(346i) Surface Modification of Cellulose Nanocrystals Using Alkyl Groups

The extremely low solubility of the cellulose nanocrystals (CNCs) in non-aqueous systems prohibited the integration of this novel compound into many research or industrial areas. For example, despite the high affinity of the CNCs to stabilize graphene flakes, their insolubility in ethanol forbids their utilization in graphene-based inks formulated in the ethanol solvent. Also, to the best of our knowledge, there has been a rare number of attempts to improve the CNCs' dispersibility in ethanol by surface modification. Hence, in the current study, we carried out molecular dynamics simulation to investigate the fundamental reasons for the CNCs' low dispersibility in ethanol and the impacts of the surface functionalization on their phase behavior. The solvation free energy calculations of a single cellulose chain in ethanol, as well as the end-to-end distance measurements, revealed that the ethanol molecules dissolve the cellulose chains, and the solute molecule preserves its linear form in the ethanol maintaining its maximum interaction with the solvent. However, the umbrella sampling simulations and the gained potential of mean force (PMF) profile explained that the aggregation of the CNCs through their hydrophilic surfaces drives the CNCs' insolubility in ethanol. The PMFs derived from the binding of functionalized CNCs (CNC-CO-Rs) with alkylamine groups suggested enhanced solubility in ethanol compared to the pristine CNCs, either due to the reduced strength between the binding partners or a developed kinetic barrier along the binding pathway.