Ion-Pair Conductivity Model and Its Application for Predicting Conductivity in Non-Polar Systems
Creators: Parlia, Sean
Publisher: name: Columbia University
Year: 2020
Subjects: subject: Chemical engineering
subject: FOS: Chemical engineering
subject: FOS: Chemical engineering
subject: Ionization
subject: Environmental engineering
subject: FOS: Environmental engineering
subject: FOS: Environmental engineering
subject: Electric conductivity
subject: Electrochemistry

description: While the laws of ionization and conductivity in polar systems are well understood and appreciated in the art, theories related to nonpolar systems and their conductivities remain elusive. Currently, multiple conflicting models, with limited experimental verification, exist that aim to explain and predict the mechanisms by which ionization occurs in nonpolar media. A historical overview of the field of nonpolar electrochemistry, dating back to the 1800’s, is presented herein with a focus on the work of prominent scientists such as Fuoss, Bjerrum, and Onsager, who’s pioneering discoveries serve as the scientific foundation for our understanding of ionization in nonpolar systems, from which our knowledge of ion-pairs (i.e. re-associated solvated ions which do not contribute to the overall conductivity of the system) stems. Recent work in the field of nonpolar electrochemistry has focused on ionization models such as the Disproportionation Model and the Fluctuation Model, which ignore ion-pair formation and the existence of these neutral entities altogether. While, the “Ion-Pair Conductivity Model”, the novel conductivity model introduced and explored herein, primarily focuses on the critical role these neutral entities play with regards to the electrochemistry in these systems. The “Ion-Pair Conductivity Model” for predicting and modeling the conductivity of mixtures of nonpolar liquids, arises from the Dissociation Model, a third ionization model for predicting conductivity in nonpolar systems which accounts for ion-pair formation, and is rooted in the foundational work of Fuoss, Bjerrum, Onsager, and others. The Ion-Pair Conductivity Model’s relationship to and derivation from the Dissociation Model is provided, including the justified assumptions and simplifications of the model to create a more concise approach for predicting conductivity in nonpolar systems that can be readily applied to real-world scenarios. In order to substantiate this model as a reliable method for predicting conductivity in nonpolar solutions, experimental results from studies examining various two-component solutions comprised of an amphiphile and nonpolar liquid, analyzed under a variety of conditions, across the entire concentration spectra, from pure nonpolar liquid to pure amphiphile, are compared to the Ion-Pair Conductivity Model. The role additional properties such as water contamination, ion size, concentration of free ions, range of ion-pair existence, shear and longitudinal rheology in these nonpolar solutions are also explored. The fitting of the experimental data and theoretical model demonstrates the ability of the Ion-Pair Conductivity Model to accurately predict conductivity in two-component solutions of an amphiphile and nonpolar liquid. Furthermore, it emphasizes the importance that ion-pairs play in the conductivity of such a system. Lastly, it reinforces the usefulness of the Ion-Pair Conductivity Model as a tool for investigating the mechanisms by which ionization in nonpolar media occur. Ultimately, the goal of this study is to validate the Ion-Pair Conductivity Model as a robust and precise model for characterizing conductivity in nonpolar solutions across a diverse set of nonpolar systems. Allowing us, and others, to better understand and exploit the intrinsic properties of conductivity in these systems to advance a number of technologies in the field electrochemistry, such as a-polar paints, electrophoretic inks, and electrorheological fluids.