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By excluding metals from synthesis, growth of carbon nanostructures via unreduced oxide nanoparticle catalysts offers wide technological potential. We report new observations of the mechanisms underlying chemical vapor deposition (CVD) growth of fibrous carbon nanostructures from zirconia nanoparticles. Transmission electron microscope (TEM) observation reveals distinct differences in morphological features of carbon nanotubes and nanofibers (CNTs and CNFs) grown from zirconia nanoparticle catalysts versus typical oxide-supported metal nanoparticle catalysts. Nanofibers borne from zirconia lack an observable graphitic cage consistently found with nanotube-bearing metal nanoparticle catalysts. We observe two distinct growth modalities for zirconia: (1) turbostratic CNTs 2–3 times smaller in diameter than the nanoparticle localized at a nanoparticle corner, and (2) nonhollow CNFs with approximately the same diameter as the nanoparticle. Unlike metal nanoparticle catalysts, zirconia-based growth should proceed via surface-bound kinetics, and we propose a growth model where initiation occurs at nanoparticle corners. Utilizing these mechanistic insights, we further demonstrate that preannealing of zirconia nanoparticles with a solid-state amorphous carbon substrate enhances growth yield., United States. Army Research Office (Contract W911NF-13-D-0001)

Flexible capacitive pressure sensors fabricated with nanocomposites were experimentally characterized and results compared with simulations from analytical modeling. Unlike traditional diaphragm silicon pressure sensors, the flexible nanocomposite sensors present a linear response over a large pressure range due to the changes in the volume of the dielectric that cause the pressure inside the dielectric cavity to change. Several devices with different geometries were used and the model results compare well with the experimental data. Sensitivities ranging from 2.5- 20 fF/kPa were obtained and the devices dynamic response show a dual behavior, i.e., response time of the sensor during a pressure decreasing step is lower than for a pressure increasing step. This comportment is explained by the viscoelastic behavior of the PDMS-based nanocomposites used for fabrication of the capacitive sensor electrodes., Fundação para a Ciência e a Tecnologia (FCT)

We demonstrate the layer-by-layer (LbL) assembly of polyelectrolyte multilayers (PEM) on three-dimensional nanofiber scaffolds. High porosity (99%) aligned carbon nanotube (CNT) arrays are photolithographically patterned into elements that act as textured scaffolds for the creation of functionally coated (nano)porous materials. Nanometer-scale bilayers of poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/SPS) are formed conformally on the individual nanotubes by repeated deposition from aqueous solution in microfluidic channels. Computational and experimental results show that the LbL deposition is dominated by the diffusive transport of the polymeric constituents, and we use this understanding to demonstrate spatial tailoring on the patterned nanoporous elements. A proof-of-principle application, microfluidic bioparticle capture using N-hydroxysuccinimide-biotin binding for the isolation of prostate-specific antigen (PSA), is demonstrated., National Science Foundation (U.S.) (Award DMR-0819762)

The landmark theoretical properties of low dimensional materials have driven more than a decade of research on carbon nanotubes (CNTs) and related nanostructures. While studies on isolated CNTs report behavior that aligns closely with theoretical predictions, studies on cm-scale aligned CNT arrays (>10[superscript 10] CNTs) oftentimes report properties that are orders of magnitude below those predicted by theory. Using simulated arrays comprised of up to 105 CNTs with realistic stochastic morphologies, we show that the CNT waviness, quantified via the waviness ratio (w), is responsible for more than three orders of magnitude reduction in the effective CNT stiffness. Also, by including information on the volume fraction scaling of the CNT waviness, the simulation shows that the observed non-linear enhancement of the array stiffness as a function of the CNT close packing originates from the shear and torsion deformation mechanisms that are governed by the low shear modulus (∼1 GPa) of the CNTs., Massachusetts Institute of Technology. Nano-engineered Composite aerospace STructures (NECST) Consortium, United States. Army Research Office (Contract W911NF-07-D-0004), United States. Army Research Office (Contract W911NF-13-D-0001), United States. Dept. of Defense. National Defense Science & Engineering Graduate Fellowship Program

The effect of nanofiber proximity on the mechanical behavior of nanofiber arrays with volume fractions (V f) from 1% to 20% was quantified via nanoindentation of an aligned carbon nanotube (A-CNT) array. The experimental results show that the indentation modulus for A-CNT arrays has a highly non-linear scaling with the CNT V f, leading to modulus enhancements of up to ∼600× at V f = 20%. Modeling illustrates that the origin of the highly non-linear trend with V f is due to the minimum inter-CNT spacing, which is shown to be more than an order of magnitude larger than the graphitic spacing., United States. Army Research Office (Contract No. W911NF- 07-D-0004), United States. Army Research Office (Contract No. W911NF-13-D-0001), Scientific and Technical Research Council of Turkey (2214-International Research Fellowship Programme), NECST Consortium

