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- All Subjects: Ionic Liquid
- Creators: Dai, Lenore L
Description
Liquid-liquid interfaces serve as ideal 2-D templates on which solid particles can self-assemble into various structures. These self-assembly processes are important in fabrication of micron-sized devices and emulsion formulation. At oil/water interfaces, these structures can range from close-packed aggregates to ordered lattices. By incorporating an ionic liquid (IL) at the interface, new self-assembly phenomena emerge. ILs are ionic compounds that are liquid at room temperature (essentially molten salts at ambient conditions) that have remarkable properties such as negligible volatility and high chemical stability and can be optimized for nearly any application. The nature of IL-fluid interfaces has not yet been studied in depth. Consequently, the corresponding self-assembly phenomena have not yet been explored. We demonstrate how the unique molecular nature of ILs allows for new self-assembly phenomena to take place at their interfaces. These phenomena include droplet bridging (the self-assembly of both particles and emulsion droplets), spontaneous particle transport through the liquid-liquid interface, and various gelation behaviors. In droplet bridging, self-assembled monolayers of particles effectively "glue" emulsion droplets to one another, allowing the droplets to self-assembly into large networks. With particle transport, it is experimentally demonstrated the ILs overcome the strong adhesive nature of the liquid-liquid interface and extract solid particles from the bulk phase without the aid of external forces. These phenomena are quantified and corresponding mechanisms are proposed. The experimental investigations are supported by molecular dynamics (MD) simulations, which allow for a molecular view of the self-assembly process. In particular, we show that particle self-assembly depends primarily on the surface chemistry of the particles and the non-IL fluid at the interface. Free energy calculations show that the attractive forces between nanoparticles and the liquid-liquid interface are unusually long-ranged, due to capillary waves. Furthermore, IL cations can exhibit molecular ordering at the IL-oil interface, resulting in a slight residual charge at this interface. We also explore the transient IL-IL interface, revealing molecular interactions responsible for the unusually slow mixing dynamics between two ILs. This dissertation, therefore, contributes to both experimental and theoretical understanding of particle self-assembly at IL based interfaces.
ContributorsFrost, Denzil (Author) / Dai, Lenore L (Thesis advisor) / Torres, César I (Committee member) / Nielsen, David R (Committee member) / Squires, Kyle D (Committee member) / Rege, Kaushal (Committee member) / Arizona State University (Publisher)
Created2013
Description
Electrolytes play a critical role in electrochemical devices and applications, and therefore design and development of electrolytes with tailored properties are much desired to accommodate variety of operation requirements. Extreme temperatures are considered as one of the challenging environmental conditions, especially for devices rely on liquid state electrolytes, rendering failure of operations once the electrolyte systems undergo phase transitions. This work focuses on development of low-temperature iodide-containing liquid electrolyte systems, specifically designed for the molecular electronic transducer (MET) sensors in space applications. Utilizing ionic liquids, molecular liquids, and salts, multiple low-temperature liquid electrolytes were designed with enhancements in thermal, transport, and electrochemical properties. Effects of intermolecular interactions were further investigated, revealing correlations between optimization of microscopic dynamics and improvements of macroscopic characteristics. As a result, three low-temperature electrolyte systems were reported utilizing ethylammonium/water, gamma-butyrolactone/propylene carbonate, and butyronitrile as solvent with ionic liquid, 1-butyl-3-methylimidazolium iodide, and lithium iodide salt. Consequently, the liquidus range of these systems have been extended to -108 ˚C, -120 ˚C, and -152 ˚C, respectively, marking the lowest liquidus temperature of liquid electrolytes to the author’s best knowledge. Moreover, transport properties of designed systems were characterized from 25 to -75 ˚C. Effects of selected cosolvent/solvent on evolutions of transport properties were observed, revealing interplay between two governing mechanisms, ion disassociation and ion mobility, and their dominance at different temperatures. Experimental spectroscopy characterization techniques validated the hypothesized intermolecular interactions between solvent-cation and solvent-anion, complimented by computational simulation results on the complex dynamics between constituent ions and molecules. To support MET sensing technology, the essential iodide/triiodide redox were investigated in developed electrolytes. Effects of different molecular solvents on electrochemical kinetics were elucidated, and steady performances were validated under a properly controlled electrochemical window. Optimized electrolytes were tested in the MET sensor prototypes and showcased adequate functionality from calibration. The MET sensor prototype has also successfully detected real-time earthquake with low noise floor during long term testing at ASU seismology facility. The presented work demonstrates a facile design strategy for task-specific electrolyte development, which is anticipated to be further expanded to high temperatures for broader applications in the future.
ContributorsLin, Wendy Jessica (Author) / Dai, Lenore L (Thesis advisor) / Wiegart, Yu-chen Karen (Committee member) / Emady, Heather (Committee member) / Lind Thomas, MaryLaura (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2022