Three-phase contact line dynamics on moving fibers measured by X-ray holography

TL;DR

This study introduces a novel X-ray holography method to measure dynamic contact angles on moving fibers with sub-microscopic resolution, advancing understanding of wetting phenomena at small scales.

Contribution

The paper presents the first application of X-ray phase contrast imaging to quantify dynamic contact angles on moving fibers with nanometer spatial resolution.

Findings

Dynamic receding contact angle decreases with increasing contact line velocity.

X-ray holography achieves 50 nm/pixel resolution with 450 nm spatial error.

Method demonstrates potential for high-resolution studies of wetting dynamics.

Abstract

Wetting of solid surfaces by a liquid is important for many natural and industrial processes such as printing, painting and coating. However, a quantitative description of the dynamic receding and advancing contact angle is still debated, in particular for aqueous solutions. One reason for our lack of quantitative understanding is the limited spatial resolution of currently used optical methods. We therefore present a new approach to access the sub-microscopic region. We use X-ray phase contrast imaging to measure the dynamic receding contact angle on a moving glass fiber of 17 um diameter. The fiber was pulled out of a liquid bath which was filled with a mixture of glycerol and Milli-Q water. The dynamic receding contact angle decreased with increasing contact line velocity for all mixtures. In the holograms we achieved a resolution of 50 nm/pixel with a spatial error of 450 nm. This spatial error is due to an extended surface region of the fiber and the liquid surface in the holograms. Our results demonstrate the feasibility of X-ray holography as a method to investigate dynamic contact angle phenomena and thereby opening pathways to higher spatial and temporal resolution.