Study of dynamics and nanosegregation in ionic liquids and deep eutectic solvents by fluorescence correlation spectroscopy

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2020-01-01
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Mendivelso-P?rez, Deyny
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Emily A. Smith
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Chemistry
Abstract

Ionic liquids (ILs) and deep eutectics solvents (DESs) have emerged as a promising alternative to traditional organic solvents. This is due to their unique properties such as extremely low volatility, electroconductivity, unusual solvation and tuned miscibility, among other properties. Although, ILs and DESs are different types of solvents based on their molecular structures, they share many characteristics and properties that make them potentially attractive for a diversity of applications such as electrochemistry, synthesis, separation technologies, catalysis, materials science, and biochemistry. These unique properties have been interpreted as the result of their organization at the nanoscale level. Thus, the presence of nanosegregation in ILs and DESs is proposed to be important for many applications using these solvents, yet this nanoscale heterogeneity is poorly understood. In this dissertation, the translational diffusion dynamics of fluorophores in ILs and DESs films is reported as measured by fluorescence correlation spectroscopy.

Theoretical studies have predicted a high degree of nanosegregation in tetraalkylphosphonium-based ILs. However, experimental studies that confirm these findings are scarce. To this end, fluorescence correlation spectroscopy was used to study molecular diffusion in a series of tetraalkylphosphonium ILs films. The primary motivation for this study was to understand how the nanostructural organization affects the diffusion behavior of fluorophores of different polarities, polar (Atto 590), and nonpolar fluorophore (DiD), when the cation and anion in tetraalkylphosphonium ILs are altered. From the results, it was concluded that spatial heterogeneity is present in these classes of ILs, given that the diffusion of the fluorescent probes deviates from the Brownian diffusion behavior. These deviations are attributed to the presence of structural heterogeneities in the tetraalkylphosphonium ILs.

DESs have demonstrated increased potential for a diversity of applications, especially in separation technologies. Similar to ILs, nanostructural heterogeneity has been observed in DESs by theoretical and experimental studies. However, the fundamental understanding of DESs structure at the molecular level remains in a relatively early stage. To gain further insight into the presence of nanostructural heterogeneity in carboxylic-based DESs, fluorescence correlation spectroscopy experiments were performed for studying the translational diffusion properties of a hydrophilic (Atto 590) and a hydrophobic (DiI) fluorophore. Anomalous diffusion behavior was observed for the fluorescent molecules in all studied DESs. This anomalous diffusion behavior is characteristic of heterogeneous systems.

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Fri May 01 00:00:00 UTC 2020