Translational and rotational dynamics in dense suspensions of smooth and rough colloids.

We demonstrate that colloidal particles with surface roughness exhibit hindered rotational diffusion in quiescent dense suspensions. This is accomplished by the use of confocal microscopy and particle tracking to follow the translational and rotational dynamics of smooth and rough colloids suspended in a refractive index and density matched organic solvent. Measurement of the three-dimensional rotational diffusion is enabled by the addition of inert Janus tracers made of native colloids coated with a thin layer of aluminum. These experiments show that the mean square displacement (MSD) is unaffected by particle roughness, while the mean square angular displacement (MSAD) decreases for rough colloids at high volume fractions. Our results quantify the slowdown in the rotational dynamics of rough colloids, which is evidently due to steric frustration caused by the surface topography of the particles.