Filip Moučka - Academia.edu (original) (raw)

Papers by Filip Moučka

Research paper thumbnail of Molecular dynamics of preferential adsorption in mixed alkali–halide electrolytes at graphene electrodes

The Journal of Chemical Physics

Understanding the microscopic behavior of aqueous electrolyte solutions in contact with graphene ... more Understanding the microscopic behavior of aqueous electrolyte solutions in contact with graphene and related carbon surfaces is important in electrochemical technologies, such as capacitive deionization or supercapacitors. In this work, we focus on preferential adsorption of ions in mixed alkali–halide electrolytes containing different fractions of Li+/Na+ or Li+/K+ and/or Na+/K+ cations with Cl− anions dissolved in water. We performed molecular dynamics simulations of the solutions in contact with both neutral and positively and negatively charged graphene surfaces under ambient conditions, using the effectively polarizable force field. The simulations show that large ions are often intuitively attracted to oppositely charged electrodes. In contrast, the adsorption behavior of small ions tends to be counterintuitive. In mixed-cation solutions, one of the cations always supports the adsorption of the other cation, while the other cation weakens the adsorption of the first cation. In...

Research paper thumbnail of Polarizable force fields for accurate molecular simulations of aqueous solutions of electrolytes, crystalline salts, and solubility: Li+, Na+, K+, Rb+, F−, Cl−, Br−, I−

Journal of Molecular Liquids

Research paper thumbnail of Molecular dynamics of the interfacial solution structure of alkali-halide electrolytes at graphene electrodes

Journal of Molecular Liquids, 2022

Research paper thumbnail of Molecular dynamics simulation study of the effect of a strong electric field on the structure of a poly(oxyethylene) chain in explicit solvents

Journal of Molecular Liquids, 2021

A non-halogenated type of chiral ionic liquids (CIL's) called 1-butyl-3-methylimidazolium (T-4)-b... more A non-halogenated type of chiral ionic liquids (CIL's) called 1-butyl-3-methylimidazolium (T-4)-bis[(αS)-α-(hydroxy-O) benzeneacetato-κO] borate, [BMIm+] [BSMB−], has been used for enantioseparation of propranolol enantiomers. Experimental studies indicate that carbon nanotubes (CNT's) increase the Enantioselectivity of chiral ionic liquids through the enhancement of the interaction surface of chiral selectors with the compounds enantiomers. With the aim of investigating the mechanism under this observation, we used Molecular Dynamics (MD) Simulations to investigate the molecular level picture of the behavior of CIL and propranolol enantiomers on the Single-Walled Carbon Nanotube (SWCNT) surface. The density profiles, micro structure, radial distribution function, dimer existence autocorrelation function (DAF) and dynamic properties of propranolol enantiomers were studied in the CIL/CNT solution. The results are indicative of stronger interactions between R-propranolol enantiomers with CIL and CNT surface. Furthermore stronger interactions were seen between the Rpropranolol molecules with one another. This leads to the difference in the replacement of propranolol enantiomers on the CNT surface in such a way that R-propranolol molecules propagate more along the CNT to have the maximum interactions with CIL molecules. The diffusion coefficient difference between S-propranolol and Rpropranolol molecules shows a higher value in comparison to the system that CNT is absent. Consequently, the interactions, propagation and mobility of propranolol enantiomers are strongly influenced by CNT presence.

