Sedimentation and depletion attraction directing glass and liquid crystal formation in aqueous platelet/sphere mixtures

We present an experimental study on mixtures of the gibbsite platelets and silica nanospheres of the same charge sign. In these mixtures the spheres act as depletants changing the phase behaviour of the platelet system, for which two very different time scales can be distinguished. At short times as a result of a strong depletion attraction in the system a kinetically arrested phase was split off. Subsequently, on a time scale of months the top phase separated in an isotropic and a columnar phase on top of the arrested phase. We rationalize this gravity induced liquid crystal formation in terms of a platelet sedimentation and a strong depletion attraction. The sedimentation driven columnar phase is highly ordered as we show by microradian X-ray diffraction experiments.