Dielectric relaxation in associated liquids

Abstract

The dielectric properties of the associated liquids butanediol 1,3, 2-methyl pentanediol 2,4, glycerol, and hexanetriol 1,2,6 have been measured over the temperature range -20° to +10°C, and over a frequency range of 0.01 to 1200 Me/sec. Dielectric relaxation times and their distributions have been determined and indicate the following: (a) All four liquids exhibit an asymmetric distribution of relaxation times of the Davidson-Cole form, (b) With the exception of hexanetriol 1,2,6, the distribution of relaxation times becomes narrower with increasing temperature. It is proposed that groups (regions of appreciable order) exist in these liquids, and that dielectric orientation is closely related to the structural breakup of these groups, this breakup being a necessary condition for dipole reorientation. It is further proposed that the structural breakup is a cooperative process which does not proceed exponentially, therefore giving rise to a nonexponential decay of dielectric polarization. This concept offers an explanation for the observed distribution of relaxation times. The temperature dependence of the width of the distribution is explained by assuming that the group-size decreases with increasing temperature, and that as the groups become smaller, the structural-decay process becomes more exponential.