Wettability

The contact angle θ is the determining parameter for the shape of a droplet placed in contact with a surface. The shape of the droplet is a manifestation of surface energy, which depends on the chemical structure and roughness of the surface. The measurement itself is very simple. A droplet of suitable size is placed onto the surface using a capillary so that it is not deformed by its own weight, it is photographed, and the contact angle is measured from the image using software developed in our department. The contact angle on an ideally smooth surface results from the competition between the surface energy of the liquid and the sample, and is described by the Young equation.If the contact angle of water on a substance is greater than 90°, the substance is called hydrophobic; if it is less than 90°, it is called hydrophilic.

Furthermore, our goniometers can also be used to study the dynamics of droplet drying, which represents a very interesting area of applied research. In addition to studying drying by measuring the evolution of contact angles and contact areas of drying droplets, we also use gravimetric measurements, where the mass of the drying droplets is recorded.