Materials comprising carbon nanotube (CNT) aligned nanowire (NW) polymer nanocomposites (A-PNCs) are emerging as next-generation materials for use in aerospace structures. Enhanced operating regimes, such as operating temperatures, motivate the study of CNT aligned NW ceramic matrix nanocomposites (A-CMNCs). Here we report the synthesis of CNT A-CMNCs through the pyrolysis of CNT A-PNC precursors, thereby creating carbon matrix CNT A-CMNCs. Characterization reveals that the fabrication of high strength, high temperature, lightweight next-generation aerospace materials is possible using this method. Additional characterization and modeling are planned., Comment: 7 pages, 5 figures, conference proceeding

The average inter-wire spacing in aligned nanowire systems strongly influences both the physical and transport properties of the bulk material. Because most studies assume that the nanowire coordination is constant, a model that provides an analytical relationship between the average inter-wire spacings and measurable physical properties, such as nanowire volume fraction, is necessary. Here we report a continuous coordination number model with an analytical relationship between the average nanowire coordination, diameter, and volume fraction. The model is applied to vertically aligned carbon nanotube (VACNT) and nanofiber (VACNF) arrays, and the effective nanowire coordination number is established from easily accessible measures, such as the nanowire spacing and diameter. VACNT analysis shows that the coordination number increases with increasing nanowire volume fraction, leading the measured inter-CNT spacing values to deviate by as much as 13% from the spacing values predicted by the typically assumed hexagonal packing. VACNF analysis suggests that, by predicting an inter-fiber spacing that is within 6% of the reported value, the continuous coordination model outperforms both square and hexagonal packing in real nanowire arrays. Using this model, the average inter-wire spacing of nanowire arrays can be predicted, thus allowing more precise morphology descriptions, and thereby supporting the development of more accurate structure–property models of bulk materials comprised of aligned nanowires., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-07-D-0004)

A new approach for the fabrication of flexible pressure sensors based on aligned carbon nanotubes (A-CNTs) is described in this paper. The technology is suitable for blood pressure sensors that can be attached to a stent-graft and deployed during an endovascular aneurysm repair (EVAR) procedure. Given the specifications of EVAR, the device should be foldable (extremely flexible) and characterized by a (very small) profile that integrates with the stent-graft cross section. A-CNTs embedded in a flexible substrate of polydimethylsiloxane (PDMS), a transparent, nontoxic and biocompatible silicone elastomer, are used to fabricate elements of the capacitive sensors. Fabricated prototypes validate our approach and show that CNTs/PDMS layered composites can be used to create highly flexible pressure sensors., Fundação para a Ciência e a Tecnologia (MIT-PT/EDAM-EMD/0007/2008), NECST Consortium

Nanoyapıların kontrolu? yeni malzemelerin örneğin karbon nanotu?p (CNT) esaslıfiberler, 3D nano-mu?hendislik kompozitleri ve metamalzemeleri de içeren geniş bir grupmalzemelerin özelliklerini anlamak ve öngörmek için önemlidir. Bu çalışmada dikeyyönelimli ve su?rekli karbon nanotu?pler (A-CNT) ile gu?çlendirilmiş polimernanokompozitler (A-PNC) yu?ksek hacim oranı ile hazırlanmıştır. Bu işlem yeni birmekanik sıkıştırma tekniği kullanılarak yapılmıştır. Bu sayede yu?ksek hacim yu?zdesinde(Vf) hazırlanması istenilen literatu?rde yaygın olarak çalışılmış rastgele yönelimliCNT'ler ile gu?çlendirilmiş polimer nanokompozitlere (R-PNC) özgu? olan dispersiyon vedağılım problemi ile karşılaşılmamıştır. PNC'lerin yapılarının kontrol edilmesi mekaniközelliklerinin yorumlanması açısından çok kritiktir ve taramalı elektron mikroskobu ilePNC'lerin yapısıyla alakalı çok detaylı bilgi alınabilir. A-PNC'lerin mekaniközelliklerinin performanslarının karşılaştırılması amacıyla R-PNC'lerde u?retilmiştir.Elde edilen sonuçlara göre A-PNC'lerin modu?l değeri CNT aksisi yönu?ndemaksimumdur ve bu zamana kadar literatu?rde rapor edilen değerler arasında su?reklidikey yönelimli A-CNT'lerin ve yapısal kullanımından dolayı en yu?ksektir. A-PNC'lerinelektriksel özellikleri ise farklı hacim yu?zdesinde ve eksenlerinde ölçu?lmu?ştu?r. Eldeedilen sonuçlara göre A-PNC'lerin elektriksel iletkenlikleri CNT aksisi yönu?ndeliteratu?r değerlerinden 10 kat daha yu?ksek olduğu göru?lmu?ştu?r. Üretilen A-PNC'lerpek çok ileri malzeme alanlarında uygulama bulabilecektir. Bu çalışmada u?ç adetuygulama incelenmiş ve karakterize edilmiştir. Control of nanostructure morphology is essential for predicting properties of a broadarray of new materials, including CNT-based fibers, 3D nano-engineered composites,and metamaterials. In this study, an aligned-CNT polymer composite (A-PNC) isfabricated using a high-performance thermoset and anisotropic mechanical propertiesquantified and discussed relative to morphology of the samples. High volume fraction(Vf) continuous A-PNCs are fabricated via a novel mechanical densification technique.Controlling morphology of the PNCs is critical for interpreting the mechanical propertyresults, and both scanning electron microscopy (SEM) provide detailed investigation ofPNC morphology herein. Randomly oriented PNCs (R-PNCs) are also fabricated forcomparison of unaligned vs. aligned reinforcement. Modulus values of A-PNCs are thehighest reported for epoxy resin, due to the CNT alignment at all volume fractions forcomparisons with literature. The electrical property measurements of A-PNCs wereperformed for low and high volume fractions in different directions such as axial andtransverse. The results for electrical conductivity of A-PNCs found to be approximately10 times higher than the reported values in the literature in CNT axial direction. Thefabricated A-PNCs can found applications as advanced materials in many fields. In thisstudy, three different applications of A-PNCs is fabricated, studied and characterized. 220

