177 results found
Muscatello J, Muller EA, Mostofi AA, et al., 2016, Multiscale molecular simulations of the formation and structure of polyamide membranes created by interfacial polymerization, Journal of Membrane Science, Vol: 527, Pages: 180-190, ISSN: 0376-7388
Large scale molecular simulations to model the formation of polyamide membranes have been carried out using a procedure that mimics experimental interfacial polymerization of trimesoyl chloride (TMC) and metaphenylene diamine (MPD) monomers. A coarse-grained representation of the monomers has been developed to facilitate these simulations, which captures essential features of the stereochemistry of the monomers and of amide bonding between them. Atomic models of the membranes are recreated from the final coarse-grained representations. Consistent with earlier treatments, membranes are formed through the growth and aggregation of oligomer clusters. The membranes are inhomogeneous, displaying opposing gradients of trapped carboxyl and amine side groups, local density variations, and regions where the density of amide bonding is reduced as a result of the aggregation process. We observe the interfacial polymerization reaction is self-limiting and the simulated membranes display a thickness of 5–10 nm. They also display a surface roughness of 1–4 nm. Comparisons are made with recently published experimental results on the structure and chemistry of these membranes and some interesting similarities and differences are found.
Ervik A, Lysgaard MO, Herdes C, et al., 2016, A multiscale method for simulating fluid interfaces covered with large molecules such as asphaltenes, Journal of Computational Physics, Vol: 327, Pages: 576-611, ISSN: 0021-9991
The interface between two liquids is fully described by the interfacial tension only for very pure liquids. In most cases the system also contains surfactant molecules which modify the interfacial tension according to their concentration at the interface. This has been widely studied over the years, and interesting phenomena arise, e.g. the Marangoni effect. An even more complicated situation arises for complex fluids like crude oil, where large molecules such as asphaltenes migrate to the interface and give rise to further phenomena not seen in surfactant-contaminated systems. An example of this is the “crumpling drop” experiments, where the interface of a drop being deflated becomes non-smooth at some point. In this paper we report on the development of a multiscale method for simulating such complex liquid–liquid systems. We consider simulations where water drops covered with asphaltenes are deflated, and reproduce the crumpling observed in experiments. The method on the nanoscale is based on using coarse-grained molecular dynamics simulations of the interface, with an accurate model for the asphaltene molecules. This enables the calculation of interfacial properties. These properties are then used in the macroscale simulation, which is performed with a two-phase incompressible flow solver using a novel hybrid level-set/ghost-fluid/immersed-boundary method for taking the complex interface behaviour into account. We validate both the nano- and macroscale methods. Results are presented from nano- and macroscale simulations which showcase some of the interesting behaviour caused by asphaltenes affecting the interface. The molecular simulations presented here are the first in the literature to obtain the correct interfacial orientation of asphaltenes. Results from the macroscale simulations present a new physical explanation of the crumpled drop phenomenon, while highlighting shortcomings in previous hypotheses.
Ervik AS, Serratos GJ, Müller EA, 2016, raaSAFT: A framework enabling coarse-grained molecular dynamics simulations based on the SAFT-γ Mie force field, Computer Physics Communications, Vol: 212, Pages: 161-179, ISSN: 0010-4655
We describe here raaSAFT, a Python code that enables the setup and running of coarse-grained molecular dynamics simulations in a systematic and efficient manner. The code is built on top of the popular HOOMD-blue code, and as such harnesses the computational power of GPUs. The methodology makes use of the SAFT-γ Mie force field, so the resulting coarse grained pair potentials are both closely linked to and consistent with the macroscopic thermodynamic properties of the simulated fluid. In raaSAFT both homonuclear and heteronuclear models are implemented for a wide range of compounds spanning from linear alkanes, to more complicated fluids such as water and alcohols, all the way up to nonionic surfactants and models of asphaltenes and resins. Adding new compounds as well as new features is made straightforward by the modularity of the code. To demonstrate the ease-of-use of raaSAFT, we give a detailed walkthrough of how to simulate liquid–liquid equilibrium of a hydrocarbon with water. We describe in detail how both homonuclear and heteronuclear compounds are implemented. To demonstrate the performance and versatility of raaSAFT, we simulate a large polymer-solvent mixture with 300 polystyrene molecules dissolved in 42 700 molecules of heptane, reproducing the experimentally observed temperature-dependent solubility of polystyrene. For this case we obtain a speedup of more than three orders of magnitude as compared to atomistically-detailed simulations.
