E. M. Piotrovskaya

Molecular dynamic simulation of micellar solutions: A coarse-grain model

Molecular dynamic simulation of surfactant solutions is performed using a coarse-grain model. Aqueous butyl-, octyl-, dodecyl-, and hexadecyltrimethylammonium chloride solutions are investigated. The polydispersity of micellar solutions and micelle structure are studied, and the degree of counterion binding is estimated. It is shown that, when studying solutions of ionic surfactants, it is necessary to correctly account for electrostatic interactions.

A computer simulation of the mechanism of self-conservation of gas hydrates

Local density profiles and local component pressure profiles were obtained for two model systems containing methane hydrate and ice by molecular dynamics simulation. The ice matrix with methane hydrate clusters inserted into it was shown to be stable at normal pressure and even at a temperature higher than the temperature of methane hydrate dissociation. Calculations showed that the pressure in such a methane hydrate cluster inserted into ice was higher than in the ice phase. There were, however, no strong structure distortions because of the formation of a network of strong hydrogen bonds between the hydrate and ice phases.

A molecular dynamics simulation of micellar aggregates in aqueous solutions of hexadecyltrimethylammonium chloride with admixtures of low-molecular-weight substances

A molecular dynamics simulation was performed for spherical and cylindrical hexadecyltrimethylammonium chloride micelles in aqueous solutions containing admixtures of isopropanol, acetone, and sodium benzoate. Local particle (atom, atomic group, and ion) density profiles were obtained depending on the distance to the center of a micelle. The stationary size of aggregates was determined, and the micelle surface area per surfactant polar head was estimated.

Adsorption of gas-water binary systems in carbon micropores: Computer simulation

The adsorption of gas-water mixture in micropores of carbon materials at 298 K has been studied using computer simulation. Methane, nitrogen, ammonia, carbon dioxide, and hydrogen sulfide were considered as gas components. In the grand canonical ensemble Monte-Carlo simulation of adsorption, the displacement of a gas component from a pore as a result of the formation of water microclusters was observed for all systems studied. Cluster growth conditions on graphite-like and activated surfaces differ significantly. The comparative stability of adsorbed gas-water mixtures has been determined for all gases.

New version of Monte Carlo expanded ensemble method for precise calculations of free energy difference

A new version of Monte Carlo (MC) expanded ensemble (EE) method is proposed for the calculations of free energy difference (FED) between two different systems with close values of the free energy. In order to check the method the FED between simple model systems (fluid of hard spheres and freely jointed polymer chain of hard spheres) was calculated. The free energy of the mentioned above systems was also calculated by a standard MC EE method in order to compare the results of two simulations. It was shown that the accuracy of a new algorithm is the same as of a standard one. At the same time new version of EE allows us to obtain FED between two systems having quite different structures, but similar free energies, during one simulation run.

Free energy calculations of spherical and cylindrical micelles using Monte Carlo expanded ensemble method

The expanded ensemble Monte Carlo method has been modified for more precise estimation of the free energy of complicated systems. The first modification is based on simultaneous treatment of two systems, while in the second one the simulation is separated into two stages. The application of the second method allows one to decrease the time for computer simulation. Free energy differences between the micelles of different shapes (spherical and cylindrical) have been calculated over a wide temperature range with the help of the proposed modification. A simple complimentary model was used for the description of the micelles.

Connectivity effects for slit pores linked by a channel

This paper describes a Monte Carlo computer simulation study of connectivity effects in a system of two parallel slit pores and a quasi-one-dimensional joint. A numerical method for evaluation of accessible volume in computer simulation studies of adsorption in pores is presented and applied to simple slit pores and systems of interconnected pores. A local version of the grand canonical ensemble Monte Carlo method is used to study adsorption under conditions mimicking mass transfer limitations.