Extensional viscosity (also known as elongational viscosity) is a viscosity coefficient when the applied stress is extensional stress. It is often used for characterizing polymer solutions. Extensional viscosity can be measured using rheometers that apply extensional stress. Acoustic rheometer is one example of such devices.

:

where

1. is the extensional viscosity or elongational viscosity

2. is the normal stress along direction n.

3. is the rate of strain

and the dynamic viscosity is known as Trouton's Ratio. For a Newtonian Fluid, the Trouton ratio equals three.

See also

• Rheology

References