Anisotropic Frictional Properties Induced by Cellulose Nanofibril Assembly.

The alignment of geometrically anisotropic nanomaterials regulates their functions. Self-ordering of rod-like cellulose nanocrystals (CNCs) results in liquid-crystal formation, and the ordering of the CNCs exhibits unique optical properties. Native cellulose nanofibrils (CNFs) are considered to be oriented, and thus the orientation is correlated with their functions, such as their mechanical strength and cell responses. In contrast, the ordering of artificially pulverized CNFs with high aspect ratios is restricted by their long fibrous shape. Here, we propose a facile fabrication method for non-uniaxial, fingerprint-like alignment of CNFs using the Langmuir-Blodgett technique. The obtained Langmuir-Blodgett films of CNFs exhibited anisotropic frictional properties depending on the orientation direction. This process for fabrication of CNF ultrathin films is expected to be used for novel surface design with desired structure-function correlations, which provides anisotropic surface properties to the material surface.