Bragg-microscopic experiments on solidifying colloidal melts
Due to the colloid specific length scales the size, form and distribution of colloidal crystals can conveniently be studied using a combination of light scattering and microscopy. Further nucleation, growth and ripening in systems of colloidal shear melts are accessible by performing time resolved experiments. The contrast mechanism is given by the difference in Si(q) the static structure factor of different phases i under a given observation direction. We report several experimental realisations and give representative examples with a particular focus on the crystallisation kinetics.
Two applications are discussed in some detail. First we observe the quasi-homoepitactic growth kinetics of oriented, monolithic but highly twinned body centred cubic crystals to obey a Wilson-Frenkel growth law above the melting line. Below, i.e. in coexistence, we observe a different growth mechanism giving rise to non-linear advancement of the crystal-melt interface as a function of time. Secondly, we investigate the coarsening behaviour of the mentioned twin domains and observe kinetics compatible with Lifschitz-Allen-Cahn behaviour. Lateral coarsening, however, ceases above a critical crystal height, and a columnar morphology results. Further applications and the limitations of the method are discussed.
M. R. Maaroufi, A. Stipp, Th. Preis, Th. Palberg
Inst. f. Physik, Johannes Gutenberg-Universität, Mainz
Scientific and Technical Information
Edition CDR 5, pp. 35-51
December 2001