Liquid-Liquid Phase Behavior of Solutions of 1,3-Diethylimidazolium Bis((trifluoromethyl)sulfonyl)amide in n-Alkyl Alcohols

The cloud point method is applied for the characterization of the limited miscibility of ionic liquid (IL) solutions. Here, we report the phase behavior of binary mixtures of the ionic liquid 1,3-diethylimidazolium bis((trifluoromethyl)sulfonyl)amide (C(2)C(2)imNTf(2)) with n-alkyl alcohols (propan-1-ol, butan-1-ol, hexan-1-ol, and octan-1-ol) in a temperature range (T) of 258-386 K. The two components exhibit partial miscibility with upper critical solution temperatures (UCSTs) between 284 and 386 K. In concordance with previous studies, a detailed shape analysis presuming Ising behavior of the phase diagrams reveals the critical points and further properties of the phase diagrams. The results are compared with the isomeric IL C(3)mimNTf(2) from the C(x)mimNTf(2) family. Unraveling the influence of the molecular structure of the cation on the phase behavior is the main focus of the present investigation. The comparison between the two isomeric ILs, C(2)C(2)imNTf(2) and C(3)mimNTf(2), shows an increase of the UCST for the symmetric cation. A clear trend of lifting the UCST toward higher values is observed when dealing with longer chained n-alkyl alcohols. This behavior is put into context with a more generalized view on the phase behavior of the C(x)mimNTf(2) IL family. An effective number of carbon atoms of the cationic side chains is determined for the mixtures with different alcohols. For alcohols with chains <= 6, the effective carbon number is constant and about 3.79, while for octan-1-ol, a slightly lower value of 3.55 was observed. That gives evidence of a change of the molecular ordering of the system. The experimental study is supported by molecular dynamics (MD) simulations to attain a better understanding at the molecular level. The local dynamics and structures are analyzed in detail and reveal the effect of the symmetry on different physicochemical properties.