Phase Behaviour of Ionic Liquid Water

The mutual solubilities of ionic liquids and water are primarily defined by the type of anion and the cation alkyl side chain length of the ionic liquid. An increase in the alkyl chain length of the cation decreases the mutual solubility. Ionic liquids with bis(trifluoromethylsulfonyl)amide anions and hexafluorophosphate anions are more hydrophobic than ionic liquids with tetra-fluoroborate anions. However, even the most hydrophobic ionic liquids still [Pg.372]

Some (ionic liquid + water) systems do not exhibit the usual UCST behaviour, but show a lower critical solution temperature (LCST) behaviour instead. Here, the phase separation takes place at higher temperatures and mutual solubilities increase upon cooling until a homogeneous solution is reached. Only a small change in ionic liquid structure can already change the type of phase behaviour (UCST or LCST). For example, the tetrabutyl-phos-phonium-based ionic liquid with trans 2-butenedione (fumarate) as anion shows UCST behaviour, whereas the similar ionic liquid with the cis 2-bute-nedione (maleate) shows LCST behaviour after mixing with water. [Pg.373]

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