Abstract
The evaporation of sessile water droplets on hydrophobic surfaces is a topic which led to numerous investigations. However, how does the liquid behave when the evaporation occurs between two of these particular substrates? The drying stage is governed by capillary phenomena which takes place in a confined space. In the field of material shaping, it is also possible that some regions of a green body exhibit hydrophobic properties. As part of a better understanding of the local mechanisms during drying, liquid bridges have been reproduced in an ideal case. Drying kinetics and parameters measurements from 303 to 343 K (relative humidity of 55%) of deionized water liquid bridges between two plates of hydrophobic substrates are presented. Experimental work was carried out using a specific device to create liquid bridges, coupled with image analysis within an adapted instrumented climatic chamber. While the volume and the exchange surface of liquid bridges decrease regularly throughout the process, contact angles constantly diminish and more significantly at the end. This is different from the evaporation between two hydrophilic plates. From these measurements, the change of curvature of the liquid bridges during evaporation is highlighted.
Highlights
Hydrophobic materials arouse interest as their applications are widespread, from limiting friction in the aeronautic field, self-cleaning surfaces or modifying heat transfer properties
To the best knowledge of the authors, the evaporation of liquid bridges between two hydrophobic substrates has never been reported in the literature, the only observations were on drying liquid bridges between hydrophilic substrates
Using a specific device to create liquid bridges within a humid environment and between hydrophobic surfaces, values of geometrical parameters, namely the volume, the exchange surface and contact angles of liquid bridges as a function of the drying time have been evaluated for temperatures from 303 to 343 K and a fixed relative humidity of 55%
Summary
Hydrophobic materials arouse interest as their applications are widespread, from limiting friction in the aeronautic field, self-cleaning surfaces or modifying heat transfer properties. Among the different types of contacts that can be realized, an increasing interest appears for the study of hydrophobic surfaces (contact angle with water > 90 ̊) [5] [6] [7] These surfaces often mimic nature, for instance the super-hydrophobic surface of a lotus leaf (Figure 1(a)). Such materials can be created using several methods, among which surface treatments, coatings or by controlling the initial composition. Hydrophobic materials, coatings, textured surfaces were used in microelectromechanical systems and in microfluidic fields They promote dropwise condensation instead of liquid spreading, which prevents water damage in electronics (Figure 1(b)). To the best knowledge of the authors, the evaporation of liquid bridges between two hydrophobic substrates has never been reported in the literature, the only observations were on drying liquid bridges between hydrophilic substrates
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