When a liquid does not spread on a
substrate (usually a solid), a contact
angle(
) 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

. It is often necessary to distinguish between the '
advancing contact angle'
(
), the '
receding contact angle'
(
) and the '
equilibrium contact angle'
(
).
When

the system is said to exhibit contact
anglehysteresisSource:
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
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.