Density fluctuations in aqueous solution of ionic liquid with lower critical solution temperature: Mixture of tetrabutylphosphonium trifluoroacetate and water

- Aqueous solution of ionic liquid [P4444]CF3COO shows LCST-type phase separation.
- The solution exhibits unique mixing states in meso scale.
- A quantitative expression of mixing state is density fluctuations.
- We experimentally obtain the density fluctuations.
- The density fluctuations drastically increase as approach to the critical point.