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

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

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 $(\sqrt{3}\times\sqrt{3})R30^\circ$ 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

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

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

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