Tuning of the chiral nematic phase of cellulose nanocrystals by the adsorption of a short polymer on their surface

Concentrated cellulose nanocrystal (CNC) suspensions are known to self-assemble into liquid crystalline cholesteric phase. However, the origin of this chirality transfer is still matter of discussion. In this work, we used a tailor-made biopolymer, xyloglucan (XG), at a very small molar mass (20,000 g/mol) that adsorb flat on the cellulose surface. We showed that the addition to a dispersion of CNCs at 60 g/L of XG up to 10 g/L decreased the anisotropic volume fraction, increased the cholesteric pitch, and kept constant the inter-CNC distance implying a change in the twist angle and a lower chiral strength. These results indicate that a very limited modification of CNCs on surface can induce important variation of the cholesteric order. Above 10 g/L XG, XG-covered CNCs decreased the cholesteric pitch and preferentially concentrated in the isotropic phase, decreasing the global cholesteric liquid crystalline (CLC) order.