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Journal articleMuller EA, Matar OK, Jaeger F, et al., 2016,
Optimising water transport through graphene-based membranes: Insights from non-equilibrium molecular dynamics
, ACS Applied Materials & Interfaces, Vol: 8, Pages: 12330-12336, ISSN: 1944-8244Recent experimental results suggest that stacked layers of graphene oxide exhibitstrong selective permeability to water. To construe this observation the transportmechanism of water permeating through a membrane consisting of layered graphenesheets is investigated via non-equilibrium and equilibrium molecular dynamics simulations.The effect of sheet geometry is studied by changing the offset between theentrance and exit slits of the membrane. The simulation results reveal that the permeabilityis not solely dominated by entrance effects; the path traversed by watermolecules has a considerable impact on the permeability. We show that contrary tospeculation in the literature, water molecules do not pass through the membrane as ahydrogen-bonded chain; instead, they form well-mixed fluid regions confined betweenthe graphene sheets. The results of the present work are used to provide guidelinesfor the development of graphene and graphene oxide membranes for desalination andsolvent separation.
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Journal articleFerretti GL, Nania M, Matar OK, et al., 2016,
Wrinkling measurement of the mechanical properties of drying salt thin films
, Langmuir, Vol: 32, Pages: 2199-2207, ISSN: 1520-5827 -
Journal articlePavlidis D, Gomes JLMA, Xie Z, et al., 2016,
Compressive advection and multi-component methods for interface-capturing
, International Journal for Numerical Methods in Fluids, Vol: 80, Pages: 256-282, ISSN: 0271-2091This paper develops methods for interface-capturing in multiphase flows. The main novelties of these methods are as follows: (a) multi-component modelling that embeds interface structures into the continuity equation; (b) a new family of triangle/tetrahedron finite elements, in particular, the P1DG-P2(linear discontinuous between elements velocity and quadratic continuous pressure); (c) an interface-capturing scheme based on compressive control volume advection methods and high-order finite element interpolation methods; (d) a time stepping method that allows use of relatively large time step sizes; and (e) application of anisotropic mesh adaptivity to focus the numerical resolution around the interfaces and other areas of important dynamics. This modelling approach is applied to a series of pure advection problems with interfaces as well as to the simulation of the standard computational fluid dynamics benchmark test cases of a collapsing water column under gravitational forces (in two and three dimensions) and sloshing water in a tank. Two more test cases are undertaken in order to demonstrate the many-material and compressibility modelling capabilities of the approach. Numerical simulations are performed on coarse unstructured meshes to demonstrate the potential of the methods described here to capture complex dynamics in multiphase flows.
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Journal articleKovalchuk NM, Matar OK, Craster RV, et al., 2016,
The effect of adsorption kinetics on the rate of surfactant-enhanced spreading
, Soft Matter, Vol: 12, Pages: 1009-1013, ISSN: 1744-6848A comparison of the kinetics of spreading of aqueous solutions of two different surfactants on an identical substrate and their short time adsorption kinetics at the water/air interface has shown that the surfactant which adsorbs slower provides a higher spreading rate. This observation indicates that Marangoni flow should be an important part of the spreading mechanism enabling surfactant solutions to spread much faster than pure liquids with comparable viscosities and surface tensions.
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Journal articleChe Z, Deygas A, Matar OK, 2015,
Impact of droplets on inclined flowing liquid films
, Physical Review E, Vol: 92, ISSN: 1539-3755The impact of droplets on an inclined falling liquid film is studied experimentally using high-speed imaging.The falling film is created on a flat substrate with controllable thicknesses and flow rates. Droplets with differentsizes and speeds are used to study the impact process under various Ohnesorge and Weber numbers, and filmReynolds numbers. A number of phenomena associated with droplet impact are identified and analyzed, suchas bouncing, partial coalescence, total coalescence, and splashing. The effects of droplet size, speed, as well thefilm flow rate are studied culminating in the generation of an impact regime map. The analysis of the lubricationforce acted on the droplet via the gas layer shows that a higher flow rate in the liquid film produces a largerlubrication force, slows down the drainage process, and increases the probability of droplet bouncing. Our resultsdemonstrate that the flowing film has a profound effect on the droplet impact process and associated phenomena,which are markedly more complex than those accompanying impact on initially quiescent films.
