  We consider the sedimentation of a colloidal gel under confinement in the
direction of gravity. The confinement allows us to compare directly experiments
and computer simulations, for the same system size in the vertical direction.
The confinement also leads to qualitatively different behaviour compared to
bulk systems: in large systems gelation suppresses sedimentation, but for small
systems sedimentation is enhanced relative to non-gelling suspensions, although
the rate of sedimentation is reduced when the strength of the attraction
between the colloids is strong. We map interaction parameters between a model
experimental system (observed in real space) and computer simulations.
Remarkably, we find that when simulating the system using Brownian dynamics in
which hydrodynamic interactions between the particles are neglected, we find
that sedimentation occurs on the same timescale as the experiments, however the
thickness of the "arms" of the gel is rather larger in the experiments,
compared with the simulations. An analysis of local structure in the
simulations showed similar behaviour to gelation in the absence of gravity.
