Physical Properties and Interactions of Ionic Liquids and Ionic Liquid Li-salt mixtures

Ionic liquids (ILs) is a new class of salts with melting points <100 °C. Typically, an ionic liquid consists of a large organic cation and a charge−delocalized inorganic or organic anion. The unique variability of the ions allows, for the design of a large number of different ionic liquids. However, the relation between the molecular structure, interactions, and the physical properties of ionic liquids is not fully understood. This thesis addresses the effect of cation and anion structure on fundamental physical properties of ionic liquids such as melting, glass transition, decomposition, and transport of ions and aggregates. The influence of the cation on these properties is investigated using several imidazolium cations for a fixed anion, bis(trifluoromethanesulfonyl)imide [TFSI]. Similarly, the anion influence is investigated using tetrafluoroborate [BF4¯], tetracyanoborate [B(CN)4¯] trifluoromethanesulfonamide [TFSAm], and phosphonate anions with the imidazolium and pyrrolidinium cations. Lithium salts doped ionic liquids are suitable for applications as electrolytes in rechargeable lithium batteries. However, it has been shown that the introduction of Li-salts into ionic liquids causes the viscosities to increase and the conductivities to decrease. In order to further develop and optimise these systems it is important to understand the structure and the interactions of the ionic liquid/Li-salt mixtures as well as how the properties might change when these mixtures are incorporated into e.g. a polymer membrane. These issues have been addressed in this thesis for LiTFSI doped TFSI anion based ionic liquids. This thesis also investigates the phase behaviour and transport properties of imidazolium and pyrrolidinium based ionic liquids doped with LiTFSI over a large concentration range, xLiTFSI/(1−x)IL, 0.01<x<0.4. The influence of the physical properties and interactions of ionic liquid/LiTFSI mixtures in a confining matrix, a Poly(vinylidene fluoride-co-hexafluoropropylene) copolymer (PVdF-HFP) membrane, is investigated using pyrrolidinium based ionic liquids. Finally, issues like solvation structure and the influence of change in interactions in the system on macroscopic properties i.e. ionic conductivity and glass transition temperature is discussed. Keywords: ionic liquids, glass transition temperature, ionic conductivity, Li−ion solvation

Thermal Mechanical Property Enhancement with Silicon Carbide Ceramic Filled Composites for Industrial Applications

Epoxy composites with glass fiber reinforcement can be found in the automotive and aerospace industries. In this study, the properties of the epoxy matrix were enhanced by processing composites filled with ceramic particles of silicon carbide (SiC). At first, SiC-filled E-glass fiber-reinforced epoxy composites/sandwich structures were processed using the hand layup technique. Next, processed composites were characterized using a tensile tester and an Izod impact tester to determine the best mixing ratio of ceramic-embedded epoxy composites. The highest mechanical properties were obtained according to ASTM D638 and D256 standards. Next, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), analysis of differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) were carried out respectively to find out the presence of functional groups, surface morphology, crystallographic structure, glass transition temperature (Tg) and thermal/material stability of processed composites. In the end, the study elaborates that the mechanical properties of epoxy matrix composites were improved by the addition of SiC ceramic fillers, and among processed composites, 10% SiCE composite carried the highest properties, including the Tg value of 62.8 &deg;C, 69.87 MPa for tensile strength and 57.12 kJ m&minus;1 for impact strength

Thermal Mechanical Property Enhancement with Silicon Carbide Ceramic Filled Composites for Industrial Applications

Epoxy composites with glass fiber reinforcement can be found in the automotive and aerospace industries. In this study, the properties of the epoxy matrix were enhanced by processing composites filled with ceramic particles of silicon carbide (SiC). At first, SiC-filled E-glass fiber-reinforced epoxy composites/sandwich structures were processed using the hand layup technique. Next, processed composites were characterized using a tensile tester and an Izod impact tester to determine the best mixing ratio of ceramic-embedded epoxy composites. The highest mechanical properties were obtained according to ASTM D638 and D256 standards. Next, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), analysis of differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) were carried out respectively to find out the presence of functional groups, surface morphology, crystallographic structure, glass transition temperature (Tg) and thermal/material stability of processed composites. In the end, the study elaborates that the mechanical properties of epoxy matrix composites were improved by the addition of SiC ceramic fillers, and among processed composites, 10% SiCE composite carried the highest properties, including the Tg value of 62.8 °C, 69.87 MPa for tensile strength and 57.12 kJ m−1 for impact strength

