Disjoining Pressure Effects in Ultra-Thin Liquid Films in Micropassages—Comparison of Thermodynamic Theory With Predictions of Molecular Dynamics Simulations

Abstract

The concept of disjoining pressure, developed from thermodynamic and hydrodynamic analysis, has been widely used as a means of modeling the liquid-solid molecular force interactions in an ultra-thin liquid film on a solid surface. In particular, this approach has been extensively used in models of thin film transport in passages in micro evaporators and micro heat pipes. In this investigation, hybrid μPT molecular dynamics (MD) simulations were used to predict the pressure field and film thermophysics for an argon film on a metal surface. The results of the simulations are compared with predictions of the classic thermodynamic disjoining pressure model and the Born-Green-Yvon (BGY) equation. The thermodynamic model provides only a prediction of the relation between vapor pressure and film thickness for a specified temperature. The MD simulations provide a detailed prediction of the density and pressure variation in the liquid film, as well as a prediction of the variation of the equilibrium vapor pressure variation with temperature and film thickness. Comparisons indicate that the predicted variations of vapor pressure with thickness for the three models are in close agreement. In addition, the density profile layering predicted by the MD simulations is in qualitative agreement with BGY results, however the exact density profile is dependent upon simulation parameters. Furthermore, the disjoining pressure effect predicted by MD simulations is strongly influenced by the allowable propagation time of injected molecules through the vapor region in the simulation domain. A modified thermodynamic model is developed that suggests that presence of a wall-affected layer tends to enhance the reduction of the equilibrium vapor pressure. However, the MD simulation results imply that presence of a wall layer has little effect on the vapor pressure. Implications of the MD simulation predictions for thin film transport in micro evaporators and heat pipes are also discussed.

Acoustothermal Atomization of Water Nanofilms

“…4(a) this equation is used to plot P D , using Π ¼ 5.99 × 10 −21 J [44]. Figure 4(a) indicates that, once h f < 1 nm, the intermolecular forces gain importance and likely suppress evaporation to achieve equilibrium, consistent with NEMD studies of thermal nonevaporating layers [45,46]. An interesting consequence is that h ∞ is independent of the initial film dimensions, and depends only on the balance between acoustic and intermolecular forces.…”

Development of force field parameters for oxyluciferin on its electronic ground and excited states

“…Even though some values are already available [71][72][73][74], we actually have refit the parameters with well-established aromatic side chain molecules (PHE, TRP, TYR, and HIS) from the OPLS parameter set [18] with the same scanning approach. We believe this refit parameters are more reliable for our purpose as the existing Ar parameters were often optimized for fluidic argon state, which may not be relevant in biological systems.…”

Molecular Dynamics Simulations on Evaporation of Droplets with Dissolved Salts

“…The system behavior and temporal evolution of its thermodynamic and transport properties can be obtained by statistically averaging the results of all molecular motions. Molecular dynamics simulating an evaporation process has no need of some assumptions made by CFD (computational fluid dynamics), so this method was adopted to study the droplet evaporation [4][5][6][7][8][9][10][11] and the evaporation of flat thin liquid films on solid surfaces [12][13][14]. These studies focused on evaporation of droplets consisting of one component under various conditions, and compared the evaporation rates simulated by molecular dynamics and predicted by classical kinetic theory, such as the D 2 law [5,6,9].…”