Helical Fibers via Evaporation-Driven Self-Assembly of Surface-Acylated Cellulose Nanowhiskers.

Many natural materials have helical or twisting shapes. Herein, we show the formation of helical fibers with the lengths of micrometers by the evaporation-driven self-assembly on silicon wafers of functionalized cellulose nanowhiskers (CNWs) with surface-attached acyl chains. The self-assembly process and the final helical structures were affected by parameters including the wettability of substrates, dispersing solvents, the amount of 10-undecenoyl groups, the crystallinity, the dimension of CNWs, and the length of acyl chains. In particular, surface-acylated CNWs with a certain amount of 10-undecenoyl groups (ca. 3.52 mmol g-1 ), an appropriate crystallinity (ca. 40 %), a length of about 135 nm, and a diameter of around 4 nm, preferentially self-assembled into explicit left-handed helical fibers from their THF suspensions on wafers. Thus, we showed novel particular self-assembly behaviors of surface-acylated CNWs, and we expanded the materials spectrum for the construction of helical structures.