Work

Weak Anion Hydration Drives LCST Behavior in Ionic Liquid–Water Mixtures: Insights from Calorimetry and Neutron Diffraction

Year: 2026

Type: article

Abstract: Isothermal titration calorimetry (ITC) combined with neutron diffraction and isotopic substitution (NDIS) has been used to elucidate the molecular origins of lower critical solution temperature (LCST) behavior in the tetrabutylphosphonium 5-phenyltetrazolate/water ([P4444][Ph-tet]/H2O) system. Comparison with the structurally similar but fully water-miscible analogue, tetrabutylphosphonium benzoate ([P4444][Bz]) reveals a much smaller negative enthalpy of mixing with water. This is indicative that weaker solvation of the [Ph-tet]- anion drives an entropy-dominated desolvation process upon heating, leading to phase separation into IL-rich and water-rich domains and is supported by observation from NDIS that the [Ph-tet]- anion is only weakly hydrated by water.

Source: The Journal of Physical Chemistry B

DOI: 10.1021/acs.jpcb.6c04727