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The physics underlying operation of cold (room-temperature) ionic-liquid emitter sources for use in propulsion shows that such thrusters are advantaged relative to all other “rockets” because of the direct scaling of power with emitter array density. Nanomaterials and their integration through nano- and microfabrication can propel these charged-particle sources to the forefront and open up new applications including mass-efficient in-orbit satellite propulsion and high-thrust-density deep-space exploration. Analyses of electrostatic, fluid-dynamic, and electrochemical limits all suggest that arrays of such ionic-liquid thrusters can reach thrust densities beyond most in-space propulsion concepts, with a limit on nanoporous thruster packing density of ∼1 μm due to ionic-liquid viscous flow and electrochemistry. Nanoengineered materials and manufacturing schemes are suggested for the implementation of microfabricated and nanostructured thruster arrays. [ABSTRACT FROM PUBLISHER]

The carbon nanotube comprised nanocomposite further provides multifunctionality via strain-and damage-sensing, to create a multifunctional high performance lattice for a variety of applications including patient-specific smart orthopedic braces. Multifunctionality of Nanoengineered Self-Sensing Lattices Enabled by Additive Manufacturing Enhanced mechanical performance across many parameters is achieved via nanoengineering of polymer lattices realized via fused filament fabrication additive manufacturing, as described in the article number 2200194 by Shanmugam Kumar and co-workers. [Extracted from the article]

An asymmetric supercapacitor, exploiting nm-scale conformal coating of conducting polymer (CP) on aligned carbon nanotubes (A-CNTs) as the negative electrode and ultra-high density A-CNTs as the positive electrode, has been developed. The conformal CP coating on the A-CNTs enhances charge storage while the aligned nanotube morphology provides straight and fast ion transport pathways. The A-CNT electrode, densified using a unique mechanical method, possesses high volumetric capacitance while preserving the aligned morphology to maintain the high power, provides an ideal positive electrode for the asymmetric supercapacitor. By complementary tailoring of the asymmetric electrodes, the device exhibits a wide operation voltage of 4 V with maximum energy and power densities of 82.8 Wh L −1 and 130.6 kW L −1 in volumetric performance. In this paper, a new method was introduced which is simple but can determine directly the energy storage efficiency of a supercapacitor cell. An equivalent circuit was developed to model the performance of each electrode and investigate the asymmetric design of the cell. [ABSTRACT FROM AUTHOR]

The flow interception efficiency, which provides a measure of the fraction of streamlines that intercept a porous collector, is an important parameter in applications such as particle capture, filtration, and sedimentation. In this work, flow permeation through a porous circular cylinder located symmetrically between two impermeable parallel plates is investigated numerically under different flow and geometrical conditions. A flow interception efficiency is defined and calculated based on the flow permeation rate for a wide range of system parameters. The dependencies on all physical variables can be captured in three dimensionless numbers: the Reynolds number, the Darcy number (ratio of permeability to the square of cylinder diameter), and the plate separation relative to the cylinder size. The flow interception efficiency is very low in the limit of unbounded cylinders but significantly increases by restricting the flow domain. The fluid permeation rate through the porous cylinder varies nonlinearly with the relative plate/cylinder spacing ratio, especially when the gap between the cylinder and the confining plates is small compared to the cylinder size. In general, the effects of the Reynolds number, the Darcy number, and confinement on the flow interception efficiency are coupled; however, for most practical cases it is possible to factorize these effects. For practical ranges of the Darcy number (D a 10 − 4, which means that the pore size is at least one order of magnitude smaller than the porous cylinder diameter), the interception efficiency varies linearly with D a, is independent of the Reynolds number at low Reynolds numbers (R e D10), and varies linearly with Reynolds number at higher flow rates. In addition to numerical solutions, theoretical expressions are developed for the flow interception efficiency in two limiting cases of confined and unbounded flow, based on modeling the system as a network of hydrodynamic resistances, which agree well with the numerical results. Furthermore, an expression for the drag coefficient on the porous cylinder is proposed as a function of the Darcy number which can be used in the limit of large plate/cylinder relative spacing. [ABSTRACT FROM AUTHOR]

