We report a simple process to solubilize high weight fraction single-wall carbon nanotubes in water by the nonspecific physical adsorption of sodium dodecylbenzene sulfonate. The diameter distribution of nanotubes in the dispersion, measured by atomic force microscopy, showed that even at 20 mg/mL ∼63 ± 5% of single-wall carbon nanotube bundles exfoliated into single tubes. A measure of the length distribution of the nanotubes showed that our dispersion technique reduced nanotube fragmentation.

Aerogels are ultralight, highly porous materials typically fabricated by subjecting a wet-gel precursor to critical-pointdrying (CPD) or lyophilization (freeze-drying) in order to remove background liquid without collapsing the network. Microscopically, aerogels are composed of tenuous networks of clustered nanoparticles, and the materials often have unique properties, including very high strength-to-weight and surface-area-to-volume ratios. To date most aerogels are fabricated from silica [1] or pyrolized organic polymers. [2,3] Practical interest in the former stems from their potential for ultralight structural media, radiation detectors, and thermal insulators, [1] and in the latter from their potential for battery electrodes and supercapacitors. [2] In this paper we investigate the properties of a new class of aerogels based on carbon nanotubes (CNTs). Small-diameter CNTs, such as single-and few-wall CNTs, are exciting candidates for electrically conducting aerogels. Individually, these nanotubes are extraordinarily stiff [4] and their electrical conductivity can be very large. [4,5] Furthermore, ensembles of such nanotubes are useful aerogel precursors: they form electrically percolating networks at very low volume fractions [6] and elastic gels in concentrated suspensions through van der Waals interaction mediated cross-linking. [7,8] Here we report the creation of CNT aerogels from aqueousgel precursors by CPD and freeze-drying. CNT aerogels have been produced previously as intermediate phases during the process of drawing nanotube fibers [9] from a furnace and during the process of making sheets from multiwall CNT forests.[10] By contrast, our aerogels were derived directly from CNT networks in suspension, and we could readily manipulate the network properties as a result. The flexibility afforded by this process enabled us to control CNT concentration, to utilize optimized CNT dispersion processes, [11] to reinforce the networks with, for example, polyvinyl alcohol (PVA), and to infiltrate or backfill them with polymeric fluids. Here we describe these CNT aerogels and the processing methodologies used to synthesize them, and we characterize their electrical and mechanical properties. The CNT aerogels supported thousands of times their own weight after PVA-reinforcement, and, depending on processing conditions, their electrical conductivity ranged as high as ca. 1 S cm -1. Although our starting chemical vapor deposition (CVD) nanotube material contained single-and few-wall CNTs (the latter being predominantly double-wall CNTs, DWNTs), the dispersion and preparation processes employed here are directly applicable to pure single-wall CNTs (SWNTs).[11] CNT aerogel electrical and structural properties are also expected to be similar to pure SWNT samples because the electrical [12] and tensile [13] properties of bulk SWNTs and DWNTs are comparable. Images of typical critical-point-dried aerogels are seen in Figure 1. Unreinforced aerogels were fragile, but strong enough to permit careful handling. Reinforceme...

Premelting is the localized loss of crystalline order at surfaces and defects at temperatures below the bulk melting transition. It can be thought of as the nucleation of the melting process. Premelting has been observed at the surfaces of crystals but not within. We report observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy. The crystals are equilibrium close-packed, three-dimensional colloidal structures made from thermally responsive microgel spheres. Particle tracking reveals increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. Our observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and atomic-scale crystals.

(M w = 70 000, Aldrich) and poly(styrene sulfonate) (PSS, M w = 500 000, Polysciences), according to the procedure by Barker et al [20]. The PSS layer was sandwiched between two PAH layers.Tetramethylorthosilicate (TMOS, Aldrich) was hydrolyzed under acidic conditions (molar ratio of TMOS/HCl/H 2 O was 1:1:55.6) for 30 min. The hydrolyzed solution was diluted with H 2 O in a ratio of 1:100. The diluted solution was then introduced into a two-compartment chamber separated by the nanonozzle-array film. The reaction was carried out in the presence of a direct-current electric field (80 V cm ±1 ), with the cathode immersed in the chamber facing the sharp end and the anode facing the large end. In this arrangement, the direction of EOF was from the sharp end to the large end. The reaction proceeded for 15 min, after which the nanonozzle array was taken out, rinsed thoroughly with water and dried. [2] radio-frequency shielding, and field-emission sources. [3,4] Recently, single-walled carbon nanotubes (SWNTs) have emerged as an attractive option for conductive composite materials. Their small size, large aspect ratio, and high conductivity make it possible to create conductive composites at very low filling concentrations and with smaller inhomogeneities than can be achieved with larger particles. Lower filling fractions imply smaller perturbations of bulk physical properties, such as strength and optical transparency, as well as lower cost. We describe here a simple procedure for making conductive SWNT±epoxy composites that result in exceptionally low threshold concentrations with minimal modification of the epoxy matrix material. Thus far, studies on the conductivity of SWNT±polymer composites [5±24] have reported low thresholds at volume fractions ranging from [7]~1 10 ±4 to several percent, [10] in some cases outperforming current technologies. Many aspects of the problem, however, are poorly understood and optimization remains elusive. The starting formulations of dispersed SWNTs frequently contain dense aggregates of nanotubes, as well as amorphous carbon and metallic impurities that can persist throughout processing and affect performance. Stabilizing the nanotubes in suspension can reduce aggregates, but introduces other problems. For example, covalent stabilization modifies the intrinsic SWNT conductivity, while steric stabilization can degrade contacts between nanotubes, and generally introduces additional impurities into the matrix. In addition, while welldispersed SWNTs typically have a higher length-to-diameter ratio than aggregates, which is important for obtaining low thresholds, [25] interactions between particles also contribute to the formation of percolating networks. Network formation through particle chaining, in particular, can be a key factor in COMMUNICATIONS

