Molecular dynamics simulation of interfacial tension and contact angle of Lennard-Jones fluid.

摘要

Molecular techniques have been used to study interfacial tension for more than half century. Interfacial tensions regulate various phase change phenomena and heat transfer, especially when phase change occurs. At the sub-micron scales of MEMS devices, microscale evaporation and condensation, surface effects can dominate. The dynamics of thin film is studied here to quantify the effect of film thickness, system temperature and wall strength. When the film is thick, liquid-vapor interfacial tension is evaluated by integrating the difference between normal and tangential components of pressure tensor across the interface. Interfacial tension dependence on the film thickness is investigated and found to be weakly dependent. Strength of the solid surface plays an important role for a stable film adjacent to the solid surface.; Liquid droplet is simulated adjacent to a semi-infinite solid surface. Contact angle of a static droplet is investigated at different temperatures and the solid-fluid interaction strength. Hamaker constant of the fluid-solid combination, fluid density and solid-fluid Lennard-Jones length parameter are found to be important parameters controlling the contact angle. Variation of the contact angle with all necessary parameters are discussed.; Interfacial tension of the liquid-vapor interface is calculated using Molecular Dynamics simulation with tail correction to correct the finite cutoff radius used in the simulation. The resultant surface tension, liquid density and vapor density are found to be well predicted when compared with experimental data for Ar (LJ fluid). Liquid and vapor densities were found to depend on the finite cutoff radius which motivates the use of an untruncated force/potential calculation using p3M (particle-particle particle-mesh) method which was implemented for force and surface tension evaluation. Each term is computed by splitting it into short and long range parts. This does not require the tail correction. It is found to be very accurate as well as promise to be computationally efficient for larger system. In our case, it is found to be similar to computational time for neighbor-list method with cutoff radius of 4.5sigma.