  It is intuitive that the diffusivity of an isolated particle differs from
those in a monodisperse suspension, in which hydrodynamic interactions between
the particles are operative. Batchelor (1976,1983) calculated how hydrodynamic
interactions influenced the diffusivity of a dilute suspension of spherical
particles and Russel et al.(1991), and Brady (1994) treated non-dilute (higher
particle volume fraction) suspensions. Although most particles lack perfect
sphericity, little is known about the effects of hydrodynamic interactions on
the diffusivity of spheroidal particles, which are the simplest shapes that can
be used to model anisotropic particles. Here, we calculate the effects of
hydrodynamic interactions on the translational and rotational diffusivities of
spheroidal particles of arbitrary aspect ratio, in dilute monodisperse
suspensions. The origin of the hydrodynamic anisotropy is that found in the
stresslet field for the induced-dipole induced-dipole interaction. However, in
the dilute limit the anisotropy effects are at the level of a few percent.
These effects have influence in a vast range of settings, from partially frozen
colloidal suspensions to the dynamics of cytoplasm.
