"de Gennes" narrowing in supercooled molecular liquids : Evidence for center-of-mass dominated slow dynamics
Abstract
The density correlation function F(q,t) of the two similar substituted aromatic liquids, Toluene and m-Toluidine, is studied by coherent neutron spin-echo and time-of-flight scattering for wave vectors q around the maximum qmax of the total static structure factor Sm(q) in the supercooled i.e. high density state far away from the normal fluid state. The wave-vector dependence of the mean structural relaxation time tau shows in both liquids a very pronounced de Gennes-like narrowing centered around q0 < qmax, where q0 corresponds to the first maximum in the center-of-mass static structure factor SCOM(q). We find that the narrowing can be described quantitatively by using SCOM(q)/q2 instead of Sm(q)/q2 indicating that at the corresponding molecular length scales the relaxation of F(q,t) is dominated by purely translational motion.
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