Question

What do you mean by the angle of contact of a liquid with a solid surface? What are the factors that affect it?

Answer 1

The wettability of the solid due to a liquid is measured by the angle of contact, which is also known as the wetting angle. Between plain water and clean glass, the angle of contact is approximately zero.

Complete answer:
The angle of contact is known as the angle subtended between the tangents drawn at the liquid surface and the solid surface within the liquid at the point of contact. It can also be explained as the angle formed between the tangents drawn at the solid surface and the liquid surface inside the liquid at the point of contact.

The angle of contact is affected by the following factors:
-The nature of the liquid and the solid: The angle of contact is formed by the interaction of the liquid and the solids that are in contact. For any given liquid-solid pair, the contact angle remains constant.
-The medium by which the angle of contact is made: The area above the liquid's surface. If there is air above the mercury surface, for example, the angle of contact between mercury and glass is different from when there is water above the mercury surface.
-The cleanliness of liquids and solids: The degree to which the inclination of a solid is inclined to the liquid surface is independent of the angle of contact. The angle of contact will change if the liquid is not clear and the solid's surface is not clean.
-The contact angle can be tuned using surface geometry: as the surface roughness increases, the apparent contact angle decreases for hydrophilic materials and increases for hydrophobic materials.

Note: To view the angle directly, commercial contact angle goniometry use a microscope focus. A drop is placed on a surface, and the contact angle can be determined by looking at the drop using a goniometer in the static method. The goniometer is an instrument that measures contact angles.