Matthew K Borg

Matthew K Borg
The University of Edinburgh | UoE · School of Engineering

B.Eng. (Hons)(Melit.), PhD (Strathclyde)

About

76
Publications
19,449
Reads
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1,496
Citations
Additional affiliations
May 2011 - August 2015
University of Strathclyde
Position
  • Research Associate

Publications

Publications (76)
Article
Revealing the scattering behaviour of gas molecules on porous surfaces is essential to develop accurate boundary conditions for kinetic transport models that describe the gas dynamics in shale reservoirs. Here, we use high-fidelity molecular dynamics simulations to resolve the gas–surface interactions between methane molecules and realistic organic...
Article
Ice accumulation on solid surfaces is a severe problem for safety and functioning of a large variety of engineering systems, and its control is an enormous challenge that influences the safety and reliability of many technological applications. The use of molecular dynamics (MD) simulations is popular, but as ice nucleation is a rare event when com...
Article
Carbon nanotubes (CNTs) have long been heralded as the material of choice for next-generation membranes. Some studies have suggested that boron nitride nanotubes (BNNTs) may offer higher transport of pure water than CNTs, while others conclude otherwise. In this work, we use a combination of simulations and experimental data to uncover the causes o...
Article
Molecular transport through tight porous media is crucial to shale gas exploration, but deeper insights of the elemental physics are still required, particularly under high pressures and nanoscale confinements, where Navier–Stokes and Boltzmann solutions are no longer valid. In this work, we carry out a fundamental and systematic study of self-diff...
Article
The collapse of cavitation bubbles often releases high-speed liquid jets capable of surface damage, with applications in drug delivery, cancer treatment, and surface cleaning. Spherical cap-shaped surface nanobubbles have previously been found to exist on immersed substrates. Despite being known nucleation sites for cavitation, their collapsing dyn...
Article
Molecular dynamics (MD) and volume of fluid (VOF) are powerful methods for the simulation of dynamic wetting at the nanoscale and macroscale, respectively, but the massive computational cost of MD and the sensitivity and uncertainty of boundary conditions in VOF limit their applications to other scales. In this work, we propose a multiscale simulat...
Article
Shale gas flow at the pore scale is very challenging to simulate due to high Knudsen numbers (Kn), low speeds and complicated pore geometries. The direct simulation BGK (DSBGK) method and the discrete velocity method (DVM) are promising methods to simulate three-dimensional (3D) gas flows in the shale rock. As the grid-convergence accuracy and comp...
Article
Full-text available
Ultrasonic surface vibration at high frequencies ( O (100 GHz)) can nucleate bubbles in a liquid within a few nanometres from a surface, but the underlying mechanism and the role of surface wettability remain poorly understood. Here, we employ molecular simulations to study and characterize this phenomenon, which we call acoustothermal nucleation....
Article
Surface nanobubbles have potential applications in the manipulation of nanoscale and biological materials, waste-water treatment, and surface cleaning. These spherically capped bubbles of gas can exist in stable diffusive equilibrium on chemically patterned or rough hydrophobic surfaces, under supersaturated conditions. Previous studies have invest...
Article
Based on an accurate numerical solution of the kinetic equation using well-resolved spatial and velocity grids, the separation of rarefied gas flow in a microchannel with double rectangular bends is investigated over a wide range of Knudsen and Reynolds numbers. Rarefaction effects are found to play different roles in flow separation (vortex format...
Article
Modeling dense gas flows inside channels with sections comparable to the diameter of gas molecules is essential in porous medium applications, such as in non-conventional shale reservoir management and nanofluidic separation membranes. In this paper, we perform the first verification study of the Enskog equation by using particle simulation methods...
Article
Next-generation processor-chip cooling devices and self-cleaning surfaces can be enhanced by a passive process that require little to no electrical input, through coalescence-induced nanodroplet jumping. Here, we describe the crucial impact thermal capillary waves and ambient gas rarefaction have on enhancing/limiting the jumping speeds of nanodrop...
Article
The rejection of particles with different charges and sizes, ranging from a few Ångstrom to tens of nanometers, is key to a wide range of industrial applications, from wastewater treatment to product purification in biotech processes. Carbon nanotubes (CNTs) have long held the promise to revolutionize filtration, with orders of magnitude higher flu...
Article
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Classical Navier-Stokes equations fail to describe some flows in both the compressible and in-compressible configurations. In this article, we propose a new methodology based on transforming the fluid mass velocity vector field to obtain a new class of continuum models. We uncover a class of continuum models which we call the re-casted Navier–Stoke...