Morgado P, Lobanova O, Almedia M, et al., 2016, SAFT-γ force field for the simulation of molecular fluids: 8. hetero-group coarse-grained models of perfluoroalkylalkanes assessed with new vapour-liquid interfacial tension data, Molecular Physics, Vol: 114, Pages: 2597-2614, ISSN: 1362-3028
The air-liquid interfacial behaviour of linear perfluoroalkylalkanes (PFAAs) is reportedthrough a combined experimental and computer simulation study. The surfacetensions of seven liquid PFAAs (perfluorobutylethane, F4H2; perfluorobutylpentane,F4H5; perfluorobutylhexane, F4H6, perfluorobutyloctane, F4H8; perfluorohexylethane,F6H2; perfluorohexylhexane, F6H6; and perfluorohexyloctane, F6H8) are experimentallydetermined over a wide temperature range (276 to 350 K). The corresponding surfacethermodynamic properties and the critical temperatures of the studied compounds areestimated from the temperature dependence of the surface tension. Experimentaldensity and vapour pressure data are employed to parameterize a genericheteronuclear coarse-grained intermolecular potential of the SAFT- γ family for PFAAs.The resulting force field is used in direct molecular dynamics simulations to predictwith quantitative agreement the experimental tensions and to explore theconformations of the molecules in the interfacial region revealing a preferentialalignment of the PFAA molecules towards the interface and an enrichment of theperfluoro-groups at the outer interface region.
Ervik A, Mejia A, Muller EA, 2016, Bottled SAFT: a web app providing SAFT-γ Mie force field parameters for thousands of molecular fluids, Journal of Chemical Information and Modeling, Vol: 56, Pages: 1609-1614, ISSN: 1549-960X
Coarse-grained molecular simulation has become a popular tool for modelling simpleand complex fluids alike. The defining aspects of a coarse grained model are theforce field parameters, which must be determined for each particular fluid. Since thenumber of molecular fluids of interest in nature and in engineering processes is immense,constructing force field parameter tables by individually fitting to experimental data isa futile task. A step towards solving this challenge was taken recently by Mejia et al.,who proposed a correlation that provides SAFT-γ Mie force field parameters for a fluidprovided one knows the critical temperature, the acentric factor and a liquid density,all relatively accesible properties. Building on this, we have applied the correlationto more than 6000 fluids, and constructed a web application, called “Bottled SAFT”which makes this data set easily searchable by CAS number, name or chemical formula. Alternatively, the application allows the user to calculate parameters for componentsnot present in the database. Once the intermolecular potential has been found throughBottled SAFT, code snippets are provided for simulating the desired substance usingthe “raaSAFT” framework, which leverages established molecular dynamics codes torun the simulations. The code underlying the web application is written in Pythonusing the Flask microframework; this allows us to provide a modern high-performanceweb app while also making use of the scientific libraries available in Python. BottledSAFT aims at taking the complexity out of obtaining force field parameters for a widerange of molecular fluids, and facilitates setting up and running coarse-grained molecularsimulations. The web application is freely available at http://www.bottledsaft.org.The underlying source code is available on Bitbucket under a permissive license.
Muller EA, Jackson G, Avendaño C, et al., 2016, Assembly of porous smectic structures formed from interlocking high-symmetry planar nanorings, Proceedings of the National Academy of Sciences of the United States of America, Vol: 113, Pages: 9699-9703, ISSN: 1091-6490
Materials comprising porous structures, often in the form of interconnected concave cavities, are typically assembled from convex molecular building blocks. The use of nanoparticles with a characteristic non-convex shape provide a promising strategy to create new porous materials, an approach that has been recently employed with cage-like molecules to form remarkable liquids with “scrabbled” porous cavities [Giri, N. et al. (2015) Nature 527:216]. Nonconvex mesogenic building blocks can be engineered to form unique self-assembled open structures with tunable porosity and long-range order that is intermediate between that of isotropic liquids and of crystalline solids. Here we propose the design of highly open liquid-crystalline structures from rigid nanorings with unique classes of geometry. By exploiting the entropic ordering characteristics of athermal colloidal particles [Allen, M. P., Evans, G. T., Frenkel, D., Mulder, B. (1993) Adv. Chem. Phys.86:1], we demonstrate that high-symmetry nonconvex rings with large internal cavities interlock within a two-dimensional layered structure leading to the formation of distinctive liquid-crystalline smectic phases. We show that these novel smectic phases possess uniquely high free volumes of up to∼95%, a value significantly larger than the 50% that is typically achievable with smectic phases formed by more conventional convex rodor disc-like mesogenic particles.
