Water Dynamics in Hydrated Carboxylated Cellulose Nanofibril Membranes

Cellulose nanofibrils (CNF) are a class of materials with good mechanical properties, surface functionality and bio-/environmental friendliness. They have been used in many applications as loading material or function materials, where water-cellulose interaction determines the materials performance. Especially, CNF with carboxylated groups can be used as the separation membrane in polymer electrolyte membrane fuel cell. The water dynamics is closely related to the proton conductivity. The Non-destructive quasi-elastic neutron scattering (QENS) is used to characterized water movement in hydrated membrane made of CNF prepared by TEMPO-oxidation with different surface charges. However, neither surface charge nor the nanoconfinement due to membrane swelling has large impact on water dynamics mechanism. A slow diffusive motion is found with the diffusion coefficient close to bulk water and that in hydrated Nafion membrane regardless the surface charge, while a fast motion is rather localized with a correlation time increasing as temperature increase, which might related to the hydrogen bond network formation between water and CNF.