Research paper thumbnail of Structure of supercooled water: Polarizable BK3 model versus non-polarizable models

Journal of Molecular Liquids, 2018

Research paper thumbnail of Molecular Dynamics of Graphene–Electrolyte Interface: Interfacial Solution Structure and Molecular Diffusion

The Journal of Physical Chemistry C, 2019

Research paper thumbnail of Thermodynamics of supersaturated steam: Towards an equation of state

Fluid Phase Equilibria, 2018

Thermodynamics of supersaturated (supercooled) steam at conditions occurring in steam turbines, a... more Thermodynamics of supersaturated (supercooled) steam at conditions occurring in steam turbines, and inaccessible thus to experiments, has been studied by a number of theoretical and semi-theoretical methods with the goal to assess available theoretical tools for developing an equation of state. Extended virial expansions with different reference systems have been used along with two, qualitatively different equations of state. According to the proposed strategy, all equations were first used for the vapor-liquid coexistence curve and then extended to the metastable region and tested against computer simulation data. Despite the fact that no specificities of supersaturated steam have been accounted for, all the considered methods provide results with deviations from (pseudo)experimental data up to about 5% over the entire range of thermodynamic conditions except the critical region. It turns out that the perturbed virial expansion with a suitably chosen reference system outperforms other methods, including equations of state originally developed for liquid water.

Research paper thumbnail of Saturated aqueous NaCl solution and pure water in Na-montmorillonite clay at thermodynamic conditions of hydraulic fracturing: Thermodynamics, structure and diffusion from molecular simulations

Journal of Molecular Liquids, 2018

We present a Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation study of a... more We present a Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation study of an aqueous NaCl solution in Na-montmorillonite (Na-MMT) clay pores, including the thermodynamic, structural and dynamical properties. We represent the clay pores by Na-MMT slits of an interlayer separation ranging from about 10 to 32Å, covering clay pores from dry clay to clay pores with a bulk-like water layer in the middle of the pore. We consider the clay in equilibrium with the saturated salt solution at a typical shale gas reservoir condition of a temperature of 365 K and a pressure of 275 bar. The equilibrium amount of the adsorbed ions and water molecules obtained from the GCMC simulations are employed in MD to simulate the disjoining pressure and in turn the swelling free energy curve which determines the number of stable states in the clay, their composition, and the corresponding equilibrium interlayer separations. In addition, using MD simulations, we evaluate the hydration energy, atomic and charge density profiles, orientation distribution, hydrogen-bond network, and in-plane self-diffusivity of the water and ions to provide insight into the microscopic behaviour of the aqueous NaCl solution in the interlayer galleries of the hydrophilic Na-MMT pores. We compare the simulation results for the confined aqueous NaCl solutions with those obtained for the Na-MMT in equilibrium with a pure water reservoir at the same temperature and pressure.

Research paper thumbnail of Higher virial coefficients of water

Journal of Molecular Liquids, 2018

Virial coefficients B 2 to B 4 for the non-polarizable TIP4P/2005 model of water and the polariza... more Virial coefficients B 2 to B 4 for the non-polarizable TIP4P/2005 model of water and the polarizable BK3 model were computed. An analysis and assessment of available experimental and pseudoexperimental data is carried out. Various forms of the virial expansion are examined with respect to their potential use for the description of steam (working agent in turbines). At higher temperatures (higher densities) the expansion starts exhibiting an irregular behavior indicating that at these conditions the vapor can likely not be viewed as a system made up only of individual molecules, and the occurrence of clusters of different size must be accounted for.

Research paper thumbnail of Recent progress in the molecular simulation of thermodynamic properties of aqueous electrolyte solutions

Fluid Phase Equilibria, 2018

We review progress in the development and application of molecular simulation methodology to pred... more We review progress in the development and application of molecular simulation methodology to predict the thermodynamic properties of aqueous electrolytes, focussing on work published since our previous review along similar lines [I. Nezbeda, et al., Mol. Phys. 114 (2016) 1665]. We consider such developments in the context of the use of Monte Carlo (MC) or Molecular Dynamics (MD) simulation methodologies using classical force fields. Special attention is paid to the incorporation of charge scaling approaches in the force fields, as well as to the simulation methodology used to compute solubility and osmotic pressure, and the use of the latter quantity to calculate the water activity and osmotic coefficient, and the electrolyte activity coefficient. We emphasize the importance of the statistical analysis of thermodynamic properties obtained from simulation data, and illustrate it with an example analyzing simulation osmotic pressure and electrolyte chemical potential data.

