Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 28: Colloids and Complex Liquids I
CPP 28.1: Hauptvortrag
Mittwoch, 28. März 2012, 15:00–15:30, C 130
The glass transition is continuous but gelation is discontinuous in sticky spheres — •Paddy Royall1, Stephen Williams2, and Hajime Tanaka3 — 1University of Bristol, UK — 2Australian National University, Canberra, Australia — 3The University of Tokyo, Japan
We identify dynamic and structural signatures which distinguish gels and glasses in a colloidal model system of hard and sticky spheres. Since gels are identified with arrested spinodal decomposition, this presents a thermodynamic basis upon which to identify gelation, and distinguish it from vitrification. We base our findings on confocal microscopy experiments of and confirm these with molecular dynamics simulations.
In the gel transition, upon crossing the spinodal line at a packing fraction 0.35, we find a sharp change in the structural relaxation time, and enter an ageing regime. Simultaneously, our novel structural analysis shows a large and sudden change in local structure. This is confirmed in simulation where the pressure turns negative upon gelation. Thus gelation is `first-order-like'. By contrast, the approach to the glass is continuous, and not associated with any phase transition.
In `sticky spheres', since gelation occurs at the spinodal line, it appears `first-order-like', while on the timescales we access, the glass transition is continuous. Arrested states lying in the metastable gas-liquid regime are gels and those outside glasses. Significantly, the gel extends to packing fractions of at least 0.59.