PD Dr. Hans-Joachim Schöpe "Experimental determination of structural and dynamical heterogeneities in a metastable colloidal fluid"

Understanding the process that drives an under cooled fluid to the solid state is still a challenging issue for condensed matter physics and plays a key role in designing new materials. The solidification of the meta stable melt to a solid via crystallization or vitrification is one of the most important non equilibrium phenomena in physics. Colloidal model systems have been used successfully for several decades to study fundamental aspects of the phase transition kinetics and the results have expanded the knowledge of crystallization and vitrification in an impressive manner.

Recent studies provide initial evidence that the solidification process is linked in a fundamental way to the physical properties of the meta stable melt [1-3]. An interesting property of the meta stable melt is that it exhibits both, spatial heterogeneous structure and dynamics [1-3]. The meta stable melt contains higher order regions (clusters) embedded in a “pure” fluid structure. The dynamics can be understood as an accumulation of mobile and immobile particles. Recent computer simulations suggested that the local structure and the local dynamics of the metastable melt are correlated [4].

In order to investigate these phenomena we used highly cross-linked polystyrene particles dispersed in a good solvent 2-ethylnaphtalene serving as a hard sphere model system. Using advanced time resolved static light scattering [5] and advanced time and space resolved dynamic light scattering techniques [6] we determined the temporal evolution of the structure and the dynamics during solidification. Analyzing the temporal evolution of the local particle dynamics, the ensemble intermediate scattering function, the static structure factor and the solidification kinetics we are able to quantity the correlation between structural and dynamical heterogeneities and their role in the process of solidification.

[1] T. Schilling, H. J. Schöpe, M. Oettel, G. Opletal, I. Snook: Phys. Rev. Lett. 105, 025701 (2010).
[2] T. M. Truskett et al Phys. Rev. E 58, 3083 (1998)
[3] L. Berthier and G. Biroli, Reviews of Modern Physics, vol. 83, 2011
[4] T. Kawasaki and H. Tanaka, Journal of Physics-Condensed Matter, vol.22, no.23, 2010
[5] S. Iacopini, T. Palberg, H. J. Schöpe: J. Chem. Phys. 130, 084502 (2009).
[6] S. Golde, M. Franke and H. J. Schöpe: AIP Conf. Proc. 1518, 304 (2013)