Yu. G. Bushuev

Determination of the intermolecular interaction parameters in the water-amide systems based on the data of the excess thermodynamic functions

The molar excess enthalpiesHE for the water +N-methyl-2-pyrrolidinone binary mixtures have been measured as functions of mole fraction at 298.15, 308.15 and 318.15 K, using isoperibol rotating calorimeter. A hydrogen bonding pairs model proposed by Luzar was fitted to the experimental dataHE,GE for the binary mixtures of water with hexamethylphosphoric triamide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidinone.ZusammenfassungUnter Anwendung eines isothermischen Rotationskalorimeters wurden die molaren ÜberschußenthalpienHE für binäre Gemische aus Wasser+N-Methyl-2-pyrrolidinon als eine Funktion des Molenbruches bei 298.15 und 318.15 K ermittelt. Das von Luzar empfohlene Wasserstoffbindungspaar-Modell wurde an die experimentellen DatenHE undGE für die binären Gemische aus Wasser und Hexamethylphosphortriamid, N,N-Dimethylformamid, N,N-Dimethylacetamid und N-Methyl-2-pyrrolidinon angepaßt.

STRUCTURAL PROPERTIES OF LIQUID ACETONE

Monte Carlo simulation of liquid acetone was carried out. The effect of electrostatic and van der Waals interactions on the regularities of mutual arrangement of the molecules was studied. Spatial structure of liquid acetone is determined by the molecular shape, repulsive intermolecular interactions, and steric factors and is close to the structure of a random closely packed system of soft spheres. Electrostatic interactions affect only the mutual orientation of the molecules.

Structural properties of liquid water

Monte Carlo simulations of molecular configurations of liquid water in theNVT-ensemble atT=298 K using unit cells containing 125 and 1000 molecules were, carried out. Comparison of experimental and calculated radial distribution functions suggests the existence of two types of spatial ordering in water. Structural properties of low-energy molecular clusters and associates of closed cycles of H-bonds were determined. The properties of the network of H-bonds can be described by a set of fundamental constants and one free parameter,viz., the probability of bond formation. The existence of long-range correlations in spatial arrangement of both the molecules and the cycles of bonds was established.

Structural properties of dilute aqueous solutions of dimethylformamide and acetone based on computer simulation

The Monte Carlo simulation of molecular configurations for aqueous solutions ofN,N-dimethylformamide and acetone was carried out. The atom-atom radial distribution functions were determined. The topological properties of the H-bond system were investigated. The concentrations of closed H-bond cycles and the radial distribution functions of their geometric centers were found. It was shown that the local arrangement of molecules and supermolecular assemblies typical of the H-bond network in neat water is retained in the solutions studied.

Structural properties of liquidN,N-dimethylformamide

Monte-Carlo simulation of liquidN,N-dimethylformamide was performed. The influence or electrostatic and van der Waals interactions on regularities of the mutual molecular arrangement was investigated. The spatial structure of liquid DMF is determined by the type of molecular packing and steric factors and is close to a random closely packed system of soft spheres. The electrostatic interactions only affect the mutual orientation of the molecular

The influence of universal and specific interactions on structural properties of liquid formamide

Monte Carlo simulation of the structure of liquid formamide at 298 K was carried out. Intermolecular interactions were calculated using five different potentials. No essential changes in the spatial structure and topological properties of the network of hydrogen bonds of liquid formamide occur upon varying the electrostatic intermolecular interactions, strength of H-bonds, and temperature. Fragments of crystal structure are partly retained in liquid formamide. It was found that the network of H-bonds is structurally inhomogeneous and contains long-lived associates of closed cycles of H-bonds as well as tree-like and chain-like structures. The energy, topological, and statistical characteristics of closed cycles of H-bonds were determined.

Structural properties of liquid formamide

Computer simulations of liquid formamide were carried out by the Monte Carlo method at 298 and 348 K. The atom-atom spatial distribution functions, the concentrations of closed H-bonded ring, the radial distributions functions of the geometric centers of the rings, and a number of other characteristics of hydrogen-bonded systems were calculated. It was found that the open chains dominate over cyclic structures, which are prone to association and formation of structural heterogeneities. Characteristic types of molecular associates were determined.

Molecular dynamics simulation of the kinetics of nucleation of supercooled NaCl melt clusters

Approaches to describing the structure of metastable liquids are considered. A criterion for the classification of particles in a supercooled NaCl melt is suggested. The criterion is based on the Q6 method and structural features of salt crystals. It was applied to analyze the configurations of clusters calculated by the molecular dynamics method. The results were interpreted using classic nucleation theory and the probabilistic approach. It was shown that crystalline phase nuclei with subcritical sizes existed in a metastable liquid. The evolution of nucleus sizes follows a complex mechanism. Along with monomer attachment and detachment reactions, collective structural fluctuations play a noticeable role.

Structural properties of liquid formamide—N,N-dimethylformamide mixtures

Monte Carlo simulations of formamide—N,N-dimethylforamide mixtures in the whole range of compositions were carried out at 298 K. Structural properties were investigated by calculating the atom-atom spatial distribution functions, generalized spatial distribution functions, concentrations of closed cycles of H-bonds, and other properties of the system of hydrogen bonds. It was found that local spatial regions with the structure of pure components are conserved in a wide range of concentrations. The regularities of manifestation of solvophobic effects have been established.

Properties of the network of the hydrogen bonds of water

Networks of the hydrogen bonds and those consisting of lines connecting nearby molecules were constructed using configurations of water molecules obtained by the Monte-Carlo method. The concentrations of closed cycles of hydrogen bonds were established to be determined only by the probability of hydrogen bond formation. Characteristics of a model ideal water network were determined. Topological properties of the Polk model and those of the network of nearest neighbors substantially differ from the properties of the ideal network. The totality of the hydrogen bonds in pure water was proposed to be considered as a hierarchical system. Three topologically different structures of water associates were determined.