A liquid contact line receding on a soft gel surface : dip-coating geometry investigation

TL;DR

This study investigates how a liquid contact line recedes on a soft gel surface using a dip-coating setup, revealing different motion regimes influenced by substrate velocity and gel elasticity, with implications for wetting behavior on soft materials.

Contribution

It provides a systematic analysis of contact line dynamics on soft gels, highlighting the influence of elastic deformation and velocity-dependent regimes, which was not thoroughly explored before.

Findings

Different contact line motion regimes depend on substrate velocity.

Elastic deformation near the contact line affects wetting behavior.

Transitions between motion regimes relate to material relaxation frequencies.

Abstract

We studied the dynamics of a liquid contact line receding on a hydrophobic soft gel (SBS-paraffin). In order to realize a well-defined geometry with an accurate control of velocity, a dip-coating setup was implemented. Provided that the elastic modulus is small enough, a significant deformation takes place near the contact line, which in turn drastically influences the wetting behaviour. Depending on the translation velocity of the substrate, the contact line exhibits different regimes of motions. Continuous motions are observed at high and low velocities, meanwhile two types of stick-slip motion, periodic and erratic, appear at intermediate velocities. We suggest that the observed transitions could be explained in terms of the competition between different frequencies, i.e., the frequency of the strain field variation induced by the contact line motion and the crossover frequency of the gel related to the material relaxation. Our results provide systematic views on how the wetting of liquid is modified by the rheological properties of a complex soft substrate.