  The diffusion of a Janus rod-shaped nanoparticle in a dense Lennard-Jones
fluid is studied using molecular dynamics (MD) simulations. The Janus particle
is modeled as a rigid cylinder whose atoms on each half-side have different
interaction energies with fluid molecules, thus comprising wetting and
nonwetting surfaces. We found that both rotational and translational diffusion
coefficients are larger for Janus particles with higher wettability contrast,
and these values are bound between the two limiting cases of uniformly wetting
and nonwetting particles. It was also shown that values of the diffusion
coefficients for displacements parallel and perpendicular to the major axis of
a uniformly wetting particle agree well with analytical predictions despite a
finite slip at the particle surface present in MD simulations. It was further
demonstrated that diffusion of Janus particles is markedly different from that
of uniform particles; namely, Janus particles preferentially rotate and orient
their nonwetting sides along the displacement vector to reduce drag. This
correlation between translation and rotation is consistent with the previous
results on diffusive dynamics of a spherical Janus particle with two
hemispheres of different wettability.
