41 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
Gas-liquid critical point of the ultrasoft restricted primitive model from analytic theory
Gas-liquid criticality in the ultrasoft restricted primitive model (URPM) of
polyelectrolytes is studied using the collective variables-based theory. For
the model, an effective Hamiltonian is derived and explicit expressions for all
the coefficients are found in a one-loop approximation. Based on this
Hamiltonian, the phase and critical behaviour is analysed. Our results provide
evidence that the nature of the gas-liquid criticality in the URPM is the same
as in the restricted primitive model that includes a hard core.Comment: 6 pages, 2 figure
Gas-liquid phase equilibrium in ionic fluids: Coulomb versus non-Coulomb interactions
Using the collective variables theory, we study the effect of competition
between Coulomb and dispersion forces on the gas-liquid phase behaviour of a
model ionic fluid, i.e. a charge-asymmetric primitive model with additional
short-range attractive interactions. Both the critical parameters and the
coexistence envelope are calculated in a one-loop approximation as a function
of the parameter measuring the relative strength of the Coulomb to
short-range interactions. We found the very narrow region of bounded
from the both sides by tricritical points which separates the models with
"nonionic" and "Coulombic" phase behaviour. This is at variance with the result
of available computer simulations where no tricritical point is found for the
finely-discretized lattice version of the model.Comment: 10 pages, 8 figure
Spatial inhomogeneities in ionic liquids, charged proteins and charge stabilized colloids from collective variables theory
Effects of size and charge asymmetry between oppositely charged ions or
particles on spatial inhomogeneities are studied for a large range of charge
and size ratios. We perform a stability analysis of the primitive model (PM) of
ionic systems with respect to periodic ordering using the collective variables
based theory. We extend previous studies [A. Ciach et al., Phys. Rev.E
\textbf{75}, 051505 (2007)] in several ways. First, we employ a non-local
approximation for the reference hard-sphere fluid which leads to the
Percus-Yevick pair direct correlation functions for the uniform case. Second,
we use the Weeks-Chandler-Anderson regularization scheme for the Coulomb
potential inside the hard core. We determine the relevant order parameter
connected with the periodic ordering and analyze the character of the dominant
fluctuations along the -lines. We show that the above-mentioned
modifications produce large quantitative and partly qualitative changes in the
phase diagrams obtained previously. We discuss possible scenarios of the
periodic ordering for the whole range of size- and charge ratios of the two
ionic species, covering electrolytes, ionic liquids, charged globular proteins
or nanoparticles in aqueous solutions and charge-stabilized colloids
A mesoscopic field theory of ionic systems versus a collective variable approach
We establish a link between the two functional approaches: a mesoscopic field
theory developed recently by A.Ciach and G.Stell [A. Ciach and G. Stell, J.
Mol. Liq. 87 (2000) 253] for the study of ionic models and an exact statistical
field theory based on the method of collective variables.Comment: 7 page
The method of collective variables: a link with the density functional theory
Recently, based on the method of collective variables the statistical field
theory for multicomponent inhomogeneous systems was formulated [O. Patsahan, I.
Mryglod, J.-M. Caillol, Journal of Physical Studies, 2007, 11, 133]. In this
letter we establish a link between this approach and the classical density
functional theory for inhomogeneous fluids.Comment: 6 page