Institute for Complex Systems - Sapienza - CNR

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ISC Sapienza Glass-forming liquids

Glass-forming liquids

Physics of supercooled liquids and structural glasses


Structural Glasses and Glass Forming Liquids: an introduction

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Glass is a very present element in everyday life, so much so that it becomes a complicated and long exercise to imagine being without it: no windows, no spectacles, no bottles, no street lamps, no screens for computer, mobile phone and television, no windscreen in the car, no light bulbs, no watches, just to mention a few examples. Indeed, it is a necessary material. Yet, besides its practical use, glass, e.g., in the form of lenses, mirrors, flasks or pipes, has been fundamental in the development of scientific research and visual art, helping and guiding the human sight to look at things in different perspectives and on widely different length-scales, from the microscopic world of cells and bacteria to the open space of planets and stars.
From the point of view of physics, all glasses represent an excited state, and may, in due course, relax to the crystalline ground state. Crystallization involves two steps: (i)the nucleation of microscopic bubbles of crystal in the liquid phase and (ii) their growth, rapidly transforming the whole material into a solid whose structure is an ordered pattern. Nucleation processes tend to be extremely slow in glassy systems on experimental times.

Last Updated on Wednesday, 05 November 2008 12:47

The growth of amorphous order in supercooled liquids

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Close to the glass transition supercooled liquids display an impressive increase of the relaxation time, without any clear sign of growing thermodynamic order, nor correlation length. This is at variance with physical intuition, which suggests that a large relaxation time is always associated to a large correlation length. Even though dynamical length scales were introduced and measured, nothing similar was thought to be possible for thermodynamic lengths.

We have found a way to detect the growth of amorphous order in supercooled liquids by using a smartly chosen, non-standard order parameter. In this way it was possible to measure for the first time a thermodynamic correlation length and show that it grows significantly in the low temperature phase.

Moreover, it was possible to detect a thermodynamic anomaly in the relaxation of this order parameter, able to distinguish at a qualitative level the low temperature phase from the high temperature one in supercooled liquids. Up to now, this was only possible by means of dynamical measurements, not thermodynamical ones. Our results, thus, opens the way to a new thermodynamical description of the low temperature phase of supercooled liquids.

We are also trying to measure the surface tension between different amorphous phases in deeply supercooled liquids. In this way we are able to detect the temperature where the surface tension goes to zero, and compare it with the Mode Coupling transition temperature. Finally, the large fluctuations in the surfece tension that we find, can be put in direct connection with the relaxation mechanism of supercooled liquids.
In 2009 I wrote an easy review on supercooled liquids and the glass transition. You can find it here.


Static correlations functions and domain walls in glass-forming liquids: the case of a sandwich geometry
G. Gradenigo, R. Trozzo, A. Cavagna, T.S. Grigera, P. Verrocchio

Dynamic relaxation of a liquid cavity under amorphous boundary conditions
A. Cavagna, T.S. Grigera, P. Verrocchio

Numerical simulations of liquids with amorphous boundary conditions
A. Cavagna, T.S. Grigera, P. Verrocchio

Phase-separation perspective on dynamic heterogeneities in glass-forming liquids
C. Cammarota, A. Cavagna, I. Giardina, G. Gradenigo, T.S. Grigera, G. Parisi, P. Verrocchio

Supercooled liquids for pedestrians
A. Cavagna

Evidence for a spinodal limit of amorphous excitations in glassy systems
C. Cammarota, A. Cavagna, G. Gradenigo, T.S. Grigera, P Verrocchio

Numerical determination of the exponents controlling the relationship between time, length and temperature in glass-forming liquids
C. Cammarota, A. Cavagna, G. Gradenigo, T.S. Grigera, P. Verrocchio

Surface tension fluctuations and a new spinodal point in glass-forming liquids
C. Cammarota, A. Cavagna, G. Gradenigo, T.S. Grigera, P. Verrocchio

Thermodynamic signature of growing amorphous order in glass-forming liquids
G. Biroli, J.-P. Bouchaud, A. Cavagna, T. S. Grigera, P. Verrocchio
Nature Physics 4, 771 - 775 (2008)

A novel method for evaluating the critical nucleus and the surface tension in systems with first order phase transition
C. Cammarota, A. Cavagna
Journal of Chemical Physics 127, 214703 (2007)

Mosaic Multistate Scenario Versus One-State Description of Supercooled Liquids
A. Cavagna, T. S. Grigera and P. Verrocchio
Physical Review Letters 98, 187801 (2007)

If you are a student and you are interested in this topic, please contact Andrea Cavagna.
Last Updated on Saturday, 20 April 2013 10:50