Oyewunmi OA, Kirmse CJW, Haslam AJ, et al., 2016, Working-fluid selection and performance investigation of a two-phase single-reciprocating-piston heat-conversion engine, Applied Energy, Vol: 186, Pages: 376-395, ISSN: 0306-2619
We employ a validated first-order lumped dynamic model of the Up-THERM converter, a two-phase unsteadyheat-engine that belongs to a class of innovative devices known as thermofluidic oscillators, which containfewer moving parts than conventional engines and represent an attractive alternative for remote or off-gridpower generation as well as waste-heat recovery. We investigate the performance the Up-THERM withrespect to working-fluid selection for its prospective applications. An examination of relevant working-fluidthermodynamic properties reveals that the saturation pressure and vapour-phase density of the fluid play importantroles in determining the performance of the Up-THERM – the device delivers a higher power outputat high saturation pressures and has higher exergy efficiencies at low vapour-phase densities. Furthermore,working fluids with low critical temperatures, high critical pressures and exhibiting high values of reducedpressures and temperatures result in designs with high power outputs. For a nominal Up-THERM designcorresponding to a target application with a heat-source temperature of 360 ◦C, water is compared withforty-five other pure working fluids. When maximizing the power output, R113 is identified as the optimalfluid, followed by i-hexane. Fluids such as siloxanes and heavier hydrocarbons are found to maximize theexergy and thermal efficiencies. The ability of the Up-THERM to convert heat over a range of heat-sourcetemperatures is also investigated, and it is found that the device can deliver in excess of 10 kW when utilizingthermal energy at temperatures above 200 ◦C. Of all the working fluids considered here, ammonia, R245ca,R32, propene and butane feature prominently as optimal and versatile fluids delivering high power over awide range of heat-source temperatures.
Muller 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: 1944-8244
Recent 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.
Mejia A, Garrido JM, Piñeiro MM, et al., 2016, Interfacial tensions of industrial fluids from a molecular-based square gradient theory, AICHE Journal, Vol: 62, Pages: 1781-1794, ISSN: 0001-1541
This work reports a procedure for predicting the interfacial tension of pure fluids. It is basedon scaling arguments applied to the influence parameter of the van der Waals theory of inhomogeneousfluids. The molecular model stems from the application of the Square Gradient Theory tothe SAFT-VR Mie equation of state. The theory is validated against computer simulation resultsfor homonuclear pearl-necklace linear chains made up to six Mie (λ−6) beads with repulsive exponentsspanning from λ = 8 to 44 by combining the theory with a corresponding states correlationto determine the intermolecular potential parameters. We provide a predictive tool to determineinterfacial tensions for a wide range of molecules including hydrocarbons, fluorocarbons, polarmolecules, among others. The proposed methodology is tested against comparable existing correlationsin the literature, proving to be vastly superior, exhibiting an average absolute deviation of2.2 %.
Muller EA, jackson G, Muscatello J, et al., 2016, Nonequilibrium study of the intrinsic free-energy profile across a liquid-vapour interface, Journal of Chemical Physics, Vol: 144, ISSN: 1089-7690
We calculate an atomistically detailed free-energy profile across a heterogeneous system using anonequilibrium approach. The path-integral formulation of Crooks fluctuation theorem is used inconjunction with the intrinsic sampling method (ISM) to calculate the free-energy profile for theliquid-vapour interface of the Lennard-Jones fluid. Free-energy barriers are found correspondingto the atomic layering in the liquid phase as well as a barrier associated with the presence of anadsorbed layer as revealed by the intrinsic density profile. Our findings are in agreement withprofiles calculated using Widom’s potential distribution theorem applied to both the average andthe intrinsic profiles as well as literature values for the excess chemical potential.
