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

Abstract

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.

Surfactant-Mediated Co-Existence of Single-Walled Carbon Nanotube Networks and Cellulose Nanocrystal Mesophases

“…Yet, recent studies of hydrophobic particles of different size (from a few nanometers to hundreds of nanometers) and shape (spherical and elongated) indicate that carbonaceous inclusions are excluded from the N*, irrespective of their shape and size. This observation suggests that in the hybrid systems, hydrophobic interactions may play a more significant role than expected [12].…”

“…Liquid suspensions of CNCs and SWNTs can be used as colloidal inks for additive manufacturing [51] and layer-by-layer deposition [18] of multifunctional nanocomposites with novel combinations of optical, electrical, mechanical, and thermal properties [18,[52][53][54]]. Yet, mismatch in the physical characteristics of the two components, including diameter, aspect ratio, rigidity, and interfacial interactions, results in segregation of the components and depletion of the SWNTs from the liquid-crystalline phases of the CNCs [12].…”

“…CNCs are known to disperse SWNTs in dilute suspensions, probably via interactions with the π electrons of the SWNTs. While the CNC-dispersed SWNTs are excluded from the N* phase [12], it was found that it is possible to utilize evaporation induced selfassembly (EISA) of CNCs suspensions [13][14][15][16][17] for preparation of thin dried films of CNC-SWNT hybrids. The EISA process is initiated from CNC suspensions in the isotropic phase (ϕ < ϕ*) [18] and the SWNTs are trapped in the drying suspension.…”

“…Studies of nanometric inclusions embedded in CNC LC phases envision the incorporation of nanoparticles into the N* phase as a size-selective process [19]. Thus, the driving force for the exclusion of the SWNTs from the N* would be the mismatch in the excluded volume (entropic) interactions [12] or elastic inter-particle interactions [20]. Yet, recent studies of hydrophobic particles of different size (from a few nanometers to hundreds of nanometers) and shape (spherical and elongated) indicate that carbonaceous inclusions are excluded from the N*, irrespective of their shape and size.…”

All-Aqueous Bicontinuous Structured Liquid Crystal Emulsion through Intraphase Trapping of Cellulose Nanoparticles

“…Confining anisotropic LC fluid into an emulsion system is widely explored as a LC emulsion and displays distinctive nano- and microstructures. − When the prepared LC emulsion shows microscale droplet morphology, the LC orientational order can be frustrated in confined spherical geometries by the interplay between boundary conditions and energy minimization, yielding complex behaviors to control microscale colloidal self-assembly with super structures that are distinguished from the bulk phase. − Interestingly, some colloidal particles can self-align along a common axis at high concentrations, resulting in the anisotropic LC phase with long-range ordered particle assembly. For example, cellulose nanocrystals (CNCs) are charged, rod-like nanoparticles that can self-assemble into a cholesteric LC phase above the critical concentration. − The cholesteric organized CNC suspension is extremely stable with the presence of polymers, micro-/nanoparticles, and surfactants and can be further solidified into photonic films upon slow solvent evaporation. − Several studies have shown that CNCs could be used as a robust LC building block for designing custom-tailored functional materials in the dry state; − in contrast, few works have focused on the CNC colloidal self-assembly as LC emulsions. Owing to the nanoparticle stabilizing effect at the liquid–liquid interface, the aqueous CNC cholesteric phase can be confined directly within the suspended droplet (water-in-oil), in the inverted continuous phase (oil-in-water), or both phases (water-in-water), generating a immiscible LC-fluid interface with hierarchically ordered structures.…”