Glass Transition Behavior of the Quaternary Ammonium-Type Ionic Liquid: N,N-Diethyl-N-methyl-N-(2-methoxyethyl)ammonium Bromide-H_2O Mixtures

摘要

By a simple differential thermal analysis (DTA) system, the concentration dependence of the glass transition temperatures (T_gs) for the quaternary ammonium-type ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bromide [DEME] [Br] and H_2O mixtures, after quick precooling was measured as a function of water concentration x (mol% H_2O). We compared the results with the previous results of [DEME] [I]-H_2O and [DEME] [BF_4] -H_2O mixtures in which a double-glass transition behavior was observed. Remarkably, the [DEME] [Br]-H_2O mixtures basically show one-T_g behavior and the T_g decreases monotonically with increasing H_2O content up to around x = 91.5. But it suddenly jumps to higher T_g value at a specific x =～ 92. At this very limited point, two T_gs (T_(g1), T_(g2)) which we might consider as a transition state from the structure belonging to the T_(g1) group to another one due to the T_(g2) group were observed. These results clearly reflect the difference in the anionic effects among Br~-, I~-, and BF_4~-. The end of the glass-formation region of [DEME] [Br]-H_2O mixtures is around x = 98.9 and moves to more water-rich region as compared to those of [DEME] [BF_4]-H_2O (x = 96.0) and [DEME] [I]-H_2O (x = 95.0) mixtures.