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 (PULEx) 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 PULEx 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.