Speaker
Description
PEDOT:PSS is a water-dispersable and electrically conductive polymer blend that is increasingly applied as organic electronics in numerous fields such as batteries, super-capacitors, and solar cells. While many studies focus on performance optimization, long-term degradation issues because of humid environments are rarely discussed. PEDOT:PSS absorbs significant amounts of water (~50 wt%), which leads to a pronounced swelling factor of up to 1.6.
The integration of PEDOT:PSS into a cellulose nanofibrils (CNFs) matrix solves this challenge as it enhances significantly the mechanical integrity and limits water absorption. Furthermore, a complex nanocomposite morphology is generated, which changes in dependence on the ambient relative humidity: high humidity leads to de-wetting of PEDOT:PSS from CNF bundles and the formation of larger PEDOT:PSS clusters. As a result, the conductivity decreases. Generally, upon drying, this behavior is reversible, however only after a first drying/humidifying cycle.
By investigating the water dynamics via quasi-elastic neutron scattering, (QENS), we identified two water species inside the films: fast-moving bulk water and slow-moving hydration water. In dry conditions, bulk water is completely released from the films, while parts of the hydration water remain inside the films. The remaining hydration water fraction provides a certain mobility for the PEDOT:PSS chains and supports their wetting on the CNF bundles. Upon temperature increase, we see an increase in hydration water fraction, whereas the bulk water fraction remains constant. In addition, the diffusion, which can be described with the isotropic jump diffusion model) of both water species accelerates, however due to a different reason: while hydration water features similar jump lengths and shorter residency times at elevated temperatures, bulk water moves in larger jumps, but with similar residency times. Raman measurements complement the data obtained from QENS and provide information about the polymer specific hydration and temperature behavior. In combination with conductivity measurements, we establish a link between fundamental water – polymer interactions on the molecular scale to a certain functionality on the macroscopic scale. This will contribute to develop novel types of organic electronic applications with enhanced performance and durability.
