Freezing and Melting: Action at Grain Boundaries

In his Perspective, Pusey discusses papers by Alsayed and de Villeneuve in this week's issue that examine the processes of melting and freezing. The movement of particles can be followed by video microscopy while thermosensitive colloidal particles are melted by temperature manipulation. Melting begins heterogeneously, with initial premelting occurring primarily at grain boundaries. In addition, freezing is impaired by the presence of impurities in the liquid, which preserve grain boundaries and prevent final uniform annealing of the crystal.