  Nanofibrous networks are the foundation and natural building strategy for all
life forms on our planet. Apart from providing structural integrity to cells
and tissues, they also provide a porous scaffold allowing transport of
substances, where the resulting properties rely on the nanoscale network
structure. Recently, there has been a great deal of interest in extracting and
reassembling biobased nanofibers to create sustainable, advanced materials with
applications ranging from high-performance textiles to artificial tissues.
However, achieving structural control of the extracted nanofibers is
challenging as it is strongly dependent on the extraction methods and source
materials. Furthermore, the small nanofiber cross-sections and fast Brownian
dynamics make them notoriously difficult to characterize in dispersions. In
this work, we study the diffusive motion of spherical gold nanoparticles in
semi-dilute networks of cellulose nanofibers (CNFs) using X-ray Photon
Correlation Spectroscopy (XPCS). We find that the motion becomes increasingly
subdiffusive with higher CNF concentration, where the dynamics can be
decomposed into several superdiffusive relaxation modes in reciprocal space.
Using simulations of confined Brownian dynamics in combination with simulated
XPCS-experiments, we observe that the dynamic modes can be connected to pore
sizes and inter-pore transport properties in the network. The demonstrated
analytical strategy by combining experiments using tracer particles with a
digital twin may be the key to understand nanoscale properties of nanofibrous
networks.
