Abstract
Abstract Mixtures of the ionic liquids 1-methyl-3-octylimidazolium phenylazophenolate, abbreviated as [C8mim][AzoO] and 1-methyl-3-octylimidazolium hexafluorophosphate, abbreviated as [C8mim][PF6], have been known as smart materials with high moldability, electric conductivity, and self-healing properties. However, the structure and the phase behavior at low temperature are not well known in detail, which may change depending on the composition. Differential scanning calorimetry shows that a tiny amount of water is required for the crystallization of neat [C8mim][AzoO]. X-ray diffraction profiles indicate the coexistence of the crystalline phase and the liquid state for the one-component ionic liquid. Polarized optical microscopy indicates that the crystalline phase comprises needle-like microcrystals and coarse crystals. As a result, the phase diagram of the mixture [C8mim][AzoO]n[PF6]1−n is established. The mixture undergoes a complex phase behavior containing glass transition and crystallization, which drastically changes depending on the composition. Noteworthy, it is indicated that [C8mim][PF6] promotes the formation of microcrystals of [C8mim][AzoO], but not coarse crystals. On the other hand, [C8mim][AzoO] facilitates the supercooling of the liquid [C8mim][PF6]. These asymmetric effects enable [C8mim][AzoO]n[PF6]1−n to display moldable but electroconductive features.
Published Version
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