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Colloidal Glass Transition

Compared to atomic systems the colloidal glass transition is not driven by temperature. The density increase is realized by concentrating the sample, so that the relevant quantity is the amount of colloidal component (the volume fraction).
 
 

At low concentration, the particles can move around freely. With increacing concentration the mobility is constrained by the nearest neighbours. This is termed "cage" of the nearest neighbours. This cage effect becomes stronger with larger concentration up to the point, where the long time dynamics freezes at the glass transition. The colloids are caught in the cage of their neighbours and can only perform fast dynamics around their center of mass. One expects the following quantitative correlation curves: 


 

At lowest concentration, one expects exponential decay and with increasing volume fractions the cage effect becomes more and more visible: The correlation function decays with a streched exponential. The curves still decay because of the mobility of the nearest neighbours which leads to a breaking of the cages. This structural relaxation shifts with increasing density to larger times and forms a plateau. At the volume fraction of the glass transition jg this plateau no longer decays to zero because of the freezing of long time dynamics. Additional concentration then only leads to an increase of the plateau height.


 

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