The hydrodynamic radius of a macromolecule or colloid particle has two meanings. Some books use it as a synonym for the Stokes radius. [1]
Others books define a theoretical hydrodynamic radius . They consider the macromolecule or colloid particle to be a collection of subparticles. This is done most commonly for polymers; the subparticles would then be the units of the polymer. is defined by
where is the distance between subparticles and , and where the angular brackets represent an ensemble average. [2] The theoretical hydrodynamic radius was originally an estimate by John Gamble Kirkwood of the Stokes radius of a polymer.
The theoretical hydrodynamic radius arises in the study of the dynamic properties of polymers moving in a solvent. It is often similar in magnitude to the radius of gyration.
Grosberg AY and Khokhlov AR. (1994) Statistical Physics of Macromolecules (translated by Atanov YA), AIP Press. ISBN 1-56396-071-0