The nuclear lamina is a network of structural filaments, the A and B type lamins, located at the nuclear envelope and throughout the nucleus. Lamin filaments provide the nucleus with mechanical stability and support many basic activities, including gene regulation. Mutations in LMNA, the gene encoding A type lamins, cause numerous human diseases, including the segmental premature aging disease Hutchinson-Gilford progeria syndrome (HGPS). Here we show that structural and mechanical properties of the lamina are altered in HGPS cells. We demonstrate by live-cell imaging and biochemical analysis that lamins A and C become trapped at the nuclear periphery in HGPS patient cells. Using micropipette aspiration, we show that the lamina in HGPS cells has a significantly reduced ability to rearrange under mechanical stress. Based on polarization microscopy results, we suggest that the lamins are disordered in the healthy nuclei, whereas the lamins in HGPS nuclei form orientationally ordered microdomains. The reduced deformability of the HGPS nuclear lamina possibly could be due to the inability of these orientationally ordered microdomains to dissipate mechanical stress. Surprisingly, intact HGPS cells exhibited a degree of resistance to acute mechanical stress similar to that of cells from healthy individuals. Thus, in contrast to the nuclear fragility seen in lmna null cells, the lamina network in HGPS cells has unique mechanical properties that might contribute to disease phenotypes by affecting responses to mechanical force and misregulation of mechanosensitive gene expression.laminopathy ͉ mechanics ͉ nucleus ͉ photobleaching ͉ micropipette aspiration H utchinson-Gilford progeria syndrome (HGPS) is a rare genetic disease that causes segmental premature aging in children. HGPS patients are mentally normal, but fail to reach full stature and experience hair loss, thin wrinkled skin, and joint stiffness, and usually die in their early teens of cardiovascular disease or stroke (1, 2). Mutations in LMNA, the gene encoding lamins A and C, were recently identified as the cause of HGPS (3, 4). Lamins A and C are major constituents of the nuclear lamina, the meshwork of nuclear intermediate filaments that support the inner nuclear membrane and also extend throughout the nucleus (5). Other major components of the nuclear lamina are lamins B1 and B2, which are encoded by two distinct genes (6). Most HGPS cases are caused by a de novo single-point mutation (G608G; GGCϾGGT) in one allele of LMNA (3, 4). This substitution activates a cryptic splice site in exon 11, which affects only the lamin A protein, and the mutant allele produces an alternatively spliced truncated variant of the lamin A mRNA lacking the 3Ј terminal 150 nt of exon 11. The resulting polypeptide, ⌬50 lamin A, has an internal deletion of 50 residues in the C-terminal tail domain and also lacks an endoproteolytic cleavage site required for normal processing of the lamin A precursor (3, 4, 7). HGPS patient fibroblasts often are characterized by numerous nuclear defe...

Lightweight materials that are both highly compressible and resilient under large cyclic strains can be used in a variety of applications. Carbon nanotubes offer a combination of elasticity, mechanical resilience and low density, and these properties have been exploited in nanotube-based foams and aerogels. However, all nanotube-based foams and aerogels developed so far undergo structural collapse or significant plastic deformation with a reduction in compressive strength when they are subjected to cyclic strain. Here, we show that an inelastic aerogel made of single-walled carbon nanotubes can be transformed into a superelastic material by coating it with between one and five layers of graphene nanoplates. The graphene-coated aerogel exhibits no change in mechanical properties after more than 1 × 10(6) compressive cycles, and its original shape can be recovered quickly after compression release. Moreover, the coating does not affect the structural integrity of the nanotubes or the compressibility and porosity of the nanotube network. The coating also increases Young's modulus and energy storage modulus by a factor of ∼6, and the loss modulus by a factor of ∼3. We attribute the superelasticity and complete fatigue resistance to the graphene coating strengthening the existing crosslinking points or 'nodes' in the aerogel.

We investigate the viscoelastic properties of an associating rigid rod network: aqueous suspensions of surfactant stabilized single wall carbon nanotubes (SWNTs). The SWNT suspensions exhibit a rigidity percolation transition with an onset of solidlike elasticity at a volume fraction of 0.0026; the percolation exponent is 2.3+/-0.1. At large strain, the solidlike samples show volume fraction dependent yielding. We develop a simple model to understand these rheological responses and show that the shear dependent stresses can be scaled onto a single master curve to obtain an internanotube interaction energy per bond approximately 40k(B)T. Our experimental observations suggest SWNTs in suspension form interconnected networks with bonds that freely rotate and resist stretching. Suspension elasticity originates from bonds between SWNTs rather than from the stiffness or stretching of individual SWNTs.

We report thermal conductivity measurements of purified single-wall carbon nanotube ͑SWNT͒ epoxy composites prepared using suspensions of SWNTs in N-N-Dimethylformamide ͑DMF͒ and surfactant stabilized aqueous SWNT suspensions. Thermal conductivity enhancement is observed in both types of composites. DMF-processed composites show an advantage at SWNT volume fractions between ϳ 0.001 to 0.005. Surfactant processed samples, however, permit greater SWNT loading and exhibit larger overall enhancement ͑64± 9͒% at ϳ 0.1. The enhancement differences are attributed to a tenfold larger SWNT/solid-composite interfacial thermal resistance in the surfactant-processed composites compared to DMF-processed composites. The interfacial resistance is extracted from the volume fraction dependence of the thermal conductivity data using effective medium theory. ͓C.