Ethylene-Vinyl Acetate—A Promising Alternative to Polydimethylsiloxane for Stretchable Electronics

Conductive stretchable polymer composites based on microparticles (CSPC-MPs), employing micron-scale features on conformable smart electronics are of outstanding importance for the realization of the wide variety of applications such as wearable electronics, health monitoring, and flexible and stretchable electrodes for example for robotic joints[1, 2]. Foremost, the ever-growing interest in deformable printed electronics calls for reliable conductivity while being highly flexible, and stretchable.<br/>The nature of the elastomeric polymer used in CSPC-MPs in an integrated stretchable printed electronic device modulates to a large extent the degree of deformability and electromechanical responses of the final composite. For stretchable inks and functional 3D structures polydimethylsiloxane (PDMS) is the most common elastomer candidate being used and its performance for lab-on-chip devices is analyzed thoroughly in several publications [3, 4]. The reasons behind this popularity are its strong chemical bonds amongst cross-linked polymer chains and low glass transition temperature that renders good chemical resistance, good heat durability, and favorable elasticity.<br/>In this work, we are comparing PDMS to the alternative Ethylene-Vinyl Acetate (EVA) by blending both materials with equal amounts of conductive microparticles (MPs) and investigating the electromechanical response of the composite systems. Those studies are correlated to morphologic differences on the micron-scale studied by SEM images demonstrating different levels of agglomeration depending on the filler polymer. The formation of large agglomerates of MPs enveloped in a blanket of EVA increases the overall conductivity. Hereby we could demonstrate that the ability of EVA to host conductive silver MPs is superior compared to PDMS. Furthermore, EVA-containing composites demonstrate a promising self-healing response after being under vigorous strain. Devices made with EVA recover from complete disconnection back to high conductivity in a matter of a few seconds making it attractive for applications requiring high sensitivity and long-term stability.<br/>[1] J. Chen <i>et al.</i>, ‘An overview of stretchable strain sensors from conductive polymer nanocomposites’, <i>J. Mater. Chem. C</i>, vol. 7, no. 38, pp. 11710–11730, 2019, doi: 10.1039/C9TC03655E.<br/>[2] F. Wen, Z. Zhang, T. He, and C. Lee, ‘AI enabled sign language recognition and VR space bidirectional communication using triboelectric smart glove’, <i>Nat. Commun.</i>, vol. 12, no. 1, p. 5378, Sep. 2021, doi: 10.1038/s41467-021-25637-w.<br/>[3] D. Qi, K. Zhang, G. Tian, B. Jiang, and Y. Huang, ‘Stretchable Electronics Based on PDMS Substrates’, <i>Adv. Mater.</i>, vol. 33, no. 6, p. 2003155, Feb. 2021, doi: 10.1002/adma.202003155.<br/>[4]K. Huang <i>et al.</i>, ‘Three-dimensional printing of a tunable graphene-based elastomer for strain sensors with ultrahigh sensitivity’, <i>Carbon</i>, vol. 143, pp. 63–72, Mar. 2019, doi: 10.1016/j.carbon.2018.11.008.