Define angle of contact and mention the dependent factors of it
Answers
the angle between the meniscus and the containing walls of a column of liquid measured from the vertical wall below the surface of the liquid to the position of the tangent to the meniscus at its point of contact with the wall.
(a) The nature of liquid and solid.
b) The medium above the surface of the liquid. For example, angle of contact between mercury and glass when there is air above mercury surface is different than the angle of contact between them when water is there above mercury surface.
(c) Purity of liquids and solids. If the liquid is not pure and the surface of solid is not clean, then angle of contact will change. The angle of contact between pure water and clean glass is nearly zero. But for a slightly oily glass plate the angle of contact increases, may even become more than 90°.
(d) Surface geometry can be used to tune the contact angle; with increasing surface roughness the apparent contact angle decreases for hydrophilic materials and increases for hydrophobic materials.