Anomalous phase behavior of excess iodide in room-temperature ionic liquid: 1-methyl-3-propylimidazolium iodide

Phase diagrams of room-temperature ionic liquid (RTIL), polyiodides, were obtained by simultaneous Xray diffraction and differential scanning calorimetry measurements. The original RTIL is 1-methyl-3-propylimidazolium iodide, [C(3)mim][I]. By adding iodine to [C(3)mim][I], polyiodides were formed in the mixtures, which are expressed as [C(3)mim][I-m]. At both low temperature and high pressure, I-3 is found to be a crystal forming factor (Abe et al., 2017). Upon cooling, an amorphous phase appeared at around m = 3.66. The mixture [C(3)mim][I-3.66], as a non-stoichiometric system containing excess iodide, was redefined as [C(3)mim][I-3] - 7.1 mol% I-2, assuming that I-3 is an anion. The desorption process of polyiodides in the mixture was measured under vacuum. A relatively long desorption time was observed due to ionic interactions. (C) 2018 Elsevier B.V. All rights reserved.