Dynamics of glass-forming liquids. XI. Fluctuating environments by dielectric spectroscopy

The dielectric relaxation of a 1 wt % mixture of di- n -butylether in 3-methylpentane has been measured across a range of eight decades, in which the characteristic relaxation time varies from 5 s to 50 ns. Each loss spectrum is a superposition of the dispersive solvent peak and a Debye peak which is one decade slower and readily assigned to the larger and more dipolar solute molecules. Fluctuating environments or rate exchange is made responsible for the Debye nature of probe rotation, implying that the environmental relaxation times fluctuate on time scales which are faster than the rotational correlation decay of the probe molecule. Within the experimental range from 2.2 s to 42 ns regarding the mean α -relaxation time, the results are consistent with the exchange time matching the upper limit of structural relaxation times or two to three times their average value. As Tg is approached, no indication for a variation in exchange behavior or for slower environmental fluctuations is found.