STRUCTURE AND TRANSPORT IN TRIALKYLTRIAZOLIUM IONIC LIQUIDS: A COMBINED PFG-NMR DIFFUSION AND CONDUCTIVITY STUDY

Ionic liquids (ILs), the class of salts with melting points below 100 °C, are promising alternatives to molecular solvents. Their great chemical tuneability opens the possibility of tailoring ILs for specific tasks; however, data from systematic structure-property studies of ILs, as well as a more complete understanding of the liquid structure and interionic interactions within ILs, are required for the rational design of ILs. In this thesis, a systematic study of the effect of alkyl chain length and alkyl chain branching on the transport properties and carbon dioxide solubility in trialkyltriazolium ionic liquids is described. The viscosities, diffusion coefficients, and conductivities of 15 1,2,4-trialkyl-1,2,3-triazolium bis(trifluoromethylsulfonyl)imide ILs are reported, and are found to be greatly reduced in ILs that incorporate multiple branched alkyl groups on the cation. The interrelationships among the transport properties are analyzed by comparing the deviations of the transport properties of each IL from Walden’s Rule, the Stokes-Einstein equation, and the Nernst-Einstein equation. Preliminary evidence is given for a connection between the formation of polar and non-polar nanodomains within ILs, and the Nernst-Einstein deviation ratio. Henry’s Law constants for the solubility of carbon dioxide in the ILs are reported and found to be most strongly correlated to the molar volume of the IL; evidence supporting a relationship between the Nernst-Einstein deviation ratio and carbon dioxide solubility for a given IL is not found

Toward a Materials Genome Approach for Ionic Liquids: Synthesis Guided by Ab Initio Property Maps

The Materials Genome Approach (MGA) aims to accelerate development of new materials by incorporating computational and data-driven approaches to reduce the cost of identification of optimal structures for a given application. Here, we use the MGA to guide the synthesis of triazolium-based ionic liquids (ILs). Our approach involves an IL property-mapping tool, which merges combinatorial structure enumeration, descriptor-based structure representation and sampling, and property prediction using molecular simulations. The simulated properties such as density, diffusivity, and gas solubility obtained for a selected set of representative ILs were used to build neural network models and map properties for all enumerated species. Herein, a family of ILs based on ca. 200 000 triazolium-based cations paired with the bis(trifluoromethanesulfonyl)amide anion was investigated using our MGA. Fourteen representative ILs spreading the entire range of predicted properties were subsequently synthesized and then characterized confirming the predicted density, diffusivity, and CO2 Henrys Law coefficient. Moreover, the property (CO2, CH4, and N-2 solubility) trends associated with exchange of the bis(trifluoromethanesulfonyl)amide anion with one of 32 other anions were explored and quantified

Toward a Materials Genome Approach for Ionic Liquids: Synthesis Guided by <i>Ab Initio</i> Property Maps

The Materials Genome Approach (MGA) aims to accelerate development of new materials by incorporating computational and data-driven approaches to reduce the cost of identification of optimal structures for a given application. Here, we use the MGA to guide the synthesis of triazolium-based ionic liquids (ILs). Our approach involves an IL property-mapping tool, which merges combinatorial structure enumeration, descriptor-based structure representation and sampling, and property prediction using molecular simulations. The simulated properties such as density, diffusivity, and gas solubility obtained for a selected set of representative ILs were used to build neural network models and map properties for all enumerated species. Herein, a family of ILs based on ca. 200 000 triazolium-based cations paired with the bis­(trifluoromethanesulfonyl)­amide anion was investigated using our MGA. Fourteen representative ILs spreading the entire range of predicted properties were subsequently synthesized and then characterized confirming the predicted density, diffusivity, and CO₂ Henry’s Law coefficient. Moreover, the property (CO₂, CH₄, and N₂ solubility) trends associated with exchange of the bis­(trifluoromethanesulfonyl)­amide anion with one of 32 other anions were explored and quantified