Elasticity of Dispersions Based on Carbon Nanotubes Dissolved in a Lyotropic Nematic Solvent

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.