Development of a setup to characterize capillary liquid bridges between liquid infused surfaces

Capillary liquid bridges are ubiquitous in nature and are present in many industrial processes. In order to model their behavior, it is essential to develop suitable experimental tools that are able to characterize the bridges' geometry and the associated capillary force they induce on the contacting surfaces. While many existing setups are capable of characterizing capillary bridges formed between conventional surfaces, quantitative measurements on smart surfaces such as liquid infused surfaces remain challenging. These surfaces typically exhibit weak contact line pinning and contact angle hysteresis, resulting in unusually small changes in the capillary force they exert upon extension or compression of the bridge. Although it is precisely these properties that drive the interest into liquid infused surfaces, they render experimental characterization challenging when compared to non-infused surfaces. Here, we tackle this issue by developing a relatively inexpensive setup capable of measuring capillary forces with sensitivity in the micronewton range while quantifying the bridge's geometry. The setup is fully motorized and can vary the relative position of the contacting surfaces while maintaining synchronous force and geometry measurements. We also present a new analysis software developed to retrieve the relevant geometrical parameters of the bridge from optical observations while minimizing errors and noise. Using example surfaces, we demonstrate the setup's capabilities, including for bridges between liquid infused surfaces. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

Capillary liquid bridges are widely present in nature and industrial processes. Quantitative measurements of their behavior on smart surfaces, such as liquid infused surfaces, are challenging due to weak contact line pinning and contact angle hysteresis. In this study, a relatively inexpensive setup capable of measuring capillary forces with sensitivity in the micronewton range and quantifying the bridge's geometry was developed. A new analysis software was also introduced to minimize errors and noise in retrieving the relevant geometrical parameters of the bridge from optical observations.