Size Matters : Competing Relaxation Mechanisms in Size-Polydisperse Supercooled Liquids

Despite decades of intense efforts, the physics of the glass transition is still not fully understood. A recent methodological breakthrough has enabled access to the unprecedentedly deep supercooled regime, opening new vistas for the study of the glass transition. This technique achieves optimal results for systems in which the particle size polydispersity varies continuously and over a wide range of particle sizes. While generally necessary to form stable supercooled liquids, the effects of continuous polydispersity on the microscopic dynamics remains unclear. In this work, we take a step in this direction by using a combination of state-of-the-art computer simulations (Phys. Rev. Research 5, 033120, 2023) and statistical-physical theory (Phys. Rev. Research 5, 033121, 2023). Our work reveals that particle-size-dependent effects emerge in the dynamics of highly polydisperse supercooled liquids, with different particle sizes giving rise to fundamentally different and possibly competing relaxation mechanisms. Overall, our work highlights the importance of particle-size-resolved analyses in the study of deeply supercooled liquids, and we argue that care must be taken when generalizing results of strongly polydisperse glassformers to less polydisperse systems.