Morphology and dynamics of a separating immiscible binary liquid mixture under gravity

A homogeneous mixture of a phase separated binary liquid mixture is produced by mechanical mixing and the subsequent demixing process is studied experimentally. It is found that the morphology (e.g. which phase becomes the continuum phase) of the mixing zone depends not only on the relative volume fraction φ but may also depends on the relative affinity of the two coexisting phases at the container wall. We find a volume fraction range (transition range 0.4<φ<0.48) in which the morphology of the mixing zone is very complicated and the demixing rate measured in this range fluctuates from one experiment to another. An explanation, based on the higher affinity of the lower phase at the wall, is suggested to account for the shifted transition range from the symmetric value of φ = 0.5. The temperature dependence of the demixing rate is also investigated. The result is consistent with the diminishing density difference and the vanishing surface tension at the critical point as well as the change in the structure of the mixing zone.