Contact angle

⭐ In the context of surface science, contact angle is considered


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⭐ Core Definition: Contact angle

The contact angle (symbol ξC) is the angle between a liquid surface and a solid surface where they meet. More specifically, it is the angle between the surface tangent on the liquid–vapor interface and the tangent on the solid–liquid interface at their intersection.It quantifies the wettability of a solid surface by a liquid via the Young equation.

A given system of solid, liquid, and vapor at a given temperature and pressure has a unique equilibrium contact angle. However, in practice a dynamic phenomenon of contact angle hysteresis is often observed, ranging from the advancing (maximal) contact angle to the receding (minimal) contact angle. The equilibrium contact is within those values, and can be calculated from them. The equilibrium contact angle reflects the relative strength of the liquid, solid, and vapour molecular interaction.

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In this Dossier

Contact angle in the context of Hydrophobe

In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water.

Hydrophobic molecules tend to be nonpolar and, thus, prefer other neutral molecules and nonpolar solvents. Because water molecules are polar, hydrophobes do not dissolve well among them. Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.

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Contact angle in the context of Superhydrophobic

In chemistry and materials science, ultrahydrophobic (or superhydrophobic) surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. This is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet striking these kinds of surfaces can fully rebound like an elastic ball. Interactions of bouncing drops can be further reduced using special superhydrophobic surfaces that promote symmetry breaking, pancake bouncing or waterbowl bouncing.

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LINKED FROM (PARENTS)
← Hydrophobe ← Superhydrophobic ← Hydrophobicity ← Hydrophobic ← Ultrahydrophobicity
LINKS TO (CHILDREN)
Angle → Liquid → Surface → Solid → Surface tangent → Vapor → Interface (chemistry) → Wettability → Young–DuprĂ© equation → Hysteresis → Intermolecular force →