PEDOT:PSS Stretchability Enhancement Induced by Hard-Cation-Soft-Anion Ionic Liquids: Simulated Mixing, Drying, Pulling, and Scale Bridging

PEDOT:PSS is a promising material for electronic-skin applications but it still exhibits limited conductivity and stretchability. Vigorous mixing with hard-cation-soft-anion ionic liquids (ILs) has emerged as a powerful tool to enhance its conductivity. Recent experiments have demonstrated that such IL treatments improve its stretchability as well, but the molecular mechanism behind such enhancements remains unclear. Herein we use molecular dynamics simulations to investigate structural and mechanical effects of treating PEDOT:PSS with two hard-cation-soft-anion ILs such as 1-ethyl-3-methylimidazolium and 3-methylimidazolium tetracyanoborates. Starting from the simulations on the aqueous solution models of pristine and IL-treated PEDOT:PSS (simulated mixing), we mimic water evaporation at various temperatures (simulated drying and annealing up to 140^oC). The resulting fibular structure of PEDOT:PSS is then subjected to uniaxial deformation to mimic the stress-strain curves (simulated pulling). This series of simulations reveal that the IL treatment indeed reduces the elastic modulus and the maximum stress of PEDOT:PSS, agreeing with the experimental findings. Hydrophilic (hard) cations, such as the protic 3-methylimidazolium, indeed plays a critical role in this improvement by holding water around them in the dry film. This is a showcase where IL-induced rearrangements at the molecular level translate into improved macroscopic stretchability and mechanical robustness. Such molecular-level insights would provide a foundation to develop intrinsically stretchable conducting polymer films and pave a way for their application in stretchable electronic devices. To draw more realistic picture of the materials and processes at a larger scale, we are now developing a coarse-grained model of PEDOT:PSS from the above atomistic simulation data, utilizing AI for the scale bridging.