Single-wall carbon nanotubes (SWNTs) have been widely touted as attractive candidates for use as fillers in composite materials due to their extremely high Young's modulus, stiffness, and flexibility. 1 Successful applications of such composite systems require well-dispersed nanotubes with good adhesion with the host matrix, which, unfortunately, is not easily realized. Processing is rendered difficult by poor solubility of SWNTs, and the exfoliation of nanotube bundles is a major challenge. Moreover, inherently weak nanotube-polymer interactions result in poor interfacial adhesion, which can lead to nanotube aggregation within the matrix. Although a variety of chemical routes have been investigated to achieve nanotube solubility, 2 most methods either shorten the nanotubes or induce excessive functionalities that disrupt the original structure of the tubes. Polymer grafting, to improve the nanotube-polymer interface, has mainly been achieved on acidtreated nanotubes, 3 which may result in partial destruction of the tubular framework.Here, we report the development of a novel approach to in situ composite synthesis by attachment of polystyrene (PS) chains to full-length pristine SWNTs without disrupting the original structure, based on an established anionic polymerization scheme. 4 The process requires no nanotube pretreatment and works well with asproduced SWNTs. Both debundling of SWNT ropes and polymer attachment were achieved in a single step, and well-defined composites with a homogeneous dispersion of nanotubes were obtained.SWNTs produced by the HiPCO process 5 were used without further purification, as purification procedures might introduce functionalities that hinder carbanion formation. Dried pristine SWNTs were dispersed by sonication in purified cyclohexane. secButyllithium in slight excess of a predetermined amount (to ensure the removal of protic impurities on the SWNT surface) was added to this dispersion and sonicated in a bath for an hour. A homogeneous light yellow solution was obtained to which styrene monomer was added and polymerized at 48°C for 2 h under sonication. Carbanions are introduced on the SWNT surface by treatment with the anionic initiator that serves to exfoliate the bundles and provide initiating sites for the polymerization of styrene ( Figure 1). The negatively charged nanotubes are separated from the bundles and stay in solution due to mutual electrostatic repulsion between individual tubes, which was confirmed by long-term solution homogeneity. When styrene is added, both free secbutyllithium and the nanotube carbanions initiate polymerization, resulting in an intimately mixed composite system. The polymerization was terminated using degassed n-butanol, and the composite was recovered by precipitation with methanol. The composites were soluble in organic solvents such as dimethyl formamide, chloroform, and tetrahydrofuran.Composites with matrix molecular weights ranging from 1600 to 100 000 g mol -1 and polydispersities of ∼1.02 (determined using size exclusion chromatog...

Carbon nanotubes (CNT) are attractive for use in fiber-reinforced composite materials due to their very high aspect ratio, combined with outstanding mechanical and electrical properties. Composite materials comprising a collagen matrix with embedded CNT were prepared by mixing solubilized Type I collagen with solutions of carboxylated single-walled carbon nanotubes (SWNT) at concentrations of 0, 0.2, 0.4, 0.8, and 2.0 weight percent. Living smooth muscle cells were incorporated at the time of collagen gelation to produce cell-seeded collagen-CNT composite matrices. Constructs containing 2.0 wt % CNT exhibited delayed gel compaction, relative to lower concentrations that compacted at the same rate as pure collagen controls. Cell viability in all constructs was consistently above 85% at both Day 3 and Day 7, whereas cell number in CNT-containing constructs was lower than in control constructs at Day 3, though statistically unchanged by Day 7. Scanning electron microscopy showed physical interactions between CNT and collagen matrix. Raman spectroscopy confirmed the presence of CNT at the expected diameter (0.85-1.30 nm), but did not indicate strong molecular interactions between the collagen and CNT components. Such collagen-CNT composite matrices may have utility as scaffolds in tissue engineering, or as components of biosensors or other medical devices.

Electrospinning is a versatile process used to prepare micro-and nano-sized fibers from various polymers dissolved in volatile solvents. In this report, cellulose and cellulose-heparin composite fibers are prepared from nonvolatile room temperature ionic liquid (RTIL) solvents by electrospinning. RTILs are extracted from the biopolymer fiber after the fiber formation using a cosolvent. Micron to nanometer sized, branched fibers were obtained from 10% (w/w) concentration of polysaccharide biopolymer in RTIL solution with an applied voltage of 15-20 kV. Cellulose-heparin composite fibers showed anticoagulant activity, demonstrating that the bioactivity of heparin remained unaffected even on exposure to a high voltage involved in electrospinning. IntroductionElectrospinning is a widely used simple technique to prepare micron-to nanometer-sized fibers of various polymers. 1 Electrospun fibers find applications in the making of fiber-reinforced composites, membranes, biosensors, electronic and optical devices, and as enzyme and catalytic supports. 2 The electrospinning technique is useful even in large-scale manufacturing environments such as textile industries. 3 A variety of novel tissue engineering scaffolds have been prepared by electrospinning various synthetic and natural biodegradable polymers. 4 However, the range of the polymers that can be electrospun is still limited by the availability of volatile solvents and their limited capability of dissolving polymers of different types. In this report, we conceive of making electrospun fibers from a relatively novel solvent system: room temperature ionic liquids (RTILs). RTILs have become more important in a wide array of chemical processes owing to their capability of dissolving both polar and nonpolar compounds. 5 Other desirable properties of RTILs include low or zero vapor pressure, low melting point, large liquidus range, high thermal stability, large electrochemical window, and recyclability. 6 Further, the properties of an RTIL can be modified by adjusting the structures of its anion or cation or both, and hence, RTILs are also called designer solvents. RTILs have proven to be a promising solvent system for the reactions involving biopolymers such as enzymes 7 and carbohydrates. [8][9][10] The successful application of RTILs in electrospinning could increase the number and types of materials from which the fibers can be made.Electrospinning can be considered as a derivative of the electrospray process, as both use high voltage to form a liquid jet. In the electrospinning process, a polymer solution is held by its surface tension at the end of a capillary. When a sufficiently large electric field is applied, the solution at the tip of the capillary elongates to form a cone because of coupled effects of the electrostatic repulsion within the charged droplet and attraction to a grounded electrode of opposite polarity. As the strength of the electric field is increased, the charge overcomes the surface tension, and a fine jet is ejected from the apex of the cone...

