watercontacthoek

Watercontacthoek, in English commonly called the water contact angle, is the angle formed at the contact line where a water droplet meets a solid surface and the surrounding air. It is a measure of surface wettability: low angles indicate high wettability (hydrophilic surfaces), while high angles indicate low wettability (hydrophobic surfaces). Typical values place surfaces as hydrophilic below about 90 degrees, hydrophobic above 90 degrees, and very high angles (often above 150 degrees) describing superhydrophobic behavior where droplets bead up.

The contact angle is described by interfacial tensions and is often explained by Young’s equation, which relates the solid–vapor, solid–liquid, and liquid–vapor interfacial tensions to the angle inside the liquid. Real surfaces are frequently rough or chemically heterogeneous, which can modify the observed angle through models such as Wenzel and Cassie-Baxter. In practice, many surfaces show contact angle hysteresis: the advancing angle during droplet growth and the receding angle during withdrawal differ due to surface roughness, chemical heterogeneity, or contamination.

Measurement is commonly performed with the sessile-drop method using a goniometer or microscope, by placing a small water droplet on the surface and analyzing the droplet profile to determine the angle. Other methods include the captive-bubble technique or the Wilhelmy plate method. Factors such as temperature, droplet size, surface cleanliness, roughness, and chemical composition influence the results.

Applications of watercontacthoek measurements include characterizing coatings and materials for adhesion and wetting, optimizing printing and coating processes, designing biomaterials and medical implants, evaluating corrosion resistance, and informing the development of microfluidic devices. The measurement provides a practical proxy for surface energy and wettability in material science.