Q-DEPENDENCE OF THE RELAXATION-TIMES OF THE ALPHA-RELAXATION AS OBSERVED BY QUASI-ELASTIC NEUTRON-SCATTERING

In a quasielastic neutron scattering investigation of three polymers, poly(vinyl methyl ether), poly(vinyl chloride) and poly(bisphenol A, 2 -hydroxypropylether), it was found that the incoherent quasielastic br oadening corresponding to the alpha-relaxation can be well described a ssuming a Kohlrausch-Williams-Watts intermediate scattering function I (Q,t) proportional to exp[ - (t/tau(WW))(beta)]. The relaxation time, tau(WW)(Q,T), varies with Q (momentum transfer) as Q(-kappa)(kappa > 2 ; kappa being dependent on the system) in the Q-range investigated. It was also found that this Q-behaviour and the non-Debye behaviour, def ined by the beta parameter, are directly correlated. In this paper, it is shown that these features are also found in different glass-formin g systems (PIB, PDMS, PPO, OTP,...) when the available quasielastic ne utron scattering and relaxation data of the literature are reinterpret ed. Finally, a very simple scenario based on the coupling model of Nga i, which accounts for the experimental behaviour found, is described.