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Cecile Dalle-Ferrier: „Temperature dependence of the number of dynamically correlated molecules in viscous liquids approaching the glass transition”
Laboratoire de Chimie Physique, Universitè Paris Sud and CNRS

What causes the dramatic slowing down of flow and relaxation that leads to glass formation in liquids as temperature decreases is hardly understood so far and subject of intensive research work. It is tempting to ascribe the strong temperature dependence of the dynamics, irrespective of molecular details, to a collective or cooperative behaviour characterized by a length scale that grows as one approaches the glass transition.

To access this length experimentally, we use the recently introduced three-point dynamic susceptibility, from which can be extracted a number of molecules dynamically correlated molecules during the structural relaxation, Ncorr.

The three-point function is related to the sensitivity of the averaged two-time dynamics to external control parameters, such as temperature and density. We studied Ncorr values in an important temperature range for a large number of liquids, and found that it systematically grows when approaching the glass transition. We specially emphasize here the case of glycerol for which we combined dielectric spectroscopy and neutron spin-echo to cover more than 16 decades in relaxation time.