Aggregation of rodlike colloidal particles is investigated here through the aggregation process by either increasing ionic strength or decreasing surface charge density of cellulose nanocrystals (CNCs). The form factor of the nanoparticles is characterized up to the Guinier plateau using small-angle neutron scattering (SANS) extended to very small scattering vector Q. Ionic strength, above the threshold of screening charges, brings aggregative conditions that induced fractal organizations for both charged and uncharged CNCs. These two structures display respective fractal dimensions of 2.1 for charged CNCs at high ionic strength and 2.3 for desulfated CNCs over more than a decade of the scattering vector Q, irrespective of salinity, revealing a denser structuration for neutral particles. This is discussed in the framework of aggregation of rodlike particles with an aspect ratio higher than 8. Furthermore, dilution of the rod gel led to disentanglement of the network of fractal aggregates with a subsequent macroscopic sedimentation of the suspensions, with a characteristic time that depends upon the ionic strength and surface charge density. It revealed a threshold independent of salt content around 2.5 g/L and the metastable out-of-equilibrium character of CNC suspensions.

The cotton cellulose nanocrystals (CNCs) used in this study are rod-like particles with dimensions in the nanoscale (195 nm long, 23 nm width and 6 nm thick) able to stabilize Pickering emulsions. The adsorption of CNCs at an oil-water interface has been investigated by small angle neutron scattering (SANS) with and without surface charge, and varying CNC concentration from 2 to 5 g/L. Average thicknesses of the interfacial CNC layer around the emulsion droplets of 7 and 18 nm were determined for charged and uncharged CNC, respectively, regardless of their concentration in suspension. This suggests that CNC particles lie as a monolayer varying in surface density. Using several phase contrast variations, the neutron wave vector (Q) dependence with the intensity showed that CNCs are in contact with the oil phase only via the surface of the CNC and not immersed in oil since the Porod behavior is observed over the whole Q-range revealing no deformation of the oil surface at a nanometer scale. This result promotes the postulate that the (2 0 0) crystalline plane of the CNC directly interacts with the interface.

Cellulose nanocrystals (CNCs) are negatively charged colloidal particles well known to form highly stable surfactant-free Pickering emulsions. These particles can vary in surface charge density depending on their preparation by acid hydrolysis or applying post-treatments. CNCs with three different surface charge densities were prepared corresponding to 0.08, 0.16 and 0.64 e nm −2 , respectively. Posttreatment might also increase the surface charge density. The well-known TEMPO-mediated oxidation substitutes C 6 -hydroxyl groups by C 6 -carboxyl groups on the surface. We report that these different modified CNCs lead to stable oil-in-water emulsions. TEMPO-oxidized CNC might be the basis of further modifications. It is shown that they can, for example, lead to hydrophobic CNCs with a simple method using quaternary ammonium salts that allow producing inverse water-in-oil emulsions. Different from CNC modification before emulsification, modification can be carried out on the droplets after emulsification. This way allows preparing functional capsules according to the layer-by-layer process. As a result, it is demonstrated here the large range of use of these biobased rod-like nanoparticles, extending therefore their potential use to highly sophisticated formulations.

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