(742b) The Effect of Selective Fluorination on the Structure and Thermodynamics of Ionic Liquids

A number of molten salts cannot be classified as ionic liquids (ILs) because they are not liquids at or below 100 C. These materials may have interesting or desirable properties however because they remain solids at standard temperatures this is likely to severely restrict their usage in a given process. Lowering the melting points of these materials without significantly affecting their structure or properties, effectively extending their liquidus range, could alleviate this issue helping to facilitate their adoption in a given process.

Recently, it was shown that the addition of different functionalized groups to an IL cation base could have a very substantial effect on the melting point of a given IL class, without significantly affecting its structure. It was concluded that electron withdrawing effects in these groups created polarity within the cations, which could align, lowering the repulsion in these systems leading to a depression in the melting point. Even so, it remains unclear to what extent this method of lowering the melting point can be extended to other, more common ILs.

In this talk we present a systematic study of selective fluorination on the structure and thermodynamics of alkylimidazolium and quaternary ammonium-based ionic liquids. By exchanging hydrogen atoms for electronegative fluorine atoms at different positions in the alkyl chains of these ILs, we are able to alter the cation polarity without significantly affecting their steric interactions. Using molecular dynamics simulations, we study in great the effects that positional dependence, chain length and the addition of multiple electronegative sites has on the structure and thermodynamics of these ionic liquids.