Abstract: Intrinsic and scale-dependent properties of carbon nanotubes (CNTs) have led aligned CNT architectures to emerge as promising candidates for next-generation multifunctional applications. Enhanced operating regimes motivate the study of CNT-based aligned nanofiber carbon matrix nanocomposites (CNT A-CMNCs). However, in order to tailor the material properties of CNT A-CMNCs, porosity control of the carbon matrix is required. Such control is usually achieved via multiple liquid precursor infusions and pyrolyzations. Here we report a model that allows the quantitative prediction of the CNT A-CMNC density and matrix porosity as a function of number of processing steps. The experimental results indicate that the matrix porosity of A-CMNCs comprised of ∼1% aligned CNTs decreased from ∼61% to ∼55% after a second polymer infusion and pyrolyzation. The model predicts that diminishing returns for porosity reduction will occur after 4 processing steps (matrix porosity of ∼51%), and that >10 processing steps are required for matrix porosity <50%. Using this model, prediction of the processing necessary for the fabrication of liquid precursor derived A-CMNC architectures, with possible application to other nanowire/nanofiber systems, is enabled for a variety of high value applications. [Copyright &y& Elsevier]

Abstract: A hybrid composite architecture of carbon nanotubes (CNTs), advanced fibers and a matrix is described, from CNT synthesis and characterization through to standard mechanical and electrical laminate tests. Direct growth of aligned CNTs on the surface of advanced fibers in a woven fabric enables enhancement in multifunctional laminate performance, as demonstrated by a 69% increase in interlaminar shear strength and 106 (in-plane) and 108 (through-thickness) increases in laminate-level electrical conductivity. Processes developed include dip-coating of CNT growth catalyst and atmospheric-pressure chemical vapor deposition of dense aligned CNTs. A capillarity-driven mechanism is presented to explain the observed effective and uniform wetting of the aligned CNTs in the interior of the laminate by unmodified thermoset polymer resins. [Copyright &y& Elsevier]

The response of transversely point-loaded composite shells is investigated via the finite element method. The thin, circular cylindrical shells are hinged at a fixed distance apart on the straight edges and are free on the curved edges. Stability issues are considered, including nonlinear prebuckling, limit points, bifurcation, and postbuckling. In the finite element formulation, a novel technique is utilized to identify and traverse bifurcation points efficiently in the nonlinear elastic response. A classic shell buckling benchmark problem is solved here correctly for the first time; previous studies have found the isotropic shell to have a limit point, when, in fact, the shell bifurcates before reaching a limit point. Predicted results for graphite/epoxy laminated shells are in excellent agreement with measured load-deflection and mode-shape evolutions as previously reported. Two cases of extraordinarily good agreement between the data and model, particularly large-deflection asymmetric deformations modes through a bifurcation point and far into the postbuckling regime, clearly establish validated new benchmarks. Asymmetries in both directions of the shell plane, relative to the centrally applied point load, are discussed with regard to bifurcation and material couplings in the composite laminate. Asymmetric stress distributions are discussed in the context of composite damage resistance and previous experimental findings on atypical shell damage mode and extent. The influence of test fixture compliance is evaluated and briefly discussed. [ABSTRACT FROM AUTHOR]

Examines the response of composite structures to transverse loading through impact and quasi-static testing. Configuration of graphite/epoxy composite structures; Occurrence of a large-amplitude oscillatory impact loading response; Implications of composite structures for testing and design of damage-tolerant aerospace components.

