Glossary of surface technology

Contact angle

The contact angle or wetting angle is the angle formed by the tangent to the drop contour with the surface of the solid at the three-phase point when observing the projection of the horizontal drop on the solid body. According to the physical definition, a surface with a contact angle of smaller 90° is hydrophilic (wettable) and greater 90° hydrophobic (non-wettable). By means of plasma treatment the contact angle can be modified (increased or reduced). Via a suitable plasma process or application of a suitable coat in a plasma process, hydrophilic surfaces can be made hydrophobic (and vice versa by hydrophilic coats). The determination of the surface energy pursuant to DIN 55660-2 is based on measuring the contact angle.

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