Muller EA, jackson G, Forte E, et al., 2016, Predicting the adsorption of n-perfluorohexane in BAM P109 standard activated carbon by molecular simulation using SAFT-c Mie coarse-grained force fields, Adsorption Science & Technology, Vol: 34, Pages: 64-78, ISSN: 0263-6174
This work is framed within the 8th International Fluid Properties Simulation Challenge(IFPSC), with the aim of assessing the capability of molecular simulation methodsand force fields to accurately predict adsorption in porous media for systems of relevantpractical interest. The current challenge focuses on predicting adsorption isotherms ofn-perfluorohexane in the certified reference material BAM P109 standard activated carbon.A temperature of T = 273 K and pressures of p/p0 = 0.1, 0.3, and 0.6 relative tothe bulk saturation pressure p0 (as predicted by the model) are the conditions selectedin this challenge. In our methodology we use coarse-grained (CG) intermolecular modelsand a top-down technique where an accurate equation of state (EoS) is used to link theexperimental macroscopic properties of a fluid to the force-field parameters. The stateof-the-artversion of the statistical associating fluid theory for potentials of variable rangeas reformulated in the Mie group contribution incarnation (SAFT-γ Mie) is employedhere. The parameters of the SAFT-γ Mie force field are estimated directly from thevapour pressure and saturated liquid density data of the pure fluids using the EoS, andfurther validated by molecular dynamic simulations. The coarse-grained intermolecularpotential models are then used to obtain the adsorption isotherm kernels for argon, carbondioxide, and n-perfluorohexane in graphite slit pores of various widths using GrandCanonical Monte Carlo (GCMC) simulations. A unique and fluid-independent pore sizedistribution (PSD) curve with total micropore volume of 0.5802 cm3/g is proposed for theBAM P109. The PSD is obtained by applying a non-linear regression procedure over theadsorption integral equation to minimise the quadratic error between the available ex-perimental adsorption isotherms for argon and carbon dioxide and purpose-built GCMCkernels.The predicted adsorption levels of n-perfluorohexane at 273K in BAM P109 are72.75±0.01, 7
Jackson G, Lau GV, Muller EA, et al., 2015, Water droplet excess free energy determined by cluster mitosis using guidedmolecular dynamics, Journal of Chemical Physics, Vol: 143, ISSN: 1089-7690
Atmospheric aerosols play a vital role in affecting climate by influencing the properties and lifetimes of clouds and precipitation. Understanding the underlying microscopic mechanisms involved in the nucleation of aerosol droplets from the vapour phase is therefore of great interest. One key thermodynamic quantity in nucleation is the excess free energy of cluster formation relative to that of the saturated vapour. In our current study, the excess free energy is extracted for clusters of pure water modelled with the TIP4P/2005 intermolecular potential using a method based on nonequilibrium molecular dynamics and the Jarzynski relation. The change in free energy associated with the “mitosis” or division of a cluster of N water molecules into two N/2 sub-clusters is evaluated. This methodology is an extension of the disassembly procedure used recently to calculate the excess free energy of argon clusters [H. Y. Tang and I. J. Ford, Phys. Rev. E 91, 023308 (2015)]. Our findings are compared to the corresponding excess free energies obtained from classical nucleation theory (CNT) as well as internally consistent classical theory (ICCT). The values of the excess free energy that we obtain with the mitosis method are consistent with CNT for large cluster sizes but for the smallest clusters, the results tend towards ICCT; for intermediate sized clusters, we obtain values between the ICCT and CNT predictions. Furthermore, the curvature-dependent surface tension which can be obtained by regarding the clusters as spherical droplets of bulk density is found to be a monotonically increasing function of cluster size for the studied range. The data are compared to other values reported in the literature, agreeing qualitatively with some but disagreeing with the values determined by Joswiak et al. [J. Phys. Chem. Lett. 4, 4267 (2013)] using a biased mitosis approach; an assessment of the differences is the main motivation for our current study.
