Water Shedding Angle: A New Technique to Evaluate the Water-Repellent Properties of Superhydrophobic Surfaces

Abstract

A new technique is introduced to evaluate the wetting properties of superhydrophobic textiles which are not accessible by classical contact angle measurement techniques. The principle behind the new water shedding angle technique is the ability of a superhydrophobic surface to repel drops of water upon impact. In this sense it shows a strong reference to application and its results are easily understood in terms of water protection. The procedure is simple and straightforward and the experimental setup can be easily built or adapted to most available contact angle measurement systems. In view of the significant potential of superhydrophobic coatings for textile applications, the water shedding angle provides a reliable and comparable measure to judge the quality of a superhydrophobic textile in terms of water repellency. It constitutes a useful addition to existing techniques and has proven to be better suited to evaluate the wetting properties of superhydrophobic textiles than the contemporary methods presently in use.

A superoleophobic textile repellent towards impacting drops of alkanes

“…Unfortunately this comparison fails due to the impossibility of determining contact angles on macroscopically rough and non-reflecting samples as on our textile. This problem is well documented in the literature [22,29] and also conforms to our experience (see figure S3 in the electronic supplementary material). For this reason we want to forgo any further discussion of contact angles.…”

“…In order to gain information about the robustness and the penetration behaviour of an impacting drop we measured the shedding angle ω with several alkanes. A detailed description and discussion of this experimental method is given in the literature [22]. In brief, the sample is mounted on a table with an adjustable inclination angle.…”

“…2 cm by 5 cm were cut out and carefully attached to glass slides using double sided adhesive tape. Measurements were performed with the Contact Angle System OCA (Dataphysics, Germany) and a custom-made tilting device according to the literature [22]. Experiments were started at an inclination angle 4 of 70°.…”

Superamphiphobic surfaces

“…19 In order to characterize the superhydrophobicity of a macroscopically textile, a new technique named shedding angle was developed recently. 14 In essence, a water drop of defined volume is released onto the substrate from a defined height. The minimum angle of inclination at which the substrate needs to be tilted for the drop to completely roll or bounce off the substrate is 5 determined (Fig.…”

One-dimensional silicone nanofilaments

“…For this type of sample, the 'shedding angle' was introduced by Zimmermann et al [20]. This method determines the minimum inclination angle at which an impacting droplet does not penetrate the surface but rolls off without leaving a trace.…”