A facile and novel surface activation approach using a strong-base solution enables the synthesis of carbon nanomaterials (CNMs) directly from bulk copper substrates via chemical vapor deposition. Amorphous carbon nanofibers (CNFs) were grown at temperatures as low as 250 °C, whereas at 600 °C the nanofibers were observed to be turbostratic, and at 700 °C turbostratic CNFs were synthesized together with a new aerogel-like 3D porous turbostratic CNM. A mechanistic model for the observed growth of CNMs from surface activated bulk copper is proposed. Our process is shown to yield conformal CNF growth on various complex-shaped copper substrates, such as meshes and wires, as well as copper-coated materials including carbon fibers and polymer films. [Display omitted] • Synthesis of carbon nanomaterials directly from the surface of a metallic substrate. • Catalytically active surface of bulk copper via basic aqueous solution treatment. • Catalyst nanoparticle formation via oxidation/roughening plus reduction steps. • Amorphous or turbostratic carbon nanofibers growth tunable by synthesis temperature. • Novel 3D "aerogel-like" turbostratic carbon by CVD, with sub-micron porosity. [ABSTRACT FROM AUTHOR]

Three-dimensional axisymmetric elasticity solutions for pull-out stresses in bonded anchors with spatially stiffness-varying adhesive are presented. A stiff rod embedded in a semi-infinite rigid half-space through an adhesive bondlayer, representing a general anchor problem is analyzed. The adhesive layer is considered to have a smoothly varying stiffness over embedded length. Two cases of particular engineering relevance are considered: (i) stiffness grading of the bondlayer to enhance performance while retaining the critical length characteristics of bonded anchors, and (ii) modulus reduction of the bondlayer representing adhesive degradation proximal to the loaded-end. Theoretical solutions are developed adopting a stress function approach in conjunction with a variational method that compare well with 3D axisymmetric finite element (FE) results. Both theoretical and FE results indicate that the maximum shear stress in the adhesive decreases over 60% for a graded bondlayer for the parameters considered here without warranting a longer embedment length. In contrast, the degraded bondlayer reduces shear stress peaks significantly but warrants a larger embedment length to enable shear-dominated stress-transfer, disadvantageously loading the embedded-end in tension. A design map showing the critical embedment length required for degraded bondlines as a function of fractional embedment length over which bondline is regarded to have degraded is presented. In addition, interfacial fracture behaviors of the tailored and degraded adhesive anchors were examined through FE analyses finding that the tailoring reduces the energy release rate and has the potential for enhancing damage tolerance. The findings of the study indicate that the stiffness-tailored and -degraded bondlayers significantly redistribute the stress field with concomitant influence on stress-transfer and interfacial debonding characteristics of bonded anchors. • 3D axisymmetric solution for pullout stresses in functionally graded adhesive anchor is proposed. • Analytical solutions for anchors with tailored and stiffness-degraded adhesives are developed. • Results indicate that maximum shear stress in the tailored adhesive of anchors decreases over 60%. • Shear stress reduction is higher for graded anchors with larger embedment length and thinner adhesive. • Larger length anchors can tolerate degradation retaining advantageous critical length characteristics. [ABSTRACT FROM AUTHOR]

Polymer-derived pyrolytic carbons (PyCs) are often desirable for low density high-temperature structural applications when they can be reinforced with high stiffness and strength fibers to address brittleness. Nanofibers, such as aligned carbon nanotubes (A-CNTs), can be an ideal reinforcement owing to their high mass-specific properties, and while modeling suggests that properties of A-CNTs at high volume fractions (i.e., 10–30 vol%) could yield significant enhancements, it is unknown how CNT confinement influences processing, as such materials have never been synthesized. Here, we report process development demonstrating the first successful fabrication of fully infused, void-free A-CNT carbon matrix nanocomposites (A/C-NCs) via polymer infiltration pyrolysis (PIP) that establishes a platform to study nanofiber-reinforced polymer-derived ceramics. The size of the average A/C-NC graphitic crystallites increases as CNT vol% increases up to 30 vol%, and the inter-layer separation of the PyC graphitic crystallites decreases, evidencing a nanoscale confinement effect observed in concert with increased mechanical performance. Vickers microhardness testing in the axial CNT direction of A/C-NCs shows agreement with prior data for low vol% CNTs in PyC and mechanical modeling, where specific hardness increases from ∼ 3.3 GPa/(g/cm3) for PyC to ∼ 6.7 GPa/(g/cm3) for 30 vol% A/C-NCs, demonstrating A/C-NCs as an advantaged superhard lightweight material. [Display omitted] • Fabrication of pyrolytic carbon composites with 1-30 vol% aligned carbon nanotubes. • Vacuum- and capillary-assisted infiltration of phenolic resin enable full infusion. • Four polymer infiltration pyrolysis cycles decrease porosity and increases density. • Graphitic crystallites in matrix are longer and denser with nanotube reinforcement. • Specific microhardness increases up to 30 vol% carbon nanotubes, rivaling diamond. [ABSTRACT FROM AUTHOR]

