Nanoscale non-equilibrium dynamics and the fluctuation–dissipation relation in an ageing polymer glass

Abstract

Response functions and fluctuations measured locally in complex materials should equally well characterize mesoscopic-scale dynamics. The fluctuation-dissipation-relation (FDR), relates the two in equilibrium, a fact used regularly, for example, to infer mechanical properties of soft matter from the fluctuations in light scattering. In slowly-evolving non-equilibrium systems, such as aging spin and structural glasses, sheared soft matter, and active matter, a form of FDR has been proposed in which an effective temperature, Teff, replaces the usual temperature, and universal behavior is found in mean-field models and simulations. Thus far, only experiments on spin-glasses and liquid crystals have succeeded in accessing the strong aging regime, where Teff >T and possible scaling behavior are expected. Here we test these ideas through measurements of local dielectric response and polarization noise in an aging structural glass, poly-vinyl-acetate . The relaxation-time spectrum, as measured by noise, is compressed, and by response, is stretched, relative to equilibrium, requiring an effective temperature with a scaling behavior similar to that of certain mean-field spin-glass models.