Physical Properties, Ion-Ion Interactions, and Conformational States of Ionic Liquids with Alkyl-Phosphonate Anions

We investigate the ionic conductivities, phase behaviors, conformational states, and interactions of three ionic liquids based on imidazolium cations and phosphonate anions with varying alkyl chain lengths. All three ionic liquids show high conductivities, with 1,3-dimethylimidazolium methyl-phosphonate [DiMIm(MeO)(H)- PO2] being the most conductive (7.3 x 10(-3) S cm(-1) at 298 K). The high ionic conductivities are a result of the low glass-transition temperatures, T-g, which do not change significantly upon changing the cation and/or anion size. However, there is a slight dependence of the temperature behavior of the conductivity on the size of the ions, as seen from the fragility parameter (D) obtained from fits, to the Vogel-Fulcher-Tammann equation. The molecular-level structure and interactions of the phosphonate anions were examined by Raman spectroscopy and first-principles calculations: The calculations identify two stable conformations for the methyl- and ethyl-phosphonate anions by rotation of the methyl and ethyl groups, respectively. The broad Raman signatures of the anions suggest the coexistence of anion conformers in the ionic liquids and non-negligible cation-anion interactions, with a dependence the position and shape of the bands of the cation species and the alkyl group of the anion

Structure and properties of Li-ion conducting polymer gel electrolytes based on ionic liquids of the pyrrolidinium cation and the bis(trifluoromethanesulfonyl)imide anion

We have investigated the structure and physical properties of Li-ion conducting polymer gel electrolytes functionalized with ionic liquid/lithium salt mixtures. The membranes are based on poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, PVdF-HFP, and two ionic liquids: pyrrolidinium cations, N-butyl-N-methylpyrrolidinium (PyR14+), N-butyl-N-ethylpyrrolidinium (PyR24+), and bis(trifluoromethanesulfonyl) imide anion (TFSI). The ionic liquids where doped with 0.2 mol kg(-1) LiTFSI. The resulting membranes are freestanding, flexible, and nonvolatile. The structure of the polymer and the interactions between the polymer and the ionic liquid electrolyte have been studied using Raman spectroscopy. The ionic conductivity of the membranes has been studied using dielectric spectroscopy whereas the thermal properties were investigated using differential scanning caloriometry (DSC)

Coordination and interactions in a Li-salt doped ionic liquid

We report on the coordination and interactions in the LiTFSI doped ionic liquid PyR14TFSI over a large concentration range, 0.01 <= x <= 0.4, using Raman spectroscopy. We find that the concentration dependence of the average number of TFSI anions coordinating to one Li-ion (N-TFSI/Li) can be divided into three regimes. For low concentrations, x <= 0.05, we find that a large number TFSI anions coordinate each Li-ion, N > 2. The number decreases with increasing salt concentration and the interaction between the Li-ion and the TFSI anions is rather weak in this concentration range. At intermediate concentrations, 0.1 <= x <= 0.2, the number of TFSI anions coordinating each Li-ion (N-TFSI/Li) is similar to 2 pointing towards the formation of [Li(TFSI)(2)](-) ionic clusters. At higher concentrations, x> 0.2, N-TFSI/Li decreases further indicating the transition to more complex structures with Li-ions bridging TFSI anions. We also show that the evolution of the microscopic structure as a function of Li-salt concentration is mirrored in the behaviour of macroscopic properties such as the ionic conductivity and the glass transition temperature, which also show a crossover in the same concentration range

A New Class of Ionic Liquids: Anion Amphiprotic Ionic Liquids

We here present a new class of protic ionic liquids, anion amphiprotic ionic liquids (AAILs). These materials are protonation equilibrium free protic ionic liquids and interesting in their own right by not following the classical Bronsted acid-base neutralization concept Due to the very simple synthesis route applied and their stable basic chemistry, we believe in a potential use for manifold applications. This is supported by the combination of practical material properties, foremost, a general intrinsic stability versus reversal of the formation reaction toward neutral species, broad liquidus ranges, long-term thermal stabilities, high conductivities, protic characteristics, and a general stability versus water