Critical Scattering in Room-Temperature Ionic Liquid–Propanol Solutions

Critical scattering, derived from the phase separation of room-temperature ionic liquid (RTIL)–propanol solutions, was observed by small- and wide-angle X-ray scattering (SWAXS). The RTILs were 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [Cnmim][TFSI] (n = 2–8). Critical scattering of the [C2mim][TFSI]–propanol system was enhanced in a propanol-rich region and corresponded to liquid–liquid equilibria in the mixture. The propanol isomer effect was obtained from a correlation length that represents fluctuations in density. By SWAXS, RTIL–propanol solutions had a prepeak that indicates nanoheterogeneity, and two kinds of fluctuation coexisted in the RTIL–propanol system.