Research paper thumbnail of {"__content__"=>"Chemical potentials of alkaline earth metal halide aqueous electrolytes and solubility of their hydrates by molecular simulation: Application to CaCl, antarcticite, and sinjarite.", "sub"=>{"__content__"=>"2"}}

The Journal of chemical physics, Jan 14, 2018

We present a molecular-level simulation study of CaCl in water and crystalline hydrates formed by... more We present a molecular-level simulation study of CaCl in water and crystalline hydrates formed by CaCl at ambient (298.15 K, 1 bar) conditions and at a high-temperature high-pressure state (365 K, 275 bars) typical of hydraulic fracturing conditions in natural-gas extraction, at which experimental properties are poorly characterized. We focus on simulations of chemical potentials in both solution and crystalline phases and on the salt solubility, the first time to our knowledge that such properties have been investigated by molecular simulation for divalent aqueous electrolytes. We first extend our osmotic ensemble Monte Carlo simulation technique [F. Moučka et al., J. Phys. Chem. B 115, 7849-7861 (2011)] to such solutions. We then describe and apply new methodology for the simulation of the chemical potentials of the experimentally observed crystalline hydrates at ambient conditions (antarcticite, CaCl·6HO) and at high-temperature conditions (sinjarite, CaCl·2HO). We implement our ...

Research paper thumbnail of Thermodynamics of supersaturated steam: Molecular simulation results

The Journal of Chemical Physics, 2016

has been simulated at conditions occurring in steam turbines using the multiple-particle-move Mon... more has been simulated at conditions occurring in steam turbines using the multiple-particle-move Monte Carlo for both the homogeneous phase and also implemented for the Gibbs ensemble Monte Carlo molecular simulation methods. Because of these thermodynamic conditions, a specific simulation algorithm has been developed to bypass common simulation problems resulting from very low densities of steam and cluster formation therein. In addition to pressure-temperature-density and orthobaric data, the distribution of clusters has also been evaluated. The obtained extensive data of high precision should serve as a basis for development of reliable molecular-based equations for properties of metastable steam.

Research paper thumbnail of Recent progress in molecular simulation of aqueous electrolytes: force fields, chemical potentials and solubility

Molecular Physics, 2016

Although aqueous electrolytes are among the most important solutions, the molecular simulation of... more Although aqueous electrolytes are among the most important solutions, the molecular simulation of their intertwined properties of chemical potentials, solubility and activity coefficients has remained a challenging problem, and has attracted considerable recent interest. In this perspectives review, we focus on the simplest case of aqueous sodium chloride at ambient conditions and discuss the two main factors that have impeded progress. The first is lack of consensus with respect to the appropriate methodology for force field (FF) development. We examine how most commonly used FFs have been developed, and emphasize the importance of distinguishing between "Training Set Properties" used to fit the FF parameters, and "Test Set Properties", which are pure predictions of additional properties. The second is disagreement among solubility results obtained, even using identical FFs and thermodynamic conditions. Solubility calculations have been approached using both thermodynamic-based methods and direct molecular dynamics-based methods implementing coexisting solution and solid phases. Although convergence has been very recently achieved among results based on the former approach, there is as yet no general agreement with simulation results based on the latter methodology. We also propose a new method to directly calculate the electrolyte standard chemical potential in the Henry-Law ideality model. We conclude by making recommendations for calculating solubility, chemical potentials and activity coefficients, and outline a potential path for future progress.

Research paper thumbnail of Modelling aqueous solubility of sodium chloride in clays at thermodynamic conditions of hydraulic fracturing by molecular simulations

Physical Chemistry Chemical Physics, 2017

To address the high salinity of flow-back water during hydraulic fracturing, we have studied the ... more To address the high salinity of flow-back water during hydraulic fracturing, we have studied the equilibrium partitioning of NaCl and water between the bulk phase and clay pores.

