Contact angle of sessile drops in Lennard-Jones systems

TL;DR

This study uses molecular dynamics simulations to analyze how nanoscale sessile drops interact with solid surfaces, revealing size, temperature, and surface density effects on contact angles and providing a predictive correlation.

Contribution

It introduces a comprehensive correlation for contact angles based on temperature, dispersive interaction, and solid density, including size effects and wall model variations.

Findings

Contact angle decreases with smaller droplet size below 10,000 particles.

A stable contact angle is observed for larger system sizes.

The effective solid-fluid dispersive interaction at 90° contact angle is independent of temperature.

Abstract

Molecular dynamics simulation is used for studying the contact angle of nanoscale sessile drops on a planar solid wall in a system interacting via the truncated and shifted Lennard-Jones potential. The entire range between total wetting and dewetting is investigated by varying the solid--fluid dispersive interaction energy. The temperature is varied between the triple point and the critical temperature. A correlation is obtained for the contact angle in dependence of the temperature and the dispersive interaction energy. Size effects are studied by varying the number of fluid particles at otherwise constant conditions, using up to 150 000 particles. For particle numbers below 10 000, a decrease of the contact angle is found. This is attributed to a dependence of the solid-liquid surface tension on the droplet size. A convergence to a constant contact angle is observed for larger system sizes. The influence of the wall model is studied by varying the density of the wall. The effective solid-fluid dispersive interaction energy at a contact angle of 90 degrees is found to be independent of temperature and to decrease linearly with the solid density. A correlation is developed which describes the contact angle as a function of the dispersive interaction, the temperature and the solid density. The density profile of the sessile drop and the surrounding vapor phase is described by a correlation combining a sigmoidal function and an oscillation term.