Phase behavior of ionic fluids in slitlike pores: A density functional approach for the restricted primitive model

Abstract

We present a density functional theory of nonuniform ionic fluids. This theory is based on the application of the electrostatic contribution to the free energy functional arising from mean spherical approximation for a bulk restricted primitive model and from the energy route bulk equation of state. In order to employ this functional we define a reference fluid and additional averaged densities, according to the approach introduced by Gillespie, Nonner and Eisenberg [J. Phys.: Condens. Matter 14, 12129 (2002)]. In the case of bulk systems the proposed theory reduces to the mean spherical approximation equation of state, arising from the energy route and thus it predicts the first-order phase transition. We use this theory to investigate the effects of confinement on the liquid-vapor equilibria. Two cases are considered, namely an electrolyte confined to the pore with uncharged walls and with charged walls. The dependence of the capillary evaporation diagrams on the pore width and on the electrostatic potential is determined.

Electric double layer capacitance of restricted primitive model for an ionic fluid in slit-like nanopores: A density functional approach

“…21,22 This development can be called "an energy route MSA-based solution." In contrast to the compressibility route approaches, the energy route theory is the only method capable to predict ionic gas-ionic liquid transition for confined RPM, 16,17 as well as the existence of a maximum of the double layer capacitance on temperature dependence. 18,19 However, at high temperatures comparing to the critical temperature of the RPM, for quite high bulk electrolyte densities as well as for high wall charges, the microscopic structure of electric double layer predicted by the energy route approach is less accurate than that emerging from some compressibility route theories.…”

“…In our previous works [16][17][18][19][20] we have proposed and applied the approach that uses nonuniform fluid weighted densities as the reference state and the free energy functional for the residual contribution from the MSA energy route for the bulk equation of state. 21,22 This development can be called "an energy route MSA-based solution."…”

“…Usually, in DF theories of nonuniform electrolytes, the ion-ion correlations are divided into the direct Coulomb contribution, the hard-sphere contribution and the electric residual contribution that results from coupling between Coulomb and hard-sphere interactions. [10][11][12][13][14][15][16] The difference between various DF approaches is due to different ways of evaluation of the residual contributions. According to the compressibility route approaches, [10][11][12][13][14] the residual contribution is evaluated using a perturbation of the intrinsic Helmholtz free energy around a bulk reference state.…”

Particle Indistinguishability Symmetry within a Field Theory. Entropic Effects

“…Experimentally and in numerical simulations, scientists have shown systems where the electric capacitance decreases at low reduced temperature [39][40][41][42][43][44][45][46][47][48][49]. This phenomenon is non intuitive as one expects the electric response of the system to decrease with increasing thermal agitation as in GouyChapman and MSA theories.…”

Exploring fluid-solid interfaces with Stefan Sokołowski

“…The principal focus there, was on the application of the density functional approach to EDL (in the version proposed previously in [33]), evaluation of the accuracy of the theory with respect to computer simulation data and searching for possible applications related to biology, see e.g., [34][35][36][37][38] for some important results. In search of better tools to deal with Coulomb interactions between ions in the restricted primitive model under geometric confinement and under the effect of the electric field, S. Sokołowski et al proposed to apply the energy route to the free energy combined with a particular weighting procedure [39], in contrast to the commonly used compressibility route [33]. This appeared to be the only scheme permitting to capture the liquid-vapor phase transition in fluids of charged species that still can be improved to satisfy the contact conditions for the charge at the interface [40].…”