The measure of the degree of wetting of a surface by a liquid. It is the angle a liquid creates with the solid or liquid when deposited on/into it. This angle is determined by properties of the surface and liquid, the repulsion & interaction forces between the surface and liquid, and three-phase interface qualities (solid, gas, and liquid). A contact angle of 90° is considered as the threshold value. When the figure is below 90°, wettability is deemed to be good, and when higher, it is considered weak.