γ-Radiation effect on ionic liquid [bmim][BF4]

The effect of γ radiation on 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) was investigated in detail. It was found that radiation induced an increase of UV absorption of the ionic liquid but no change in its glass transition point. Raman spectroscopy analysis indicates that the radiolysis of [bmim][BF4] induces detectable destruction of alkyl-chain and scission of H-atoms of ring of imidizolium cation, and the relatively small changes of BF4− anion. Viscosities of irradiated [bmim][BF4] samples were measured at different shear rates and temperatures, and compared with irradiated [bmim][PF6] samples. The plots of shear stress against shear rate indicates that [bmim][BF4] is a Newtonian fluid, no matter with irradiation. The viscosity of irradiated [bmim][BF4] decreased with increasing of temperature and followed an Arrhenius equation. However, radiation caused no change in the viscosity of [bmim][BF4], but a decrease in the viscosity of [bmim][PF6] by up to 10%. We conclude that the radiation stability of [bmim][BF4] is higher than [bmim][PF6].