key term - Contact angle

Definition

The contact angle is the angle formed between a liquid droplet and a solid surface. It quantifies the wettability of the solid surface by the liquid.

5 Must Know Facts For Your Next Test

1. A contact angle less than 90 degrees indicates good wetting properties, meaning the liquid spreads easily on the surface.
2. A contact angle greater than 90 degrees signifies poor wetting, where the liquid tends to form droplets.
3. The contact angle is influenced by the cohesive forces within the liquid and adhesive forces between the liquid and solid.
4. It can be measured using methods such as the sessile drop technique or a goniometer.
5. The Young-Laplace equation describes how surface tension influences the shape of a droplet, which in turn affects the contact angle.

Review Questions

Related terms

Surface Tension:

The elastic tendency of liquids that makes them acquire the least surface area possible. It results from cohesive forces among liquid molecules.

Cohesion:

The intermolecular attraction between like molecules within a substance, such as water molecules attracting each other.

Adhesion:

The attraction between different types of molecules, such as those of a liquid and a solid.