Stokes-Einstein Diffusion Coefficent

The Stokes-Einstein calculator estimates the diffusion rate of spherical particles through a liquid with a low Reynolds number.

INSTRUCTIONS: Choose units and enter the following:

• (T) Temperature
• (η) Viscosity of Material
• (r) Radius of Spherical Particles

Diffusion Rate (D): The calculator returns the diffusion rate in square millimeters per second.  However, this can be automatically converted to compatible units via the pull-down menu. 

The Math /  Science

The Stokes-Einstein equation is useful for evaluating diffusion of spherical particles through a liquid with low Reynolds number.  The Stokes-Einstein formula is:

`D = (k_B * T )/ (6 pi * eta * r)`

 where:

• D = diffusion rate
• k_B =  is the Boltzmann constant
• T = the temperature
• η = the medium viscosity.

`D` is the diffusion coefficient of the Brownian particle.

For spherical particles of radius r, `D` is determined by the Stokes-Einstein equation.