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- E. R. Smith
- Department of Mechanical Engineering, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, United Kingdom
| | - D. M. Heyes
- Department of Mechanical Engineering, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, United Kingdom
| | - D. Dini
- Department of Mechanical Engineering, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, United Kingdom
| | - T. A. Zaki
- Department of Mechanical Engineering, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, United Kingdom
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