  Roughening the surface of spherical colloids can drastically change their
translational and rotational dynamics in dense suspensions. Using 3D confocal
microscopy, we show that roughness not only lowers the concentration of the
translational colloidal glass transition, but also generates a broad
concentration range in which the rotational Brownian motion changes signature
from high-amplitude diffusive to low-amplitude rattling. This hitherto not
reported second glass transition for rough spherical colloids emerges when the
particle intersurface distance becomes comparable to the roughness length
scale. Interlocking contacts are responsible for restricting the particle
rotations.
