Incoherent Inelastic Neutron Scattering on Polybutadiene under Pressure

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We report on first results from incoherent inelastic neutron scattering on PB-h6 (Tg = 178 K at Patm) between T = 2 K and 340 K and for pressures between Patm and 4 kbar, employing the new backscattering spectrometer IN16 and the TOF spectrometer IN6 at the ILL. The strictly elastic scattering (t -_>l 10^<-8>s), observed by temperature scans on IN16, shows indirectly the onset of the fast relaxation process and the onset of the α-relaxation at the isobars of Patm, P = 1,2,3 and 4 kbar. The observed temperature dependence may be interpreted by a change towards lower fragility when applying pressure. Clearly, the apparent activation energy changes in the temperature range of the α-relaxation. Quasielastic spectra were measured for several isotherms as well as for an isochore. The results allowed the determination of an isochrone on the ns time scale, which has a slope of dTiso/dP ap 18 K/kbar, compared to a Tg variation of dTg/dP ap 13 K/kbar. Isochoric spectra certainly do show different relaxation behaviour. Using IN6 we observe for the first time a shift of the Boson peak with pressure by about 0.13 meV/kbar between ambient pressure and 4 kbar. This is visible at low temperatures where relaxations are not yet active. classification: polymer glasses, glass transition, scattering, viscoelastic-systems
理論物理学刊行会の論文
1997-06-27