For steady state deformations a surface shear viscosity
, and an area viscosity or surface dilatational
can be defined. In a Cartesian system with the
-axis normal to the surface, they are defined by the equations:
is the shear component of the surface stress
components of the surface velocity vector, respectively,
is the surface area,
is the time, and
is the difference between the (steady state) dynamic surface tension
and the equilibrium surface tension.
PAC, 1979, 51, 1213
(Manual of symbols and terminology for physicochemical quantities and units. Appendix
II: Definitions, terminology and symbols in colloid and surface chemistry. Part 1.13.
Selected definitions, terminology and symbols for rheological properties)
on page 1218
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