Contact angle measurement

The contact angle or wetting angle is determined by the interaction between the surface tension of a liquid and the surface energy of a solid. The manner in which liquid droplets behave on a surface can predict the behaviors of this surface.

In practice, a drop of liquid is placed on a surface and the contact angle is measured. Low contact angle values, i.e. below 90°, are related to good wetting whereas high contact angle values, above 90 °, indicate poor wetting. When the contact angle is 0°, the surface is said to wet completely.

Application of contact angle

The most obvious example is the application of different types of coatings and surface treatments. For example, if contact angle between the paint and the surface to be painted is high, that will lead to poor spreading and non-uniform coating.

Contact angles can also be used to check if a surface treatment has been successful. Plasma treatment is often utilized to improve the adhesion between the substrate and the coating to be applied. The low contact angle between water and treated substrate indicate the success of the surface treatment.