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A flocculation-based process has been developed for spinning polymer-free carbon nanotube fibers from aqueous dispersions. This spinning process works for single-walled nanotubes (SWNTs), double-walled nanotubes, one-to-three mixtures by weight of single-and multiwalled nanotubes, and one-to-one mixtures by weight of single-walled nanotubes and imogolite (a naturally occurring silicate nanofiber). It produces hollow fibers, folded ribbon fibers, and solid fibers, meaning those without aggregated space. After annealing, the fibers spun from the SWNTs exhibited relatively high electrical conductivities (~140 S cm ±1 at room temperature) and high values of mass-normalized electrochemical capacitance (~100 F g ±1 ). Polarized Raman measurements indicate partial nanotube alignment in the spun fibers. Fiber supercapacitors were fabricated using these spun fibers. Individual SWNTs have remarkable properties, including high strength, modulus, and electrical and thermal conductivities.[1] In order to utilize these properties for most applications, the individual nanotubes must be assembled into macroscopic structures like fibers, ribbons, and films. Spinning SWNT/poly(vinyl alcohol) (PVA) composite fibers was initially reported by Vigolo et al. [2] and further advanced by Dalton et al. [3] This process involves injection of surfactant-dispersed SWNTs into a flowing solution of aqueous PVA to produce gel fibers, which are optionally washed and then dried. When PVA is largely retained, the obtainable SWNT/polymer composite fibers are quite strong, with toughness values over an order of magnitude higher than those previously reported for graphite fibers and synthetic organic fibers.[3] However, reflecting the high loading of PVA (over 40 wt.-%), which is a non-conductive polymer, the electrical and thermal conductivities of these nanotube/polymer composite fibers are much lower than can be obtained for SWNT sheets (bucky paper).[4] The presence of this polymer is problematic for applications such as fiber-based artificial muscles and supercapacitors, which require high electrochemical accessibility to the nanotubes and high electrical conductivity of the fibers. In a process developed at Rice University, [5] SWNTs are first dispersed in 102 % sulfuric acid and then wet-spun into either diethyl ether, 5 % sulfuric acid, or water. Very high nanotube concentrations in the spinning solutions are possible for this superacid spinning and the achieved nanotube orientation and electrical and thermal conductivities are very high. However, some protonation of the material occurs because of prolonged contact with the sulfuric acid and, like for superacid processes used in industry, special protection equipment is needed. The presently described wet-spinning process provides polymer-free nanotube fibers without the need for superacids. The fibers are spun from solutions comprising nanotubes, surfactant, and water. Various types of nanotubes have been spun by this method, including HiPco SWNTs obtained from a carbon-monoxide process (C...

Artificial muscles and electric motors found in autonomous robots and prosthetic limbs are typically battery-powered, which severely restricts the duration of their performance and can necessitate long inactivity during battery recharge. To help solve these problems, we demonstrated two types of artificial muscles that convert the chemical energy of high-energy-density fuels to mechanical energy. The first type stores electrical charge and uses changes in stored charge for mechanical actuation. In contrast with electrically powered electrochemical muscles, only half of the actuator cycle is electrochemical. The second type of fuel-powered muscle provides a demonstrated actuator stroke and power density comparable to those of natural skeletal muscle and generated stresses that are over a hundred times higher.

The lanthanide(III) complexes of three tetraamide DOTA bearing pyridyl, phenolic and hydroxypyridyl substituents have been studied by NMR, luminescence and cyclic voltammetry. The relaxivity profiles of the gadolinium complexes of the pyridyl and phenolic ligands were flat and essentially the same between pH 2 and 8. The hydroxypyridyl ligand, however, exhibited two regions of enhanced relaxivity. The small relaxivity enhancement (25 %) at lower pH (pH 2-4) has been attributed to an increase in the prototropic exchange of the coordinated water molecule while the slightly larger enhancement (84 %) at higher pH (pH 6-9) reflects deprotonation of the ligand amide protons. Deprotonation of the amides results in the formation of an intramolecular acid-base pair interaction with the phenolic protons and this, in turn, causes a highly organized second hydration sphere to come into effect, thereby increasing the relaxivity. The water relaxivity of the Gd(3+)-hydroxypyridyl complex is further enhanced upon binding to serum albumin.

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...