Stability Of Single-walled Nanotubes Research Articles

Synthesis of a Conductive Copolymer and Phase Diagram of Its Suspension with Single-Walled Carbon Nanotubes by Microfluidic Technology

Amphiphilic block copolymers composed of a poly(3-hexylthiophene) (P3HT) segment and a sulfonated polystyrene (PS-stat-PSS) sequence with well-defined and easily tunable structure were synthesized through Grignard metathesis polymerization (GRIM), RAFT polymerization and sulfonation of PS. Because of the hydrophilic nature and ionic conductivity of the PSS segment, such copolymer shows good solubility in water and high conductivity ∼1 S/m in form of dry film. Conductivity can be further enhanced with the addition of single-walled nanotubes (SWNTs). The present amphiphilic block copolymer enables efficient unbundling and stabilization of SWNTs in water. With the help of an original microfluidic technique referred to as microf luidic pervaporation, we investigated the concentration process of SWNT/copolymer suspensions up to dry films and obtained a complete phase diagram which reveals the aggregation of SWNTs during the concentration process in a given concentration range. High conductivity of about 370 S/m is achieved for SWNT/copolymer nanocomposites at high concentration of SWNTs. The microfluidic pervaporation method is also shown to provide a direct determination of the CNT percolation threshold.

Dispersion of Single Walled Carbon Nanotubes by Self Assembly of Polymers

ABSTRACTDispersion and stability of single walled nanotubes (SWNT) is one of the inhibiting factors affecting their tailorability for various electronic, chemical and mechanical applications . The realization of these applications depends on dispersing the SWNTs in aqueous media by inducing high forces of repulsion among the nanotubes. Steric repulsions are induced to the nanotubes by attaching polyelectrolytes, like poly styrene sulfonate (PSS) and poly allyl amine hydrochloride (PAH). In this work, Self Assembly technique is employed to attach polyelectrolytes, and thereby enhance the dispersion of SWNTs in aqueous media. The steric forces produced by the attached polyelectrolytes overcome the high van der waals force of attraction between the nanotubes and aid in the nanotubes dispersion. Characterization of the dispersions with UV-Vis Spectrophotometric method in kinetic mode revealed that nanotubes treated at pH 3 are seen to be more stable than the ones treated at pH 7. The effect of pH of the polyelectrolyte solutions in the assembly and its consequence on dispersion stability is also studied with zeta potential measurements. The morphology of the films produced by drying the nanotubes in vacuum on a silicon substrate is characterized by field emission scanning electron microscopy (FESEM).

Effects of MeV Ions on Thermal Stability of Single Walled Carbon Nanotubes

AbstractThe properties of carbon nanotubes (CNTs) are closely dependent on their structures, and therefore may be tailored by controllably introducing defects in the nanotube systems. In this work, we have investigated the effects of energetic ions (H+ and He+) on the thermal stability of single wall nanotubes (SWNTs) against oxidation in air. SWNTs were irradiated with MeV ions to various doses in the range 1013-1016 cm−2. Thermogravimetric analysis (TGA) was used to determine the loss of CNT masses as a result of oxidation processes. As opposed to the case of pristine SWNTs for which the temperature (Tmax) corresponding to maximum oxidation rate was found to be ∼ 495 °C, ion beam processing significantly enhanced the thermal stability of nanotubes, e.g., Tmax increased by about 30 °C after H+ implantation (dosage: 1015 cm−2) and 17 °C after He+ implantation (dosage: 1013 cm−2). The activation energies for thermal oxidation under various conditions were also extracted from TGA data, with values ranging from 1.13 eV (for pristine SWNTs) to 1.37 eV, depending on ion doses and species. Raman spectroscopy was used to determine the characteristics of the G band (C-C stretching mode) and D band (disorder induced mode) in CNTs. The work suggests that the SWNTs modifies to more stable structure (may be cross-linked SWNTs) at small doses. Once the number of defects exceeds some critical value (depending on the type and dosage of bombarding ion) the bonding energy in CNTs weakens, leading to the reduced thermal stability of CNTs against oxidation.