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...

This paper describes a strategy for functionalizing graphite and carbon nanotube surfaces with multilayered polymeric films. Poly(amphiphiles) adsorb noncovalently onto these surfaces from aqueous solutions, due to hydrophobic interactions. The covalent attachment of a second polymer layer to this initial adsorbed layer results in the formation of a cross-linked polymer bilayer; additional layers can be deposited by the covalent or electrostatic attachment of polyelectrolytes. We used these multilayered polymer films to mediate the attachment of gold nanoparticles to graphite, single-walled nanotube (SWNT), and multiwalled nanotube (MWNT) surfaces. This approach provides a convenient method for attaching other nanostructures, biological molecules, or ligands to carbon nanotubes.

We present an approach to the synthesis of biofunctionalized block copolymer nanoparticles based on ring‐opening metathesis polymerization; these nanoparticles may serve as novel scaffolds for the multivalent display of ligands. The nanoparticles are formed by the self‐assembly of diblock copolymers composed of a hydrophobic block and a hydrophilic activated block that can be functionalized with thiolated ligands in aqueous media. The activated block enables control over the orientation of the displayed ligands, which may be sugars, peptides, or proteins engineered to contain cysteine residues at suitable locations. The nanoparticle diameter can be varied over a wide range through changes in the composition of the block copolymer, and biofunctionalization of the nanoparticles has been demonstrated by the attachment of a peptide previously shown to inhibit the assembly of anthrax toxin. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 928–939, 2006

Controlled introduction of defects into aligned multiwalled carbon nanotubes (MWCNTs) was achieved by time-dependent plasma etching. The subsequent morphological changes in MWCNTs have been fingerprinted using Raman and x-ray photoelectron spectroscopy, by which induction of defects by functionalization was confirmed. We found that the introduction of defects along the nanotube body affects all Raman vibrational modes. A systematic analysis of the relationship between D, D′, D*, and G modes leads us to believe that no one peak can be used as an accurate standard for estimation of defects in nanotubes.

This article describes the formation and characterization of self‐assembled nanoparticles of controlled sizes based on amphiphilic block copolymers synthesized by ring‐opening metathesis polymerization. We synthesized a novel hydrophobic derivative of norbornene; this monomer could be polymerized using Grubbs' catalyst [Cl2Ru(CHPh)(PCy3)2] forming polymers of controlled molecular weight. We synthesized amphiphilic block copolymers of controlled composition and showed that they assemble into nanoparticles of controlled size. The nanoparticles were characterized using dynamic light scattering and transmission electron microscopy. Tuning the composition of the block copolymer enables the tuning of the diameters of the nanoparticles in the 30‐ to 80‐nm range. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3352–3359, 2004