203 research outputs found
Domain-walls formation in binary nanoscopic finite systems
Using a simple one-dimensional Frenkel-Kontorowa type model, we have
demonstrated that finite commensurate chains may undergo the
commensurate-incommensurate (C-IC) transition when the chain is contaminated by
isolated impurities attached to the chain ends. Monte Carlo (MC) simulation has
shown that the same phenomenon appears in two-dimensional systems with
impurities located at the peripheries of finite commensurate clusters.Comment: 9 pages, 6 figure
The mechanism of domain-wall structure formation in Ar-Kr submonolayer films on graphite
Using Monte Carlo simulation method in the canonical ensemble, we have
studied the commensurate-incommensurate transition in two-dimensional finite
mixed clusters of Ar and Kr adsorbed on graphite basal plane at low
temperatures. It has been demonstrated that the transition occurs when the
argon concentration exceeds the value needed to cover the peripheries of the
cluster. The incommensurate phase exhibits a similar domain-wall structure as
observed in pure krypton films at the densities exceeding the density of a
perfect commensurate phase, but the size of
commensurate domains does not change much with the cluster size. When the argon
concentration increases, the composition of domain walls changes while the
commensurate domains are made of pure krypton. We have constructed a simple
one-dimensional Frenkel-Kontorova-like model that yields the results being in a
good qualitative agreement with the Monte Carlo results obtained for
two-dimensional systems.Comment: 14 pages, 9 figure
Solvent primitive model of an electric double layer in slit-like pores: microscopic structure, adsorption and capacitance from a density functional approach
We investigate the electric double layer formed between charged walls of a
slit-like pore and a solvent primitive model (SPM) for electrolyte solution.
The recently developed version of the weighted density functional approach for
electrostatic interparticle interaction is applied to the study of the density
profiles, adsorption and selectivity of adsorption of ions and solvent species.
Our principal focus, however, is in the dependence of differential capacitance
on the applied voltage, on the electrode and on the pore width. We discuss the
properties of the model with respect to the behavior of a primitive model,
i.e., in the absence of a hard-sphere solvent. We observed that the
differential capacitance of the SPM on the applied electrostatic potential has
the camel-like shape unless the ion fraction is high. Moreover, it is
documented that the dependence of differential capacitance of the SPM on the
pore width is oscillatory, which is in close similarity to the primitive model.Comment: 10 pages, 5 figure
On the contact values of the density profiles in an electric double layer using density functional theory
A recently proposed local second contact value theorem [Henderson D., Boda
D., J. Electroanal. Chem., 2005, 582, 16] for the charge profile of an electric
double layer is used in conjunction with the existing Monte Carlo data from the
literature to assess the contact behavior of the electrode-ion distributions
predicted by the density functional theory. The results for the contact values
of the co- and counterion distributions and their product are obtained for the
symmetric valency, restricted primitive model planar double layer for a range
of electrolyte concentrations and temperatures. Overall, the theoretical
results satisfy the second contact value theorem reasonably well, the agreement
with the simulations being semi-quantitative or better. The product of the co-
and counterion contact values as a function of the electrode surface charge
density is qualitative with the simulations with increasing deviations at
higher concentrations.Comment: 10 pages, 8 figure
Changes in the structure of tethered chain molecules as predicted by density functional approach
We use a version of the density functional theory to study the changes in the
height of the tethered layer of chains built of jointed spherical segments with
the change of the length and surface density of chains. For the model in which
the interactions between segments and solvent molecules are the same as between
solvent molecules we have discovered two effects that have not been observed in
previous studies. Under certain conditions and for low surface concentrations
of the chains, the height of the pinned layer may attain a minimum. Moreover,
for some systems we observe that when the temperature increases, the height of
the layer of chains may decrease.Comment: 13 pages, 7 figure
First-order phase transitions in lattice bilayers of Janus-like particles: Monte Carlo simulations
The first-order phase transitions in the lattice model of Janus-like
particles confined in slit-like pores are studied. We assume a cubic lattice
with molecules that can freely change their orientation on a lattice site.
