Physical Gels of [BMIM][BF4] by N-tert-Butylacrylamide/Ethylene Oxide Based Triblock Copolymer Self-Assembly: Synthesis, Thermomechanical, and Conducting Properties

摘要

We report a strategy to prepare and characterize mechanically robust, transparent, thermoreversible physical gels of an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF_4], to harness its good ionic conductivity and electrolytic properties for solid-state electrolyte and lithium ion battery applications. Physical gels are prepared using a triblock copolymer comprising central polyethylene oxide block that is soluble in [BMIM][BF_4] and the end blocks, poly(N-tert-butylacrylamide), that are insoluble in [BMIM][BF_4]. Transparent, strong, physical ion-gels with significant mechanical strength can be formed at low concentration of the triblock copolymer (~5 wt %), unlike previous reports in which chemical gels of [BMIM][BF_4] are obtained at very high polymer concentration. Our gels are thermoreversible and thermally stable, showing 1-4% weight loss up to 200℃ in air. Gelation behavior, mechanical properties, and ionic conductivity of these ion-gels can be easily tuned by varying the concentration or N-tert-butylacrylamide block length in the triblock copolymer. These new non-volatile, reprocessable, mechanically robust, [BMIM][BF_4]-based physical ion-gels obtained from a simple and convenient preparation method are promising materials for solidstate electrolyte applications.