We present the fabrication and electrical characterization of a flexible hybrid composite structure using aligned multiwall carbon nanotube arrays in a poly(dimethylsiloxane) (PDMS) matrix. Using lithographically patterned nanotube arrays, one can make these structures at any length scale from submicrometer levels to bulk quantities. The PDMS matrix undergoes excellent conformal filling within the dense nanotube network, giving rise to extremely flexible conducting structures with unique electromechanical properties. We demonstrate its robustness against high stress conditions, under which the composite is found to retain its conducting nature. We also demonstrate that these structures can be utilized directly as flexible field-emission devices. Our devices show some of the best field-enhancement factors and turn-on electric fields reported so far.

) states that the film pinholes in the evaporated device give rise to the growth of dark spots. However, physical lamination by soft, conformable electrodes has an advantage in that film pinholes will not make contact with the conformable electrodes. Although we did not observe the symptoms of pinholes from the current density at low voltages of our evaporated devices, pinholes could be a source for growth of dark spots in evaporated devices. The ultimate goal of carbon nanotube research is the fabrication of functional macroscopic structures that can fully utilize the individual nanotube properties. Although ordered nanotube assemblies [1,2] are required for making integrated devices, simpler macroscopic constructs that reflect the intrinsic random fiber morphology of the nanotubes offer potential applications such as media for aerosol filtration. Although gas-phase filtration properties of nanotube macrostructures have never been studied, there have been reports on nanotube pore structure [3,4] and gas permeability of nanotube membranes. [5] In this communication, we present the first investigation of the use of multiwalled carbon nanotubes (MWNTs) as highly efficient, airborne particulate filter media. Filter efficiencies in excess of 99 % were achieved from films of MWNTs deposited onto cellulose fiber filters. The MWNT-coated filters exhibited low pressure drops and better filter quality than cellulose filters even for very low MWNT coverages (0.07 mg cm ±2 ). The MWNT filter performance was comparable to the highest efficiency HEPA (high efficiency particulate air) filter standards. Filtration of airborne particulate matter is essential in many instances, including air purifiers, respiratory protection equipment, and clean rooms. Fibrous filters are the most common type of filter media used for such applications, and are usually made from cellulose, glass, or polymer fibers. Fibrous aerosol filters do not work like sieves (that allow only particles smaller than the holes to pass through), rather, the mechanisms of interception of particles by the fiber surface, inertial impaction of a particle on a fiber, and Brownian diffusion of particles in the filter pores are mainly responsible for particle retention in the filter. These three mechanisms each dominate for different particle sizes. Fiber diameter is an important parameter that affects filter performance. Typically filters have fiber diameters on the order of 10 lm, therefore filters made from nanotubes with diameters in the range of 20±50 nm should display unique properties due to their small dimensions. Figure 1 shows scanning electron microscopy (SEM) images of the MWNT-coated filter morphology. We also thank George Karles, Vicki Baliga, Randall Baren, and Prof. P. M. Ajayan (RPI) for valuable assistance and fruitful discussions relating to this work. We are grateful to NanoTechLabs Inc., for the MWNT samples.

We demonstrate the one-step synthesis of a silica-gold nanocomposite by simultaneous hydrolysis and reduction of gold chloride. The aminophenyl group was used as a reducing agent, and the trimethoxy silane group acts a precursor for the formation of silica. The porous gold nanoparticles were formed by etching out the silica-gold nanocomposite by hydrofluoric acid. The electron diffraction of porous gold nanoparticles showed that the particle are polycrystalline with FCC structure. The silica-gold nanocomposite exhibited nonlinear current-voltage behavior, and the porous gold nanoparticles displayed linear current-voltage behavior.

A certain level of hairiness in yarn is generally acknowledged as unavoidable because of the practical limitations of mechanical processing machines. Spinners are therefore interested to know the effect of fiber properties on yarn hairiness when selecting suitable raw materials. The literature on parameters such as fiber fineness and short fibre percent reports contradictory trends, while the influence on hairiness of other param eters such as uniformity ratio and fiber quality index is not considered. In this paper, we have investigated the influence of fiber characteristics on the hairiness of cotton yarns.

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