Hydrophilic vs. hydrophobic. The meaning of contact angle

Hydrophilicity, comes from the Greek ύδωρ, (water) and φιλία (friendship). It refers to a physical property of a material that can transiently bond with water (H₂O) through hydrogen bonding.

A hydrophilic material is a friend of water. Friends like to come closer, so a water droplet would spread on a hydrophilic surface. Furthermore water can enter the pores of a hydrophilic material and totally wet it. Most natural materials are hydrophilic.

The evaluation of hydrophilicity is made through water contact angle measurements. A water droplet would occupy as long surface of the hydrophilic material as possible. So the water contact angle will be significantly low.

Hydrophobicity comes also from the Greek ύδωρ, (water) and φόβος (fear). It refers to the physical property of a material (known as a hydrophobic) that repels a mass of water.

Water would be afraid of a hydrophobic material. So a water droplet would try not to touch large area of the surface and the shape of the droplet would be spherical. Hydrophobic natural materials are waxes, oils and fats.

The evaluation of hydrophobicity is made through water contact angle measurements. A water droplet would be spherical so the water contact angle will be significantly high.

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