8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.160Wed 711:10-14:00Local structures in crystallization of nearly hard spheresJade Taffs, 1 Stephen Williams, 2 Hajime Tanaka, 3 and C. Patrick Royall 11 University of Bristol, School of Chemistry, University of Bristol BS8 1TS, Bristol,United Kingdom2 Australian National University, Canberra, Australia3 University of Tokyo, Tokyo, JapanDespite the everyday familiarity of the freezing phenomenon, we still do not have a full understandingof the mechanism by which it occurs. Although hard spheres and related systemsare among the simplest systems which exhibit nucleation, and are accessible both to simulationand experiment, allowing insight into the structural mechanism [1, 2], the process remains atopic of active research. Confocal microscopy is used to enable the real-space analysis of theexperimental system, which is compared with Brownian Dynamics simulations of nearly hardspheres. The effective colloid-colloid interactions of the two systems are closely matched usingthe result from the Ornstein-Zernike relation that for a fluid with a pair-wise additive, sphericallysymmetric interaction potential at a specific density, the radial distribution function is uniquelydefined by the pair potential. Electrostatic interactions, which have a significant impact onnucleation rate [3], are modelled with a short-ranged Yukawa potential. The transition fromfluid to crystal in both systems is characterised at the single particle level using the TopologicalCluster Classification algorithm [4]. This identifies locally favoured structures (LFSs) of 5 to13 particles which minimise the radius of gyration of the structure. A strong similarity existsbetween the LFSs found in experiment and simulation. In particular, a 10 particle LFS appears tobe prevalent in metastable fluids, and has been shown to be much less popular in equilibrium fluids.[1] T. Kawasaki, H. Tanaka, Proc. Natl. Acad. Sci 107, 14036 (2010).[2] L. Fillion, R. Ni, D. Frenkel, M. Dijkstra, J. Chem. Phys. 134, 134901 (2011).[3] S. Auer, D. Frenkel, J. Phys. : Condens. Matter 14, 7667 (2002).[4] C. P. Royall, S. R. Williams, T. Ohtsuka, H. Tanaka, Nature Mater. 7, 556 (2008).[5] J. Taffs, A. Malins, S. R. Williams, C. P. Royall, J. Chem. Phys. 133, 244901 (2010).160