High-pressure-driven multiple-glass transitions of ionic liquids: 1-alkyl-3-methylimidazolium nitrate

[Display omitted] •High-pressure multiple-glass transitions in ionic liquids were observed.•Nanoheterogeneous glass–homogeneous glass appeared in [C8mim][NO3].•The [C8mim]+ conformers were connected with the HP glass transitions. Ionic liquids, specifically 1-alkyl-3-methylimidazolium nitrate, [Cnmim][NO3] (n = 4, 6, and 8), underwent pressure-induced amorphization. High-pressure-driven multiple-glass transitions were clarified through Raman spectroscopy. Both double- and triple-glass transitions were observed in [Cnmim][NO3]. Small- and wide-angle X-ray scattering revealed a prepeak representing nanoheterogeneity in [Cnmim][NO3] (n = 6 and 8) at ambient pressure. Despite the decrease in intensity at glass transition pressure, the prepeak of [C8mim][NO3] still existed. In [C8mim][NO3], the first glass–glass transition occurred a nanoheterogeneous double glass. The second glass–glass transition marked the transition from a heterogeneous to a homogeneous glass.