Hierarchical nanoengineered composite laminates were created with through-thickness-aligned carbon nanotube (A-CNT) reinforcement of unidirectional carbon (micro) fiber/epoxy laminae in their failure-prone interlaminar regions, forming a multiscale "nanostitched" architecture. Motivated by previous mechanical enhancements for similar nanostitched laminates in ambient environments, hygrothermal effects on the 3D strengthening and toughening mechanisms of nanostitched laminates are investigated here for the first time, focusing on standard open-hole compression (OHC) testing of quasi-isotropic laminates. We report that the hygrothermal conditions of −55 °C/DRY and 100 °C/DRY correspond to ultimate strength increases of 2.6% and 5.9%, respectively, for nanostitched laminates over the baseline; and, room temperature/50% relative humidity (RT/50% RH) and 100 °C/wet conditions exhibit no change in ultimate strength, suggesting correlation of positive nanostitch effects with increased polymer brittleness. Subsequently, damage progression in step-wise interrupted OHC loading for selected hygrothermal conditions (RT/50% RH and 100 °C/DRY) was performed in coordination with high-resolution ex situ X-ray micro-computed tomography for various load steps up to 98% of failure load. No clear differences due to nanostitch in the damage progression are found up to 98% of ultimate strength, suggesting that the reinforcement effect is associated with interlaminar strength at ultimate load, and not pre-ultimate damage. This study contributes first insights from high-resolution experimental mapping of nanostitched composite progressive damage subjected to hygrothermal conditions that may guide and inform mechanical enhancement approaches and improved progressive damage models. Future work is suggested to expand the environmental conditions considered, as well as visualize progressive damage nearer to failure to identify nanostitch effects on complex multimodal failure. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional reinforcement of woven advanced polymer–matrix composites using aligned carbon nanotubes (CNTs) is explored experimentally and theoretically. Radially-aligned CNTs grown in situ on the surface of fibers in a woven cloth provide significant three-dimensional reinforcement, as measured by Mode I interlaminar fracture testing and tension-bearing experiments. Aligned CNTs bridge the ply interfaces giving enhancement in both initiation and steady-state toughness, improving the already tough system by 76% in steady state (more than 1.5kJ/m2 increase). CNT pull-out on the crack faces is the observed toughening mechanism, and an analytical model is correlated to the experimental fracture data. In the plane of the laminate, aligned CNTs enhance the tension-bearing response with increases of: 19% in bearing stiffness, 9% in critical strength, and 5% in ultimate strength accompanied by a clear change in failure mode from shear-out failure (matrix dominated) without CNTs to tensile fracture (fiber dominated) with CNTs. [Copyright &y& Elsevier]

