calque

Workshops

The role of local structure in dynamical arrest

July 21, 2015 to July 23, 2015
Location : Johannes Gutenberg University Mainz, Germany

Organisers

  • Paddy Royall (University of Bristol, United Kingdom)
  • Thomas Speck (Institute of Physics, JGU Mainz, Germany)

Supports

   CECAM

SPICE

Graduate School MAINZ

TRR 146

Description

For updated informations and instructions, please see here.

Description

A key theme of materials science is that the structure assumed by the constituent atoms and molecules underlies the nature of the material. Glasses challenge this notion, and indeed whether one can even distinguish glasses and liquids structurally remains a matter of heated debate [1] although in recent years a growing amount of evidence suggests the tendency of glass-forming systems to undergo structural change approaching the glass transition [2,3,4].

There are two major challenges (one technical and one fundamental) that we foresee will strongly influence the direction research in this field is going to take. The first, technical, challenge is the gap between the structural data accessible in experiments and the dynamical range achievable with simulations. In experiments on molecular and metallic glass formers one is typically restricted to two-body correlations such as the static structure factor [5], which makes the identification of local structural motifs a major challenge [3]. Simulation, which provides access to all coordinates, is itself limited in the dynamic range it can access. As an operational definition, a liquid is termed a glass when its relaxation time has reached 100 seconds, which is still nine decades slower than current brute force techniques can reach in simulation.

Second, in addition to the challenge of identifying structural change in the relevant dynamical regime, the question arises as to whether this change is responsible for, or merely a by-product of, the dynamic slowdown that characterises the glass transition. Different communities are divided on this topic: those who study dynamical arrest from a fundamental viewpoint are divided on the role of structure [3,4]. Some theories such as geometric frustration [6], quasispecies [7] and the two-order parameter model [8] are centred around geometric motifs, others for example random first order transition theory [9] assume a structural origin while some such as dynamic facilitation hold that local structure should play a more peripheral role [8]. On the other hand those who study practical glass-forming materials such as metallic glasses often closely associate local structure with slow dynamics [9]. Going further, the exploitation of metallic [11] and chalcogenide [12] materials in particular requires control of the delicate balance between vitrification and crystallisation [3].

To move beyond the current impasse, this workshop will bring together these communities. The aim here is twofold: on the one hand new techniques have been developed both in simulation (such as pinning [13] and the discovery of dynamical phase transitions [7,14]) and in experiment (such as nanobeam electron diffraction [15]). By combining the knowledge from a theoretical viewpoint with practical structural studies on glass-forming materials, we aim for an improved consensus to emerge.

In summary, if we accept that there is some change in structure approaching dynamical arrest we are left with three major questions that we seek to tackle in this workshop: (i) Does the development of locally favoured structures (such as the canonical icosahedron) really drive dynamical arrest, or is it simply a by-product of cooling down a liquid? How do we bridge the gap from simulation to experiment? (ii) What is the relation between local structure and crystallization? (iii) How universal is any role of structure across the range of dynamically arrested systems including, e.g., gels and colloidal and granular systems?

References

[1] “The Nature of Glass Remains Anything but Clear”, New York Times, 29th July (2008).
[2] Ediger M.D. and Harrowell, P. “Perspective: Supercooled liquids and glasses”, J. Chem. Phys. 137, 080901 (2012).
[3] Royall C.P. and Williams S.W. “The role of local structure in dynamical arrest”, ArXiV:1405.5691 (2014). Invited review submitted to Phys. Rep.
[4] Berthier L. and Biroli, G. “Theoretical perspective on the glass transition and amorphous materials” Rev. Mod. Phys. 83 587-645 (2011).
[5] Salmon, P.S. and Zeidler, A. “Identifying and characterising the different structural length scales in liquids and glasses: an experimental approach”, Phys. Chem. Chem. Phys. 15, 15286-15308 (2013).
[6] Tarjus, G., Kivelson, S.A., Nussinov, Z. and Viot, P. “The frustration-based approach of supercooled liquids and the glass transition: a review and critical assessment” J. Phys.: Condens. Matter 17 R1143-R1182 (2005).
[7] Boué, L.; Lerner, E.; Procaccia, I. & Zylberg, J. “Predictive statistical mechanics for glass forming systems”, J. Stat. Mech.: Theory and Experiment, P11010 (2009).
[8] Tanaka, H. “Roles of bond orientational ordering in glass transition and crystallization”, J Phys.: Condens. Matter, 25, 284115 (2010).
[9] Lubchenko, V. and Wolynes, P. “Theory of Structural Glasses and Supercooled Liquids” Annu. Rev. Phys. Chem. 58 235-266 (2007).
[10] Chandler, D. and Garrahan, J. P. “Dynamics on the way to forming glass: bubbles in space-time.” Annu. Rev. Phys. Chem. 61 191-217 (2010).
[11] Cheng Y.Q. and Ma, E. “Atomic-level structure and structure–property relationship in metallic glasses” Prog. Mat. Sci 56 379-473 (2011).
[12] Lencer, D. et al. “A map for phase-change materials”Nature Mater. 7 972-977 (2008).
[13] Cammarota, C. and Biroli, G. “Ideal glass transitions by random pinning”
Proc. Nat. Acad. Sci 109 8850-8855 (2012).
[14] Speck,T., Malins, A. and Royall, C.P. “First-Order Phase Transition in a Model Glass Former: Coupling of Local Structure and Dynamics” Phys. Rev. Lett. 109 195703 (2012).
[15] Hirata, A et al. “Direct observation of local atomic order in a metallic glass”
Nature Mater. 10 28-33 (2010).