We examine one of a number of possible classes of exceptions to the usual rule that non-Arrhenius behavior in supercooled liquids is accompanied by a departure from exponential relaxation kinetics. The exceptions we study are the dielectric relaxations of monohydric alcohols and supercooled water, in which also the dielectric relaxation times may greatly exceed their mechanical relaxation counterparts. This paper gives evidence that the exceptional behavior is due to a clustering or self-micellization phenomenon by showing how both the relaxation time ratio and Debye relaxation anomalies can be removed by small additions of ionic solutes. These compete with the hydrogen bonding interactions responsible for the clustering. The study, which uses the electrical modulus formalism for data analysis, is restricted by the rapid merging of conductivity and dielectric loss peaks at salt content increases. The relaxation times extracted from a given data set depend on the formalism employed in the data analysis, and the importance of consistency in this respect when comparing mechanical and electrical pheonomena is emphasized. We conclude that comparisons between different responses are most appropriately made in the susceptibility formalism, that the dielectric response in n-propanol is ∼160 times slower than the mechanical response at ∼130°C, and that the difference is due to the fact that slowly relaxing hydrogen bonded molecular clusters dominate the dielectric susceptibility, hence also the dielectric relaxation. Using the susceptibility formalism for companions, we then infer that in water the dielectric relaxation process is considerably slower than the mechanical relaxation process, and that this fact, as well as the fact that the dielectric relaxation in supercooled water remains exponential while uniquely non-Arrhenius in temperature dependence, is to be explained by the dominance of the dielectric relaxation process by "network clusters."
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry