  We study translational and rotational diffusion of anisotropic gold
nanoparticles (NPs) dispersed in the bulk of a nematic liquid crystal fluid
host. Experimental data reveal strong anisotropy of translational diffusion
with respect to the uniform far-field director, which is dependent on shape and
surface functionalization of colloids as well as on their ground-state
alignment. For example, elongated NPs aligned parallel to the far-field
director translationally diffuse more rapidly along the director whereas
diffusion of NPs oriented normal to the director is faster in the direction
perpendicular to it while they are also undergoing elasticity-constrained
rotational diffusion. To understand physical origins of these rich diffusion
properties of anisotropic nanocolloids in uniaxially anisotropic nematic fluid
media, we compare them to diffusion of prolate and oblate ellipsoidal particles
in isotropic fluids as well as to diffusion of shape-isotropic particles in
nematic fluids. We also show that surface functionalization of NPs with
photosensitive azobenzene groups allows for in situ control of their
diffusivity through trans-cis isomerization that changes surface anchoring.
