Breakdown of diffusivity-entropy scaling in colloidal glass forming liquids

TL;DR

This study investigates the breakdown of diffusivity-entropy scaling in colloidal glass-forming liquids, revealing how kinetic slowing down and free energy landscape ruggedness relate to entropy and fragility.

Contribution

It experimentally demonstrates the breakdown of translational diffusivity-entropy scaling at low densities and links this to glassy effects and free energy landscape changes.

Findings

Breakdown of diffusivity-entropy scaling at low area fractions.

Enhanced translation-rotation coupling at the transition point.

Correlation between transition density and liquid fragility.

Abstract

Glass is a liquid that has lost its ability to flow. Why this particular substance undergoes its dramatic slowing down in kinetics while remaining barely distinguishable in structure from the fluid state upon cooling constitutes the central question of glass transition physics. Here, we experimentally tested the pathway of kinetic slowing down in glass$\textrm{-}$forming liquids that consisted of ellipsoidal or binary spherical colloids. In contrast to rotational motion, the exponential scaling between diffusion coefficient and excess entropy in translational motion was revealed to break down at startlingly low area fractions ($\phi_\textrm{T}$) due to glassy effects. At $\phi_\textrm{T}$, anormalous translation-rotation coupling was enhanced and the topography of the free energy landscape became rugged. Basing on the positive correlation between $\phi_\textrm{T}$ and fragility, the measurement of $\phi_\textrm{T}$ offers a novel method for predicting liquids' relaxation while circumventing the prohibitive increase in equilibrium times required in high density regions. Our results highlight the role that thermodynamical entropy plays in glass transitions.