Wu L, Malijevsky A, Jackson G, et al., 2015, Orientational ordering and phase behaviour of binary mixtures of hard spheres and hard spherocylinders (vol 143, 044906, 2015), Journal of Chemical Physics, Vol: 143, ISSN: 1089-7690
Theodorakis PE, Müller EA, Craster RV, et al., 2015, Modelling the superspreading of surfactant-laden droplets with computer simulation., Soft Matter, Vol: 11, Pages: 9254-9261, ISSN: 1744-6848
The surfactant-driven superspreading of droplets on hydrophobic substrates is considered. A key element of the superspreading mechanism is the adsorption of surfactant molecules from the liquid-vapour interface onto the substrate through the contact line, which must be coordinated with the replenishment of interfaces with surfactant from the interior of the droplet. We use molecular dynamics simulations with coarse-grained force fields to provide a detailed structural description of the droplet shape and surfactant dynamics during the superspreading process. We also provide a simple method for accurate estimation of the contact angle subtended by the droplets at the contact line.
Muller EA, Jackson G, Lobanova O, et al., 2015, SAFT-γ Force Field for the Simulation of Molecular Fluids 6. Binary and ternary mixtures comprising water, carbon dioxide, and n-alkanes, The Journal of Chemical Thermodynamics, Vol: 93, Pages: 320-336, ISSN: 0021-9614
The SAFT-γ coarse graining methodology [E. A. Muller and G. Jackson, Ann. Rev. Chem. Biomol. Eng. ¨ 5, 405(2014)] is used to develop force fields for the fluid-phase behaviour of binary and ternary mixtures comprising water,carbon dioxide, and n-alkanes. The effective intermolecular interactions between the coarse grained (CG) segmentsare directly related to macroscopic thermodynamic properties by means of the SAFT-γ equation of state for molecularsegments represented with the Mie (generalized Lennard-Jones) intermolecular potential [V. Papaioannou, T. Lafitte,C. Avendano, C. S. Adjiman, G. Jackson, E. A. M ˜ uller, and A. Galindo, J. Chem. Phys. ¨ 140, 054107 (2014)].The unlike attractive interactions between the components of the mixtures are represented with a single adjustableparameter, which is shown to be transferable over a wide range of conditions. The SAFT-γ Mie CG force fieldsare used in molecular-dynamics simulations to predict the challenging vapour-liquid and liquid-liquid fluid-phaseequilibria characterising these mixtures, and to study properties that are not accessible directly from the equation ofstate, such as the interfacial properties. The description of the fluid-phase equilibria and interfacial properties predictedwith the SAFT-γ Mie force fields is in excellent with the corresponding experimental data, and of comparable if notsuperior quality to that reported for the more sophisticated atomistic or united-atom models.
Jover J, Galindo A, Jackson G, et al., 2015, Fluid-fluid coexistence in an athermal colloid-polymer mixture: thermodynamic perturbation theory and continuum molecular-dynamics simulation, MOLECULAR PHYSICS, Vol: 113, Pages: 2608-2628, ISSN: 0026-8976
Jackson G, Wu L, Avendano C, et al., 2015, Orientational ordering and phase behaviour of binary mixtures of hardspheres and hard spherocylinders, The Journal of Chemical Physics, Vol: 143, ISSN: 0021-9606
We study structure and fluid-phase behaviour of a binary mixture of hard spheres(HSs) and hard spherocylinders (HSCs) in isotropic and nematic states using theNPnAT ensemble Monte Carlo (MC) method in which a normal pressure tensorcomponent is fixed in a system confined between two hard walls. The method allowsone to estimate the location of the isotropic-nematic phase transition and to observethe asymmetry in the composition between the coexisting phases, with the expectedincrease of the HSC concentration in the nematic phase. This is in stark contrastwith the previously reported MC simulations where a conventional isotropic NP Tensemble was used. We further compare the simulation results with the theoreticalpredictions of two analytic theories that extend the original Parsons-Lee theory usingthe one-fluid and the many-fluid approximation [Malijevsk´y at al J. Chem. Phys.129, 144504 (2008)]. In the one-fluid version of the theory the properties of themixture are mapped on an effective one-component HS system while in the many-fluid theory the components of the mixtures are represented as separate effective HSparticles. The comparison reveals that both the one- and the many-fluid approachesprovide a reasonably accurate quantitative description of the mixture including thepredictions of the isotropic-nematic phase boundary and degree of orientational orderof the HSC-HS mixtures.
