Edge-on (cellulose II) and face-on (cellulose I) adsorption of cellulose nanocrystals at the oil/water interface; a combined entropic and enthalpic process

International audience; Nanocelluloses can be used to stabilize oil/water surfaces, forming so-called Pickering emulsions. In this work, we compare the organization of native and mercerized cellulose nanocrystals (CNC-I and CNC-II) adsorbed on the surface of hexadecane droplets dispersed in water at different CNC 2 concentrations. Both types of CNC have an elongated particle morphology and form a layer strongly adsorbed at the interface. However, while the layer thickness formed with CNC-I is independent of the concentration at 7 nm, CNC-II forms a layer ranging from 9 to 14 nm thick with increasing concentration, as determined using small angle neutron scattering with contrast matched experiments. Molecular dynamics (MD) simulations showed a preferred interacting crystallographic plane for both crystalline allomorphs that exposes the CH groups (1 0 0 and 0 1 0) and is therefore considered hydrophobic. Furthermore, this study suggests that whatever the allomorph, the migration of CNCs to the oil-water interface is spontaneous and irreversible, and is driven by both enthalpic and entropic processes.