Method and device for contact angle determination from radius of curvature of drop by optical distance measurement

A method for determining the contact angle between a sample surface, a gaseous environment and a drop arranged on the sample surface, the drop having a curved surface, a symmetry axis and a defined volume, comprising:

• imaging an object on the basis of the reflection properties of the surface of the drop, the position of the object with respect to the optical axis of an optical measuring system and the position of the object with respect to the sample surface being known, and the symmetry axis of the drop being arranged in or in the vicinity of the optical axis;
• measuring the distance between the image of the object and the symmetry axis of the drop;
• determining the radius of curvature of the drop from the measured distance;
• and
• determining the contact angle from the radius of curvature.