Tuning optical properties of cellulose nanofibrils based multi-layered thin films

International audienceUltrathin multilayer films, assembled by the layer-by-layer (LbL) technique, are recently attracting more interest due to the simple way of their preparation and to their different possible coatings applications (optics, electrics, biosensors…) [C. Cerclier et al. (2011). Advanced Materials, 23 , 3791-3795]. In this framework, thin multilayer films were successfully prepared using TEMPO-oxidized cellulose nanofibrils (CNF) as an anionic polyelectrolyte and poly-(allylamine hydrochloride) (PAH) as a cationic one. The aim of this work was to control the architecture of these films in order to obtain materials with tunable properties. The key-parameter we used in the construction process was the ionic strength. Adding salt to PAH solution (1M) caused a change in the polymer conformation which influences directly the thickness increment per bilayer of the films [C. Moreau et al. (2012). Langmuir, 28 , 10425−10436], while adding small amount of salt to the NFC suspension caused a slight aggregation of the nanoparticles that modifies the architecture of the films as seen by atomic force microscopy. The change in architecture is accompanied by a modification of the films porosity showed by neutron reflectivity experiments. Finally, the impact of the architecture on the films optical properties was evaluated by light transmittance measurements