Exclusion and Trapping of Carbon Nanostructures in Nonisotropic Suspensions of Cellulose Nanostructures

Incorporation of carbon nanotubes (CNTs) into liquid crystalline phases of cellulose nanocrystals (CNCs) may be used for preparation of hybrids with novel optical, electrical, and mechanical properties. Here, we investigated the effect of nanoparticle diameter, geometry, aspect ratio, and flexibility on the exclusion of dispersed carbon nanostructures (CNs) from the chiral nematic phase (N) of the CNCs. Although the CNs are nicely dispersed in isotropic suspensions of CNCs, we observe that fullerenes, carbon black, and CNTs are depleted from the N∗ phase. This observation is surprising as theoretical predictions and previous observations of nanoparticles indicate that nanometric inclusions would be incorporated within the N∗ phase. Cryogenic transmission electron microscopy imaging reveals that the dispersed CNs induce misorientation of the CNCs, irrespective of their geometry and size. Rheological measurements suggest that about 10% of the CNCs are affected by the CNs. The multiparticle nature of the interaction may be the origin of the nonsize selective exclusion of the CNs. Re-entrant behavior is observed at high CNC concentrations (about 13 wt %), where a (nematic) gel-like phase kinetically traps the CNs. These phases exhibit non-Newtonian flow behavior and birefringence, offering a pathway for preparation of nonisotropic CNCs-CNT composites and thin films via liquid processing.