Humidity-dependent water dynamics in PEDOT:PSS films

PEDOT:PSS is a conjugated polymer blend known for its dual electronic and ionic conductivity. Electrons are transported via the PEDOT backbone, while ionic conductivity primarily occurs through the hydrophilic PSS domains. Water uptake in humid environemnts significantly enhances ionic conductivity, whereas the strong increase in conductivity occurs at low water contents (≤30 wt%). Based on recent QENS studies, we hypothesize that at low water content, most water molecules form a hydration shell around PSS, weakening ion–polymer interactions, which leads to an accelerated ion diffusion. Beyond ~30 wt% water, additional molecules are present as bulk water between PSS chains, not significantly affecting ion diffusion. Our proposal aims to investigate the dynamical behavior of hydration and bulk water in PEDOT:PSS films under controlled low and intermediate humidity (8–65% RH). Prior QENS measurements at extreme humidity conditions (5% and 90% RH) will complement the here proposed intermediate humidity levels. The experimental data will be supported by molecular dynamics simulations that incorporate improved water models. Preliminary results already show that the water dynamics sensitively depends on the water content. With the proposed QENS study, we aim to shine light on the role of hydration and bulk water in ionic conductive polymer systems such as PEDOT:PSS, while in parallel, the results can be directly used for verification of our developed water models.