The liquid crystalline phase behavior and sol-gel transition in halloysite nanotubes (HNTs) aqueous dispersions have been investigated by applying polarized optical microscopy (POM), macroscopic observation, rheometer, small-angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The liquid crystalline phase starts to form at the HNT concentration of 1 wt %, and a full liquid crystalline phase forms at the HNT concentration of 25 wt % as observed by POM and macroscopic observation. Rheological measurements indicate a typical shear flow behavior for the HNT aqueous dispersions with concentrations above 20 wt % and further confirm that the sol-gel transition occurs at the HNT concentration of 37 wt %. Furthermore, the HNT aqueous dispersions exhibit pH-induced gelation with more intense birefringence when hydrochloric acid (HCl) is added. The above findings shed light on the phase behaviors of diversely topological HNTs and lay the foundation for fabrication of the long-range ordered nano-objects.

No abstract

Highly ordered, homogeneous and enhanced microcrystalline cellulose (MCC)/halloysite nanotubes (HNTs) composite fibers have been successfully prepared from MCC/1-allyl-3-methylimidazolium chloride (AMIMCl)/HNTs dispersions with liquid crystal (LC) phases by a wet-spinning method, and their structures, morphology, mechanical, thermal and water barrier properties were investigated. The results revealed that the dispersions displayed stronger birefringence with increasing HNTs content, and became intensely birefringent when sheared; the birefringence also persisted for minutes after shearing was stopped. Rheological measurements showed that the dispersions had stronger shear thinning behavior. The thermal stability and tensile strength of the cellulose nanocomposite fibers were significantly improved compared with those of the pure MCC fiber. A more significant result is that the addition of HNTs significantly improved the moisture barrier properties of the regenerated MCC fibers.The above findings shed light on the liquid crystal phase behavior of HNTs dispersions and lay the foundation for fabrication of high performance fibers by liquid crystalline spinning.

No abstract

No abstract