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Seminars

Contact :
Matthieu Labousse
matthieu.labousse (arobase) espci.psl.eu
Tel : +33 (0) 1 40 79 45 97

Joshua McGraw
joshua.mcgraw (arobase) espci.fr
Tel : +33 (0) 1 40 79 59 62

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Gulliver seminars take place on Mondays at 11:30 AM in the F304 room, and typically last one hour including questions. The seminars are in English, and the scientific topics are mainly those studied in the laboratory.



Seminar Gulliver, Paddy Royall (University of Bristol)

Lundi 8 octobre 2018 11:30-12:30 - Bibliothèque PCT - F3.04

Revealing the Nature of Solidification : Fivefold Symmetry at the Nanoscale

That fivefold symmetry should play a crucial role in the non-equilibrium behaviour of condensed matter was proposed by Sir Charles Frank in the 1950s. Six decades later, the basic mechanism of the solidification of liquids remains unexplained, either in the case that the material crystallises, or that it forms an amorphous solid, a glass. We will explore the implications of fivefold symmetry in the solidification of liquids and discuss two recent developments.

Crystallisation is among the most common everyday physical phenomena. Yet in the prinicple material in which quantitative comparison has been made between experiment and theory (hard spheres) predictions of crystal nucleation rates are up to 20 orders of magnitude slower than measurements, the second worst prediction in physics. This discrepancy casts doubt upon the theoretical methods concerned (importance sampling) which is important not only for crystallisation, because these methods are used to tackle a very wide range of problems, such as drug uptake in cells and chemical reaction pathways. While particle-resolved studies reveal in intimate detail local mechanisms of structural change, they can only access rather fast crystallisation, where there is no discrepancy. However gravitational sedimentation may influence the local structure of the colloidal liquid, which we show can drastically alter crystallisation. We further image nano-particles with STED nanoscopy, whose timescales are orders of magnitude faster than the larger colloids : thus by \it rescaling time, we access new dynamical regimes where the massive discrepancy is found.

The nature of amorphous solids (glasses) is not understood : the possibility of a phase transition to a thermodynamically stable ideal glass is a contentious and challenging issue. Mutually exclusive theories give equally good descriptions of experimental data . Again, rescaling time enables us to approach this putative transition closer than other techniques, revealing exceptional levels of fivefold symmetry and a tantalising drop in configurational entropy.

Revealing the Nature of Solidification : Fivefold Symmetry at the Nanoscale

That fivefold symmetry should play a crucial role in the non-equilibrium behaviour of condensed matter was proposed by Sir Charles Frank in the 1950s. Six decades later, the basic mechanism of the solidification of liquids remains unexplained, either in the case that the material crystallises, or that it forms an amorphous solid, a glass. We will explore the implications of fivefold symmetry in the solidification of liquids and discuss two recent developments.

Crystallisation is among the most common everyday physical phenomena. Yet in the prinicple material in which quantitative comparison has been made between experiment and theory (hard spheres) predictions of crystal nucleation rates are up to 20 orders of magnitude slower than measurements, the second worst prediction in physics. This discrepancy casts doubt upon the theoretical methods concerned (importance sampling) which is important not only for crystallisation, because these methods are used to tackle a very wide range of problems, such as drug uptake in cells and chemical reaction pathways. While particle-resolved studies reveal in intimate detail local mechanisms of structural change, they can only access rather fast crystallisation, where there is no discrepancy. However gravitational sedimentation may influence the local structure of the colloidal liquid, which we show can drastically alter crystallisation. We further image nano-particles with STED nanoscopy, whose timescales are orders of magnitude faster than the larger colloids : thus by rescaling time, we access new dynamical regimes where the massive discrepancy is found.

The nature of amorphous solids (glasses) is not understood : the possibility of a phase transition to a thermodynamically stable ideal glass is a contentious and challenging issue. Mutually exclusive theories give equally good descriptions of experimental data . Again, rescaling time enables us to approach this putative transition closer than other techniques, revealing exceptional levels of fivefold symmetry and a tantalising drop in configurational entropy.

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General recommendations for the speakers

The audience is often heterogeneous - because of the wide range of scientific topics covered in the lab - so planning a talk for a broader audience would be preferred. The seminar is in English, and speakers are thus invited to prepare their slides in English.

The seminar starts at 11:30 AM. The speaker is asked to arrive in the lab at least 15 minutes in advance to set up their computer. The talks last typically 45 minutes, and are followed by a discussion time.

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