Wetting of two-component drops: Marangoni contraction versus autophobing

TL;DR

This study investigates the wetting behavior of two-component alkane diol-water droplets, revealing that contact angles are governed by either Marangoni contraction or autophobing, depending on molecular structure, thus linking molecular physics to macroscopic wetting.

Contribution

It uncovers two distinct mechanisms controlling contact angles in complex fluid mixtures and shows how molecular structure influences wetting behavior.

Findings

Contact angles are surprisingly large for alkane diol-water mixtures.

Two mechanisms, Marangoni contraction and autophobing, determine wetting behavior.

The alkyl tail length dictates which mechanism dominates.

Abstract

The wetting properties of multi-component liquids are crucial to numerous industrial applications. The mechanisms that determine the contact angles for such liquids remain poorly understood, with many intricacies arising due to complex physical phenomena, for example due to the presence of surfactants. Here, we consider two-component drops that consist of mixtures of vicinal alkane diols and water. These diols behave surfactant-like in water. However, the contact angles of such mixtures on solid substrates are surprisingly large. We experimentally reveal that the contact angle is determined by two separate mechanisms of completely different nature, namely Marangoni contraction (hydrodynamic) and autophobing (molecular). It turns out that the length of the alkyl tail of the alkane diol determines which mechanism is dominant, highlighting the intricate coupling between molecular physics and the macroscopic wetting of complex fluids.