INCOHERENT INELASTIC NEUTRON-SCATTERING ON POLYBUTADIENE UNDER PRESSURE

We report on first results from incoherent inelastic neutron scatterin g on PB-h6 (T-g = 178 K at P-atm) between T = 2 K and 340 K and for pr essures between P-atm and 4 kbar, employing the new backscattering spe ctrometer IN16 and the TOF spectrometer IN6 at the ILL. The strictly e lastic scattering (t greater than or equal to 10(-8) s), observed by t emperature scans on IN16, shows indirectly the onset of the fast relax ation process and the onset of the cr-relaxation at the isobars of P-a tm, P = 1, 2, 3 and 4 kbar. The observed temperature dependence may be interpreted by a change towards lower fragility when applying pressur e. Clearly, the apparent activation energy changes in the temperature range of the ol-relaxation. Quasielastic spectra were measured for sev eral isotherms as well as for an isochore. The results allowed the det ermination of an isochrone on the ns time scale, which has a slope of dT(iso)/dP approximate to 18 K/kbar, compared to a T-g variation of dT (g)/dP approximate to 13 K/kbar. Isochoric spectra certainly do show d ifferent relaxation behaviour. Using IN6 we observe for the first Lime a shift of the Boson peak with pressure by about 0.13 meV/kbar betwee n ambient pressure and 4 kbar. This is visible at low temperatures whe re relaxations are not yet active.