Self-Healable and Remoldable Transparent Polyurethane Film with High Dielectric Constant from the Synergistic Effect between Lithium Salt and Ionic Liquid

The rapid development of new-generation flexible touch display panels puts forward more requirements on the overlays, not only including colorlessness and transparency but also having self-healing and remolding abilities as well as high dielectric constant. Herein, new self-healable and remoldable polyurethane films (PULE<i>x</i>) with high dielectric constant have been developed through building of reversible cross-linked networks with special synergistic effect between lithium salt and ionic liquid. The integrated performance of PULE<i>x</i> was systematically investigated. Results show that as the loadings of lithium salt and ionic salt increase, films show increased dielectric constant and self-healing ability. The film with suitable composition (PULE7.5) has the best comprehensive performance; its dielectric constants (10⁴–10⁶ Hz) range from 9.6 to 6.1, which are comparable to those of glass (commonly used overlay for rigid capacitive touchscreen panels). The construction of reversible covalent cross-linking endows PULE7.5 with good mechanical strength, high self-healing efficiency after complete fracture (92.7%), and high recovery of mechanical properties after remolding (91.8%). In addition, the colorless PULE7.5 has high transparency (90.7% transmittance at 550 nm) and can freely convert among three shapes of bending, scrolling, and S-shape, showing great prospects in fabricating flexible display devices. The mechanism behind these outstanding integrated performances of PULE films is investigated through correlation with structures.