Mechanical spectroscopy study of ionic liquids with quaternary cations: Effect of conformational flexibility

Mechanical spectroscopy measurements were performed on ionic liquids (ILs) with quaternary cations, either ammonium or phosphonium, and two anions, bis(trifluoromethanesulfonyl)imide ([NTf2]-) bis(trifluoromethanesulfonyl)methanide ([CHTf2]-), which have almost the same molecular weight degree of fluorination but exhibit different flexibility. Furthermore, effect multiple ether functionalization was studied by measuring mechanical spectrum [P(2O2)31][CHTf2]. The measured data evidence occurrence a relaxation process in liquid phase ILs flexible [NTf2]- anion [P(2O2)31][CHTf2], is analyzed means modified Debye model relating peak to ion hopping between non-equivalent configurations. analysis confirms involvement nonequivalent configurations as well their energy separation. For other having rigid ions, instead, fast dynamic at local level rarely observed since partial transition solid state favored. these liquids, suggest formation aggregates suppressed functionalization.