Memory Effects in Contact Line Friction

TL;DR

This paper develops a theoretical framework to analyze contact line friction, revealing that the contact line exhibits long-lasting memory effects and frequency-dependent dissipation, which influence how liquids wet surfaces.

Contribution

It introduces an exact method using the Mori-Zwanzig formalism to extract contact line friction from equilibrium data, highlighting memory effects and frequency-dependent behavior.

Findings

Contact line exhibits power-law decay in memory effects.

Friction decreases beyond a characteristic frequency.

System shows elastic behavior at high frequencies.

Abstract

When a drop of liquid comes into contact with a solid surface, it relaxes towards an equilibrium configuration, either wetting the surface or remaining in a droplet-like shape with a finite contact angle. The force driving the process towards equilibrium is the corresponding out-of-balance Young's force. However, the speed with which the liquid front advances depends strongly on an opposing friction force arising from dissipative processes due to the moving solid-liquid-gas contact line. In analogy to the treatment of hydrodynamic friction we present an exact method, based on the Mori-Zwanzig formalism, to extract this friction from equilibrium data. We find that the contact line exhibits long-lasting memory with a characteristic power-law decay due to coupling to the systems hydrodynamic modes. Within linear response regime, we obtain the frequency-dependent dissipative and elastic response of the contact line to an external perturbation, including a frequency-dependent friction coefficient. Similar to hydrodynamic friction in liquids, we find that the friction decreases beyond a characteristic frequency and the system exhibits predominantly elastic behavior.