Also contains definitions of: area viscosity, surface dilatational viscosity

https://doi.org/10.1351/goldbook.S06189

For steady state deformations a surface shear viscosity η s, and an area viscosity or surface dilatational viscosity ζ s can be defined. In a Cartesian system with the *x*-axis normal to the surface, they are defined by the equations: \[\eta ^{\text{s}} = \frac{\sigma _{xy}}{\frac{\partial \nu_{y}}{\partial \nu_{x}}}\] \[\zeta ^{\text{s}}=\frac{\Delta \gamma }{\frac{\mathrm{d}(\ln A)}{\mathrm{d}t}}\] where σ x y is the shear component of the surface stress tensor, v x and v y are the x and y components of the surface velocity vector, respectively, A is the surface area, t is the time, and Δ γ is the difference between the (steady state) dynamic surface tension and the equilibrium surface tension.*Source: *

PAC, 1979,*51*, 1213. 'Terminology and Symbols in Colloid and Surface Chemistry Part 1.13. Definitions, Terminology and Symbols for Rheological Properties' on page 1218 (https://doi.org/10.1351/pac197951051213)

PAC, 1979,