  We perform molecular dynamics simulations to understand the translational and
rotational diffusion of Janus nanoparticles at the interface between two
immiscible fluids. Considering spherical particles with different affinity to
fluid phases, both their dynamics as well as the fluid structure around them
are evaluated as a function of particle size, amphiphilicity, fluid density,
and interfacial tension. We show that as the particle amphiphilicity increases
due to enhanced wetting of each side with its favorite fluid, the rotational
thermal motion decreases. Moreover, the in-plane diffusion of nanoparticles at
the interface becomes slower for more amphiphilic particles, mainly due to
formation of a denser adsorption layer. The particles induce an ordered
structure in the surrounding fluid that becomes more pronounced for highly
amphiphilic nanoparticles, leading to increased resistance against nanoparticle
motion. A similar phenomenon is observed for homogeneous particles diffusing in
bulk upon increasing their wettability. Our findings can provide fundamental
insight into the dynamics of drugs and protein molecules with anisotropic
surface properties at biological interfaces including cell membranes.
