Slowing down of dynamics and orientational order preceding crystallization in hard-sphere systems

The correlation of structure and dynamics in hard-sphere samples in the vicinity crystallisation and glass transition are investigated in this combined XCCA and XPCS study performed at an beamlines ID10 of ESRF, P10 of PETRA III and SACLA.

Despite intensive studies in the past decades, the local structure of disordered matter remains widely unknown. We show the results of a coherent x-ray scattering study revealing higher-order correlations in dense colloidal hard-sphere systems in the vicinity of their crystallization and glass transition. With increasing volume fraction, we observe a strong increase in correlations at both medium-range and next-neighbor distances in the supercooled state, both invisible to conventional scattering techniques. Next-neighbor correlations are indicative of ordered precursor clusters preceding crystallization. Furthermore, the increase in such correlations is accompanied by a marked slowing down of the dynamics, proving experimentally a direct relation between orientational order and sample dynamics in a soft matter system. In contrast, correlations continuously increase for nonequilibrated, glassy samples, suggesting that orientational order is reached before the sample slows down to reach (quasi-)equilibrium.

Science Advances, 6, eabc5916 (2020).