  A gold-capped Janus particle suspended in a near-critical binary liquid
mixture can self-propel under illumination. We have immobilized such a particle
in a narrow channel and studied the nonequilibrium dynamics of a binary solvent
around it, using experiment and numerical simulations. For the latter we
consider both a purely diffusive and a hydrodynamic model. All approaches
indicate that the early time dynamics is purely diffusive and characterized by
composition layers traveling with a constant speed from the surface of the
colloid into the bulk. Subsequently, hydrodynamic effects set in and the
transient state is destroyed by strong nonequilibrium concentration
fluctuations, which arise as a result of the temperature gradient and the
vicinity of the critical point of the binary liquid mixture. They give rise to
a complex, permanently changing coarsening patterns. For a mobile particle, the
transient dynamics results in propulsion in the direction opposite to that
observed after the steady state is attained.
