Structure and dynamics in cellulose-based, electrically conductive polymer films

Zoom webinar | Replay on Youtube (soon)

Lucas Kreuzer,

Heinz Maier-Leibnitz Zentrum (MLZ, FRM II) Technical University of Munich, Germany

PEDOT:PSS is a water-dispersable and electrically conductive polymer blend that is increasingly applied in numerous fields such as batteries and super-capacitors. While
many studies focus on performance optimization, 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 nanofibril (CNF) matrix enhances significantly the mechanical integrity and prevents film swelling, whereas a certain water
amount is still absorbed into the PEDOT:PSS/CNF films (~24 wt%). By studying the water dynamics under varying ambient relative humidity (RH) conditions, we identified
two water species inside the films: fast-moving bulk water and slow-moving hydration water. Under dry conditions, bulk water is completely released from the films, while
some of the hydration water remains within them. In humid environments, both water species are present.

The altered water content inside the PEDOT:PSS/CNF films in dependence of RH, leads to changing water-cellulose interactions, structural re-arrangements, and tunable
electrical conductivity. Under dry conditions, only some hydration water is present in the films and PEDOT:PSS – CNF interactions become more dominant. As a consequence,
PEDOT:PSS wets on the CNF, thereby leading to an increased conductivity. Under high RH conditions this is reversed: the high water content inside the films promotes de-
wetting of PEDOT:PSS and the electrical conductivity decreases.

Water – polymer interactions have been studied using quasi-elastic neutron scattering (QENS), while the film nano-morphology of the PEDOT:PSS/CNF films was investigated
with grazing-incidence small angle neutron scattering (GISANS) and time-of-flight neutron reflectivity (ToF-NR).