Weak Secondary Relaxation in Molecular Glass Formers*

The physics of glass formers and the glassy dynamics is one of the great mysteries in science. For example, the structural α relaxation, which characterizes the freezing of molecular motions on approaching the glass transition, is well known. However, in recent years in addition to the α relaxation additional secondary dynamic processes were found. Like the so-called excess wing relaxation so far mostly been investigated by dielectric spectroscopy, a method that mainly couples to only one aspect of molecular mobility, namely reorientational motions of molecules carrying a dipolar moment. We present neutron-scattering results, sensitive to density-density fluctuations, on glycerols, in presence of salts and nanoparticles, to identify the nature of this secondary relaxation.
New aspects in neutron scattering have been revealed: (i) The first is the unprecedented detection of the excess wing using neutron-scattering experiments, (ii) the systematic comparison between neutron scattering and dielectric measurements, (iii) the characteristic length scale of the secondary relaxation, and (iv) The importance of dynamic heterogeneities in these relaxations.

S. Gupta et al., Eur. Phys. J. E, 38, 1 (2015); Eur. Phys. J. E., 39, 40 (2016); Scientific Reports, 6, 35034 (2016).