text: 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.