  The dynamics of anisotropic nano- to microscale colloidal particles in
confined environments, either near neighboring particles or boundaries, is
relevant to a wide range of applications. We utilized Brownian dynamics
simulations to predict the translational and rotational fluctuations of a Janus
sphere with a cap of non-matching density. The presence of the cap
significantly impacted the rotational dynamics of the particle as a consequence
of gravitational torque at experimentally relevant conditions. Gravitational
torque dominated stochastic torque for a particle > 1 micrometer in diameter
and with a 20 nm thick gold cap. Janus particles at these conditions sampled
mostly cap-down or quenched orientations. Although the results summarized
herein showed that particles of smaller diameter (< 1 micrometer) with a thin
gold coating (< 5 nm) behave similar to an isotropic particle, small increases
in either particle diameter or coating thickness drastically quenched the polar
rotation of the particle. Histogram landscapes of the separation distance from
the boundary and orientation observations of particles with larger diameters or
thicker gold coatings were mostly populated with quenched configurations.
Finally, the histogram landscapes were inverted to obtain the potential energy
landscapes, providing a path for experimental data to be interpreted.