Moreover, the molecules can interact with the pore walls with
orientation-dependent forces. The performed calculations are limited to the
cases of bilayers. Our emphasis is on the competition between the fluid-wall
and fluid-fluid interactions. The oriented structures formed in the systems in
which the fluid-wall interactions acting contrary to the fluid-fluid
interactions differ from those appearing in the systems with neutral walls or
with walls attracting the repulsive parts of fluid molecules.Comment: 12 pages, 11 figure
Orest Pizio: scientist and friend
The Editorial Board of "Condensed Matter Physics" congratulates our good friend and a member of the Editorial Board on the occasion of his birthday anniversary and acknowledges his unique and valuable contribution to science. We also wish him to stay in good health, be happy and prosperous
Two hard spheres in a pore: Exact Statistical Mechanics for different shaped cavities
The Partition function of two Hard Spheres in a Hard Wall Pore is studied
appealing to a graph representation. The exact evaluation of the canonical
partition function, and the one-body distribution function, in three different
shaped pores are achieved. The analyzed simple geometries are the cuboidal,
cylindrical and ellipsoidal cavities. Results have been compared with two
previously studied geometries, the spherical pore and the spherical pore with a
hard core. The search of common features in the analytic structure of the
partition functions in terms of their length parameters and their volumes,
surface area, edges length and curvatures is addressed too. A general framework
for the exact thermodynamic analysis of systems with few and many particles in
terms of a set of thermodynamic measures is discussed. We found that an exact
thermodynamic description is feasible based in the adoption of an adequate set
of measures and the search of the free energy dependence on the adopted measure
set. A relation similar to the Laplace equation for the fluid-vapor interface
is obtained which express the equilibrium between magnitudes that in extended
systems are intensive variables. This exact description is applied to study the
thermodynamic behavior of the two Hard Spheres in a Hard Wall Pore for the
analyzed different geometries. We obtain analytically the external work, the
pressure on the wall, the pressure in the homogeneous zone, the wall-fluid
surface tension, the line tension and other similar properties
Entropic solvation force between surfaces modified by grafted chains: a density functional approach
The behavior of a hard sphere fluid in slit-like pores with walls modified by grafted chain molecules composed of hard sphere segments is studied using density functional theory. The chains are grafted to opposite walls via terminating segments forming pillars. The effects of confinement and of "chemical" modification of pore walls on the entropic solvation force are investigated in detail. We observe that in the absence of adsorbed fluid the solvation force is strongly repulsive for narrow pores and attractive for wide pores. In the presence of adsorbed fluid both parts of the curve of the solvation force may develop oscillatory behavior dependent on the density of pillars, the number of segments and adsorption conditions. Also, the size ratio between adsorbed fluid species and chain segments is of importance for the development of oscillations. The choice of these parameters is crucial for efficient manipulation of the solvation force as desired for pores of different width.Поведінку плину твердих сфер у щілиноподібних порах зі стінками, модифікованими розгалуженими ланцюговими молекулами, які складаються із твердосферних сегментів, досліджено з використанням теорії функціонала густини. Ланцюги є розгалуженими до протилежних стінок через скінченні сегменти, що формують опори колони. Досліджено вплив обмеження та "хімічної" модифікації стінок пори на ентропійну силу сольватації. Спостережено, що за відсутності адсорбованого плину сила сольватації є сильно відштовхувальною для вузьких пор і притягальною для широких. Коли адсорбований плин є присутнім, обидві частини кривої сили сольватації можуть розвивати осциляційну поведінку залежно від густини опор колон, числа сегментів та умов адсорбції. Також, розмірний коефіцієнт між частинками адсорбованого плину та сегментами ланцюгів є важливим для розвитку осциляцій. Вибір цих параметрів є дуже суттєвим для ефективного керування силою сольватації для пор різної ширини
Density functional approach for inhomogeneous star polymers
We propose microscopic density functional theory for inhomogeneous star
polymers. Our approach is based on fundamental measure theory for hard spheres,
and on Wertheim's first- and second-order perturbation theory for the
interparticle connectivity. For simplicity we consider a model in which all the
arms are of the same length, but our approach can be easily extended to the
case of stars with arms of arbitrary lengths.Comment: 4 pages, 3 figures, submitte
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