Stokes radius - Citizendia

The Stokes radius, Stokes-Einstein radius, or hydrodynamic radius R_H, named after George Gabriel Stokes , is not the effective radius of a hydrated molecule in solution as often mentioned. The hydrodynamic radius of a Macromolecule or Colloid particle has two meanings Sir George Gabriel Stokes 1st Baronet FRS ( 13 August 1819 &ndash 1 February 1903) was a mathematician and physicist Rather it is the radius of a hard sphere that diffuses at the same rate as the molecule. The behavior of this sphere includes hydration and shape effects. Since most molecules are not perfectly spherical, the Stokes radius is smaller than the effective radius (or the rotational radius). A more extended molecule will have a larger Stokes' radius compared to a more compact molecule of the same molecular weight.

In liquids where there are considerable interactions between solute and solvent molecule, the Stokes' radius (of a perfect sphere) is proportional to frictional coefficient f and inverse proportional to viscosity η as follows:

$\ R_H=\frac{k_BT}{6\pi \eta D}.$

where, $k B$ is the Boltzmann constant (in J K^-1), $D$ is the diffusion coefficient (in m²s^-1) and $T$ is the temperature in Kelvin. Bridge from macroscopic to microscopic physics Boltzmann's constant k is a bridge between Macroscopic and microscopic physics Fick's laws of diffusion describe Diffusion and can be used to solve for the diffusion coefficient D. The frictional coefficient is determined by the size and shape of the molecule under consideration.

Capillary electrophoresis ( CE) also known as capillary zone electrophoresis (CZE can be used to separate ionic species by their charge and frictional forces The hydrodynamic radius of a Macromolecule or Colloid particle has two meanings Dynamic light scattering (also known as Photon Correlation Spectroscopy or Quasi-Elastic Light Scattering) is a technique in Physics, which can be used In 1851, George Gabriel Stokes derived an expression now known as Stokes' law, for the frictional force — also called Drag force — exerted on

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