Author Manuscript 2011 July 22, Solid materials, such as silicon, glass, and polymers, dominate as structural elements in microsystems including microfluidics. Porous elements have been limited to membranes sandwiched between microchannel layers or polymer monoliths. This paper reports the use of micropatterned carbon-nanotube forests confined inside microfluidic channels for mechanically and/or chemically capturing particles ranging over three orders of magnitude in size. Nanoparticles below the internanotube spacing (80 nm) of the forest can penetrate inside the forest and interact with the large surface area created by individual nanotubes. For larger particles (>80 nm), the ultrahigh porosity of the nanotube elements reduces the fluid boundary layer and enhances particle–structure interactions on the outer surface of the patterned nanoporous elements. Specific biomolecular recognition is demonstrated using cells (≈10 μm), bacteria (≈1 μm), and viral-sized particles (≈40 nm) using both effects. This technology can provide unprecedented control of bioseparation processes to access bioparticles of interest, opening new pathways for both research and point-of-care diagnostics., National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant P41 EB002503), United States. Department of State (Fulbright Science and Technology Award)

Tailorable anisotropic intrinsic and scale-dependent properties of carbon nanotubes (CNTs) make them attractive elements in next-generation advanced materials. However, in order to model and predict the behavior of CNTs in macroscopic architectures, mechanical constitutive relations must be evaluated. This study presents the full stiffness tensor for aligned CNT-reinforced polymers as a function of the CNT packing (up to ∼20 vol. %), revealing noticeable anisotropy. Finite element models reveal that the usually neglected CNT waviness dictates the degree of anisotropy and packing dependence of the mechanical behavior, rather than any of the usually cited aggregation or polymer interphase mechanisms. Combined with extensive morphology characterization, this work enables the evaluation of structure-property relations for such materials, enabling design of aligned CNT material architectures., NECST Consortium, United States. Army Research Office (Contract No. W911NF- 07-D-0004), United States. Army Research Office (Contract No. W911NF-13-D-0001), United States. National Aeronautics and Space Administration (NASA Space Technology Research Fellowship Grant No. NNX11AN79H), National Science Foundation (U.S.) (Grant No. CMMI-1130437)

Non-destructive evaluation techniques can offer viable diagnostic and prognostic routes to mitigating failures in engineered structures such as bridges, buildings and vehicles. However, existing techniques have significant drawbacks, including poor spatial resolution and limited in situ capabilities. We report here a novel approach where structural advanced composites containing electrically conductive aligned carbon nanotubes (CNTs) are ohmically heated via simple electrical contacts, and damage is visualized via thermographic imaging. Damage, in the form of cracks and other discontinuities, usefully increases resistance to both electrical and thermal transport in these materials, which enables tomographic full-field damage assessment in many cases. Characteristics of the technique include the ability for real-time measurement of the damage state during loading, low-power operation (e.g. 15 °C rise at 1 W), and beyond state-of-the-art spatial resolution for sensing damage in composites. The enhanced thermographic technique is a novel and practical approach for in situ monitoring to ascertain structural health and to prevent structural failures in engineered structures such as aerospace and automotive vehicles and wind turbine blades, among others., Linda and Richard Hardy Fellowship, MIT-Spain/La Cambra de Barcelona

Author Manuscript 2011 October 8, Recent advances in fabricating controlled-morphology vertically aligned carbon nanotubes (VA-CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter-VA-CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA-CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA-CNTs to further enhanced performance., United States. Army Research Office (Grant W911NF-07-1-0452), National Institutes of Health (U.S.) (Grant R01-EY018387-02), United States. Multidisciplinary University Research Initiative