Composite Films with Ordered Carbon Nanotubes and Cellulose Nanocrystals

Composite films with oxidized carbon nanotubes (o-CNTs) incorporated in the chiral nematic liquid crystals (CNLCs) formed by cellulose nanocrystals (CNCs) were fabricated for the first time. Induced by solvent evaporation, the isotropic aqueous dispersion containing o-CNTs and CNCs gradually forms lyotropic CNLCs, and the framework of the CNLCs can be retained in the final solid films, confirmed by polarized optical microscopy observations and scanning electron microscopy observations. During this evaporation-induced self-assembly process, the predispersed o-CNTs were spontaneously integrated in the liquid crystal matrix. It is found that the incorporation of a trace amount of o-CNTs (∼1.5 wt %) can induce obvious structural changes of the films. The reflection spectrum shifts to higher wavelengths with increasing content of o-CNTs, resulting in a continuous increase of the helical pitch of the CNLC phase. Confined in the liquid crystal matrix, the randomly oriented o-CNTs in the aqueous dispersion are forced to adopt a higher degree of order. This ordered arrangement of o-CNTs combined with the intrinsic anisotropy of the CNLCs impart the composite film anisotropic conductivity as proved by the electrical resistance measurements. This new type of CNTs/CNCs composites could find applications in various fields such as sensors and photoelectronics