Hetcher, week of April 11

Our reading this week concerned one of the earliest papers, I believe, on the idea of compensating the Arrhenius equation. It addressed the assumed lack of temperature dependence of the dielectric constant for computations of ion transport in organic liquid electrolytes. The data analyzed by Petrowsky and Frech showed that scaling the temperature dependence of conductivities allowed the exponential pre-factors of the Arrhenius expression to cancel, and seemingly verified their assumption that the dependence held within was the primary component holding previous plots to low correlation.  This compensation held true for both a family of alcohol- and ketone-based electrolyte solutions.

These results are more interesting if we consider applying this method to the article read for last week. Tokuda et al. had, in their investigation of room temperature ionic liquids, not accounted for a temperature dependence in the dielectric constant, and hence observed non-linear correlations between conductivities, temperature, and viscosities. It is possible, then, that these physicochemical properties are being misrepresented, and under a different paradigm might be correlated.

A final thought concerning the reading I’ve done for this week lies within the relation between hydrogen bonding and viscosity of imidazolium-based ionic liquids. The Hunt article, although primarily conceptual in its conclusions, again takes a differing viewpoint to the reason behind unexpected experimental evidence. The addition of a methyl group in the C2 position should decrease the melting point and viscosity of the ionic liquid, although the inverse is observed. Hunt proposes that the addition of this methyl group reduces, in addition to the hydrogen bonding, the entropy of the system, thus resulting in a greater ordering of the liquid. This restriction of available conformers sounds very plausible, and it is my presumption (hunch?) that application of the Compensated Arrhenius Formalism will explain a portion of this unexpected variance, though more in-depth thermodynamic tests may be required.



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