We have made electrical measurements on a system using carbon nanotubes as the dopant material. A semiconjugated, organic polymer was mixed with carbon nanotubes to form a wholly organic composite. Composite formation from low to high nanotube concentration increases the conductivity dramatically by ten orders of magnitude, indicative of percolative behavior. Effective mobilities were calculated from the spacecharge regions of the current-voltage characteristics for the 0-8 % mass fractions. After an initial rise these were seen to fall from 1-8 % doping levels as predicted by theory. From the values for conductivity and mobility, an effective carrier density was calculated. This was seen to decrease between 0% and 1%, before rising steadily. ͓S0163-1829͑98͒51536-6͔

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Carbon nanotubes have been the focus of considerable research over the last decade. Because of their remarkable structural, mechanical, electrical, and thermal properties, [1] diverse applications have been envisioned. [2] Realization of these property advantages has been frustrated by material heterogeneity and impurities: catalyst and/or impurity carbons are present and as-produced nanotubes are mixtures of moderate bandgap semiconductors, very small bandgap semiconductors, and metallic conductors. Also, single-wall nanotubes (SWNTs) aggregate into bundles and larger, morerandom assemblies, and are difficult to uniformly disperse in melt or solution as either bundles or individual nanotubes. [3] Nanomanipulation techniques have been used for fabricating single-nanotube devices, such as sensors and field effect transistors, [4±6] but the probability of selecting the proper nanotubes needed for device function is low and these techniques are generally much too inefficient and unreliable to be used for making commercial practice. Nevertheless, strategies have been developed and practiced in the laboratory for fabricating carbon nanotube forests and other oriented nanotube assemblies (which can be used for field emitting devices), [7,8] self-standing carbon nanotube films (the so-called ªbucky-papersº), [9,10] and polymer and ceramic composites. [2,11±15] The addition of carbon nanotubes to polymeric or epoxy matrices results in composites with enhanced mechanical properties and electronic transport. [2,11,13] Composites of multiwall nanotubes (MWNTs) have been employed for initial practical applications, such as enabling electrostatic painting of automotive parts, and are of great interest for radio-frequency and electromagnetic shielding. [2,16] We have recently shown that intercalation of polymers in the porous structure of nanotube sheets increases Young's modulus, strength and toughness by factors of up to 3, 9, and 28, respectively. [17] The fabrication of carbon nanotube containing fibers is of special interest for mechanical and electronic textile applications. [18,19] Vigolo et al. developed an innovative coagulationbased fiber spinning technique: first, an aqueous dispersion of arc-discharge-produced single-wall carbon nanotubes (SWNTs) and surfactant (sodium dodecyl sulfate) is injected into a rotating bath of aqueous polyvinyl alcohol (PVA) solution, which serves as coagulant. [20±22] The nanotubes collapse during coagulation to form ribbon-like elastomeric gel-fibers. [23] Such gel-fibers are washed by immersion in successive water containers to remove excess PVA, and then dried by pulling from the water bath. The gel-fibers spun by this technique are difficult to disentangle and too weak to be easily handled. As a result, the produced dried fibers were typically short (some tens of centimeters long). Tensile strength and Young's modulus values of up to 230 MPa and 40 GPa, respectively, were reported for those dried SWNT/ PVA composite fibers. [20±22] This coagulation-based fiber spinning techniq...

To prepare high-quality Langmuir films of 2D materials it is important to select a solvent optimized for both exfoliation and spreading at the air-water interface. Whereas it is generally accepted that exfoliation and stabilization of 2D materials is well-described using the Hansen solubility parameter theory, a complementary description of solvent spreading behavior is lacking. To this end we develop an understanding of solvent spreading using a Hansen solubility parameter framework. Our model accurately predicts the behavior of both water-immiscible and water-miscible solvents in Langmuir film formation experiments. We demonstrate that spreading behavior can be modified by controlling the surface pressure of the subphase using an amphiphilic species and accordingly utilize this approach to determine the maximum spreading pressure for a selection of solvents. Ultimately, by building on this understanding we open up additional routes to optimize the preparation of Langmuir films of 2D materials and other nanoparticles.

Carbon nanotubes can be efficiently separated from impurity material in carbon soot using a conjugated polymer filtration system as monitored by EPR, allowing the calculation of purity of the crude carbon soot.Carbon nanotubes have generated interest in all areas of science owing to their novel structural, mechanical and electronic properties. In the physical sciences nanodevices have already been demonstrated including transistors 1 and rectifying heterojunctions. 2 In microbiology they have been used as probes to study the structure of biomolecules 3,4 and as templates for the self assembly of proteins. 5 However, at present, as-produced carbon soot remains low in nanotube content. 6 Furthermore, neither quantitative techniques to analyse soot content nor methods to measure nanotube content exist. This work presents the first measurement of nanotube content in impure carbon soot. Using a conjugated polymer as a nanotube 'filter', carbon nanotubes are separated from all other soot components. An absolute value for the nanotube content can then be calculated for the first time using electron paramagnetic resonance and thermogravimetric measurements. This is a vital step towards making nanotubes a practical material for novel scientific developments.The necessity for a technique to measure nanotube content in carbon soot is apparent when the present fabrication and purification methods are examined. During nanotube production unwanted carbon species such as turbostratic graphite (TSG) and carbon onions are invariably formed. Purification by oxidation 7 destroys many nanotubes and alters the electronic properties of the remaining tubes. Chromatographic techniques 8 have succeeded in purifying carbon soot but no quantitative measure of purity has been obtained. Furthermore, scale-up of these processes is problematic. The process outlined in this work approaches these issues in a novel manner via the production of a polymer nanotube composite. Thus a quantifiable purification method for carbon soot is presented which leads logically to a measurement of the purity of that soot.In order to produce the polymer nanotube composites used in this work 80 mg of poly(m-phenylene-co-2,5-dioctyloxy-pphenylenevinylene) (PmPV) were mixed with 25.5 mg of multiwall nanotube (MWNT) containing arc-generated carbon soot in 4 ml of toluene. The PmPV was synthesised using a standard polycondensation reaction, 9 while the carbon soot was generated in a Krätschmer generator. 10 The mixture was sonicated for 2 min using a high power sonic tip and then for 2 h in a low power sonic bath to ensure complete dispersion of the Krätschmer generated carbon soot. This was carried out for seven composite solutions with identical constituents. These solutions were then allowed to stand undisturbed for various amounts of time, from 30 min to 90 h. At the end of its settling time each solution was carefully decanted into a new sample bottle, leaving a black sediment at the bottom of the old bottle. These sediments were then dried and weighed.To determ...