Relaxation of a dewetting contact line Part 2: Experiments

TL;DR

This experimental study investigates the dynamics of receding contact lines in dip coating, confirming hydrodynamic theory predictions, analyzing bifurcations, and revealing the influence of flow geometry on contact line behavior.

Contribution

It provides the first experimental bifurcation diagram of dynamical wetting and demonstrates the importance of flow geometry over static contact angle models.

Findings

Confirmed hydrodynamic theory of contact line dynamics

Established dispersion relation with linear sigma in q

Showed flow geometry significantly affects contact line transition

Abstract

The dynamics of receding contact lines is investigated experimentally through controlled perturbations of a meniscus in a dip coating experiment. We first characterize stationary menisci and their breakdown at the coating transition. It is then shown that the dynamics of both liquid deposition and long-wavelength perturbations adiabatically follow these stationary states. This provides a first experimental access to the entire bifurcation diagram of dynamical wetting, confirming the hydrodynamic theory developed in Part 1. In contrast to quasi-static theories based on a dynamic contact angle, we demonstrate that the transition strongly depends on the large scale flow geometry. We then establish the dispersion relation for large wavenumbers, for which we find that sigma is linear in q. The speed dependence of sigma is well described by hydrodynamic theory, in particular the absence of diverging time-scales at the critical point. Finally, we highlight some open problems related to contact angle hysteresis that lead beyond the current description.