Roll-off angle

The angle AO B is the roll-off angle. Read off the roll-off angle = 9° to the right. 

The more dramatic demonstration of the creation of interaction force between the surface and a sessile droplet of water can be seen in the measurement of the sessile droplet rolling-off angle, of which principle is depicted in Figure 23.16. If the sessile droplet contact angle is high and no surface configuration change occurs, such... 

For the characterization of wetting properties we employed dynamic contact angle measurements as well as measurements of sliding/roll-off angles using a Data-Physics OCA20 measurement system. 

The measurement of sliding angles and roll-off angles at a defined drop volume of 35 pi was performed by motorized rotation of the contact angle measurement system along its horizontal axis. 

The roll-off angle is a very important criterion to judge whether a surface can be regarded truly superhydrophobic or not. In our case this angle was 9.5° for the drop of volume of 0.2 ml. For truly superhydrophobic surface the roll-off angle should be as close to zero as possible, thus our surfaces could be defined as pseudosuperhydrophobic. 

While strong water repellence — characterized by water contact angles or drop penetration — was achieved in these chemical or physical modification techniques, but no definite statement concerning super-hydrophobic properties can be made. Most papers did not state roll-off angles or contact angle hysteresis. 

Several frequentiy used models for wetting have been tested with the acquired data. The models investigated were the Cassie— Baxter approximation, the Furmidge equation for roll-off angles, and a proposition from Patankar for receding contact angles. 

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