Yu Jiayi, Kishino Masayuki, Hisano Kyohei, Shishido Atsushi
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan.
Soft Matter. 2024 Apr 17;20(15):3248-3255. 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.
了解聚合物薄膜的时间弯曲变形是设计机械耐用的柔性电子器件的关键。然而，由于缺乏精确准确的弯曲应变分析方法，持续弯曲下的这种蠕变行为仍不清楚。在此，我们使用我们开发的应变测量方法对各种聚合物薄膜的弯曲蠕变行为进行了定量分析，该方法可以通过光学衍射精确测量表面应变。表面应变测量表明，弯曲蠕变变形因聚合物结构而异。采用四元件伯格斯模型成功地对弯曲表面上的时间应变增加进行了建模。通过将四元件模型拟合到测量的表面应变随时间的变化过程，我们发现每种聚合物薄膜在出现弯曲蠕变变形时都有不同的阈值表面应变。弯曲蠕变行为的这种差异可以通过聚合物薄膜与其弹性模型之间的应变能密度差异来解释；应变能密度差异小的聚合物薄膜显示出小的弯曲蠕变变形。本研究获得的结果有助于阐明聚合物薄膜的弯曲蠕变行为，并有助于开发在持续弯曲下工作的柔性电子器件。