Preprint
Full-text available
Classical Navier-Stokes equations fail to describe some flows in both the compressible and incompressible configurations. In this article, we propose a new methodology based on transforming the fluid mass velocity vector field to obtain a new class of continuum models. We uncover a class of continuum models which we call the re-casted Navier-Stokes...
Conference Paper
This paper aims to settle disputes in the literature about the spatial variation of the molecular mean free path (MFP) in confined geometries. The MFP of a gas is determined by using both molecular dynamics (MD) and the direct simulation Monte Carlo (DSMC) technique. In spatially-homogeneous cases, the numerical results exactly recover the kinetic...
Article
Full-text available
The molecular mean free path (MFP) of gases in confined geometries is numerically evaluated by means of the direct simulation Monte Carlo method and molecular dynamics simulations. Our results show that if calculations take into account not only intermolecular interactions between gas molecules but also collisions between gas molecules and wall ato...
Article
Full-text available
The classical notion of the coalescence of two droplets of the same radius R is that surface tension drives an initially singular flow. In this Letter we show, using molecular dynamics simulations of coalescing water nanodroplets, that after single or multiple bridges form due to the presence of thermal capillary waves, the bridge growth commences...
Article
The independent effect of nanotube surface chemistry and structure on the flow of water under nanoscale confinement is demonstrated in this paper for the first time via the synthesis of novel carbon nitride nanotube (CNNT) membranes. Using a combination of experiments and high-fidelity molecular dynamics (MD) simulations, it is here shown that the...
Article
Full-text available
Bubble cavitation is important in technologies such as non-invasive cancer treatment and diagnosis, surface cleaning, and waste-water treatment. The cavitation threshold is the critical external tensile pressure that induces unstable growth of the bubble. Surface nanobubbles have been previously shown experimentally to be stable down to −6 MPa, in...
Article
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We report nonequilibrium molecular simulations of the vibration-induced heating of nanoscale-thick water layers on a metal substrate. In addition to experimentally confirmed acoustothermal evaporation, we observe hitherto unmapped nucleate and film boiling regimes, accompanied by the generation of unprecedented heat fluxes [∼O(109) W/m2]. We develo...
Article
Water purification membranes comprising aligned, dense arrays of carbon nanotubes (CNTs) have been investigated for more than 10 years. Water transport 2–5 orders of magnitude greater than Hagen-Poiseuille predictions has been observed in CNTs of diameters 0.8–10 nm in a small number of experiments. While the measured flow rates in different experi...
Article
The successful integration of graphene in future technologies, such as filtration and nanoelectronics, depends on the ability to introduce controlled nanostructured defects in graphene. In this work, Raman spectroscopy is used to investigate the induction of disorder in graphene via gallium ion beam bombardment. Two configurations of CVD-grown grap...
Article
We report the results of molecular dynamics investigations into the behaviour of nanoscale water droplets on surfaces subjected to cyclic-frequency normal vibration. Our results show, for the first time, a range of vibration-induced phenomena, including the existence of the following different regimes: evaporation, droplet oscillation, and droplet...
Article
Full-text available
Although the modified Young’s equation is frequently applied to evaluate the line tension of droplets, debate concerning the value and even the sign of the line tension is ongoing. The reason for this is that the line tension defined in the modified Young’s equation is not a pure line tension but an apparent line tension, which includes the effects...
Article
Full-text available
A sequential multiscale strategy that combines molecular dynamics (MD) with volume of fluid (VOF) simulations is proposed to study the spreading of droplets on surfaces. In this hybrid MD/VOF approach, VOF is applied everywhere in the domain with MD pre-simulations distributed along the wetted interface providing the crucial boundary information fo...
Article
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This paper introduces mdFoam+, which is an MPI parallelised molecular dynamics (MD) solver implemented entirely within the OpenFOAM software framework. It is open-source and released under the same GNU General Public License (GPL) as OpenFOAM. The source code is released as a publicly open software repository that includes detailed documentation an...
Article
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dsmcFoam+ is a direct simulation Monte Carlo (DSMC) solver for rarefied gas dynamics, implemented within the OpenFOAM software framework, and parallelised with MPI. It is open-source and released under the GNU General Public License in a publicly available software repository that includes detailed documentation and tutorial DSMC gas flow cases. Th...
Article
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We propose the rarefied-gas-cushion model (r-GCM), as an extended version of the gas-cushion model (GCM), to estimate the apparent slip of water flowing over a gas layer trapped at a solid surface. Nanobubbles or gas nanofilms may manifest rarefied-gas effects and the r-GCM incorporates kinetic boundary conditions for the gas component in the slip...
Article
Nanotubes (NTs) with diameters less than 2 nm have been proposed for next-generation reverse osmosis membranes. At this molecular scale, the NTs are narrow enough to block salt ions and other contaminants, but still wide enough to allow water to flow along the NTs at seemingly unprecedented rates. Simulations for design of NT membranes can be chall...
