The diffusivity of spherical particles in a suspension is approximated by the Stokes–Einstein equation:
: where
*  is the temperature
*  is the particle radius
*  is the Boltzmann constant
*  is the hydrogel viscosity
Typical R-PEG hydrogel diffusivities for 2 nm quantum dots are on the order of 10 m/s, so suspensions of quantum dots tend to be very stable. Hydrogel viscosity can be determined by using rheological techniques.