Homogeneous versus heterogeneous nucleation in metals and colloids

Kurzfassung

The competition between heterogeneous and homogeneous nucleation of a charged colloidal suspension is studied close to container walls. Colloidal crystals were shear melted and a metastable melt left to solidify afterwards. The crystallization kinetics was monitored using time resolved Ultra Small Angle X-ray Scattering (USAXS) at different degrees of metastability. At high metastability the homogeneous nucleation dominates the solidification scenario leading to a small amount of oriented wall based crystals. At lower metastability the homogeneous nucleated crystals do crystallize first while the crystallization of the wall crystal is delayed. When the amount of solid crystallized near the wall shows its fasted increase the amount of polycrystalline crystal decreases indicating that the randomly oriented polycrystal is converted into a wall crystal finally resulting in a large amount of oriented wall based material. Our experiments demonstrate the complexity of the crystallization process of colloidal suspension close to container walls.