This project explored how water moves through networks built from cellulose nanofibres – fibres so thin they exist at the boundary between the molecular and the visible world. How fluids permeate nanostructured soft materials matters for a broad range of technologies, from membrane-based separation to bio-inspired carriers for active substances, yet the factors that slow or redirect molecular movement at this scale are not well established. The work approached this question by combining experimental characterisation with computational modelling, tracing how fibre concentration, ionic environment, and the presence of additional components each shape the way water flows through these materials.
Neutron scattering was the key experimental tool throughout. Because neutrons interact strongly with hydrogen atoms – the very atoms that define both water molecules and cellulose chains – they offered a direct and highly sensitive window into how the fibres arrange themselves and how they move. Diffraction at small angles revealed the spatial organisation of the network, while measurements of quasi-elastic neutron scattering picked up the subtle, thermally driven fluctuations of individual fibres suspended in solution. This dual view, of architecture and motion captured in the same experiment, was complemented by nuclear magnetic resonance measurements of molecular mobility and by simulations spanning different physical scales.
Across a range of conditions, water proved to move more sluggishly than the sheer physical obstruction of the fibres would predict. Tightly bound layers of water molecules at fibre surfaces, together with the restless flexing of the fibres themselves, together account for the additional slowdown. As the network stiffens into a gel, ionic effects take over and become the principal lever controlling both fluid mobility and network organisation. In mixed systems, pairing cellulose nanofibres with other materials introduces new interaction points that can be exploited to dial in specific transport characteristics.
The result is a practical guide for tailoring how fluids move through bio-based nanostructured materials – opening pathways for advances in purification, controlled release, and low-impact alternatives to synthetic materials.