The transverse loading response of convex composite shell structures typical of aircraft fuselage sections was investigated, and the experimental work is reported. Important mechanisms in the response, particularly instabilities (buckling), were studied by investigation of the force-deflection response and the evolution of full-field deformation shapes. Quasi-static tests were conducted to simulate impact of convex shells. The specimens were laminated, cylindrical shell sections in [±45n/0n]s configurations, where n takes on values of 1, 2, and 3. The three structural parameters of radius, span, and thickness were varied according to a scaling relation and were chosen to represent approximate fuselage dimensions of general aviation and commercial transport aircraft. All specimens were evaluated for damage with dye-penetrant enhanced x radiography and sectioning after mechanical testing. The structural response changes both quantitatively and qualitatively for the different shell geometries and was categorized into three types based on the existence of the instability transition characteristics such as deformation shapes. The presence of the instability becomes more likely for deeper, thinner specimens where the ratio of membrane stiffness to bending stiffness is higher. This can be characterized by a structural parameter involving geometric and material factors. The majority of the specimens showed no damage, but the limited experimental evidence did show plate-like damage occurring in the shell specimens before any instability. Suggestions for further work to extend these findings are made. [ABSTRACT FROM AUTHOR]

The link between manufacturing variability and the resulting environmental impact is an understudied topic. We connect manufacturing variability and greenhouse gas emissions impact through the reality of overdesign. Specifically, this study takes the case of manufacturing Carbon Fiber Reinforced Polymers, which has high manufacturing variability relative to conventional manufacturing processes and is of interest due to its light-weighting potential. Through the use of a process-based cost model, including uncertainty , the cost and energy required to fabricate a representative composite part is modeled. The model then connects to a fuel-consumption model of a Boeing 787 which allows the estimation of lifetime fuel savings. Manufacturing variability is taken as an input to the model, which allows the model to estimate the effect of variability on both the cost and energy requirements. We find that manufacturing variability has a significant impact on both part cost and energy requirements, being the fourth most impactful variable in our model for both these performance measures. Under our assumptions, reducing the coefficient of variation of the mechanical properties from 14% to 9% reduces production costs and energy by 12.3 and 11.8%, respectively. In addition, due to the weight savings, we estimate that over the lifetime of a Boeing 787 this drop in variability saves 8.3 kton of fuel, which has a present value of 3.6 million USD and would prevent 21.9 kton carbon dioxide from entering the atmosphere. [ABSTRACT FROM AUTHOR]

Synthesis of low‐dimensional carbon nanomaterials such as carbon nanotubes (CNTs) is a key driver for achieving advances in energy storage, computing, and multifunctional composites, among other applications. Here, we report high‐yield thermal chemical vapor deposition (CVD) synthesis of CNTs catalyzed by reagent‐grade common sodium‐containing compounds, including NaCl, NaHCO3, Na2CO3, and NaOH, found in table salt, baking soda, and detergents, respectively. Coupled with an oxidative dehydrogenation reaction to crack acetylene at reduced temperatures, Na‐based nanoparticles have been observed to catalyze CNT growth at temperatures below 400 °C. Ex situ and in situ transmission electron microscopy (TEM) reveal unique CNT morphologies and growth characteristics, including a vaporizing Na catalyst phenomenon that we leverage to create CNTs without residual catalyst particles for applications that require metal‐free CNTs. Na is shown to synthesize CNTs on numerous substrates, and as the first alkali group metal catalyst demonstrated for CNT growth, holds great promise for expanding the understanding of nanocarbon synthesis. [ABSTRACT FROM AUTHOR]

A carbon nanotube (CNT) electrothermal heater is shown to enable consolidation of high-temperature thermoplastic composite laminates for the first time, leveraging the CNT film's stable operation in air above 500 °C. This out-of-oven (OoO) conductive heating method without applied pressure (i.e., vacuum bag only) is used to process aerospace-grade carbon fiber/polyether ether ketone (PEEK) composite prepreg, which requires heating to 380–400 °C and is normally processed with significant applied pressure (∼2 ± 1 MPa) via a hot-press or autoclave. Micro-computed tomography verifies that the processed laminates exhibit low porosity of ≤0.1 vol%, which more than meets the desired target of <1 vol% voids. A range of thermophysical (including degree of crystallinity) and mechanical (interfacial shear strength and bending) tests show equal or improved properties vs. both hot press and autoclave processing. The CNT heaters in the OoO approach are observed to most closely match the desired processing cycle, with the observed benefit of being the only process studied to hit the target range of % crystallinity. The energy consumption comparison indicates a 98% energy saving of the CNT heater compared to the hot press. This study demonstrates autoclave-quality processing of high-temperature thermoplastic composite structures via conformal CNT heaters that can be fabricated efficiently and effectively in an out-of-autoclave (OoA) process. [ABSTRACT FROM AUTHOR]

