THE DYNAMICS OF THE ALPHA-RELAXATION AND BETA-RELAXATION IN GLASS-FORMING POLYMERS STUDIED BY QUASI-ELASTIC NEUTRON-SCATTERING AND DIELECTRIC-SPECTROSCOPY

The dynamics of the cr-relaxation in three different polymeric systems , poly(vinyl methyl ether) (PVME), poly (vinyl chloride) (PVC) and pol y (bisphenol A, 2-hydroxypropylether) (PH), have been studied by means of relaxation techniques and quasielastic neutron scattering. By usin g these techniques, we have covered a wide timescale ranging from meso scopic to macroscopic times (10(-10)-10(1) s). In this wide timescale, the dynamics of the alpha-relaxation show a clear non-Debye behaviour which can be described by assuming a Kohlrausch-Williams-Watts functi onal form for the relaxation function or the intermediate scattering f unction. The shape of the relaxation function is found to be similar f or the different techniques used and independent of temperature and mo mentum transfer, Q. Moreover, the characteristic relaxation times dedu ced from the fitting of the experimental data can also be described us ing only one Vogel-Fulcher functional form. Besides we found that the Q-dependence of the relaxation times obtained by quasielectric neutron scattering is given by a power law, tau(Q) alpha Q(-n)(n > 2), n bein g dependent on the system, and that the Q-behaviour and the non-Debye behaviour are directly correlated. In the case of PVC, the dynamics ar e also investigated in a shorter timescale (10(-11)-10(-13) s). In thi s range, we have observed the short-time part of the alpha-relaxation together with a fast process (timescale similar to 10(-12) s). It appe ars that both dynamical processes are separated by a critical time whi ch hardly depends on Q and T. The results also indicate that the fast process observed is not related to the dielectric beta-relaxation. All of these results are reviewed and discussed in the framework of the d ifferent theoretical approaches to the problem of the glass transition .