Article
Full-text available
We present molecular dynamics simulations of monolayer graphene under uniaxial tensile loading. The Morse, bending angle, torsion and Lennard-Jones potential functions are adopted within the mdFOAM library in the OpenFOAM software, to describe the molecular interactions in graphene. A well-validated graphene model using these set of potentials is n...
Article
Full-text available
Filtering of particle-based simulation data can lead to reduced computational costs and enable more efficient information transfer in multi-scale modelling. This paper compares the effectiveness of various signal processing methods to reduce numerical noise and capture the structures of nano-flow systems. In addition, a novel combination of these a...
Article
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This paper extends the hybrid computational method proposed by Docherty et al. (2014) for simulating non-isothermal rarefied gas flows at the microscale. Coupling a continuum fluid description to a direct simulation Monte Carlo (DSMC) solver, the original methodology considered the transfer of heat only, with validation performed on 1D micro Fourie...
Article
Full-text available
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....
Article
So-called "coffee-ring" stains are the deposits remaining after complete evaporation of droplets containing non-volatile solutes. In this paper we use Molecular Dynamics to simulate the evaporation of salt water nanodroplets in the presence of an applied electric field. We demonstrate, for the first time, that electrowetted nanodroplets can produce...
Article
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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 surf...
Article
The particle-continuum hybrid Laplacian method is extended as a framework for modeling all transport phenomena in fluids at the micro and nanoscale including multicomponent mass transfer and chemical reactions. The method is explained, and the micro-to-macro and macro-to-micro coupling steps are discussed. Two techniques for noise reduction (namely...
Article
Validation and verification represent an important element in the development of a computational code. The aim is establish both confidence in the algorithm and its suitability for the intended purpose. In this paper, a direct simulation Monte Carlo solver, called dsmcFoam, is carefully investigated for its ability to solve low and high speed non-r...
Article
Full-text available
We demonstrate that a computational fluid dynamics (CFD) model enhanced with molecular-level information can accurately predict unsteady nano-scale flows in non-trivial geometries, while being efficient enough to be used for design optimisation. We first consider a converging–diverging nano-scale channel driven by a time-varying body force. The tim...
Article
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We present new hybrid molecular-continuum simulations of water flow through filtration membranes. The membranes consist of aligned carbon nanotubes (CNTs) of high aspect ratio, where the tube diameters are ~1–2 nm and the tube lengths (i.e. the membrane thicknesses) are 2–6 orders of magnitude larger than this. The flow in the CNTs is subcontinuum,...
Conference Paper
We present a hybrid molecular-continuum method for the design and simulation of high-aspect-ratio nanofluidic networks. By generalising the application of constraints, we enable the geometry, i.e. channel heights and lengths, to be the output of the method, removing the need for a costly trial-and-error process. We compare multiple constraint combi...
Article
Full-text available
We present an internal-flow multiscale method ('unsteady-IMM') for compressible, time-varying/unsteady flow problems in nano-confined high-aspect-ratio geometries. The IMM is a hybrid molecular-continuum method that provides accurate flow predictions at macroscopic scales because local microscopic corrections to the continuum-fluid formulation are...
Article
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An open-source implementation of chemistry modeling for the direct simulation Monte Carlo method is presented. Following the recent work of Bird (BirdG. A., “The Q-K Model for Gas Phase Chemical Reaction Rates,” Physics of Fluids, Vol. 23, No. 10, 2011, Paper 106101), an approach known as the quantum-kinetic method has been adopted to describe chem...
Article
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We present a new coupling approach for the time advancement of multi-physics models of multiscale systems. This extends the method of E et al. (2009) [J. Comput. Phys. 228 (2009) 5437–5453] to deal with an arbitrary number of models. Coupling is performed asynchronously, with each model being assigned its own timestep size. This enables accurate lo...
Conference Paper
We present a hybrid molecular-continuum method for the simulation of general nano-fluidic networks, which consist of a multiscale system of channels with high aspect ratios. This develops on the hybrid molecular-continuum internal multiscale method recently devised by Borg et al. [1, 2] with three main additions: a) method generalisation to accurat...
Article
Full-text available
We present a new hybrid method for dilute gas flows that couples a continuum-fluid description to the direct simulation Monte Carlo (DSMC) technique. Instead of using a domain-decomposition framework, we adopt a heterogeneous approach with micro resolution that can capture non-equilibrium or non-continuum fluid behaviour both close to bounding wall...