Abstract Thin-ply carbon fiber laminates have exhibited superior mechanical properties, including higher initiation and ultimate strength, when compared to standard thickness plies and enable greater flexibility in laminate design. However, the increased ply count in thin-ply laminates also increases the number of ply-ply interfaces, thereby increasing the number of relatively weak and delamination-prone interlaminar regions. In this study, we report the first experimental realization of aligned carbon nanotube interlaminar reinforcement of thin-ply unidirectional prepreg-based carbon fiber laminates, in a hierarchical architecture termed ‘nanostitching’. We synthesize a baseline effective standard thickness laminate using multiple thin-plies of the same orientation to create a ply block, and we find an ∼15% improvement in the interlaminar shear strength via short beam shear (SBS) testing for thin-ply nanostitched samples when compared to the baseline. This demonstrates a synergetic strength effect of nanostitching (∼5% increase) and thin-ply lamination (∼10% increase). Synchrotron-based computed tomography of post mortem SBS specimens suggests a different damage trajectory and mode of damage accumulation in nanostitched thin-ply laminates, notably the complete suppression of delaminations in the nanostitched region. Finite element predictions of damage progression highlight the complementary nature of positive thin-ply and nanostitching effects that are consistent with an ∼15% improvement in Modes I and II interlaminar fracture toughness due to the aligned carbon nanotubes at the thin-ply interfaces. [ABSTRACT FROM AUTHOR]

Abstract The exceptional static and dynamic physical properties of poly(urethane-urea) (PUU) elastomers make them prime candidates for impulsive loading structural applications, such as blast protection coatings. Since the theoretical physical properties of carbon nanotubes (CNTs) are among the best for any currently known material, a number of previous studies explored the use of CNTs as nanoscale fillers to enhance the properties of PUU nanocomposites. However, due to the challenges inherent in dispersing CNTs in a PUU matrix and the resulting random orientation of the CNTs, these previous works observed marginal improvements in physical properties, and were unable to establish clear structure-property relations. Here, we report the synthesis of aligned-CNT (A-CNT) reinforced PUU polymer nanocomposites (A-PNCs) by infusing A-CNT forests with a stoveable PUU, and establish process-structure-property relations that quantify the contribution of CNT confinement on the PUU mechanical response. This stoveable process was achieved using blocked isocyanate which prevented polymerization until the blocks were removed with heat. PUUs of two distinct compositions were explored: one with 40 wt% hard-segment content (PUU211) and the other with 66 wt% hard-segment content (PUU541). Thermogravimetric analysis indicates that A-CNTs enhance the thermal stability of the hard-segment phase in PUU A-PNCs at 340 °C by up to 45% over the baseline PUUs. Atomic force microscopy reveals that the elongated nanophase hard-segment formations along the CNT axis observed only in the nanocomposites were of similar characteristic size to the average inter-A-CNT spacing (∼70 nm), indicating a strong influence of A-CNTs on the size and orientation of hard-segment nanophases, as corroborated via small angle X-ray scattering. Nanoindentation testing reveals that PUU A-PNCs possess significant elastic anisotropy, and exhibit enhanced longitudinal effective indentation moduli of ∼460 MPa (>3 × that of the PUU211 baseline) and ∼1350 MPa (∼1.5 × that of the PUU541 baseline) for PUU211 and PUU541 nanocomposites, respectively. This difference in magnitude of CNT reinforcement efficacy indicates that CNT confinement leads to significant hard-segment re-organization in the PUU211 A-PNCs, whereas the interconnected network of hard-segments in the PUU541 is affected by CNT templating to a lesser extent. Dynamic nanoindentation testing results are consistent with these interpretations, where longitudinally-loaded PUU211 A-PNCs are found to exhibit a >3 × enhancement in storage modulus at 1 Hz of ∼730 MPa, whereas the longitudinally-loaded PUU541 A-PNCs exhibit a slightly enhanced storage modulus enhancement at 1 Hz of 2190 MPa (∼1.5 × that of the PUU541 baseline). Reinforcement of PUUs with A-CNTs is a promising way to tune the physical properties of the PNCs; higher A-CNT packing densities, where the inter-CNT spacing could approach the nanophase characteristic diameter, could further enhance the PUU performance in ballistic protection applications. [ABSTRACT FROM AUTHOR]

