Glass-forming liquids

ABSTRACT

When liquids are cooled below their melting temperature T_m, sometimes they do not solidify immediately but remain in supercooled state up to temperatures far below the melting point. Under certain conditions, they can solidify into the form of amorphous solids without crystallizing. A supercooled liquid and a amorphous solid are metastable phases, which are not completely understood in terms of structural arrangement and thermodynamic behaviour. But by far the most interesting feature is the glass transition which is the manifestation of a true thermodynamic transition and a dynamic event since a dramatic dynamic arrest intervenes. A unified theory of supercooled liquids and glass transition does not yet exist and, more specifically, the link between the sharp increase of the relaxation time and the correlation length is a question still largely open. This article presents in the most elementary manner a brief overview of this delicate issue.

KEYWORDS:

• Glass transition

Acknowledgments

I am very grateful to Jean-Pierre Hansen for his criticisms of the draft of this article and would like to thank Jean-Marc Bomont for numerous and valuable discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. It is said that a horse horde plunging into the supercooled water of the Ladoga lake, during a rigorous winter, would have turned suddenly into pillars of ice at the time of solidification.

2. Such a transition in fragile glasses may also be investigated by fitting the Vogel model, for the dielectric relaxation time, to the experimental data, for which a variation similar to the viscosity is observed.

3. The confusion interval in which the transition occurs is η_f = 0.494 (considered as the freezing point) and η_m = 0.545 (considered as the melting point).

4. The neutron scattering in liquids is caused by the fluctuations in density at a wavelength of about the size of atoms, i.e. the interatomic distance (∼10⁻¹⁰ m).

5. Among the possible choices for the memory function, there are , but also M(q, t) ≃ 4γF²(q, t) , where γ is a coupling constant that varies between zero and infinity.