Large strain mechanical behaviors of optically clear adhesives for flexible electronic devices under different temperature, humidity, and strain rates

Abstract

AbstractOptically clear adhesives (OCAs), a type of polymer pressure‐sensitive adhesive, are valued for their transparency, strong bonding, thermal stability, and reliability in flexible electronics. Accurately determining the mechanical properties of OCAs is importance for effectively assessing the structural integrity of foldable screens in finite element simulations. However, previous studies have primarily focused on small strain and conventional environmental conditions. To address this gap, the present study investigates the mechanical behaviors of OCAs under extreme conditions, including large strain (up to 1000%), high/low temperatures (−40, −20, 0, 25, 65, and 80°C), and high humidity (95% relative humidity). Specifically, the tensile, simple shear, and creep properties of OCAs have been assessed in an attempt to explore their visco‐hyperelastic behavior. The experimental findings indicate that OCA exhibits noticeable temperature sensitivity and viscoelasticity, along with volume‐incompressible properties. Notably, when the temperature is varied from −40 to 25°C and from 25 to 80°C, the modulus of OCA experiences an average reduction of 84% and 41% respectively. Moreover, it has been observed that humidity has a negligible effect on the material's modulus. The Yeoh model and Prony series are employed for fitting purposes. The proposed fitting parameters are subsequently validated through numerical simulations of three‐point bending case studies. Remarkably, the simulation results closely matched with the experimental data, with errors remaining below 10%.