Vladimir G. Baidakov

Metastable extension of the liquid-vapor phase equilibrium curve and surface tension

The method of molecular dynamics has been used to calculate the parameters of liquid-vapor phase equilibrium and the surface tension in a two-phase system of 4096 Lennard-Jones particles. Calculations have been made in a range from the triple point to near-critical temperature and also at temperatures below the triple point corresponding to the metastable equilibrium of a supercooled liquid and supersaturated vapor. To determine the surface tension, along with a mechanical approach a thermodynamic one has been used as well. The latter was based on calculation of the excess internal energy of an interfacial layer. It has been shown that in accuracy the thermodynamic approach is as good as the more sophisticated mechanical one. Low-temperature asymptotics of the phase-equilibrium curve and also of liquid and vapor spinodals have been considered in the Lennard-Jones and the van der Waals models. The behavior of the surface tension and the excess internal energy of an interfacial layer at T-->0 is discussed.

Effect of the cut-off radius of the intermolecular potential on phase equilibrium and surface tension in Lennard-Jones systems

Abstract We present the molecular dynamic simulation results for the liquid–vapour interface of the pure Lennard–Jones fluid. The thermodynamical properties, the surface tension, the effective thickness of interfacial layer and the mean-square amplitude of capillary waves are determined. Calculations have been performed at cut-off radii of the intermolecular potential r c 1 =2.6 σ and r c 2 =6.78 σ . It is shown that the cut-off radius of the interaction potential in the two-phase systems should be chosen to be larger than that in the one-phase systems for an adequate representation of properties.

Kinetics of boiling in binary liquid–gas solutions: Comparison of different approaches

A comparative analysis of the results of determination of the work of critical cluster formation in nucleation theory for three different methods of evaluation—Gibbs’ method (employing the capillarity approximation), the van der Waals–Cahn and Hilliard and a newly developed modified Gibbs’ approach—is given in application to phase formation in multicomponent systems. As an example, processes of boiling in binary liquid–gas solutions, in particular, in nitrogen–helium mixtures are investigated. In addition to the work of critical cluster formation, the bulk properties of the critical bubbles, their characteristic sizes and the values of the surface tension are determined in dependence on the initial supersaturation in the system or, equivalently, on the size of the critical clusters. It is shown that latter two mentioned methods (the van der Waals–Cahn and Hilliard and the modified Gibbs’ approach) lead, in the determination of the work of critical cluster formation, to qualitatively and widely even quanti...

Crystal nucleation rate isotherms in Lennard-Jones liquids

We present the results of molecular dynamics simulations of the crystal nucleation rate in a supercooled Lennard-Jones liquid. The nucleation rate as a function of the pressure has been calculated by the method of determining the expectation time for liquid crystallization at temperatures higher than that of the triple point (T(*) = 0.865), close to the temperature of the terminal critical point of the metastable extension of the melting curve (T(*) = 0.55) and below this temperature (T(*) = 0.4). In computer experiments the nucleation rate varied from 10(32) to 10(35) s(-1) m(-3). The dimensions of critical nuclei and the pressure inside them, the surface free energy at a critical crystal nucleus-liquid interface, the height of the nucleation barrier, and the Zeldovich factor have been determined from the results of molecular dynamics simulations and their comparison with classical homogeneous nucleation theory. It is shown that the surface free energy at a curved crystal-liquid interface, as distinct from a flat interface, has also been determined at temperatures lower than the temperature of the terminal critical point of the melting curve and is a monotonically increasing function of the temperature.

Nucleation in superheated liquid argon–krypton solutions

We report nucleation-rate measurements in metastable liquid argon–krypton solutions at pressures of 1.0 and 1.6 MPa over a wide temperature and concentration range. These measurements were performed with the use of a superheated liquid lifetime measurement method. The experimental results are compared with the homogeneous nucleation theory data both using a macroscopic (capillary) approach and taking into account the dependence of critical bubble surface tension on interface curvature. The size effect in nucleation is considered in the framework of the Van-der-Waals, Cahn–Hilliard method. The experimental data indicate that the homogeneous nucleation theory quantitatively describes the kinetics of a first order phase transition in binary solutions of simple liquids if the size effect is taken into account and nucleation rates are J≳106 m−3 sec−1. At J≲106 m−3 sec−1 there is initiated nucleation. A diffusion spinodal of a solution is approximated. The attainable superheating temperature data are presented.

Crystal nucleation and the solid–liquid interfacial free energy

We present the results of molecular dynamics simulation of crystal nucleation in a supercooled Lennard-Jones liquid. Temperature and baric dependences of the nucleation rate, the Zeldovich factor, nucleus size diffusion coefficient, the radius, and the pressure in a critical crystal nucleus are defined in computer simulation. The data obtained have been used in the framework of classical nucleation theory to calculate the effective surface energy of crystal nuclei γ(e). It is shown that the value of γ(e) at T = const exceeds the value of the interfacial free energy at a flat crystal-liquid interface γ(∞) and γ(e) < γ(∞) at p = const.

Explosive cavitation in superheated liquid argon

The kinetics of explosive boiling-up of liquid argon has been investigated at negative pressures created by the reflection of a compression pulse 3-5 mus long from the free surface of a liquid by the method of liquid pulse heating on a thin platinum wire (with a rate of temperature increase of about 1 Kmus). The limiting superheats T(*) (stretches p(*)), the effective nucleation rate J(*), and the derivative G(T)=(d ln JdT)(T=T(*) ) have been determined by experimental data on the thermal perturbation of a wire probe and the results of solution of the problem on the initial stage of explosive boiling-up of a liquid. The experimental data are compared with homogeneous nucleation theory.

Extended version of the van der Waals capillarity theory

An extended version of the van der Waals capillarity theory describing the liquid-vapor interface in the temperature range from the triple to the critical point is suggested. A model functional of thermodynamic potential for a two-phase Lennard-Jones system taking into account the effect of the highest degree terms of gradient expansion has been constructed. The identity of the thermodynamic and the mechanical definition of Tolmans length has been proved in the framework of the adopted form of functional. The properties of nuclei of the liquid and the vapor phase are described. The paper determines: the work of formation of a nucleus, density profiles, size dependences of the surface tension, and the parameter delta in the Gibbs-Tolman-Koenig-Buff equation.

Surface tension at the boundaries of helium-argon and neon-argon solutions at 108–140 K

The capillary constant was measured and surface tension determined for helium-argon and neon-argon solutions by the differential version of the capillary rise method over the temperature range 108–140 K at pressures up to 4 MPa. The adsorption of helium and neon in interfacial solution layers was calculated.

NUCLEATION IN SUPERHEATED GAS-SATURATED SOLUTIONS. I. BOILING-UP KINETICS

Nucleation in a superheated gas-saturated solution is regarded as a diffusional process in the space of three variables of a nucleus: Its volume υ and the partial pressures of the components p1″,p2″. The paper determines the surface relief of the thermodynamic potential in the vicinity of the saddle point and describes the growth of vapor bubbles in a solution with allowance for its viscosity, rate of evaporation of molecules of a solvent, and a dissolved substance, rate of diffusional supply of a substance to the bubble surface. The tensor of the generalized diffusion of nuclei, the decrement of increase of an unstable variable, the stationary nucleation rate have been calculated.