Fiber Alignment and Liquid Crystal Orientation of Cellulose Nanocrystals in the Electrospun Nanofibrous Mats.

Sulfate cellulose nanocrystal (CNC) dispersions always present specific self-assembled cholesteric mesophases which is easily affected by the inherent properties of particle size, surface charge, and repulsion or affinity interaction, and external field force generated from ionic potential of added electrolytes, magnetic or electric field, and mechanical shearing or stretching. Aiming at understanding the liquid crystal orientation and fiber alignment under high-voltage electric field, randomly distributed, uniform-aligned, or core-sheath nanofibrous mats involving charged CNCs and PVA were electrospun; and among them, specific straight arrayed fine nanofibers with average diameter of 270 nm were manufactured by using a simple and versatile gap collector. Moreover, arrayed composite nanofibers regularly aligned along the vertical direction of gap plates and selectively reflected frequent and continuous birefringence which was regarded as nematic phases of CNCs induced by the uniaxial stretching under high-voltage electric field. As a synergic effect of rigidness of nanocrystals and stretching orientation of nematic phases, the aligned nanofibrous arrays exhibited a higher tensile strength and strain than the randomly oriented or core-sheath nanofibrous mats at the same loading of CNCs. By contrast, mesophase transition of CNCs from cholesteric to nematic occurred in the coaxially spun core-sheath nanofibers at a loss of long-ranged chiral twist. Hence, the structure-effect relationship between liquid crystal orientation of charged nanorods in polymer-based fine nanofibers and the flexibility or mechanical integrity of the aligned fiber array will be favorable for strategic development of functional liquid crystal fabrics.