Intrinsic viscosity is a measure of a solute's contribution to the viscosity of a solution. It should not be confused with inherent viscosity, which is the ratio of the natural logarithm of the relative viscosity to the mass concentration of the polymer.

Intrinsic viscosity is defined as

where is the viscosity in the absence of the solute, is (dynamic or kinematic) viscosity of the solution and is the volume fraction of the solute in the solution. As defined here, the intrinsic viscosity is a dimensionless number. When the solute particles are rigid spheres at infinite dilution, the intrinsic viscosity equals , as shown first by Albert Einstein.

In practical settings, is usually solute mass concentration (c, g/dL), and the units of intrinsic viscosity are deciliters per gram (dL/g), otherwise known as inverse concentration.

IUPAC definition
Intrinsic viscosity: Synonym: limiting viscosity number

The limiting value of the reduced viscosity, or the inherent viscosity, at infinite dilution of the polymer. Notes: 1. This term is also known in the literature as the Staudinger index. 2. The unit must be specified; cm3/g is recommended.

3. This quantity is neither a viscosity nor a pure number. The term is to be looked on as a traditional name. Any replacement by consistent terminology would produce unnecessary confusion in the polymer literature. Synonymous with limiting viscosity number.

Formulae for rigid spheroids

Generalizing from spheres to spheroids with an axial semiaxis (i.e., the semiaxis of revolution) and equatorial semiaxes , the intrinsic viscosity can be written

where the constants are defined

The coefficients are the Jeffery functions

General ellipsoidal formulae

It is possible to generalize the intrinsic viscosity formula from spheroids to arbitrary ellipsoids with semiaxes , and .

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.


This article uses material from the Wikipedia article Intrinsic viscosity, which is released under the Creative Commons Attribution-Share-Alike License 3.0.