Fabrication of Ultralarge Curvature Folding-Resistant Polyimide Films by Widening the Elastic Range and Intermolecular Slippery Spacing

As the electrons advanced toward foldable and lightweightcharacteristics,fabricating polyimide (PI) substrates resisting large curvature foldingunder an ultralow folding radius posed a significant challenge forflexible electronics. Here, one polyimide film (PICu) was fabricatedby introducing Cu2+ and benzimidazole, whose elastic rangeand intermolecular slippery spacing were widened thanks to the point-to-facemulti-coordination structure with larger attraction distance and variablebond angles, and it was fortunately equipped with greatly enhancedfolding resistance even under an ultralarge curvature. First, thefolding radius was confirmed to have an exponential impact on thetested folding reliability, as folding times of pure PI to form creasesdecreased sharply from 300,000 to 3000 with the folding radius droppingfrom 2 to 0.25 mm. In contrast, no crease was formed on PICu filmseven after folding over 200,000 times under an ultralow folding radiusof 0.25 mm. Importantly, the folding radius was almost 10 times smallerthan that in current reports (2-3 mm). In addition, the spreadangle of PICu films after static folding at 80 degrees C was 50-78%larger than that of pure PI films with the folding radius decreasedfrom 2 to 0.25 mm, demonstrating the excellent dynamic and staticfolding resistance of PICu films under an ultralarge curvature.