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.
Highlights
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 good descriptions of the available data
Whether the immense increase in viscosity that occurs in glass-forming liquids when they are cooled is related to a true thermodynamic transition at a non-zero (Kauzmann) temperature, or whether it is a kinetic phenomenon associated with structural relaxation times diverging only at zero temperature, remains controversial[1]
Some theories[1,2,4] anticipate an increasing dynamic lengthscale that is accompanied by a growing structural lengthscale as the temperature is reduced
Summary
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 good descriptions of the available data. Detection of non-crystalline order[24] such as LFS4 requires coordinate data, it is generally only possible to directly probe the correlation between structure and dynamics in simulations and particle-resolved experiments Both these methods provide data over a limited dynamical regime, where the relaxation time of the supercooled liquid is around four orders of magnitude larger than that of the high-temperature liquid[14,25,26,27]. This corresponds to a regime well described by mode-coupling theory[28,29,30], yet at deeper supercooling there is expected to be a crossover from a caged to an ‘activated’ type of dynamics. This regime has been accessed with such small colloids using dynamic light scattering[34] and real-space fluorescent recovery[35], but in both cases averaged dynamic properties were measured
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