Solid-that-flows picture of glass-forming liquids

TL;DR

This paper discusses how glass-forming liquids behave more like solids than liquids as they approach the glass transition, highlighting the concept of a 'solid-that-flows' state with implications for understanding their dynamics.

Contribution

It introduces the 'solid-that-flows' perspective, emphasizing the qualitative solid-like behavior of ultraviscous liquids below a certain length scale near the glass transition.

Findings

Numerical evidence supports the solidity of ultraviscous liquids.

Experimental implications include effects on dynamic heterogeneity and response functions.

Relaxation times increase dramatically near the glass transition.

Abstract

This perspective article reviews arguments that glass-forming liquids are different from those of standard liquid-state theory, which typically have a viscosity in the mPa$\cdot$s range and relaxation times of order picoseconds. These numbers grow dramatically and become $10^{12}-10^{15}$ times larger for liquids cooled toward the glass transition. This translates into a qualitative difference, and below the ``solidity length'' which is of order one micron at the glass transition, a glass-forming liquid behaves much like a solid. Recent numerical evidence for the solidity of ultraviscous liquids is reviewed, and experimental consequences are discussed in relation to dynamic heterogeneity, frequency-dependent linear-response functions, and the temperature dependence of the average relaxation time.