31 research outputs found
A self-consistent renormalized Jellium approach for calculating structural and thermodynamic properties of charge stabilized colloidal suspensions
An approach is proposed which allows to self-consistently calculate the
structural and thermodynamic properties of highly charged aqueous colloidal
suspensions. The method is based on the renormalized Jellium model with the
background charge distribution related to the colloid-colloid correlation
function. The theory is used to calculate the correlation functions and the
effective colloidal charges for suspension containing additional monovalent
electrolyte. The predictions of the theory are in excellent agreement with the
Monte Carlo simulations
Equilibrium properties of charged microgels: a Poisson-Boltzmann-Flory approach
The equilibrium properties of ionic microgels are investigated using a
combination of the Poisson-Boltzmann and Flory theories. Swelling behavior,
density profiles, and effective charges are all calculated in a self-consistent
way. Special attention is given to the effects of salinity on these quantities.
It is found that the equilibrium microgel size is strongly influenced by the
amount of added salt. Increasing the salt concentration leads to a considerable
reduction of the microgel volume, which therefore releases its internal
material -- solvent molecules and dissociated ions -- into the solution.
Finally, the question of charge renormalization of ionic microgels in the
context of the cell model is briefly addressed
Lattice Model of an Ionic Liquid at an Electrified Interface
We study ionic liquids interacting with electrified interfaces. The ionic
fluid is modeled as a Coulomb lattice gas. We compare the ionic density
profiles calculated using a popular modified Poisson-Boltzmann equation with
the explicit Monte Carlo simulations. The modified Poisson-Boltzmann theory
fails to capture the structural features of the double layer and is also unable
to correctly predict the ionic density at the electrified interface. The
lattice Monte Carlo simulations qualitatively capture the coarse-grained
structure of the double layer in the continuum. We propose a convolution
relation that semiquantitatively relates the ionic density profiles of a
continuum ionic liquid and its lattice counterpart near an electrified
interface
Structural anomalies for a three dimensional isotropic core-softened potential
Using molecular dynamics simulations we investigate the structure of a system
of particles interacting through a continuous core-softened interparticle
potential. We found for the translational order parameter, t, a local maximum
at a density and a local minimum at . Between and , the parameter
anomalously decreases upon pressure. For the orientational order parameter,
, was observed a maximum at a density . For densities between and , both the
translational (t) and orientational () order parameters have anomalous
behavior. We know that this system also exhibits density and diffusion anomaly.
We found that the region in the pressure-temperature phase-diagram of the
structural anomaly englobes the region of the diffusion anomaly that is larger
than the region limited by the temperature of maximum density. This cascade of
anomalies (structural, dynamic and thermodynamic) for our model has the same
hierarchy of that one observed for the SPC/E water.Comment: 19 pages, 8 figure
Yukawa particles in a confining potential
We study the density distribution of repulsive Yukawa particles confined by
an external potential. In the weak coupling limit, we show that the mean-field
theory is able to accurately account for the particle distribution. In the
strong coupling limit, the correlations between the particles become important
and the mean-field theory fails. For strongly correlated systems, we construct
a density functional theory which provides an excellent description of the
particle distribution, without any adjustable parameters.Comment: Submitte
Thermodynamic and dynamic anomalies for a three dimensional isotropic core-softened potential
Using molecular dynamics simulations and integral equations (Rogers-Young,
Percus-Yevick and hypernetted chain closures) we investigate the thermodynamic
of particles interacting with continuous core-softened intermolecular
potential. Dynamic properties are also analyzed by the simulations. We show
that, for a chosen shape of the potential, the density, at constant pressure,
has a maximum for a certain temperature. The line of temperatures of maximum
density (TMD) was determined in the pressure-temperature phase diagram.
Similarly the diffusion constant at a constant temperature, , has a maximum
at a density and a minimum at a density .
In the pressure-temperature phase-diagram the line of extrema in diffusivity is
outside of TMD line. Although in this interparticle potential lacks
directionality, this is the same behavior observed in SPC/E water.Comment: 16 page
Equation of state of charged colloidal suspensions and its dependence on the thermodynamic route
The thermodynamic properties of highly charged colloidal suspensions in
contact with a salt reservoir are investigated in the framework of the
Renormalized Jellium Model (RJM). It is found that the equation of state is
very sensitive to the particular thermodynamic route used to obtain it.
Specifically, the osmotic pressure calculated within the RJM using the contact
value theorem can be very different from the pressure calculated using the
Kirkwood-Buff fluctuation relations. On the other hand, Monte Carlo (MC)
simulations show that both the effective pair potentials and the correlation
functions are accurately predicted by the RJM. It is suggested that the lack of
self-consistency in the thermodynamics of the RJM is a result of neglected
electrostatic correlations between the counterions and coions
Ionic size effects on the Poisson-Boltzmann theory
In this paper, we develop a simple theory to study the effects of ionic size
on ionic distributions around a charged spherical particle. We include a
correction to the regular Poisson-Boltzmann equation in order to take into
account the size of ions in a mean-field regime. The results are compared with
Monte Carlo simulations and a density functional theory based on the
fundamental measure approach and a second-order bulk expansion which accounts
for electrostatic correlations. The agreement is very good even for
multivalent ions. Our results show that the theory can be applied with very
good accuracy in the description of ions with highly effective ionic radii and
low concentration, interacting with a colloid or a nanoparticle in an
electrolyte solution