Research paper thumbnail of Molecular modeling and simulations

Electrospun Nanofibers, 2017

Abstract This chapter reviews the application of standard molecular simulation techniques to the ... more Abstract This chapter reviews the application of standard molecular simulation techniques to the phenomenon of electrospinning. It provides a description of the basics of molecular simulations, with an emphasis on molecular dynamics, followed by an overview of specific considerations for electrospinning. The chapter also discusses the choice of simulation box arrangement, boundary conditions, and force fields, along with other technical details relevant to the molecular modeling of fluid interfaces in the presence of an electric field. We show selected applications and outline future perspectives.

Research paper thumbnail of Salt and Water Uptake in Nanoconfinement under Applied Electric Field: An Open Ensemble Monte Carlo Study

The Journal of Physical Chemistry C, 2015

ABSTRACT

Research paper thumbnail of Chemical Potentials, Activity Coefficients, and Solubility in Aqueous NaCl Solutions: Prediction by Polarizable Force Fields

Journal of Chemical Theory and Computation, 2015

We describe a computationally efficient molecular simulation methodology for calculating the conc... more We describe a computationally efficient molecular simulation methodology for calculating the concentration dependence of the chemical potentials of both solute and solvent in aqueous electrolyte solutions, based on simulations of the salt chemical potential alone. We use our approach to study the predictions for aqueous NaCl solutions at ambient conditions of these properties by the recently developed polarizable force fields (FFs) AH/BK3 of Kiss and Baranyai (

Research paper thumbnail of Application of molecular simulations: Insight into liquid bridging and jetting phenomena

Condensed Matter Physics, 2015

Molecular dynamics simulations have been performed on pure liquid water, aqueous solutions of sod... more Molecular dynamics simulations have been performed on pure liquid water, aqueous solutions of sodium chloride, and polymer solutions exposed to a strong external electric field with the goal to gain molecular insight into the structural response to the field. Several simulation methodologies have been used to elucidate the molecular mechanisms of the processes leading to the formation of liquid bridges and jets (in the production of nanofibers). It is shown that in the established nanoscale structures, the molecules form a chain with their dipole moments oriented parallel to the applied field throughout the entire sample volume. The presence of ions may disturb this structure leading to its ultimate disintegration into droplets; the concentration dependence of the threshold field required to stabilize a liquid column has been determined. Conformational changes of the polymer in the jetting process have also been observed.

Research paper thumbnail of Osmotic pressure of aqueous electrolyte solutions via molecular simulations of chemical potentials: Application to NaCl

Fluid Phase Equilibria, 2016

ABSTRACT

Research paper thumbnail of Aqueous electrolyte surfaces in strong electric fields: molecular insight into nanoscale jets and bridges

Molecular Physics, 2014

ABSTRACT Exposing aqueous surfaces to a strong electric field gives rise to interesting phenomena... more ABSTRACT Exposing aqueous surfaces to a strong electric field gives rise to interesting phenomena, such as formation of a floating water bridge or an eruption of a jet in electrospinning. In an effort to account for the phenomena at the molecular level, we performed molecular dynamics simulations using several protocols on both pure water and aqueous solutions of sodium chloride subjected to an electrostatic field. All simulations consistently point to the same mechanisms which govern the rearrangement of the originally planar surface. The results show that the phenomena are primarily governed by an orientational reordering of the water molecules driven by the applied field. It is demonstrated that, for pure water, a sufficiently strong field yields a columnar structure parallel to the field with an anisotropic arrangement of the water molecules with their dipole moments aligned along the applied field not only in the surface layer but over the entire cross section of the column. Nonetheless, the number of hydrogen bonds per molecule does not seem to be affected by the field regardless of its strength and molecule’s orientation. In the electrolyte solutions, the ionic charge is able to overcome the effect of the external field tending to arrange the water molecules radially in the first coordination shell of an ion. The ion–water interaction interferes thus with the water–electric field interaction, and the competition between these two forces (i.e., strength of the field versus concentration) provides the key mechanism determining the stability of the observed structures.

