Energy-Based Interface Detection for Phase Change Processes of Monatomic Fluids in Nanoconfinements

Abstract

An energy-based liquid−vapor interface detection method is presented using molecular dynamics simulations of liquid menisci confined between two parallel plates under equilibrium and evaporation/condensation conditions. This method defines the liquid− vapor interface at the location where the average kinetic energy of atoms first exceeds the average potential energy imposed by all neighboring molecules. This definition naturally adapts to the location of the menisci relative to the walls and can properly model the behavior of the liquid adsorbed layers. Unlike the density cutoff methods frequently used in the literature that suffer from density layering effects, this new method gives smooth and continuous liquid−vapor interfaces in nanoconfinements. Surface tension values calculated from the equilibrium MD simulations match the Young−Laplace equation better when using the radius of curvatures calculated from this method. Overall, this energy-based liquid−vapor interface detection method can be used in studies of nanoscale phase change processes and other relevant applications.

Nanoscale Meniscus Dynamics in Evaporating Thin Films: Insights from Molecular Dynamics Simulations

“…By utilizing the energy-based interface detection method, 21 the liquid−vapor interface of the evaporating meniscus is calculated for the 16 nm case, as shown in Figure 3. The magenta color corresponds to liquid argon, while the brown color represents the Pt walls.…”

“…18,20 Defining the contact line using densitybased interface detection models leads to varying adsorbed film thicknesses due to the arbitrarily chosen cutoff values, and density fluctuations near the wall impact the contact line shape. 19,21 To overcome this issue, we introduced an energybased interface detection method that identifies the contact line and eliminates the need to use an arbitrary density cutoff value. 21 This novel approach, based on the energetics of the molecular system to define the interface, offers advantages over traditional density-based interface detection methods.…”

“…Contrary to the common assumption of nonevaporating adsorbed layers, our prior molecular dynamics (MDs) works presented adsorbed film evaporation which was not reported before. , However, pinpointing the evaporating meniscus in microscale contexts presents a challenge, and the nanoscale depiction of the evaporating meniscus is even more intricate. The liquid–vapor interface is a region of nearly 2 nm in thickness, which is very close to the characteristic length of the simulation domain. , Defining the contact line using density-based interface detection models leads to varying adsorbed film thicknesses due to the arbitrarily chosen cutoff values, and density fluctuations near the wall impact the contact line shape. , To overcome this issue, we introduced an energy-based interface detection method that identifies the contact line and eliminates the need to use an arbitrary density cutoff value . This novel approach, based on the energetics of the molecular system to define the interface, offers advantages over traditional density-based interface detection methods.…”

“…19,21 To overcome this issue, we introduced an energybased interface detection method that identifies the contact line and eliminates the need to use an arbitrary density cutoff value. 21 This novel approach, based on the energetics of the molecular system to define the interface, offers advantages over traditional density-based interface detection methods. The energy-based liquid−vapor interface detection method is based on the kinetics and potential energy of atoms within the system.…”