열처리 조건에 따른 이미다졸계 이온성 액체의 열안정성

Abstract

We investigated thermostability of imidazolium based ionic liquids according to temperature and atmosphere. Mass variation of the ionic liquid corresponding to the temperature was analyzed by thermogravimetric analyzer(TGA). Imidazolium based ionic liquids of [C2mim][TFSI], [C8mim][TFSI], [C12mim][TFSI], which have different alkyl chain length, were used. The color change was evaluated by UV-visible spectrophotometer. The structure change was verified by pH measurements. As the temperature and oxygen concentration increase, the color of the ionic liquid turns to dark brown. The pH number was lowered according to color darkening. [C8mim][TFSI] showed faster color change compared to [C2mim][TFSI]. Color change of [C12mim][TFSI] was slower and to light brown despite long alkyl chain than [C8mim][TFSI]. The color change is strongly related to the thermal stability. Coulombic packing by symmetry affects the thermal stability larger than Van der Waals force generated by the alkyl chain.