Research paper thumbnail of Molecular dynamics of preferential adsorption in mixed alkali–halide electrolytes at graphene electrodes

The Journal of Chemical Physics

Understanding the microscopic behavior of aqueous electrolyte solutions in contact with graphene ... more Understanding the microscopic behavior of aqueous electrolyte solutions in contact with graphene and related carbon surfaces is important in electrochemical technologies, such as capacitive deionization or supercapacitors. In this work, we focus on preferential adsorption of ions in mixed alkali–halide electrolytes containing different fractions of Li+/Na+ or Li+/K+ and/or Na+/K+ cations with Cl− anions dissolved in water. We performed molecular dynamics simulations of the solutions in contact with both neutral and positively and negatively charged graphene surfaces under ambient conditions, using the effectively polarizable force field. The simulations show that large ions are often intuitively attracted to oppositely charged electrodes. In contrast, the adsorption behavior of small ions tends to be counterintuitive. In mixed-cation solutions, one of the cations always supports the adsorption of the other cation, while the other cation weakens the adsorption of the first cation. In...

Research paper thumbnail of Polarizable force fields for accurate molecular simulations of aqueous solutions of electrolytes, crystalline salts, and solubility: Li+, Na+, K+, Rb+, F−, Cl−, Br−, I−

Journal of Molecular Liquids

Research paper thumbnail of Molecular dynamics of the interfacial solution structure of alkali-halide electrolytes at graphene electrodes

Journal of Molecular Liquids, 2022

Research paper thumbnail of Molecular dynamics simulation study of the effect of a strong electric field on the structure of a poly(oxyethylene) chain in explicit solvents

Journal of Molecular Liquids, 2021

A non-halogenated type of chiral ionic liquids (CIL's) called 1-butyl-3-methylimidazolium (T-4)-b... more A non-halogenated type of chiral ionic liquids (CIL's) called 1-butyl-3-methylimidazolium (T-4)-bis[(αS)-α-(hydroxy-O) benzeneacetato-κO] borate, [BMIm+] [BSMB−], has been used for enantioseparation of propranolol enantiomers. Experimental studies indicate that carbon nanotubes (CNT's) increase the Enantioselectivity of chiral ionic liquids through the enhancement of the interaction surface of chiral selectors with the compounds enantiomers. With the aim of investigating the mechanism under this observation, we used Molecular Dynamics (MD) Simulations to investigate the molecular level picture of the behavior of CIL and propranolol enantiomers on the Single-Walled Carbon Nanotube (SWCNT) surface. The density profiles, micro structure, radial distribution function, dimer existence autocorrelation function (DAF) and dynamic properties of propranolol enantiomers were studied in the CIL/CNT solution. The results are indicative of stronger interactions between R-propranolol enantiomers with CIL and CNT surface. Furthermore stronger interactions were seen between the Rpropranolol molecules with one another. This leads to the difference in the replacement of propranolol enantiomers on the CNT surface in such a way that R-propranolol molecules propagate more along the CNT to have the maximum interactions with CIL molecules. The diffusion coefficient difference between S-propranolol and Rpropranolol molecules shows a higher value in comparison to the system that CNT is absent. Consequently, the interactions, propagation and mobility of propranolol enantiomers are strongly influenced by CNT presence.

Research paper thumbnail of Structure of supercooled water: Polarizable BK3 model versus non-polarizable models

Journal of Molecular Liquids, 2018

Research paper thumbnail of Molecular Dynamics of Graphene–Electrolyte Interface: Interfacial Solution Structure and Molecular Diffusion

The Journal of Physical Chemistry C, 2019

Research paper thumbnail of Thermodynamics of supersaturated steam: Towards an equation of state

