Structural-dynamical transition in the Wahnström mixture

Supercooled liquids present dynamical heterogeneities at low temperatures: on a certain length and timescale, some areas are very mobile (active) while others are much more solid-like (inactive). This feature is interpreted as the signature of the fact that the liquid, when supercooled, starts exploring different metastable regions of the free energy landscape.

A possible route to illustrate this effect is through large deviations of structural-dynamical obserables, as we first did in the case of a canonical atomistic model for glassformers, the Kob-Andersen mixture. A main observation of that work was that dynamical heterogeneities correspond to a first order phase transition in a (reweighted) space of possible steady states between high energy trajectories that are rich in structure and low energy trajectories taht are poor in structure. Moreover such a transition has a strong temperature dependence, so that the structure-rich trajectories become more and more likely to be observed as the temperature decreases.

Now, we have published a follow-up work on the European Physical Journal E, where we show that the same mechanism is at play in another glass-former (the Wahnström mixture), showing that while the overall qualitative picture may be general, the details depend on the nature of the interactions between the constituents. Moreover, we also show that configurations extracted from the structure-rich trajectories have much larger yield stresses than the normal supercooled liquid: the emerging rigidity of glasses appears to be strongly related to the structural-dynamical transition that we have highlighted.

More information in

F Turci, T Speck and C P Royall, Structural-dynamical transition in the Wahnström mixture Eur. Phys. J. E , 41: 54 (2018) https://doi.org/10.1140/epje/i2018-11662-3

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A structure-rich configuration of the Wahnström binary mixture under shear: red areas are icosahedral motifs while flashing yellow particles are those that manifest the largest non-affine square displacement

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