Structural relaxation of the fragile glass-former propylene carbonate studied by nuclear magnetic resonance

Proton, deuteron, and carbon NMR methods were applied to study various isotopic species of supercooled and glassy propylene carbonate. The molecular diffusion was investigated via static field gradient diffusometry and yielded evidence for a particularly pronounced enhancement of the translational over the reorientational dynamics. The latter was monitored using measurements of spin-lattice relaxation times and of two-time stimulated echoes. The sin-sin correlation functions exhibited a pronounced dependence on the evolution times. From these results it is concluded that the geometry of molecular reorientation can be described as a superposition of moderately small jump angles (about 30 degrees) and a quasi-diffusive component which is responsible for about one-third of the total angular displacement. Finally, four-time stimulated echoes confirmed that the nonexponential relaxation in propylene carbonate is dynamically heterogeneous in nature. (C) 2000 American Institute of Physics. [S0021-9606(00)50821-6].