The molecular dynamics around the glass transition and in the glassy state of molecular organic systems: A 2H−nuclear magnetic resonance study

Abstract

2H-nuclear magnetic resonance(NMR)-spin–lattice relaxation experiments have been performed for studying the crossover from viscous (α process) to secondary (β processes) dynamics in the van der Waals liquid orthoterphenyl and the H-bridged network glycerol. The essential and general features, observed in both systems, are the following: (a) a dominating α process in the liquid and viscous regime; (b) a change from exponential to nonexponential spin–lattice relaxation as the temperature is lowered below a characteristic temperature above Tg; (c) the existence of a slow (>10−9 s) secondary reorientational process in the highly viscous regime; and (d) the existence of a fast (∼10−12 s) local process in the glassy state. Whereas the slower process is shown to be the one known from dielectric studies, we attribute the fast mode to a β process found in quasielastic neutron scattering.