What effect does increasing hydrophobicity have on wetting?

Increasing hydrophobicity decreases wetting. This is because hydrophobic substances repel water, leading to a lower interaction between the surface and the water. When a surface is hydrophobic, water droplets tend to bead up on the surface rather than spreading out or wetting it. This phenomenon occurs because the adhesive forces between the water molecules and the hydrophobic surface are weaker than the cohesive forces within the water itself, causing the water to minimize its contact area with the surface.

Wetters are usually added in formulations to enhance wetting properties by reducing surface tension and promoting interaction with surfaces. However, when hydrophobicity is increased, the opposite effect takes place, making it even more difficult for liquids to spread over or penetrate the surface. This understanding is crucial in fields like pharmaceutical sciences, where the wetting properties of a drug or excipient can influence its dissolution and bioavailability.