Fluid Phase Equilibria, 2018

Thermodynamics of supersaturated (supercooled) steam at conditions occurring in steam turbines, a... more Thermodynamics of supersaturated (supercooled) steam at conditions occurring in steam turbines, and inaccessible thus to experiments, has been studied by a number of theoretical and semi-theoretical methods with the goal to assess available theoretical tools for developing an equation of state. Extended virial expansions with different reference systems have been used along with two, qualitatively different equations of state. According to the proposed strategy, all equations were first used for the vapor-liquid coexistence curve and then extended to the metastable region and tested against computer simulation data. Despite the fact that no specificities of supersaturated steam have been accounted for, all the considered methods provide results with deviations from (pseudo)experimental data up to about 5% over the entire range of thermodynamic conditions except the critical region. It turns out that the perturbed virial expansion with a suitably chosen reference system outperforms other methods, including equations of state originally developed for liquid water.

Research paper thumbnail of Saturated aqueous NaCl solution and pure water in Na-montmorillonite clay at thermodynamic conditions of hydraulic fracturing: Thermodynamics, structure and diffusion from molecular simulations

Journal of Molecular Liquids, 2018

We present a Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation study of a... more We present a Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation study of an aqueous NaCl solution in Na-montmorillonite (Na-MMT) clay pores, including the thermodynamic, structural and dynamical properties. We represent the clay pores by Na-MMT slits of an interlayer separation ranging from about 10 to 32Å, covering clay pores from dry clay to clay pores with a bulk-like water layer in the middle of the pore. We consider the clay in equilibrium with the saturated salt solution at a typical shale gas reservoir condition of a temperature of 365 K and a pressure of 275 bar. The equilibrium amount of the adsorbed ions and water molecules obtained from the GCMC simulations are employed in MD to simulate the disjoining pressure and in turn the swelling free energy curve which determines the number of stable states in the clay, their composition, and the corresponding equilibrium interlayer separations. In addition, using MD simulations, we evaluate the hydration energy, atomic and charge density profiles, orientation distribution, hydrogen-bond network, and in-plane self-diffusivity of the water and ions to provide insight into the microscopic behaviour of the aqueous NaCl solution in the interlayer galleries of the hydrophilic Na-MMT pores. We compare the simulation results for the confined aqueous NaCl solutions with those obtained for the Na-MMT in equilibrium with a pure water reservoir at the same temperature and pressure.

Research paper thumbnail of Higher virial coefficients of water

Journal of Molecular Liquids, 2018

Virial coefficients B 2 to B 4 for the non-polarizable TIP4P/2005 model of water and the polariza... more Virial coefficients B 2 to B 4 for the non-polarizable TIP4P/2005 model of water and the polarizable BK3 model were computed. An analysis and assessment of available experimental and pseudoexperimental data is carried out. Various forms of the virial expansion are examined with respect to their potential use for the description of steam (working agent in turbines). At higher temperatures (higher densities) the expansion starts exhibiting an irregular behavior indicating that at these conditions the vapor can likely not be viewed as a system made up only of individual molecules, and the occurrence of clusters of different size must be accounted for.

Research paper thumbnail of Recent progress in the molecular simulation of thermodynamic properties of aqueous electrolyte solutions

Fluid Phase Equilibria, 2018

We review progress in the development and application of molecular simulation methodology to pred... more We review progress in the development and application of molecular simulation methodology to predict the thermodynamic properties of aqueous electrolytes, focussing on work published since our previous review along similar lines [I. Nezbeda, et al., Mol. Phys. 114 (2016) 1665]. We consider such developments in the context of the use of Monte Carlo (MC) or Molecular Dynamics (MD) simulation methodologies using classical force fields. Special attention is paid to the incorporation of charge scaling approaches in the force fields, as well as to the simulation methodology used to compute solubility and osmotic pressure, and the use of the latter quantity to calculate the water activity and osmotic coefficient, and the electrolyte activity coefficient. We emphasize the importance of the statistical analysis of thermodynamic properties obtained from simulation data, and illustrate it with an example analyzing simulation osmotic pressure and electrolyte chemical potential data.

