What Can We Learn about PEDOT:PSS Morphology from Molecular Dynamics Simulations of Ionic Diffusion?

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate(PEDOT:PSS)is one of the most important mixed electron-ion conducting polymers,where the efficiency of the ion transport is crucial for many of itsapplications. Despite the impressive experimental progress in thedetermination of ionic mobilities in PEDOT:PSS, the fundamentals ofion transport in this material remain poorly understood, and the theoreticalinsight into the ion diffusion on the microscopical level is completelymissing. In the present paper, a Martini 3 coarse-grained moleculardynamics (MD) model for PEDOT:PSS is developed and applied to calculatethe ion diffusion coefficients and ion distribution in the film. Wefind that the ion diffusion coefficients for Na+ ions arepractically the same in the PEDOT-rich and PSS-rich regions and donot show sensitivity to the oxidation level. We compare the calculateddiffusion coefficients with available experimental results. Basedon this comparison and based on the MD morphology simulation of PEDOT:PSSrevealing the formation of pores inside the film, we revise a commonlyaccepted granular morphological model of PEDOT:PSS. Namely, we arguethat PEDOT:PSS films, in addition to PEDOT-rich and PSS-rich regions,must contain a network of pores where the ion diffusion takes place.

Automated summary

In this paper, a coarse-grained molecular dynamics (MD) model for PEDOT:PSS is developed and used to calculate the diffusion coefficients and ion distribution in the film. The study finds that the diffusion coefficients for Na+ ions in PEDOT-rich and PSS-rich regions are almost the same and are not sensitive to the oxidation level. Based on this and the simulation results, the commonly accepted granular morphological model of PEDOT:PSS is revised to include a network of pores for ion diffusion.