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-, $\lambda=\sigma_{+}/\sigma_{-}$ and charge, $z=q_{+}/|q_{-}|$, 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 ($\lambda\neq 1$, $z=1$), an equisize charge-asymmetric PM ($\lambda=1$, $z\neq 1$) and a size- and charge-asymmetric PM ($\lambda\neq 1$, $z=2$). 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 $z$, 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

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

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

Structural aspects of the clustering of curcumin molecules in water. Molecular dynamics computer simulation study

We explore clustering of curcumin molecules in water by using the OPLS-UA model for the enol conformer of curcumin (J. Mol. Liq., 223, 707, 2016) and the SPC-E water model. With this purpose, solutions of 2, 4, 8, 12, 16 and 20 curcumin molecules in 3000 water molecules are studied by using extensive molecular dynamics computer simulations. Radial distributions for the centers of mass of curcumin molecules are evaluated and the running coordination numbers are analyzed. The formation of clusters on time is elucidated. The internal structure of molecules within the cluster is described by using radial distributions of the elements of the curcumin molecule, the orientation descriptors, the order parameter and the radius of gyration. The self-diffusion coefficient of solute molecules in clusters is evaluated. The distribution of water species around clusters is described in detail. A comparison of our findings with computer simulation results of other authors is performed. A possibility to relate predictions of the model with experimental observations is discussed.Comment: 16 pages, 18 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

Aspects of the microscopic structure of curcumin solutions with water-dimethylsulfoxide solvent. Molecular dynamics computer simulation study

We explore some aspects of the microscopic structure of curcumin solutions with water-dimethylsulfoxide solvent of variable composition. Molecular dynamics computer simulations at isobaric-isothermal conditions are used for this purpose. The model consists of the OPLS-UA type model for the enol conformer of curcumin (J. Mol. Liq., 223, 707, 2016), the OPLS model for the dimethylsulfoxide (DMSO) and the SPC/E water model. Radial distributions for the centers of mass of curcumin molecules are evaluated and the corresponding running coordination numbers are analyzed. The disaggregation of curcumin clusters upon increasing the DMSO content in water-DMSO solvent is elucidated. Changes of the distribution of water and DMSO species around curcumin molecules are investigated. A qualitative comparison of our findings with the results of other authors is performed. A possibility to relate predictions of the model with the experimental observations in terms of the so-called critical wateraggregation percentage is discussed.Comment: 15 pages, 14 figure