Features of the Contact Angle Hysteresis at the Nanoscale: A Molecular Dynamics Insight

TL;DR

This study uses molecular dynamics to explore contact angle hysteresis at the nanoscale, developing an analytic model to accurately describe droplet shapes and revealing the dominance of capillary and viscous forces in this regime.

Contribution

It introduces a molecular dynamics approach combined with an analytic model to analyze nanoscale contact angle hysteresis, bridging the gap between macroscale models and nanoscale phenomena.

Findings

Capillary and viscous forces critically influence droplet shape at the nanoscale.

The Cox-Voinov model effectively describes hysteresis when capillary forces dominate.

The role of interface rolling movement is significant in droplet dynamics.

Abstract

Understanding the physics of a three-phase contact line between gas, liquid, and solid is important for numerous applications. At the macroscale, the three-phase contact line response to an external force action is often characterized by a contact angle hysteresis, and several models are presented in the literature for its description. Yet, there is still a need for more information about such model applications at the nanoscale. In this study, a molecular dynamics approach was used to investigate the shape of a liquid droplet under an external force for different wetting regimes. In addition, an analytic model for describing the droplet shape was developed. It gives us the possibility to evaluate the receding and advancing wetting angle accurately. With our modeling, we found that the interplay between capillary forces and viscous forces is crucial to characterize the droplet shape at the nanoscale. In this frame, the importance of the rolling movement of the interface between liquid and vapor was pointed out. We also demonstrate that in the range of the external forces when capillary forces are most significant compared to others, hysteresis is well described by the macroscale Cox-Voinov model.