Critical cavity in the stretched fluid studied using square-gradient density-functional model with triple-parabolic free energy

A Unified Approach to Disjoining Pressure in Liquid and Vapor Interlayer within the Framework of the Density Functional Theory

Abstract

The classical density functional theory makes it possible to explicitly calculate the local density profiles, the components of the pressure tensor, and the thicknesses of thin interlayers between a lyophilic or lyophobic solid surface and, accordingly, gas or liquid phases at different values of the chemical potentials of the phases. Within the framework of a unified approach based on the gradient approximation of the classical density functional theory, it has been shown that, at certain values of parameters characterizing the wettability or nonwettability of a solid, equilibrium liquid films or vapor layers of a uniform thickness are formed around a spherical particle, if its surface is lyophilic or lyophobic, respectively. Mechanical and thermodynamic definitions have been given for the disjoining pressure in the spherical liquid or vapor interlayer around a solid particle, and the agreement between the definitions has been proven by calculations at different interlayer thicknesses and particle radii. It has been shown that the disjoining pressure in a vapor interlayer around a nanosized lyophobic particle decreases with an increase in particle radius, with this phenomenon being opposite to the situation with liquid films.

Understanding the sensitivity of nucleation free energies: The role of supersaturation and temperature

Simulations are used to investigate the vapor-to-liquid nucleation of water for several different force fields at various sets of physical conditions. The nucleation free energy barrier is found to be extremely sensitive to the force field at the same absolute conditions. However, when the results are compared at the same supersaturation and reduced temperature or the same metastability parameter and reduced temperature, then the differences in the nucleation free energies of the different models are dramatically reduced. This finding suggests that comparisons of experimental data and computational predictions are most meaningful at the same relative conditions and emphasizes the importance of knowing the phase diagram of a given computational model, but such information is usually not available for models where the interaction energy is determined directly from electronic structure calculations.

Homogeneous nucleation and growth in simple fluids. I. Fundamental issues and free energy surfaces of bubble and droplet formation

The free energy of forming a droplet and a bubble with a given particle number n and volume v within the pure-component Lennard-Jones supercooled vapor and superheated liquid, respectively, are further explored using density-functional theory. Similar to what was found previously [M. J. Uline and D. S. Corti, Phys. Rev. Lett. 99, 076102 (2007); M. J. Uline and D. S. Corti, J. Chem. Phys. 129, 234507 (2008)], the limits of stability again appear within both free energy surfaces evaluated at two other metastability conditions, one closer to the binodal and one closer to the spinodal. Furthermore, an ad hoc bond connectivity criterion is also applied in an attempt, however approximately, to eliminate certain configurational redundancies that arise from the chosen droplet and bubble definitions. What results are free energy surfaces describing the formation of equilibrium embryos that should be an improved representation of the fluctuations that are relevant to those nonequilibrium embryos seen in an actual nucleation event. Finally, we discuss in some detail the use of the (n,v) reaction coordinate within the framework of an equilibrium-based theory and its relation to other descriptions of nucleation.