Term: contact angle
https://doi.org/10.1351/goldbook.C01290

Definition:
When a liquid does not spread on a substrate (usually a solid), a contact angle (θ) is formed which is defined as the angle between two of the interfaces at the three-phase line of contact. It must always be stated which interfaces are used to define θ. It is often necessary to distinguish between the 'advancing contact angle' θ a, the 'receding contact angle' θ r and the 'equilibrium contact angle' θ e. When θ r ≠ θ a the system is said to exhibit contact angle hysteresis

Related Terms:
1) substrate (<em>in thin films</em>) (http://doi.org/10.1351/goldbook.S06084).
2) hysteresis (<em>in thin films</em>) (http://doi.org/10.1351/goldbook.H02930).
3) angle (<em>in thin films</em>) (http://doi.org/10.1351/goldbook.A00346).

Source: PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 598 (https://doi.org/10.1351/pac197231040577)

Citation: 'contact angle' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01290

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