A molecular dynamics study of nano-bubble surface tension

Abstract

The main purpose of this paper is to numerically investigate the effect of bubble curvature on the surface tension. The effect of surface wettability on the bubble shape is also investigated due to its direct effects on the bubble curvature. Also, the validity of Young–Laplace (Y–L) equation to describe the bubble characteristics in nano order is examined using the molecular dynamics (MD) simulations method. A computer code based on the MD method is developed. The code carries out a series of simulations to generate bubbles of various radii between two planar solid surfaces. In our simulation, the total volume of the simulation box as well as the surface wettability affects the bubble curvature. The pair potential for the liquid–liquid and liquid–solid interaction is considered using the Lennard-Jones model. Pressure tensor and density profile are locally calculated. Furthermore, liquid pressure is evaluated far from the interface using the virial theorem and gas pressure is obtained using an equation of state. It is observed that the gas pressure is almost independent of the bubble radius. However, the liquid pressure becomes more negative as the radius decreases. Surface tension is computed using the Y–L equation and compared with the surface tension directly computed from the MD simulation. The amount of surface tension increases with a decrease in the radius.

Keywords:

• molecular dynamics
• bubble
• surface tension
• Young–Laplace
• wettability