Ultralarge Curvature Folding Resistance of Polyimide Films Based on Spring-Like Folding Segments
Wei Yang, Qian Yin, Yan Chen, Xiangyang Liu, Xu Wang
Abstract
With the trend toward lighter and thinner flexible electronics, developing foldable polymeric substrates that can withstand ultralow folding radiuses has become an urgent issue. Here, a strategy to develop polyimide (PI) films with excellent dynamic and static folding resistance under an ultralarge curvature through copolymerizing one "unidirectional diamine" with classic PMDA-ODA PIs to achieve a kind of folding-chain PI (FPI). It was theoretically and experimentally confirmed that the spring-like folding structure equipped PI films with an enhanced elastic behavior and thus an excellent ability to endure a large curvature. Among them, FPI-20 did not show any crease even after folding over 200000 times under a folding radius of 0.5 mm, while creases were observed on pure PI film only after folding 1000 times. It is noteworthy that the folding radius was almost 5 times smaller than that in current reports (2-3 mm). Meanwhile, the spread angle of FPI-20 films after static folding at 80 °C under a 0.5 mm folding radius get 51% larger than that of films, showing the remarkable static folding resistance.