Question

What are cohesive and adhesive forces? How do these govern the wetting and
non-wetting properties of liquids?

Answer 1

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Cohesive Forces

It is the attractive forces which acts between similar molecules.

Example: Forces between water-water molecules.

Adhesive Forces

It is the attractive forces which acts between molecules of different materials.

Example: Forces between water molecule and silica.

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When any one of these forces comes in contact with the surface of liquid then both cohesive and adhesive forces acts on it.

As a result adhesive forces allows the liquid to spread in a thin layer, which makes a uniform layer on the surface, this is how the wetting process is done by these two forces.