Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 4: Colloidal Fluids
CPP 4.8: Talk
Monday, February 25, 2008, 16:30–16:45, C 264
A local structural mechanism for dynamic arrest — •Paddy Royall1, Stephen Williams2, Takehiro Ohtsuka3, and Hajime Tanaka3 — 1School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK — 2Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia. — 3nstitute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
The mechanism by which a liquid may become arrested, forming a glass or gel, is a long standing problem of materials science. While possible dynamic mechanisms have received considerable attention, direct experimental evidence of structural mechanisms has proved elusive. The connection between long-lived (energetically) locally favoured structures (LFS), whose geometry may prevent the system relaxing to its equilibrium state, and dynamical arrest dates back at least to F.C. Frank in the 1950s. In a similar spirit, we propose a much broader definition of LFS which we identify with a novel topological method and combine these with experiments at the single particle level on a colloidal liquid-gel transition. The population and lifetime of the LFS is a strong function of (effective) temperature in the ergodic liquid phase, rising sharply approaching dynamical arrest, and indeed the LFS form a percolating network which become the 'arms' of the gel. Due to the LFS, the gel is unable to reach equilibrium, crystal-gas coexistence. Our results form the first direct experimental observation of a link between local structure and dynamical arrest, and open a new perspective on a wide range of metastable materials.