Over the past decades, flexible electronics such as flexible liquid crystal devices composed of polymer film substrates have been dramatically growing. Understanding bending behavior of polymer films is the key to designing flexible electronic devices with high mechanical durability. Although various bending analysis methods have been proposed, they are still limited to macroscopic and qualitative analyses. Recently, we have newly proposed a method for analyzing the surface bending strain in flexible materials, termed surface labeled grating method. This method enables us to quantitatively evaluate the surface bending strain by monitoring the diffraction angle of a He-Ne laser beam that passes through a grating label attached on a sample. In this study, we measure the surface bending strain in polyethylene terephthalate films and reveal that tension and compression occurs in their outer and inner surfaces, respectively.
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