Dielectric Relaxation in Glycerol, Propylene Glycol, and n-Propanol

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.

Electron spin–lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids

“…There is little temperature dependence of the value of β [46], which suggests that the use of a temperature-independent value of β to analyze the nitroxyl relaxation rates does not introduce a large error. Literature values of β are 0.144 for decalin [41], 0.39 for 3-methylpentane [47], and 1.0 for 1-propanol [18]. The value of β for decalin is among the lowest for a molecular single component supercooled liquid [41].…”

“…Literature reports based on dielectric relaxation studies give β = 0.63 at T = −7.5 °C and T = −15.3 °C; β = 0.60 at T = −19.5 °C for water:glycerol mixtures (glycerol content; 50−100%) [46] and β = 0.6 at −40 °C > T > −65.5 °C for glycerol [18]. These values of β are similar to values for nitroxyl solutes in 1:1 water:glycerol (Table 1).…”

“…9) was developed in studies of dielectric relaxation [18]. (9) where β characterizes the distribution of correlation times.…”

“…NMR relaxation studies in viscous solution indicate that 1/T 1 may not follow the BPP spectral density [44,45], which is attributed to a distribution of tumbling correlation times that can be modeled with a Cole-Davidson spectral density function (Eq. (9)) [18,19,22,45].…”

Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation

“…The initial relaxation rate R S at higher temperatures in all samples, the single relaxation rate R at lower temperatures in the pure samples, and the two relaxation rates R 1 and R 2 at lower temperatures in the samples where both compounds 1 and 2 are present, are all modeled by R = (n/N) ( [7,36,37]. As is verified by experiment, at lower temperatures in samples where both compounds 1 and 2 are present, R 1 and R 2 in the double exponential for M(t) are the same as the corresponding R values in the pure compounds.…”