Abstract Next-generation composite manufacturing processes are needed to overcome several limitations of conventional manufacturing processes (e.g., high energy consumption). Here we explore, via experiments and modeling, the characteristics of the newly developed out-of-oven (OoO) curing technique that cures a composite laminate via resistive heating of a carbon nanotube film. When compared to oven curing of an aerospace-grade out-of-autoclave (OoA) carbon fiber prepreg advanced composite laminate, the OoO curing reduces energy consumption by over two orders of magnitude (14 vs. 0.1 MJ). Thermophysical and mechanical tests including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), short beam shear (SBS), and ex-situ and in-situ double-edge notch tension (DENT) indicate that the physical and mechanical properties of OoO-cured laminates are equivalent to those of oven-cured (baseline) laminates. In addition to energy savings, the OoO curing process has the potential to reduce part-to-part variations through improved spatiotemporal temperature control. [ABSTRACT FROM AUTHOR]

Desalination technologies can increase potable water supplies worldwide. One possible approach, capacitive deionization (CDI), could prove optimal for brackish water treatment. At present, CDI development has largely focused on increasing salt adsorption capacity and desalination rates of materials and devices. In addition to these metrics, ultimately, optimizing salt rejection and throughput will be essential. In this work, we present a framework for the design of flow-between CDI cells for maximum salt rejection. We developed a model that is dependent on device specific parameters (system volume, flow rate, inlet and outlet water quality), to generalize the design of a cell for any given requirement. We showed that decreasing the advection-diffusion Péclet number and increasing the aspect ratio of the electrode compared to the channel space yield the highest salt rejection. In addition, tuning the cycle frequency time for salt rejection instead of complete electrode charging can yield faster water production rates and optimal salt rejection. These modeling results were validated through experimental prototypes that made use of vertically-aligned carbon nanotube (VA-CNT) electrodes. This framework to maximize salt rejection can be extended to a multitude of porous electrodes used in flow-between CDI devices. [ABSTRACT FROM AUTHOR]

For the first time, micro-scale digital image correlation (μDIC) is investigated for measurement of strain fields in hierarchical fiber-reinforced composites. The methodology is developed on an exemplary alumina fiber/epoxy composite laminate with aligned carbon nanotubes (A-CNTs) grown on fibers. Utilizing environmental scanning electron microscopy and nano-scale random speckle patterns, sufficient precision is achieved to detect the influence of the A-CNTs on the deformation field around the fibers. Debonded regions at the fiber/matrix interface with openings as small as 35 nm could be detected. μDIC could identify the propagation of the debonded region based on the non-linear increase of the opening. The image correlation uncertainty in the displacement analysis is estimated to be below 5 nm. The experimental results are validated by computational analysis performed on the region of interest. For this, an advanced model with two scales of reinforcement (microscopic fibers and nanotubes) and boundary conditions taken from the experiment is used. As verified by the model, A-CNTs are found to constrain matrix deformation in their longitudinal direction. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding compositematrix in the limit ofmaximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging.We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11millimeters in thickness that significantly increases the effective elasticmodulus and strength at exceptionally lowvolume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency.These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction. [ABSTRACT FROM AUTHOR]