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Journal articleHennessy M, Vitale A, Cabral JT, et al., 2015,
Role of heat generation and thermal diffusion during frontal photopolymerization
, Physical Review E, Vol: 92, Pages: 022403-022403, ISSN: 1539-3755Frontal photopolymerisation (FPP) is a rapid and versatile solidification process that can be used to fabricate complex three-dimensional structures by selectively exposing a photosensitive monomer-rich bath to light. A characteristic feature of FPP is the appearance of a sharp polymerisation front that propagates into the bath as a planar travelling wave. In this paper, we introduce a theoretical model to determine how heat generation during photopolymerisation influences the kinetics of wave propagation as well as the monomer-to-polymer conversion profile, both of which are relevant for FPP applications and experimentally measurable. When thermal diffusion is sufficiently fast relative to the rate of polymerisation, the system evolves as if it were isothermal. However, when thermal diffusion is slow, a thermal wavefront develops and propagates at the same rate as the polymerisation front. This leads to an accumulation of heat behind the polymerisation front which can result in a significant sharpening of the conversion profile and acceleration of the growth of the solid. Our results also suggest that a novel way to tailor the dynamics of FPP is by imposing a temperature gradient along the growth direction.
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Journal articleTripathi MK, Sahu KC, Karapetsas G, et al., 2015,
Bubble rise dynamics in a viscoplastic material
, JOURNAL OF NON-NEWTONIAN FLUID MECHANICS, Vol: 222, Pages: 217-226, ISSN: 0377-0257- Author Web Link
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Conference paperIbarra R, Zadrazil I, Markides CN, et al., 2015,
Towards a Universal Dimensionless Map of Flow Regime Transitions in Horizontal Liquid-Liquid Flows
, 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics -
Journal articleHennessy MG, Vitale A, Matar OK, et al., 2015,
Controlling frontal photopolymerization with optical attenuation and mass diffusion
, Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, Vol: 91, ISSN: 1063-651XFrontal photopolymerization (FPP) is a versatile directional solidification process that can be used to rapidly fabricate polymer network materials by selectively exposing a photosensitive monomer bath to light. A characteristic feature of FPP is that the monomer-to-polymer conversion profiles take on the form of traveling waves that propagate into the unpolymerized bulk from the illuminated surface. Practical implementations of FPP require detailed knowledge about the conversion profile and speed of these traveling waves. The purpose of this theoretical study is to (i) determine the conditions under which FPP occurs and (ii) explore how optical attenuation and mass transport can be used to finely tune the conversion profile and propagation kinetics. Our findings quantify the strong optical attenuation and slow mass transport relative to the rate of polymerization required for FPP. The shape of the traveling wave is primarily controlled by the magnitude of the optical attenuation coefficients of the neat and polymerized material. Unexpectedly, we find that mass diffusion can increase the net extent of polymerization and accelerate the growth of the solid network. The theoretical predictions are found to be in excellent agreement with experimental data acquired for representative systems.
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Conference paperIbarra R, Matar OK, Markides CN, et al., 2015,
An experimental study of oil-water flows in horizontal pipes
, Multiphase 2015, Publisher: BHR GroupThis paper reports an effort to investigate the effect of flow velocities and inlet configurations on horizontal oil-water flows in a 32 mm ID acrylic pipe using water and an aliphatic oil (Exxsol D140) as test fluids. The flows of interest were analysed using pressure drop measurements and high-speed photography in an effort to obtain a flow pattern map, pressure gradient profiles and measures of the in situ phase fractions. The experiments reveal a particular effect of the inlet configuration on the observed flow pattern. A horizontal plate, installed at the inlet, generates a transition to stratified flow when the plate height closely matched the in situ water height at high input oil fractions.
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