Bending creep behaviour of various polymer films analysed by surface strain measurement

• Published in: Soft matter 2024-04, Vol.2 (15), p.3248-3255
• Main Authors: Yu, Jiayi, Kishino, Masayuki, Hisano, Kyohei, Shishido, Atsushi
• Format: Article
• Language: English
• Subjects: Bend tests; Creep strength; Deformation; Electronic devices; Electronic equipment; Measurement methods; Polymer films; Polymers; Solifluction; Strain; Strain analysis; Strain energy; Strain measurement
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d3sm01566a

Understanding the temporal bending deformation of polymer films is key to designing mechanically durable flexible electronic devices. However, such creep behaviour under persistent bending remains unclear due to a lack of precise and accurate bending strain analysis methods. Herein, we quantitatively analysed the bending creep behaviour of various polymeric films using our developed strain measurement method that can precisely measure surface strain from optical diffraction. The surface strain measurement reveals that bending creep deformation differs depending on the polymer structure. The four-element Burgers model was employed to model the temporal strain increase on the bending surface successfully. By fitting the four-element model to the time course of the measured surface strain, we found that each polymer film has a different threshold surface strain for the appearance of bending creep deformation. Such disparity in the bending creep behaviour can be explained by the difference in strain energy density between the polymer films and their elastic model; polymer films with a small strain energy density difference show small bending creep deformation. The results obtained in this study contribute to the elucidation of the bending creep behaviour of polymer films and the development of flexible electronic devices operated under persistent bending. Polymer films subjected to a static bending state exhibit temporal strain increase due to their viscoelastic nature. We quantitatively measured the surface strain change in various polymer films in real time and gained insights into the occurrence of this phenomenon.