Crossover from Debye to non-Debye dynamical behavior of the α relaxation observed by quasielastic neutron scattering in a glass-forming polymer

The dynamics of a very fragile glass-forming polymer is studied by time of flight neutron scattering in a time scale from ${10}^{\mathrm{-}13}$ to ${10}^{\mathrm{-}11}$ s. We observe a crossover from a Debye-like to a non-Debye behavior at a characteristic time which is effectively independent of temperature and momentum transfer Q. We also confirm the results previously obtained about the non-Debye α relaxation in a different time scale (${10}^{\mathrm{-}11}$ to ${10}^{\mathrm{-}8}$ s). The results here reported open a new outlook for understanding the fast dynamics of glass-forming systems.