Heterogeneity of amorphous polymers as studied by quasielastic neutron scattering in positron annihilation lifetime spectroscopy

It is believed that a key to understand anomalous dynamics of glass-forming materials is dynamic heterogeneity. In this report we evaluate the spatial size of the heterogeneity of glass-forming polybutadiene on the basis of the quasielastic neutron scattering and positron annihilation lifetime spectroscopy data and compare it with the reported data. We propose an empirical relation of the spatial scale between the cooperatively arranging region CRR in the supercooled state and the Boson peak in the glassy state

Free volume in poly(propylene glycol) and its relationships to spin probe reorientation

In this work we carried out positron annihilation lifetime spectroscopy (PALS) on pure poly(propylene glycol) (PPG 4000) and an electron spin resonance (ESR) study on PPG 4000 doped with the spin probe TEMPO. The spectral and dynamic features of both the microscopic probes such as the ortho-positronium (o-Ps) lifetime, tau(3), the spectral parameter, T(50) (G), and the correlation time of spin probe, T(o), as a function of the temperature were compared. New empirical relationships between the characteristic PALS temperatures (T(b1)(L) and T(b2)(L)) and the characteristic ESR temperatures (T(X1)(L) and T(X2)(L)) have been revealed. In addition, these characteristic PALS and ESR temperatures can be connected with the Schonhals and Stickel (T(B)(SCH), T(B)(ST)) temperatures of the primary alpha relaxation process of PPG 4000 B 13 as obtained by dielectric spectroscopy (DS) studies in the literature. Next, the mean free volume hole sizes of the matrix were related to the spin probe size and to the Arrhenius or the non-Arrhenius motional regimes of TEMPO. Finally, the temperature dependences of the reorientational correlation time have been analysed using the Vogel-Fulcher-Tamman-Hesse (VFTH) equation and its generalized form, i.e., the Bendler-Shlesinger-Fontanella (BSF) one, the latter derived from the defect diffusion model of the dynamics and transport properties. The fitting parameters are then compared with those of the primary alpha relaxation process. (c) 2006 Elsevier B.V. All rights reserved

Using nuclear methods for examining the structure and magnetic transformations in Fe72A128 alloy

Translated from Czech (Kovove Mater. 1997 (4) p. 257-264)Available from British Library Document Supply Centre-DSC:9023.190(VR-Trans--8656)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo