Anisotropic Thin Films of Single-Wall Carbon Nanotubes from Aligned Lyotropic Nematic Suspensions

Lyotropic nematic aqueous suspensions of single-wall carbon nanotubes can be uniformly aligned in thin cells by shearing. Homogeneous anisotropic thin films of nanotubes can be prepared by drying the nematic. Optical transmission between parallel or crossed polarizers is measured and described in order to estimate the dichroic ratio. The order parameter is measured using polarized Raman spectroscopy and found to be quite weak due to entanglement of the nanotubes and/or to an intrinsic viscoelastic behavior of the nanotube suspensions

Highly Ordered Carbon Nanotube Nematic Liquid Crystals

Liquid crystal ordering is an opportunity to develop novel materials and applications with carbon nanotubes spontaneously aligned on macroscopic scales. Nevertheless, achievement of large orientational order parameter and extended monodomains remains challenging. In this work, we show that shortening nanotubes allows the formation of liquid crystals that can easily be oriented under the form of large macroscopic monodomains. The orientational order parameter of single-wall nanotube liquid crystals measured by polarized Raman spectroscopy at the isotropic-nematic transition exceeds by far the value reported in previous experiments. The presently measured order parameter approaches the value theoretically expected for liquid crystals made of rigid rods in solution. This finding suggests that the production of highly ordered nanotubebased liquid crystals was presumably limited in earlier contributions by the length and waviness of long nanotubes. Both factors increase the material viscosity, can yield some elasticity, and stabilize topological defects

Phase Behavior of DNA-Based Dispersions containing Carbon Nanotubes: Effects of Added Polymers and Ionic Strength on Excluded Volume

Ordered phases containing single-walled carbon nanotubes (SWNTs) are essential to exploit the highly anisotropic properties of such nanoparticles. Knowledge of the phase behavior for the above dispersions is therefore needed. Unfortunately, the processing of nanotubes at high concentration remains experimentally challenging. To date, solvent evaporation and ultracentrifugation procedures have been used to increase the volume fraction of carbon nanotubes and obtain (pseudo)-binary phase diagrams. We present here a novel phase separation strategy, allowing investigations of the phase behavior of concentrated dispersions of DNA-stabilized carbon nanotubes. This strategy is based on the osmotic compression due to added polymers such as sodium dextransulfate (SDxS) or polyethylene glycol (PEG) and on the control of the ionic strength. The phase behavior of the compressed DNA/SWNTs complexes is analyzed and discussed. It is observed that added polymers induce the separation of a SWNT-rich anisotropic phase in equilibrium with an isotropic polymer-rich one. The volume fraction of the ordered phase can be controlled by the concentration of added polymer, making this strategy efficient for investigations of concentrated nanotube dispersions and developments of novel materials based on the anisotropic phases containing such nanoparticles

Liquid Crystallinity and Dimensions of Surfactant-Stabilized Sheets of Reduced Graphene Oxide

Graphene oxide (GO) flakes dissolved in water can spontaneously form liquid crystals. Liquid crystallinity presents an opportunity to process graphene materials into macroscopic assemblies with long-range ordering, but most graphene electronic functionalities are lost in oxidation treatments. Reduction of GO allows recovering functionalities and makes reduced graphene oxide (RGO) of greater interest. Unfortunately, chemical reduction of GO generally results in the aggregation of the flakes, with no liquid crystallinity observed. We report in the present work liquid crystals made of RGO. The addition of surfactants in appropriate conditions is used to stabilize the RGO flakes against aggregation maintaining their ability to form water-based liquid crystals. Structural and thermodynamical studies allow the dimensions of the flakes to be deduced. It is found that the thickness and diameter of RGO flakes are close to that of neat GO flakes