Thermodynamic state-dependent structure-based coarse-graining of confined water

2017

Self Cite

We propose an isothermal, one-dimensional, electroosmotic flow model for slit-shaped nanochannels. Nanoscale confinement effects are embedded into the transport model by incorporating the spatially varying solvent and ion concentration profiles that correspond to the electrochemical potential of mean force. The local viscosity is dependent on the solvent local density and is modeled using the local average density method. Excess contributions to the local viscosity are included using the Onsager-Fuoss expression that is dependent on the local ionic strength. A Dirichlet-type boundary condition is provided in the form of the slip velocity that is dependent on the macroscopic interfacial friction. This solvent-surface specific interfacial friction is estimated using a dynamical generalized Langevin equation based framework. The electroosmotic flow of Na + and Cl as single counterions and NaCl salt solvated in Extended Simple Point Charge (SPC/E) water confined between graphene and silicon slit-shaped nanochannels are considered as examples. The proposed model yields a good quantitative agreement with the solvent velocity profiles obtained from the non-equilibrium molecular dynamics simulations. Published by AIP Publishing. [http://dx.

Section: Ion Concentration and Solvent Viscosity Variationmentioning

confidence: 99%

Multiscale modeling of electroosmotic flow: Effects of discrete ion, enhanced viscosity, and surface friction

Bhadauria

2017

Self Cite

“…More details on the optimization procedure and PMF matching technique can be found in Ref. 30. and hydrogen density profiles are normalized by the density of the bulk mixture which is 17.73 nm 3 .…”

Section: Simulation Detailsmentioning

confidence: 99%

“…26,27 Later, it was extended to more complex molecules such as carbon dioxide and water with electrostatic interactions. [28][29][30] In these studies, the effect of anisotropic electrostatic forces is taken into account by using the coarse-grained (CG) potentials from the detailed all-atom level. EQT is a robust and fast approach for providing accurate density and PMF profiles for confined fluids.…”

Section: Introductionmentioning

confidence: 99%

An EQT-based cDFT approach for thermodynamic properties of confined fluid mixtures

Motevaselian

2017

Self Cite

We present an empirical potential-based quasi-continuum theory (EQT) to predict the structure and thermodynamic properties of confined fluid mixtures. The central idea in the EQT is to construct potential energies that integrate important atomistic details into a continuum-based model such as the Nernst-Planck equation. The EQT potentials can be also used to construct the excess free energy functional, which is required for the grand potential in the classical density functional theory (cDFT). In this work, we use the EQT-based grand potential to predict various thermodynamic properties of a confined binary mixture of hydrogen and methane molecules inside graphene slit channels of different widths. We show that the EQT-cDFT predictions for the structure, surface tension, solvation force, and local pressure tensor profiles are in good agreement with the molecular dynamics simulations. Moreover, we study the effect of different bulk compositions and channel widths on the thermodynamic properties. Our results reveal that the composition of methane in the mixture can significantly affect the ordering of molecules and thermodynamic properties under confinement. In addition, we find that graphene is selective to methane molecules.

“…22,23 We note that, in Eq. (6), to determine the fluid-fluid potential energy, U ff (r), a mean field approximation (MFA) is invoked, i.e., the fluid-fluid pair correlations are neglected.…”

Section: A Eqtmentioning

confidence: 99%

“…, c n+1 }, using a systematic approach based on the potential of mean force (PMF) matching, which we developed in Ref. 23. PMF-matching approach optimizes structurally consistent potential parameters.…”

Section: Simulation Detailsmentioning

confidence: 99%

An EQT-cDFT approach to determine thermodynamic properties of confined fluids

Mashayak

Motevaselian

2015

Self Cite

We present a continuum-based approach to predict the structure and thermodynamic properties of confined fluids at multiple length-scales, ranging from a few angstroms to macro-meters. The continuum approach is based on the empirical potential-based quasi-continuum theory (EQT) and classical density functional theory (cDFT). EQT is a simple and fast approach to predict inhomogeneous density and potential profiles of confined fluids. We use EQT potentials to construct a grand potential functional for cDFT. The EQT-cDFT-based grand potential can be used to predict various thermodynamic properties of confined fluids. In this work, we demonstrate the EQT-cDFT approach by simulating Lennard-Jones fluids, namely, methane and argon, confined inside slit-like channels of graphene. We show that the EQT-cDFT can accurately predict the structure and thermodynamic properties, such as density profiles, adsorption, local pressure tensor, surface tension, and solvation force, of confined fluids as compared to the molecular dynamics simulation results.