Article
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We present a hybrid molecular-continuum method for the simulation of general nanofluidic networks of long and narrow channels. This builds on the multiscale method of Borg et al. (Microfluid Nanofluid 15(4):541-557, 2013; J Comput Phys 233:400-413, 2013) for systems with a high aspect ratio in three main ways: (a) the method has been generalised to...
Article
Full-text available
We present a procedure for using molecular dynamics (MD) simulations to provide essential fluid and interface properties for subsequent use in computational fluid dynamics (CFD) calculations of nanoscale fluid flows. The MD pre-simulations enable us to obtain an equation of state, constitutive relations, and boundary conditions for any given fluid/...
Article
The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually "fades-in" (inserts) or "fades-out" (deletes) molecules over a short relaxation period within a MD...
Article
Full-text available
This article compares both new and commonly used boundary conditions for generating pressure-driven water flows through carbon nanotubes in molecular dynamics simulations. Three systems are considered: (1) a finite carbon nanotube membrane with streamwise periodicity and gravity'-type Gaussian forcing, (2) a non-periodic finite carbon nanotube memb...
Article
Full-text available
We develop and apply an efficient multiscale method for simulating a large class of low-speed internal rarefied gas flows. The method is an extension of the hybrid atomistic–continuum approach proposed by Borg et al. (2013) [28] for the simulation of micro/nano flows of high-aspect ratio. The major new extensions are: (1) incorporation of fluid com...
Article
Full-text available
We present a new hybrid method for simulating dense fluid systems that exhibit multiscale behaviour, in particular, systems in which a Navier–Stokes model may not be valid in parts of the computational domain. We apply molecular dynamics as a local microscopic refinement for correcting the Navier–Stokes constitutive approximation in the bulk of the...
Conference Paper
We present a new hybrid molecular-continuum method for modelling the nano flows inside micrometer-thick membranes. Our aim is to obtain results for practical filtration membranes that are as accurate as molecular dynamics (MD) and at the same time significantly more computationally efficient. Computational savings are obtained by replacing long nan...
Article
Full-text available
We present a hybrid molecular-continuum simulation method for modelling nano- and micro-flows in network-type systems. In these types of problem, a full molecular dynamics (MD) description of the macroscopic flow behaviour would be computationally intractable, or at least too expensive to be practical for engineering design purposes. Systems that e...
Article
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We propose a new hybrid algorithm for incompressible micro and nanoflows that applies to non-isothermal steady-state flows and does not require the calculation of the Irving–Kirkwood stress tensor or heat flux vector. The method is validated by simulating the flow in a channel under the effect of a gravity-like force with bounding walls at two diff...
Conference Paper
This paper describes the development and application of a multiscale method for the efficient simulation of a large class of low-speed internal rarefied gas flows. The method is an extension of the hybrid atomistic-continuum approach recently proposed by Borg et al (2013) [J. Comp. Phys., 233, pp 400–413] for the simulation of micro/nano flows of h...
Conference Paper
In this work, the atomistic-continuum hybrid model called the Laplacian method is introduced as a framework for modeling transport phenomena at the micro and nano-scale. The method is explained and the micro-to-macro and macro-to-micro coupling steps discussed. Three techniques for noise reduction (namely the bonsai box, the seamless strategy and t...
Article
We use molecular dynamics (MD) simulations to investigate the dynamic wetting of nanoscale water droplets on moving surfaces. The density and hydrogen bonding profiles along the direction normal to the surface are reported, and the width of the water depletion layer is evaluated first for droplets on three different static surfaces: silicon, graphi...
Article
A new method is presented for the exploitation of time-scale separation in hybrid continuum-molecular models of multiscale flows. Our method is a generalisation of existing approaches, and is evaluated in terms of computational efficiency and physical/numerical error. Comparison with existing schemes demonstrates comparable, or much improved, physi...
Article
Pressure-driven, implicit boundary conditions are implemented in an open source direct simulation Monte Carlo (DSMC) solver, and benchmarked against simple micro-channel flow cases found in the literature. DSMC simulations are then carried out of gas flows for varying degrees of rarefaction along micro-channels with both one and two 90-degree bends...
Article
We develop a new multiscale scheme for simulating micro/nano flows of high aspect ratio in the flow direction, e.g. within long ducts, tubes, or channels, of varying section. The scheme couples conventional hydrodynamic conservation equations for mass and momentum-flux with molecular dynamics (MD) in a unified framework. The method is very much dif...
Article
Full-text available
Non-equilibrium molecular dynamics simulations are performed to investigate how changing the number of structural defects in the wall of a (7,7) single-walled carbon nanotube (CNT) affects water transport and internal fluid dynamics. Structural defects are modelled as vacancy sites (missing carbon atoms). We find that, while fluid flow rates exceed...