Dielectric Relaxation in Glycerol, Propylene Glycol, and <i>n</i>-Propanol

TLDR

Complex dielectric constants were measured across 20 c/s to 5 MHz and −40 °C to −140 °C in glycerol, propylene glycol, and n‑propanol. n‑Propanol follows the Debye equation, whereas glycerol and propylene glycol require a broader‑dispersion model; all three show a second high‑frequency dispersion, and their relaxation times obey an empirical rate equation that also fits viscosity data.

Abstract

Complex dielectric constants have been measured at frequencies from below 20 c/s to 5 mc/s over the temperature range −40° to −75°C in glycerol, −45° to −90° in propylene glycol, and −80° to −140° in n-propanol. The results for n-propanol are described by the Debye equation, but the values for the other two require a modified equation corresponding to a broader range of dispersion at higher frequencies. In all three liquids, evidence is found for a second dispersion region at still higher frequencies, which accounts for much of the difference between the radio frequency and optical dielectric constant. The relaxation times are quantitatively described over wide ranges by an empirical rate equation of a form which also fits viscosity data. The significance of the various results is discussed.