Neutral Mechanical Plane Shifting in Bending Elastomer Film Revealed by Quantification of Internal Strain

• Published in: Advanced engineering materials 2022-06, Vol.24 (6), p.n/a
• Main Authors: Kishino, Masayuki, Akamatsu, Norihisa, Taguchi, Ryo, Hisano, Kyohei, Kuwahara, Kohei, Tsutsumi, Osamu, Takeya, Jun, Shishido, Atsushi
• Format: Article
• Language: English
• Subjects: bending; cholesteric liquid crystals; flexible electronics; neutral mechanical planes; polydimethylsiloxane; strains
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.202101041

Flexible electronic devices composed of soft materials, such as polymers and elastomers, require high mechanical durability to maintain their performance during cyclic bending, where large bending can lead to fracture. To design the appropriate structure for such devices, it is essential to utilize a neutral mechanical plane (NMP) in which the strain becomes zero inside bending materials. Despite the importance of identifying the NMP position for this utilization, the NMP position in soft materials has rarely been studied experimentally because of the difficulty in measuring internal strain in largely bending materials. Herein, the NMP position of bending polydimethylsiloxane (PDMS) film, which is a common soft material used in flexible electronic devices, is experimentally quantified via internal strain measurement with a cholesteric liquid crystal sensor. This is the first reported identification of the NMP position, revealing that bending of the PDMS film reversibly shifts the NMP position within ≈11% of the film thickness toward the inner bending surface. Considering this large NMP shift, a flexible electronic device with high mechanical durability is fabricated. The direct identification of the NMP position, which is enabled by the internal strain measurement, facilitates the development of device designs for flexible electronic devices. Neutral mechanical plane (NMP) position of a bending polydimethylsiloxane (PDMS) film is experimentally identified by internal strain analysis with a cholesteric liquid crystal elastomer sensor. The identification reveals that the NMP of the bending PDMS film shifts toward the inner bending surface. A flexible electronic device with high mechanical durability is successfully fabricated by considering the NMP shift.