Research paper thumbnail of {"__content__"=>"Chemical potentials of alkaline earth metal halide aqueous electrolytes and solubility of their hydrates by molecular simulation: Application to CaCl, antarcticite, and sinjarite.", "sub"=>{"__content__"=>"2"}}

The Journal of chemical physics, Jan 14, 2018

We present a molecular-level simulation study of CaCl in water and crystalline hydrates formed by... more We present a molecular-level simulation study of CaCl in water and crystalline hydrates formed by CaCl at ambient (298.15 K, 1 bar) conditions and at a high-temperature high-pressure state (365 K, 275 bars) typical of hydraulic fracturing conditions in natural-gas extraction, at which experimental properties are poorly characterized. We focus on simulations of chemical potentials in both solution and crystalline phases and on the salt solubility, the first time to our knowledge that such properties have been investigated by molecular simulation for divalent aqueous electrolytes. We first extend our osmotic ensemble Monte Carlo simulation technique [F. Moučka et al., J. Phys. Chem. B 115, 7849-7861 (2011)] to such solutions. We then describe and apply new methodology for the simulation of the chemical potentials of the experimentally observed crystalline hydrates at ambient conditions (antarcticite, CaCl·6HO) and at high-temperature conditions (sinjarite, CaCl·2HO). We implement our ...

Research paper thumbnail of Thermodynamics of supersaturated steam: Molecular simulation results

The Journal of Chemical Physics, 2016

has been simulated at conditions occurring in steam turbines using the multiple-particle-move Mon... more has been simulated at conditions occurring in steam turbines using the multiple-particle-move Monte Carlo for both the homogeneous phase and also implemented for the Gibbs ensemble Monte Carlo molecular simulation methods. Because of these thermodynamic conditions, a specific simulation algorithm has been developed to bypass common simulation problems resulting from very low densities of steam and cluster formation therein. In addition to pressure-temperature-density and orthobaric data, the distribution of clusters has also been evaluated. The obtained extensive data of high precision should serve as a basis for development of reliable molecular-based equations for properties of metastable steam.

Research paper thumbnail of Recent progress in molecular simulation of aqueous electrolytes: force fields, chemical potentials and solubility

Molecular Physics, 2016

Although aqueous electrolytes are among the most important solutions, the molecular simulation of... more Although aqueous electrolytes are among the most important solutions, the molecular simulation of their intertwined properties of chemical potentials, solubility and activity coefficients has remained a challenging problem, and has attracted considerable recent interest. In this perspectives review, we focus on the simplest case of aqueous sodium chloride at ambient conditions and discuss the two main factors that have impeded progress. The first is lack of consensus with respect to the appropriate methodology for force field (FF) development. We examine how most commonly used FFs have been developed, and emphasize the importance of distinguishing between "Training Set Properties" used to fit the FF parameters, and "Test Set Properties", which are pure predictions of additional properties. The second is disagreement among solubility results obtained, even using identical FFs and thermodynamic conditions. Solubility calculations have been approached using both thermodynamic-based methods and direct molecular dynamics-based methods implementing coexisting solution and solid phases. Although convergence has been very recently achieved among results based on the former approach, there is as yet no general agreement with simulation results based on the latter methodology. We also propose a new method to directly calculate the electrolyte standard chemical potential in the Henry-Law ideality model. We conclude by making recommendations for calculating solubility, chemical potentials and activity coefficients, and outline a potential path for future progress.

Research paper thumbnail of Modelling aqueous solubility of sodium chloride in clays at thermodynamic conditions of hydraulic fracturing by molecular simulations

Physical Chemistry Chemical Physics, 2017

To address the high salinity of flow-back water during hydraulic fracturing, we have studied the ... more To address the high salinity of flow-back water during hydraulic fracturing, we have studied the equilibrium partitioning of NaCl and water between the bulk phase and clay pores.

