Intrinsic viscosity
Contents
Intrinsic viscosity is defined as
where
In practical settings,
Formulae for rigid spheroids
Generalizing from spheres to spheroids with an axial semiaxis
where the constants are defined
The
General ellipsoidal formulae
It is possible to generalize the intrinsic viscosity formula from spheroids to arbitrary ellipsoids with semiaxes
Frequency dependence
The intrinsic viscosity formula may also be generalized to include a frequency dependence.
Applications
The intrinsic viscosity is very sensitive to the axial ratio of spheroids, especially of prolate spheroids. For example, the intrinsic viscosity can provide rough estimates of the number of subunits in a protein fiber composed of a helical array of proteins such as tubulin. More generally, intrinsic viscosity can be used to assay quaternary structure. In polymer chemistry intrinsic viscosity is related to molar mass through the Mark–Houwink equation. A practical method for the determination of intrinsic viscosity is with a Ubbelohde viscometer.