Universal contact-line dynamics at the nanoscale

TL;DR

This study investigates the nanoscale dynamics of contact lines between viscous liquids and substrates, revealing universal behaviors and regimes through experiments and modeling, with implications for understanding wetting and dewetting processes.

Contribution

It introduces a comprehensive analysis of contact-line relaxation at the nanoscale, combining experiments and lubrication modeling to identify universal features and regimes.

Findings

Identification of three distinct relaxation regimes

Existence of a self-similar interface evolution

Universal critical contact angle for dewetting transition

Abstract

The relaxation dynamics of the contact angle between a viscous liquid and a smooth substrate is studied at the nanoscale. Through atomic force microscopy measurements of polystyrene nanostripes we monitor simultaneously the temporal evolution of the liquid-air interface as well as the position of the contact line. The initial configuration exhibits high curvature gradients and a non-equilibrium contact angle that drive liquid flow. Both these conditions are relaxed to achieve the final state, leading to three successive regimes along time: i) stationary-contact-line levelling; ii) receding-contact-line dewetting; iii) collapse of the two fronts. For the first regime, we reveal the existence of a self-similar evolution of the liquid interface, which is in excellent agreement with numerical calculations from a lubrication model. For different liquid viscosities and film thicknesses we provide evidence for a transition to dewetting featuring a universal critical contact angle and dimensionless time.