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Published on: March 24, 2018
Effects of Ether Bonds on Liquid-Liquid Transitions in Quaternary Ammonium and Phosphonium Ionic Liquids under High
Hiroshi Abe1, Shusei Maruyama1, Hiroaki Kishimura1
1Department of Materials Science and Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan.
Abstract:
Synchrotron small- and wide-angle X-ray scattering and Raman spectroscopy were used to investigate the high-pressure (HP) liquid-liquid transitions (LLTs) in quaternary ammonium and phosphonium ionic liquids (ILs) at room temperature. Bis(trifluoromethylsulfonyl)imide ([TFSI]-) was used as the anion, and triethyloctylammonium, (2-ethoxyethoxy)ethyltriethylammonium ([N222(2O2O2)]+), triethyloctylphosphonium, and (2-ethoxyethoxy)ethyltriethylphosphonium ([P222(2O2O2)]+) were used as cations. In diether-substituted [N222(2O2O2)][TFSI] and [P222(2O2O2)][TFSI], the polar/nonpolar nanodomains were not formed due to the flexible and curled alkyl chains. Despite no nanodomain, HP LLT occurred with changing the local structures. A series of quaternary ammonium and phosphonium ILs exhibited entirely different HP behavior, which implies that the ether bonds of the cations have an intrinsic property.
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