Breakdown of diffusivity–entropy scaling in colloidal glass-forming liquids

Glass is a liquid that has lost its ability to flow. Why this particular substance undergoes such a dramatic kinetic slowdown yet remains barely distinguishable in structure from its fluid state upon cooling constitutes the central question of glass transition physics. Here, we investigate the pathway of kinetic slowdown in glass-forming liquids that consist of monolayers of ellipsoidal or binary spherical colloids. In contrast to rotational motion, the dynamics of the translational motion begin to violently slow down at considerably low area fractions (ϕT). At ϕT, anomalous translation–rotation coupling is enhanced and the topography of the free energy landscape become rugged. Based on the positive correlation between ϕT and fragility, the measurement of ϕT offers a novel method for predicting glassy dynamics, circumventing the prohibitive increase in equilibrium times required in high-density regions. Our results highlight the role that thermodynamical entropy plays in glass transitions.