Capillary forces arising during the evaporation of liquids from dense carbon nanotube arrays are used to reassemble the nanotubes into two-dimensional contiguous cellular foams. The stable nanotube foams can be elastically deformed, transferred to other substrates, or floated out to produce free-standing macroscopic fabrics. The lightweight cellular foams made of condensed nanotubes could have applications as shock-absorbent structural reinforcements and elastic membranes. The ability to control the length scale, orientation, and shape of the cellular structures and the simplicity of the assembly process make this a particularly attractive system for studying pattern formation in ordered media.C ellular patterns arise frequently in nature on length scales ranging from microscopic to macroscopic as a result of spatially periodic and random perturbations (1-5); examples range from the morphogenesis of embryos to patterns in coffee stains. A film of aligned carbon nanotubes represents a unique, yet unstudied type of system in which pattern formation could arise from the collapse and reassembly of highly ordered, anisotropic, elastic, nanoscale rods with remarkable properties. We report the creation of intriguing two-dimensional cellular foams by the evaporation of liquids from such nanotube films (6, 7). Shrinkage and crack formation in the films caused by strong capillary forces during evaporation and strong van der Waals interactions between condensed nanotubes (8) result in the formation of visually striking, stable cellular patterns and contiguous foams. Patterns formed by nanotube aggregates differ significantly from other polygonal crack patterns (9-13) because of the inherent dimensions, strength, and flexibility of the nanotubes (14, 15). The length scale, orientation, and shape of the cellular structures can be controlled by varying the nanotube height and the rate of evaporation of liquid and by patterning the nanotube array. The nanotube foams also can be floated out to produce free-standing macroscopic films. The outstanding properties of the constituent nanotubes may lead to applications for these structures as shock-absorbent reinforcements and in nanofiltration devices. Materials and MethodsFabrication of Multiwalled Nanotube Arrays. Vertically aligned multiwalled nanotube (MWNT) arrays (Fig. 1a) were grown on rigid silica substrates by using a chemical vapor deposition process (7) based on the decomposition of ferrocene and xylene. Patterned MWNT arrays were fabricated by patterning silica (SiO 2 ) on Si(100) (6) and exposing these patterned substrates to a mixture of ferrocene and xylene at 800°C. Nanotubes grow selectively on the patterned silica regions (6).Formation of Cellular Carbon Nanotube Foams. The aligned nanotube arrays were oxidized in an oxygen plasma created in a glow discharge chamber (Harrick Scientific, Ossining, NY) at room temperature and 0.6 torr (1 torr ϭ 133 Pa) pressure for Ϸ10 min. Characterization of the oxidized MWNTs by Raman spectroscopy confirmed the preservation of the...

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...

Creating hybrid nanostructures consisting of disparate nanoscale blocks is of interest for exploring new types of quantum device architectures.Here, we demonstrate the novel anchoring of monolayer-protected gold nanoclusters of 1−3 nm diameter to sidewalls of carbon nanotubes (CNTs) via hydrophobic interactions between octanethiols capping the nanoclusters and acetone-activated CNT surfaces. Such molecularly interlinked hybrid nanoblocks are attractive for building biocompatible nanodevices.

Temperature-programmed desorption experiments show that acetone chemisorbs on nanotubes while physisorption occurs on graphite. Computed high binding energies for chemisorption using hybrid quantum mechanical and semiempirical calculations are in good agreement with the experimental thermal desorption data. The strong chemical interactions between acetone and the nanotube surface are established as being due to the effects of curvature and topological defects.