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

Abstract

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

Titration of DNA/Carbon Nanotube Complexes with Double-Chained Oppositely Charged Surfactants

“…According to the purveyor, they have an average outer diameter of 10 ± 1 nm and lengths in the 3–6 μm range. The results were confirmed by TEM [ 43 ].…”

Dispersability of Carbon Nanotubes in Biopolymer-Based Fluids

“…Because of such drawbacks, DLS bi-exponential fits are not applicable, unless extra constraints are imposed. A rationale approach to the problem implies determining dr and dt separately by independent methods, such as DLS and transmission electron microscopy, TEM [39]. When the average diameter of CNTs is determined by TEM, it is possible to deduce L from polarized light scattering, and estimates of (L/D) ratios are at hand.…”

Liquid Crystals of Carbon Nanotubes and Carbon Nanotubes in Liquid Crystals

“…This first of all renders the 'effective' nanotube surface, as experienced by the world outside the wrapped CNT, hydrophilic, second, the hydrophilic surfactant head groups or polymer chains introduce a repulsive force between the nanotubes, either of electrostatic type (for ionic head groups) or of entropic type (for flexible chains that get entangled in case of close nanotube contact, with a consequent entropy penalty), cf. Figure 10 When the dispersion medium is a liquid crystal the amphiphile-based approach is useful for lyotropic liquid crystal hosts [61][62][63][64][65][66][67][68][69][70][71][72][73]. A potential problem is however that the large number of micelles present in a surfactant-based lyotropic liquid crystal phase can act as 'depletants', that is they may induce aggregation of the nanotubes by means of depletion attraction [74].…”

“…It happens for single-wall as well as multi-wall carbon nanotubes of different types but not for fullerenes and also not if the dispersion quality of nanotubes is insufficient. Recently, the rheological properties of nanotubes suspended in purely anionic SDS-based nematic lyotropic phases were investigated thoroughly by Tardani and Camillo [62]. They found significant viscoelastic behavior at nanotube loadings above 0.25%.…”