31 research outputs found
Gas-liquid critical parameters of asymmetric models of ionic fluids
The effects of size and charge asymmetry on the gas-liquid critical
parameters of a primitive model (PM) of ionic fluids are studied within the
framework of the statistical field theory based on the collective variables
method. Recently, this approach has enabled us to obtain the correct trends of
the both critical parameters of the equisize charge-asymmetric PM without
assuming ionic association. In this paper we focus on the general case of an
asymmetric PM characterized by the two parameters: hard-sphere diameter-,
and charge, , ratios of the
two ionic species. We derive an explicit expression for the chemical potential
conjugate to the order parameter which includes the effects of correlations up
to the third order. Based on this expression we consider the three versions of
PM: a monovalent size-asymmetric PM (, ), an equisize
charge-asymmetric PM (, ) and a size- and charge-asymmetric
PM (, ). Similar to simulations, our theory predicts that
the critical temperature and the critical density decrease with the increase of
size asymmetry. Regarding the effects of charge asymmetry, we obtain the
correct trend of the critical temperature with , while the trend of the
critical density obtained in this approximation is inconsistent with
simulations, as well as with our previous results found in the higher-order
approximation. We expect that the consideration of the higher-order
correlations will lead to the correct trend of the critical density with charge
asymmetry.Comment: 23 pages, 6 figure
On the properties of a single OPLS-UA model curcumin molecule in water, methanol and dimethyl sulfoxide. Molecular dynamics computer simulation results
The properties of model solutions consisting of a solute --- single curcumin
molecule in water, methanol and dimethyl sulfoxide solvents have been studied
using molecular dynamics (MD) computer simulations in the isobaric-isothermal
ensemble. The united atom OPLS force field (OPLS-UA) model for curcumin
molecule proposed by us recently [J. Mol. Liq., 2016, 223, 707] in combination
with the SPC/E water, and the OPLS-UA type models for methanol and dimethyl
sulfoxide have been applied. We have described changes of the internal
structure of the solute molecule induced by different solvent media in very
detail. The pair distribution functions between particular fragments of a
solute molecule with solvent particles have been analyzed. Statistical features
of the hydrogen bonding between different species were explored. Finally, we
have obtained a self-diffusion coefficient of curcumin molecules in three model
solvents.Comment: 20 pages, 17 figures, 4 table
Dissipative particle dynamics study of solvent mediated transitions in pores decorated with tethered polymer brushes in the form of stripes
We study self-assembly of a binary mixture of components A and B confined in
a slit-like pore with the walls modified by the stripes of tethered brushes
made of beads of a sort A. The emphasis is on solvent mediated transitions
between morphologies when the composition of the mixture varies. For certain
limiting cases of the pore geometry we found that an effective reduction of the
dimensionality may lead to a quasi one- and two-dimensional demixing. The
change of the environment for the chains upon changing the composition of the
mixture from polymer melt to a good solvent conditions provides explanation for
the mechanism of development of several solvent mediated morphologies and, in
some cases, for switching between them. We found solvent mediated lamellar,
meander and in-lined cylinder phases. Quantitative analysis of morphology
structure is performed considering brush overlap integrals and gyration tensor
components.Comment: 14 pages, 12 figure
What is liquid in random porous media: the Barker-Henderson perturbation theory
We apply the Barker-Henderson (BH) perturbation theory to the study of a
Lennard-Jones fluid confined in a random porous matrix formed by hard sphere
particles. In order to describe the reference system needed in this
perturbation scheme, the extension of the scaled particle theory (SPT) is used.
The recent progress in the development of SPT approach for a hard sphere fluid
in a hard sphere matrix allows us to obtain very accurate results for
thermodynamic properties in such a system. Hence, we combine the BH
perturbation theory with the SPT approach to derive expressions for the
chemical potential and the pressure of a confined fluid. Using the obtained
expressions, the liquid-vapour phase diagrams of a LJ fluid in HS matrix are
built from the phase equilibrium conditions. Therefore, the effect of matrix
porosity and a size of matrix particles is considered. It is shown that a
decrease of matrix porosity lowers both the critical temperature and the
critical density, while the phase diagram becomes narrower. An increase of a
size of matrix particles leads to an increase of the critical temperature. From
the comparison it is observed that the results obtained from the theory are in
agreement with computer simulations. The approach proposed in the present study
can be extended to the case of anisotropic fluid particles in HS matrices.Comment: 17 pages, 9 figure
Gas-liquid critical point in ionic fluids
Based on the method of collective variables we develop the statistical field
theory for the study of a simple charge-asymmetric primitive model (SPM).
It is shown that the well-known approximations for the free energy, in
particular DHLL and ORPA, can be obtained within the framework of this theory.
In order to study the gas-liquid critical point of SPM we propose the method
for the calculation of chemical potential conjugate to the total number density
which allows us to take into account the higher order fluctuation effects. As a
result, the gas-liquid phase diagrams are calculated for . The results
demonstrate the qualitative agreement with MC simulation data: critical
temperature decreases when increases and critical density increases rapidly
with .Comment: 18 pages, 1 figur
The effect of short-range interaction and correlations on the charge and electric field distribution in a model solid electrolyte
A simple lattice model of a solid electrolyte presented as a xy-slab geometry
system of mobile cations on a background of energetic landscape of the host
system and a compensating field of uniformly distributed anions is studied. The
system is confined in the z-direction between two oppositely charged walls,
which are in parallel to xy-plane. Besides the long-range Coulomb interactions
appearing in the system, the short-range attractive potential between cations
is considered in our study. We propose the mean field description of this model
and extend it by taking into account correlation effects at short distances.
Using the free energy minimization at each of z-coordinates, the corresponding
set of non-linear equations for the chemical potential is derived. The set of
equations was solved numerically with respect to the charge density
distribution in order to calculate the cations distribution profile and the
electrostatic potential in the system along z-direction under different
conditions. An asymmetry of charge distribution profile with respect to the
midplane of the system is observed. The effects of the short-range interactions
and pair correlations on the charge and electric field distributions are
demonstrated