Liquid confined in nano/micro scale environments exists in a wide range of systems in chemistry, biology, and materials science, etc. It is well known that the thermodynamic properties of confined liquid, such as density, pressure, etc., are different from its bulk. Molecular dynamics (MD) simulation is a powerful tool to study the local properties of liquid confined in a nanopore, which is challenging to measure directly. Here we present a MD work of the equilibrium pressure of liquid argon (Ar) confined in a nanopore. The nanopore is formed by two hydrophilic walls and is connected a bulk liquid, which is a 5.2 nm thick continuous film. The atomic interactions among Ar atoms and between Ar and wall atom are govern by standard Lennard - Jones potential. The hydrophilic wall is mimicked by using high large potential well in Ar - Wall atom potential, which is 1.5 times as large as that in Ar - Ar potential. A hydrophilic wall consists of five-layer face centered cubic (FCC) \<111> plane atoms. A 2.2 nm thick boundary wall is present at the left edge of the domain to prevent the direct interaction between bulk liquid and vapor, which is at the other side of the domain. The interaction between Ar and boundary wall atoms is governed by Lennard - Jones potential as well, using small potential well (1% of Ar - Ar potential). The space between hydrophilic wall and simulation domain is filled with the same atoms in boundary wall. The system was equilibrated in a canonical NVT (N is the number of atoms; V is the volume; and T is the temperature) ensemble at 90 K for 3 ns using Nose-Hoover thermostat. The data of  density and pressure profile are obtained by averaging the values over the last 1 ns. It is shown that the liquid atoms are layered showing FCC \<111> configuration, adopted from wall atoms, inside the pore near the wall. The local density in layered region is higher than bulk and independent on the pore size. However, the pressure in layered region is highly dependent on the pore size, as well as the average pressure across the pore. The effects of pore dimension on pressure are investigated by 5 cases with varied  pore size from 1 nm to 5 nm. Both density and pressure profiles across the pore are obtained and the origin of the different pressure profiles are investigated.


Equilibrium Pressure of Liquid Confined in Nanopores Using Molecular Dynamics Simulations

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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