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

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 × 10⁵ Pa), which is more than five-times that (∼0.29 × 10⁵ Pa) of linear PS-r-PMMA-based ion gels at the same Sty content (∼29 mol%), irrespective of applied mechanical strains (stretching and compression). In addition, they showed outstanding thermal stability. For example, the gel-sol transition temperature (T_gel) 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 × 10⁵ Pa and T_gel 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.