Hard sphere crystal nucleation and growth near large spherical impurities

Abstract

We report how large spherical impurities affect the nucleation and growth of hard spherecolloidal crystals. Both the impurities and the colloids are fluorescently labelledpolymethylmetacrylate particles and are dispersed in an optically and densitymatching solvent mixture. Crystal growth, initiated either at the impurity surface,or at the sample bottom, was studied by imaging sequences of two-dimensionalxy-slices in the plane of the impurity’s centre of mass with a laser scanning confocalmicroscope. At least two factors determine whether a large impurity can functionas a seed for heterogeneous nucleation: timescales and impurity curvature. Thecurvature needs to be sufficiently low for crystal nuclei to form on the impuritysurface. If bulk crystal growth has already approached the impurity, bulk growthis dominant over growth of crystallites on the impurity surface. Such surfacecrystallites eventually reorient to adapt to the overall bulk crystal symmetry.