Mechanically robust and thermally stable electrochemical devices based on star-shaped random copolymer gel-electrolytes

Abstract

We synthesized 6-arm star-shaped polystyrene-ran-poly(methyl methacrylate) copolymers ((S-r-M)6) for mechanically robust and thermally stable ion gels containing an ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([EMI][TFSI]). The (S-r-M)6-based gels exhibited higher elastic modulus (E∼1.67×105Pa), which is more than five-times that (∼0.29×105Pa) of linear PS-r-PMMA-based ion gels at the same Sty content (∼29mol%), irrespective of applied mechanical strains (stretching and compression). In addition, they showed outstanding thermal stability. For example, the gel-sol transition temperature (Tgel) of (S-r-M)6 gels was ∼72°C, compared with that (∼56°C) of linear PS-r-PMMA-based ion gels. These physical properties of gels were further improved by increasing total molecular weight and the fraction of styrene, giving E of ∼3.8×105Pa and Tgel of ∼163°C. The resulting gels were functionalized by introducing electrochemiluminescence luminophores (tris(2,2′-bipyridyl)ruthenium(II) hexafluorophosphate). By utilizing the mechanical robustness of the (S-r-M)6 gels, we fabricated emissive electrochemical displays through ‘cut-and-stick’ process. Moreover, the thermally stable (S-r-M)6 gels indicated good dimensional stability, offering a chance to demonstrate ECL devices that operate even at high temperatures.