Contact angle

A contact angle is the angle between a liquid interface and a solid surface at their three-phase contact line. It quantifies how a liquid wets the surface.

Young's equation: An equilibrium relation connecting contact angle to the interfacial tensions among a solid, liquid, and surrounding fluid. It predicts the angle on an ideal, smooth, chemically uniform surface from interfacial tensions.
Contact angle goniometry: The measurement of a liquid–solid contact angle from images of droplets or interfaces. It is the standard practical method for determining contact angles on solid samples.
Contact angle hysteresis: The difference between advancing and receding contact angles measured as a contact line moves. A real droplet can sustain a range of angles rather than one equilibrium value.
Wenzel state: A wetting state in which liquid follows the texture of a rough solid surface. Its roughness correction predicts apparent angles when liquid fully contacts surface texture.
Thomas Young: An English polymath whose work included an early relation among surface tensions at a liquid–solid–gas contact line. His 1805 treatment gives the ideal force-balance relation now used for equilibrium contact angles.
Wetting: The ability of a liquid to maintain contact with a solid surface, governed by interfacial energies. Contact angle is a common measure of how strongly a liquid wets a solid.
Capillary rise: The rise or fall of a liquid in a narrow tube caused by surface tension and wetting. The contact angle determines whether a liquid rises or is depressed in a capillary.
Advancing contact angle: The largest angle sustained as a liquid contact line advances over a solid surface. It characterizes the front edge of a spreading droplet and helps bound hysteresis.
Cassie–Baxter state: A wetting state in which a liquid rests on a composite surface of solid and trapped air. It explains high apparent angles when droplets bridge texture instead of filling it.
Pierre-Simon Laplace: A French mathematician and physicist who developed mathematical accounts of capillarity and celestial mechanics. His capillarity theory helped establish the interfacial framework surrounding Young's contact-angle relation.

Linked from 19 pages