Browsing by Subject "Ionic Liquids"
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Item Block copolymers in ionic liquids.(2009-06) Simone, Peter MarkIn this thesis the self-assembly behavior of block copolymers diluted with ionic liquids has been investigated. Initial experiments involved characterizing the selfassembly of poly(styrene-b-methyl methacrylate) (PS–PMMA) and poly(butadiene-bethylene oxide) (PB–PEO) copolymers at dilute concentrations (~1 wt%) in the ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF6]) and 1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]). Dynamic light scattering and cryogenic transmission electron microscopy results showed that the ionic liquids behave as selective solvents for the PMMA and PEO blocks of the copolymers, and that the micelle morphology and self-assembly behavior of the block copolymers in the ionic liquids was analogous to that observed in conventional solvents. At increased solution concentrations (≥ 20 wt%) the lyotropic mesophase behavior for PB–PEO diluted with [BMI][PF6] and [EMI][TFSI], and poly(styrene-bethylene oxide) (PS–PEO) diluted with [EMI][TFSI] was investigated via small angle X-ray scattering. These experiments showed a microstructure phase progression with addition of ionic liquid that was analogous to that expected for an increase in the PEO volume fraction of the bulk copolymers. Additionally, an increase in the lamellar microstructure domain spacing with ionic liquid content indicated that both ionic liquids behave as strongly selective solvents for the PEO blocks of the copolymers. The ionic conductivity of the concentrated PS–PEO/[EMI][TFSI] solutions was measured via impedance spectroscopy, and found to be in the range of 10−3 S/cm at elevated temperatures (~100 °C). Additionally, the ionic conductivity of the solutions was observed to increase with both ionic liquid content and molecular weight of the PEO blocks of the copolymer. Finally, preliminary investigations of the microstructure orientation in thin films of a concentrated PS–PEO/[EMI][TFSI] solution were conducted. The copolymer microstructure was observed to align perpendicular to the film surface with short term (≤ 2 hours) thermal annealing. Longer term thermal annealing resulted in a transition to parallel alignment of the copolymer microstructure relative to the film surface.Item Dynamics and Structure-Property Relationships in Organic Single Crystal Electrical Double Layer Transistors(2017-12) Schmidt, ElliotThe goal of this dissertation is to gain a deeper understanding of the factors governing electrical double layer transistor (EDLT) performance. Specifically, the effects of ion structure on EDLT performance are examined in detail towards the end of this work (Chapters 7, 8, and 9). A deep understanding of structure property relationships is fundamental to both being able to design novel high-performance ionic liquids for EDLT applications as well as being able to choose an ideal ionic liquid for a targeted application. Ion structure is a crucial factor determining a wide variety of ionic liquid and EDLT properties with simple structural modifications leading to changes in many ionic liquid and device properties simultaneously. Chapters 1-4 provide background knowledge helpful for understanding the research presented in Chapters 5-8. Chapter 5 explores dynamics of electric double layer formation in ionic liquid-based devices and provides insight about the relevant time scales involved. Chapter 6 focuses on work done to study free charge in EDLTs through spectroscopic means. Chapter 7 explores the effects of ion volume on various EDLT performance metrics. Chapter 8 digs deeper into an interesting observation made in the work of Chapter 7 involving ion volume and EDLT threshold voltage ultimately leading to an examination of the effects of ion adsorption on threshold voltage. This work is but a drop in the bucket required to gain a thorough understanding of these exceedingly complex systems, and Chapter 9 covers the many avenues of continued research that exist.Item Investigations on the dynamics of excess electrons in pyrrolidinium bistriflimide and diacyanoamide RTILs(2015-05) Molins i Domenech, Francesc