Synergistic effect of zwitterion-modified cellulose nanocrystals and chitin nanofibrils on regulated composite membranes

Membranes organized by rigid cellulose nanocrystals (CNCs), the highly crystalline nano-objects, exhibit a wide range of potential applications attributed to their numerous advantages including excellent hydrophilicity, biocompatibility, high crystallinity, and superior strength. However, the correlation between mechanical stiffness and structural arrangements for CNC-based membranes is still a challenge, particularly in a predictive manner for the tailored macroscale performance. This study proposes a strategy of regulating the surface properties, charges and stiffness of CNC composite membranes with the incorporation of the zwitterion and chitin nanofibrils (ChNFs) components. The synthesized zwitterion ( n , n -dipropionate methyl ester octadecylamine) endows the modified CNCs with a pH-sensitively charged surface, displaying the cationic form in the acidic condition while converted to anionic surface in the alkaline state. The ionic “bridge” between semi-flexible nanofibrils and rigid CNCs can effectively reduce the nanohardness of the composite membranes, taking the uniform surface and microstructural morphologies. Graphical Abstract