Biocompatible cellulose nanofibrils (CNFs) are widely used due to their attractive properties such as low density, lightweight, thermal stability, and good mechanical properties. These prerequisites make CNFs a promising template material for the design of synthetic colloid-biocomposites and bio-inspired coatings. Latex colloids are excellently suited to be incorporated in functional films, e.g. amorphous photonic crystals, due to their tailored core-shell morphology. Hence, when combining latex colloids and CNF, one needs to understand the nanoscale architecture of cellulose nanofibrils in networks and in the presence of other nanoparticles. Especially their reaction to external fields, e.g. humidity changes, is crucial in terms of stability and reversible/irreversible structural rearrangements. Here we used depth sensitive grazing incidence small-angle neutron scattering (so-called ToF-GISANS) to evaluate the humidity-induced latex colloid (of different sizes) and CNF rearrangements in situ during cyclic humidification. The measured kinetics help to resolve the time- and depth-dependence that colloids of different sizes need to penetrate into the porous CNF network. We were able to resolve if the latex nanoparticles remain on the surface or penetrate the CNF matrix. After the first humidity cycle, a change in morphology on the scale of several 10 nm was observed, which is attributed to latex particles which diffused in the network and enlarged the pores of the CNF network acting as template.

Structural changes in cellulose nanofibril–latex hybrid films during humidity cycling

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