The wettability and thus coatability of a surface depend largely on its surface energy (surfacetension). The energy of a surface can be determined quickly and reliably by contact angle measurement. Compared to test inks, the contact angle measurement provides a quantitative result which is influenced by significantly fewer parameters (material of the surface, manufacturer of the test ink, age of the test ink).

Measuring principle

With special contact angle measuring devices two liquids with different polarity (usually water and diiodomethane) are dosed onto a surface. The generated lying drops on the surface have a volume of 0.5 - 2.0 µL. With the help of appropriate camera optics, an image of the drops on the surface is taken. The tangent at the three-phase point and the baseline can be used to determine the contact angle. With the help of Young's equation, the surface free energy of the surface can be determined.

Requirements for the sample

Due to the very small drop volume and digital image acquisition and processing, even very small or round surfaces can be examined. There are limitations, especially for measuring points that are located in depressions, such as grooves. Here it may not be possible to acquire an image, which is necessary for evaluation.