What is the Difference Between Surface Tension and Viscosity?

Surface tension and viscosity are both properties of fluids that depend on intermolecular forces, but they have different characteristics and effects on liquids.

Surface Tension:

Surface tension is the amount of energy required to increase the surface area of a liquid by a unit area.
It is the property of a liquid surface that resists force, serving as a barrier to foreign materials and keeping the liquid molecules bound together.
Surface tension is determined by the difference in interactions between the molecules of the material (fluid) with the molecules of the material in contact.
It is mostly stable and changes primarily due to temperature and chemicals that modify the bonding characteristics of the molecules.

Viscosity:

Viscosity is the resistance of a fluid to flow.
It results from the collaboration among molecules of identical molecules located in the same material (in the case of fluids).
Viscosity is related to the friction between molecules in a fluid, which causes the resistance to deformation or movement.
It varies depending on shear rate and is influenced by factors such as temperature and the presence of surface-active agents like surfactants.

While there is a common belief that high viscosity fluids should have high surface tension, this correlation is not accurate. In fact, high viscosity does not necessarily imply high surface tension, as seen in substances like glue.