Local structure in deeply supercooled liquids exhibits growing lengthscales and dynamical correlations

Abstract

Glasses are among the most widely used of everyday materials, yet the process by which a liquid’s viscosity increases by 14 decades to become a glass remains unclear, as often contradictory theories provide equally good descriptions of the available data. Knowledge of emergent lengthscales and higher-order structure could help resolve this, but this requires time-resolved measurements of dense particle coordinates—previously only obtained over a limited time interval. Here we present an experimental study of a model colloidal system over a dynamic window significantly larger than previous measurements, revealing structural ordering more strongly linked to dynamics than previously found. Furthermore we find that immobile regions and domains of local structure grow concurrently with density, and that these regions have low configurational entropy. We thus show that local structure plays an important role at deep supercooling, consistent with a thermodynamic interpretation of the glass transition rather than a principally dynamic description.

A Theory to Tackle Supercooling

“…In particular, we are able to capture the gradual reduction of the population of octahedral motifs in favor of the tripyramids at high volume fractions. This is related to the previously observed emergence of fivefold symmetric motifs (such as the full and partial icosahedron) [5,9,11,60], which is here directly predicted from liquid state theory.…”

“…In the case of supercooled liquids, theories based on pair correlations such as the standard mode-coupling framework [7] fail to account for activated events, thus predicting a spurious ergodicity breaking transition [8,9]. Activated dynamics are often rationalized through collective (i.e., many-body) effects within contrasting thermodynamic and purely dynamic scenarios [10][11][12][13][14][15].…”

Structural Ordering in Liquid Gallium under Extreme Conditions

“…Although hard-sphere features become progressively more important towards the melting curve, the deviation is always Δ ≥ 40% such that they do not model a sizable part of the emerging structural correlations. Metastable hard-sphere liquids show the formation of low configurational entropy regions [67]. These can be related to the socalled local two-body excess entropy which accounts for fluctuations in the (smoothed) local pair correlationsg i ðrÞ of particle i [42].…”

The devil is in the details: pentagonal bipyramids and dynamic arrest

“…Particle coordinates were tracked and their structure and dynamics were subsequently interrogated by considering the role of the pentagonal bipyramid structure. By studying this new data and re-evaluating data from our previous work that spans nearly seven decades of dynamic slowdown [21], we show that the relationship between pentagonal bipyramid occupancy and slow dynamics is comparable to that of icosahedra and defective icosahedra. However, we also show that large instantaneous displacements often coincide with large jumps (either positive or negative) in pentagonal bipyramid occupancy -while defective icosahedra occupancy remains the same.…”