Research paper thumbnail of Molecular modeling and simulations

Electrospun Nanofibers, 2017

Abstract This chapter reviews the application of standard molecular simulation techniques to the ... more Abstract This chapter reviews the application of standard molecular simulation techniques to the phenomenon of electrospinning. It provides a description of the basics of molecular simulations, with an emphasis on molecular dynamics, followed by an overview of specific considerations for electrospinning. The chapter also discusses the choice of simulation box arrangement, boundary conditions, and force fields, along with other technical details relevant to the molecular modeling of fluid interfaces in the presence of an electric field. We show selected applications and outline future perspectives.

Research paper thumbnail of Salt and Water Uptake in Nanoconfinement under Applied Electric Field: An Open Ensemble Monte Carlo Study

The Journal of Physical Chemistry C, 2015

ABSTRACT

Research paper thumbnail of Chemical Potentials, Activity Coefficients, and Solubility in Aqueous NaCl Solutions: Prediction by Polarizable Force Fields

Journal of Chemical Theory and Computation, 2015

We describe a computationally efficient molecular simulation methodology for calculating the conc... more We describe a computationally efficient molecular simulation methodology for calculating the concentration dependence of the chemical potentials of both solute and solvent in aqueous electrolyte solutions, based on simulations of the salt chemical potential alone. We use our approach to study the predictions for aqueous NaCl solutions at ambient conditions of these properties by the recently developed polarizable force fields (FFs) AH/BK3 of Kiss and Baranyai (

Research paper thumbnail of Application of molecular simulations: Insight into liquid bridging and jetting phenomena

Condensed Matter Physics, 2015

Molecular dynamics simulations have been performed on pure liquid water, aqueous solutions of sod... more Molecular dynamics simulations have been performed on pure liquid water, aqueous solutions of sodium chloride, and polymer solutions exposed to a strong external electric field with the goal to gain molecular insight into the structural response to the field. Several simulation methodologies have been used to elucidate the molecular mechanisms of the processes leading to the formation of liquid bridges and jets (in the production of nanofibers). It is shown that in the established nanoscale structures, the molecules form a chain with their dipole moments oriented parallel to the applied field throughout the entire sample volume. The presence of ions may disturb this structure leading to its ultimate disintegration into droplets; the concentration dependence of the threshold field required to stabilize a liquid column has been determined. Conformational changes of the polymer in the jetting process have also been observed.

Research paper thumbnail of Osmotic pressure of aqueous electrolyte solutions via molecular simulations of chemical potentials: Application to NaCl

Fluid Phase Equilibria, 2016

ABSTRACT

Research paper thumbnail of Aqueous electrolyte surfaces in strong electric fields: molecular insight into nanoscale jets and bridges

Molecular Physics, 2014

ABSTRACT Exposing aqueous surfaces to a strong electric field gives rise to interesting phenomena... more ABSTRACT Exposing aqueous surfaces to a strong electric field gives rise to interesting phenomena, such as formation of a floating water bridge or an eruption of a jet in electrospinning. In an effort to account for the phenomena at the molecular level, we performed molecular dynamics simulations using several protocols on both pure water and aqueous solutions of sodium chloride subjected to an electrostatic field. All simulations consistently point to the same mechanisms which govern the rearrangement of the originally planar surface. The results show that the phenomena are primarily governed by an orientational reordering of the water molecules driven by the applied field. It is demonstrated that, for pure water, a sufficiently strong field yields a columnar structure parallel to the field with an anisotropic arrangement of the water molecules with their dipole moments aligned along the applied field not only in the surface layer but over the entire cross section of the column. Nonetheless, the number of hydrogen bonds per molecule does not seem to be affected by the field regardless of its strength and molecule’s orientation. In the electrolyte solutions, the ionic charge is able to overcome the effect of the external field tending to arrange the water molecules radially in the first coordination shell of an ion. The ion–water interaction interferes thus with the water–electric field interaction, and the competition between these two forces (i.e., strength of the field versus concentration) provides the key mechanism determining the stability of the observed structures.