Stokes radius

Named after George Gabriel Stokes, it is closely related to solute mobility, factoring in not only size but also solvent effects.

A smaller ion with stronger hydration, for example, may have a greater Stokes radius than a larger ion with weaker hydration.

This is because the smaller ion drags a greater number of water molecules with it as it moves through the solution.

[2] Hydrodynamic radius, RH, can refer to the Stokes radius of a polymer or other macromolecule.

According to Stokes’ law, a perfect sphere traveling through a viscous liquid feels a drag force proportional to the frictional coefficient

is directly proportional to drift speed, it is inversely proportional to the frictional coefficient:

In 1905, Albert Einstein found the diffusion coefficient

of an ion to be proportional to its mobility constant:

Substituting in the frictional coefficient of a perfect sphere from Stokes’ law yields

In non-spherical systems, the frictional coefficient is determined by the size and shape of the species under consideration.

Stokes radii are often determined experimentally by gel-permeation or gel-filtration chromatography.

[3][4][5][6] They are useful in characterizing biological species due to the size-dependence of processes like enzyme-substrate interaction and membrane diffusion.

[5] The Stokes radii of sediment, soil, and aerosol particles are considered in ecological measurements and models.

[7] They likewise play a role in the study of polymer and other macromolecular systems.