Dynamics in supercooled polyalcohols:: Primary and secondary relaxation

We have studied details of the molecular dynamics in a series of pure polyalcohols by means of dielectric spectroscopy and H-2 nuclear magnetic resonance (NMR). From glycerol to threitol, xylitol and sorbitol a systematic change in the dynamics of the primary and secondary relaxation is found. With increasing molecular weight and fragility an increase in the width of the alpha-peak is observed. Details of the molecular reorientation process responsible for the alpha-relaxation were exploited by two-dimensional NMR experiments. It is found that in the same sequence of polyalcohols the appearance of the secondary relaxation changes gradually from a wing type scenario to a pronounced beta-peak. From NMR experiments using selectively deuterated samples the molecular origin of the secondary relaxation could be elucidated in more detail. (C) 2002 American Institute of Physics.