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

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Drying graphene oxide (GO) films are subject to extensive wrinkling, which largely affects their final properties. Wrinkles were shown to be suitable in biotechnological applications; however, they negatively affect the electronic properties of the films. Here, we report on wrinkle tuning and patterning of GO films under stress-controlled conditions during drying. GO flakes assemble at an air-solvent interface; the assembly forms a skin at the surface and may bend due to volume shrinkage while drying. We applied a modification of evaporative lithography to spatially define the evaporative stress field. Wrinkle alignment is achieved over cm areas. The wavelength (i.e., wrinkle spacing) is controlled in the μm range by the film thickness and GO concentration. Furthermore, we propose the use of nanoparticles to control capillary forces to suppress wrinkling. An example of a controlled pattern is given to elucidate the potential of the technique. The results are discussed in terms of classical elasticity theory. Wrinkling is the result of bending of the wet solid skin layer assembled on a highly elastic GO dispersion. Wavelength selection is the result of energy minimization between the bending of the skin and the elastic deformation of the GO supporting dispersion. The results strongly suggest the possibility to tune wrinkles and patterns by simple physicochemical routes.

Carbon nanotubes were dispersed in a sodium dodecylsulfate/decanol/water nematic fluid. The long-term stability of the dispersions is ensured by the small density gradients existing between nanotubes and the nematic fluid, and by its viscosity, as well. Presumably, surfactant or nematic micelles adsorb onto nanotubes and concur to stabilize them. A Rheo 2 H NMR characterization was performed. It was supported by classical 2 H quadrupole splitting and pulsed field gradient spin−echo NMR, allowing to ascertain the diffusive trends therein. The nematic fluid shows uniaxial spectral profiles and marked diffusion anisotropy. No such effects were observed in nanotube-containing nematic dispersions. In addition, the measured water self-diffusion values are substantially lower than the pure nematic fluid. In the absence of shear, dispersed nanotubes do not modify the quadrupole splitting amplitude, but affect the spectral profiles. The reasons for the observed behavior are briefly outlined. In the presence of shear, the spectral modifications are substantial and lead to the onset of isotropic dispersions, after long-time shearing.

The formation of liquid crystalline phases or isotropic clusters is observed in carbon nanotubes systems experiencing repulsive and attractive interactions, respectively. ssDNA-stabilized nanotubes act as strongly repulsive charged rods, showing nematic phases in (pseudo)-binary and ternary systems, in the presence of a nonadsorbing polymer. Switching between purely repulsive and attractive regime has not been investigated yet. For this reason, dispersions of ssDNA-stabilized nanotubes were added with an oppositely charged additive (i.e., protein or surfactant), and the resulting systems were investigated. In both phase diagrams a strong associative behavior was observed. At additive charge excess, a redispersion of the complex was obtained. The phenomenon was substantial in the case of surfactant system, where a charge inversion was also observed. A fine-tuning of attractive and repulsive interactions promoted aggregation and redispersion of carbon nanotube complexes. The introduction of weak attractive forces may promote the formation a cluster phase of ssDNA-stabilized nanotubes, with possible application as "multicompartimental" delivery systems

Single-walled carbon nanotubes were dispersed in a nematic solvent, made of sodium dodecyl sulfate, decanol, and water. Fine and homogeneous dispersions were obtained, depending on the preparation procedures and on the weight percent of carbon nanotubes in that solvent. Modifications in optical textures were compared to those pertinent to the original nematic fluid. According to optical polarizing microscopy and to other methods as well, it is inferred that very tiny amounts of clusters or bundles are present in such composite media. It is stated, accordingly, that the role of single tubes is dominant in the observed optical effects. A systematic investigation on the elastic properties of the above mixtures was performed by rheological methods, as a function of applied frequency, and in moderate shear stress conditions. Up to 0.25 wt % in nanotubes, the nematic dispersions show no, or negligible, elastic components in the corresponding viscoelastic relaxation spectra. Slightly larger amounts of nanotubes increase the system viscosity and give rise to significant elastic contributions in the investigated frequency range. The above findings were interpreted in terms of entanglement between nanotubes dispersed in the nematic matrix. Depending on nanotubes volume fraction, networks are formed and a significant elasticity is ensured to the resulting nematic dispersions

Catanionic vesicles are supramolecular aggregates spontaneously forming in water by electrostatic attraction between two surfactants mixed in nonstoichiometric ratios. The outer surface charges allow adsorption to the biomembrane by electrostatic interactions. The lipoplex thus obtained penetrates the cell by endocytosis or membrane fusion. We examined the possible cytotoxic effects and evaluated the transfection efficiency of one vesicle type as compared to known commercial carriers. We show that the individual components of two different vesicles types, CTAB (cetyltrimethylammonium bromide) and DDAB (didodecyldimethylammonium bromide) are detrimental for cell survival. We also assayed the cytotoxicity of SDS-DDAB vesicles and showed dose and time dependency, with the DDAB component being per se extremely cytotoxic. The transfection efficiency of exogenous RNA mediated by SDS-CTAB increases if vesicles assemble in the presence of the reporter RNA; finally, freezing abrogates the transfection ability. The results of our experimental strategy suggest that catanionic vesicles may be adopted in gene therapy and control of antiproliferative diseases.

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