Influence of Sedimentation on Convective Instabilities in Colloidal Suspensions

We investigate theoretically the bifurcation scenario for colloidal suspensions subject to a vertical temperature gradient taking into account the effect of sedimentation. In contrast to molecular binary mixtures, here the thermal relaxation time is much shorter than that for concentration fluctuations. This allows for differently prepared ground states, where a concentration profile due to sedimentation and/or the Soret effect has been established or not. This gives rise to different linear instability behaviors, which are manifest in the temporal evolution into the final, generally stationary convective state. In a certain range above a rather high barometric number there is a coexistence between the quiescent state and the stationary convective one, allowing for a hysteretic scenario.