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.