Abstract
There is mounting evidence indicating that relaxation dynamics in liquids approaching their glass transition not only become increasingly cooperative, but the relaxing regions also become more compact in shape. Of the many theories of the glass transition, only the random first-order theory—a thermodynamic framework—anticipates the surface tension of relaxing regions to play a role in deciding both their size and morphology. However, owing to the amorphous nature of the relaxing regions, even the identification of their interfaces has not been possible in experiments hitherto. Here, we devise a method to directly quantify the dynamics of amorphous–amorphous interfaces in bulk supercooled colloidal liquids. Our procedure also helped unveil a non-monotonic evolution in dynamical correlations with supercooling in bulk liquids. We measure the surface tension of the interfaces and show that it increases rapidly across the mode-coupling area fraction. Our experiments support a thermodynamic origin of the glass transition.
Highlights
There is mounting evidence indicating that relaxation dynamics in liquids approaching their glass transition become increasingly cooperative, but the relaxing regions become more compact in shape
Increasing the concentration of the pins results in a substantial growth in τα, the peak in the dynamic susceptibility, χÃ4, dynamical heterogeneities, remains nearly related to constant[33] the size of or is found to decrease[34] depending on the system under consideration. This behavior of χÃ4 is unlike what is observed in bulk liquids, where it steadily grows with supercooling, and suggests that the nature of relaxation dynamics in the pinned liquid may be quite different from the bulk
We focus on the dynamics of most-mobile particles at amorphous–amorphous interfaces
Summary
There is mounting evidence indicating that relaxation dynamics in liquids approaching their glass transition become increasingly cooperative, but the relaxing regions become more compact in shape. The mosaic size is expected to grow and eventually diverge at a bona fide thermodynamic transition to an ideal essential for tghleassstaabtiliTtyKo1,f3.thAesenmono-szaeircos13s–u1r5faacned tension, Υ, is is perhaps the most fundamental prediction of RFOT Even identifying these interfaces, let alone quantify the evolution of Υ across Tc, has not been possible in bulk liquids. Using the data acquired from optical video microscopy experiments on bulk supercooled colloidal liquids (see Methods section for details), here we devise a novel scheme to identify self-induced pins and probe their influence on local structure and dynamics We exploit this conceptual advance to side step controversies surrounding the pinning procedure and directly measure the surface tension of the interfaces delineating regions of high and low configurational overlap. Using the capillary fluctuation method (CFM)[37,38,39,40,41], we calculate the surface tension of the interfaces and show that it grows rapidly on approaching the mode-coupling area fraction as anticipated by RFOT
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