Evidence of Growing Spatial Correlations during the Aging of Glassy Glycerol

Abstract : We have measured, as a function of the age ta, the aging of the nonlinear dielectric susceptibility χ3 of glycerol below the glass transition. Whereas the linear susceptibility can be accurately accounted for in terms of an age dependent relaxation time τα(ta), this scaling breaks down for χ3, suggesting an increase of the amplitude of χ3. This is a strong indication that the number Ncorr of molecules involved in relaxation events increases with ta. For T = 0.96 × Tg, we find that Ncorr increases by ∼ 10% when ta varies from 1ks to 100ks. This sheds new light on the relation between length scales and time scales in glasses.