Spatial correlations in the dynamics of glassforming liquids: Experimental determination of their temperature dependence

Details Spatial correlations in the dynamics of glassforming liquids: Experimental determination of their temperature dependence Spatial correlations in the dynamics of glassforming liquids: Experimental determination of their temperature dependence

2007-06-13

arxiv.org/abs/0706.1906v2

Phys. Rev. E 76, 041510 (2007)

Physics

Condensed Matter

Statistical Mechanics

17 pages, 6 figs; v2: response to referee comments

Scientific paper

10.1103/PhysRevE.76.041510

We use recently introduced three-point dynamic susceptibilities to obtain an experimental determination of the temperature evolution of the number of molecules, N_corr, that are dynamically correlated during the structural relaxation of supercooled liquids. We first discuss in detail the physical content of three-point functions that relate the sensitivity of the averaged two-time dynamics to external control parameters (such as temperature or density), as well as their connection to the more standard four-point dynamic susceptibility associated with dynamical heterogeneities. We then demonstrate that these functions can be experimentally determined with a good precision. We gather available data to obtain the temperature dependence of N_corr for a large number of supercooled liquids over a wide range of relaxation timescales from the glass transition up to the onset of slow dynamics. We find that N_corr systematically grows when approaching the glass transition. It does so in a modest manner close to the glass transition, which is consistent with an activation-based picture of the dynamics in glassforming materials. For higher temperatures, there appears to be a regime where N_corr behaves as a power-law of the relaxation time. Finally, we find that the dynamic response to density, while being smaller than the dynamic response to temperature, behaves similarly, in agreement with theoretical expectations.

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