Muller EA, totton TS, Herdes C, 2015, Coarse grained force field for the molecular simulation of natural gases and condensates, Fluid Phase Equilibria, Vol: 406, Pages: 91-100, ISSN: 0378-3812
The atomistically-detailed molecular modelling of petroleum fluids is challenging, amongst other aspects, due to the very diverse multicomponent and asymmetric nature of the mixtures in question. Complicating matters further, the time scales for many important processes can be much larger than the current and foreseeable capacity of modern computers running fully-atomistic models. To overcome these limitations, a coarse grained (CG) model is proposed where some of the less-important degrees of freedom are safely integrated out, leaving as key parameters the average energy levels, the molecular conformations and the range of the Mie intermolecular potentials employed as the basis of the model. The parametrization is performed by using an analytical equation of state of the statistical associating fluid theory (SAFT) family to link the potential parameters to macroscopically observed thermophysical properties. The parameters found through this top-down approach are used directly in molecular dynamics simulations of multi-component multi-phase systems. The procedure is exemplified by calculating the phase envelope of the methane–decane binary and of two synthetic light condensate mixtures. A methodology based on the discrete expansion of a mixture is used to determine the bubble points of these latter mixtures, with an excellent agreement to experimental data. The model presented is entirely predictive and an abridged table of parameters for some fluids of interest is provided.
Theodorakis P, Kovalchuk NM, Starov VM, et al., 2015, Superspreading: Mechanisms and Molecular Design, Mainz Material Simulation Days 2015, Pages: 29-29
Ramrattan NS, Avendano C, Mueller EA, et al., 2015, A corresponding-states framework for the description of the Mie family of intermolecular potentials, MOLECULAR PHYSICS, Vol: 113, Pages: 932-947, ISSN: 0026-8976
Herdes C, Santiso EE, James C, et al., 2015, Modelling the interfacial behaviour of dilute light-switching surfactant solutions, Journal of Colloid and Interface Science, Vol: 445, Pages: 16-23, ISSN: 1095-7103
The direct molecular modelling of an aqueous surfactant system at concentrations below the critical micelle concentration (pre-cmc) conditions is unviable in terms of the presently available computational power. Here, we present an alternative that combines experimental information with tractable simulations to interrogate the surface tension changes with composition and the structural behaviour of surfactants at the water–air interface. The methodology is based on the expression of the surface tension as a function of the surfactant surface excess, both in the experiments and in the simulations, allowing direct comparisons to be made. As a proof-of-concept a coarse-grained model of a light switching non-ionic surfactant bearing a photosensitive azobenzene group is considered at the air–water interface at 298 K. Coarse-grained molecular dynamic simulations are detailed based on the use of the SAFT force field with parameters tuned specifically for this purpose. An excellent agreement is obtained between the simulation predictions and experimental observations; furthermore, the molecular model allows the rationalization of the macroscopic behaviour in terms of the different conformations of the cis and trans surfactants at the surface.
Lobanova O, Avendaño C, Avendaño C, et al., 2015, SAFT-γ force field for the simulation of molecular fluids: 4. A single-site coarse-grained model of water applicable over a wide temperature range, Molecular Physics, Vol: 113, Pages: 1228-1249, ISSN: 1362-3028
© 2015 The Author(s). In this work, we develop coarse-grained (CG) force fields for water, where the effective CG intermolecular interactions between particles are estimated from an accurate description of the macroscopic experimental vapour-liquid equilibria data by means of a molecular-based equation of state. The statistical associating fluid theory for Mie (generalised Lennard-Jones) potentials of variable range (SAFT-VR Mie) is used to parameterise spherically symmetrical (isotropic) force fields for water. The resulting SAFT-γ CG models are based on the Mie (8-6) form with size and energy parameters that are temperature dependent; the latter dependence is a consequence of the angle averaging of the directional polar interactions present in water. At the simplest level of CG where a water molecule is represented as a single bead, it is well known that an isotropic potential cannot be used to accurately reproduce all of the thermodynamic properties of water simultaneously. In order to address this deficiency, we propose two CG potential models of water based on a faithful description of different target properties over a wide range of temperatures: our CGW1-vle model is parameterised to match the saturated-liquid density and vapour pressure; our other CGW1-ift model is parameterised to match the saturated-liquid density and vapour-liquid interfacial tension. A higher level of CG corresponding to two water molecules per CG bead is also considered: the corresponding CGW2-bio model is developed to reproduce the saturated-liquid density and vapour-liquid interfacial tension in the physiological temperature range, and is particularly suitable for the large-scale simulation of bio-molecular systems. A critical comparison of the phase equilibrium and transport properties of the proposed force fields is made with the more traditional atomistic models.
