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
rigidspheres 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.
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.
Simha, R. (1940). "The Influence of Brownian Movement on the Viscosity of Solutions". The Journal of Physical Chemistry. 44 (1). American Chemical Society (ACS): 25–34.
doi:
10.1021/j150397a004.
ISSN0092-7325.
Saitô, Nobuhiko (1951-09-15). "The Effect of the Brownian Motion on the Viscosity of Solutions of Macromolecules, I. Ellipsoid of Revolution". Journal of the Physical Society of Japan. 6 (5). Physical Society of Japan: 297–301.
Bibcode:
1951JPSJ....6..297S.
doi:
10.1143/jpsj.6.297.
ISSN0031-9015.