Wetting properties at the Nanoscale

A brief introduction of the modified Young's equation for nanodroplets.

The contact angle, between the liquid-gas interface and the solid surface is used to describe the wetting property. Form thermodynamic and mechanical point of view, the contact angle is a balance between the surface tensions of solid-liquid, liquid-vapor, and solid-vapor. This relationship is the well-known Young’s equation. 

However, the wetting of nanodroplet is not only determined by the balance of surface tensions, but also by the tension of the line where three distinct phases coexist. By analogy with surface tension, which is defined as the excess free energy per unit surface of an interface separating two phases, line tension is the excess free energy per unit length of a three-phase contact line. A positive line tension make the droplet shrink, while a negative line tenison make the droplet spread. See the following picture:


To take line tension into account, Young’s equation has been modified as


Till now, the sign and magnitude of line tension remain controversial in literature. We have obtained some results for Argon, water and salt water nanodroplets. Hopefully our results will be published this year.