Molecular Weight Tailored Hydrogen Bonding Networks in PVA/PEDOT: PSS: Decoupling the Conductivity-Flexibility Trade-Off for Robust Epidermal EMG Monitoring

Flexible wearable devices have significant potential for diverse applications, prioritizing the development of portable, safe, and stable dry electrodes. This study focused on designing six poly(sodium styrenesulfonate) (PSS) variants with controlled molecular weights (10k-70k), combined with a water-soluble soft polymer, poly(vinyl alcohol) (PVA), to enhance the electrical properties, mechanical strength, and long-term stability of the Poly(3,4-ethylenedioxythiophene) (PEDOT): PSS polymer complex. We systematically examined morphological modifications, interactions, and conductive processes of PVA/PEDOT: PSS films, along with the mechanisms behind their improved stretchability and resistance stability. Results indicate that low molecular weight PSS provides the best mechanical flexibility due to stronger hydrogen bonding with PVA, enhancing elongation at break. However, insulating domains in PSS and PVA impede carrier transport, leading to a discontinuous charge hopping process along the PEDOT backbone, which decreases electrical conductivity. Conversely, high molecular weight PSS exhibits poor dispersion of rigid segments and conductive materials, resulting in decreased electrical and mechanical properties. Notably, with a molecular weight of 34k, the PVA/PEDOT: PSS film exhibits excellent electrical performance and mechanical flexibility, maintains good resistance stability after 1000 loading and unloading cycles at 30% strain, and demonstrates clear and stable electromyography (EMG) signals, indicating vast potential for EMG electrodes.