Lau GV, Ford IJ, Hunt PA, et al., 2015, Surface thermodynamics of planar, cylindrical, and spherical vapour-liquid interfaces of water, Journal of Chemical Physics, Vol: 142, ISSN: 1089-7690
Frentrup H, Hart KE, Colina CM, et al., 2015, In Silico Determination of Gas Permeabilities by Non-Equilibrium Molecular Dynamics: CO2 and He through PIM-1., Membranes, Vol: 5, Pages: 99-119, ISSN: 2077-0375
We study the permeation dynamics of helium and carbon dioxide through an atomistically detailed model of a polymer of intrinsic microporosity, PIM-1, via non-equilibrium molecular dynamics (NEMD) simulations. This work presents the first explicit molecular modeling of gas permeation through a high free-volume polymer sample, and it demonstrates how permeability and solubility can be obtained coherently from a single simulation. Solubilities in particular can be obtained to a very high degree of confidence and within experimental inaccuracies. Furthermore, the simulations make it possible to obtain very specific information on the diffusion dynamics of penetrant molecules and yield detailed maps of gas occupancy, which are akin to a digital tomographic scan of the polymer network. In addition to determining permeability and solubility directly from NEMD simulations, the results shed light on the permeation mechanism of the penetrant gases, suggesting that the relative openness of the microporous topology promotes the anomalous diffusion of penetrant gases, which entails a deviation from the pore hopping mechanism usually observed in gas diffusion in polymers.
Jover JF, Mueller EA, Haslam AJ, et al., 2015, Aspects of Asphaltene Aggregation Obtained from Coarse-Grained Molecular Modeling, ENERGY & FUELS, Vol: 29, Pages: 556-566, ISSN: 0887-0624
Yang J, Serratos MGJ, Fari-Arole DS, et al., 2015, Crude Oil Fouling: Fluid Dynamics, Reactions and Phase Change, IUTAM SYMPOSIUM ON MULTIPHASE FLOWS WITH PHASE CHANGE: CHALLENGES AND OPPORTUNITIES, Vol: 15, Pages: 186-193, ISSN: 2210-9838
Coletti F, Crittenden BD, Haslam AJ, et al., 2015, Modeling of Fouling from Molecular to Plant Scale, Crude Oil Fouling: Deposit Characterization, Measurements, and Modeling, Pages: 179-320, ISBN: 9780128012567
© 2015 Elsevier Inc. All rights reserved. Chapter 5 describes a multiscale approach to modeling of crude oil fouling focused on improving understanding from the molecular level to industrial-scale systems. At the molecular scale, modeling work allows the determination of key parameters, such as diffusion coefficients and fluid physical properties, which can be used in thermodynamic equations of state and detailed fluid-dynamic models to predict fouling deposition in simple flows. At large scale, advanced system models of refinery heat exchangers and heat exchanger networks incorporate the lessons learned from the smaller scale models and provide the ability to predict the future course of fouling. It is shown how these models can be used for accurately assessing operational costs due to fouling, assisting in heat exchanger design, and devising improved operating strategies that minimize costs.
Jimenez Serratos MG, Haslam AJ, Jackson G, et al., 2014, 5. Modeling of Fouling from Molecular to Plant Scale5.2 Thermodynamic and Molecular Modeling, Crude Oil Fouling Deposit Characterization, Measurements, and Modeling, Editors: Coletti, Hewitt, Publisher: Gulf Professional Publishing, ISBN: 9780128013595
With production from unconventional rigs continuing to escalate and refineries grappling with the challenges of shale and heavier oil feedstocks, petroleum engineers and refinery managers must ensure that equipment used with today’s crude ...
Jimenez Serratos MG, Haslam AJ, Jackson G, et al., 2014, 5. Modeling of Fouling from Molecular to Plant Scale5.2 Thermodynamic and Molecular Modeling, Crude Oil Fouling Deposit Characterization, Measurements, and Modeling, Editors: coletti, Hewitt, Publisher: Gulf Professional Publishing, ISBN: 9780128013595
With production from unconventional rigs continuing to escalate and refineries grappling with the challenges of shale and heavier oil feedstocks, petroleum engineers and refinery managers must ensure that equipment used with today’s crude ...
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