Hybrid hierarchical carbon-nanotube (CNT)-based composites, such as radially-aligned CNT arrays grown onto microfiber filaments, have significant potential to expand the performance and functionality of fiber reinforced composites. Here, a novel method for high-yield growth of aligned CNTs on aerospace-grade carbon fibers (CFs) is demonstrated at the composite level for the first time. Fuzzy carbon fiber reinforced plastics (fuzzy CFRP) unidirectional composites with >60% microfiber volume fraction are fabricated via vacuum-assisted resin infusion of CNT-grafted tows using an unmodified aerospace-grade epoxy. Preservation of microfiber tensile modulus and strength are demonstrated by longitudinal composite tensile testing, consistent with single-fiber tensile tests. Fiber–matrix interface strength is also unchanged by the CNT growth as revealed through continuously-monitored fiber fragmentation tests. Taken together, the results provide needed new composite-level understanding of hierarchical structural composite laminates and motivate future work on structural CF composite laminates with integrated multifunctionality and improved interlaminar and intralaminar performance. [ABSTRACT FROM AUTHOR]

Aligned nanoscale fibers have been shown to provide inter and intralaminar reinforcement of fiber-reinforced polymer composites. In one hierarchical architecture, aligned carbon nanotubes (CNTs) grown on advanced microfibers in a woven ply creates a 'fuzzy fiber' reinforced plastic (FFRP) laminate. Here, the mechanisms of Mode I fracture toughness enhancement for such laminates are elucidated experimentally by varying the type of epoxy and aligned CNT length. Reinforcement effectiveness is found to vary from reduced initiation toughness to over 100% increase in steady-state fracture toughness, depending upon the interlaminar fracture mechanisms. Fracture-surface morphology investigations reveal that interlaminar toughness enhancement is significantly less for an aerospace infusion resin than that for a much tougher hand lay-up marine epoxy. Long (∼20 micron) aligned CNTs add significant toughness in steady state (>1kJ/m2 increase for marine epoxy) via CNT pullout and by driving the crack through tortuous paths around and through microfiber bundles/tows, whereas shorter CNTs produce less toughening (or even reduced toughness in aerospace epoxy), which is attributed to increased microfiber-matrix cohesive failure. These findings reveal the multi-scale nature of the aligned-CNT reinforced composite ply interface, and the mechanisms at work at the micro and nanoscales that influence the macroscopic behavior. These new insights provide impetus for using aligned CNTs to tailor microfiber polymer composites by adjusting microfiber orientation, steering cracks through tortuous paths, and maximizing fracture surface area through both microfiber and nanofiber pullout. [ABSTRACT FROM AUTHOR]

Abstract: Conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) conformally coated aligned carbon nanotubes (PEDOT/A-CNTs) were developed and investigated as the active material for supercapacitor electrode applications and the results were compared to those of non-coated CNTs as well as that of PEDOT coated randomly packed CNTs. The electrochemical performance of the electrodes was evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS). The results revealed that the PEDOT conformally coated and densified (5% volume fraction, V f) A-CNTs exhibit a specific volumetric capacitance of 84.0F/cm3, much higher compared to the non-coated and non-densified A-CNTs (1% V f) that had a specific capacitance of only 3.9F/cm3. Ion insertion/de-insertion processes in the PEODT coating layers are observed in impedance spectra for the PEDOT-coated A-CNT electrodes at rates that are not limiting to cell performance relative to ion transport through the channels formed by the PEDOT/A-CNTs. Specific energy and power densities of 11.8Wh/l and 34.0kW/l, respectively, were obtained for these nano-tailored electrodes, with high capacitance retention compared with those of PEDOT coated random CNTs. [Copyright &y& Elsevier]

Abstract: The superior electrical conductivity and parallel ion pathways formed by aligned carbon nanotubes (A-CNTs) make them attractive for the nanoporous electrodes of supercapacitors. To achieve high volumetric energy and power densities, the low volume density of the as-synthesized A-CNT (<5%) should be densified. In this paper, we demonstrate a mechanical densification method that allows the density of A-CNTs to be tuned precisely over a broad range while preserving the straight ion pathway between A-CNTs. The supercapacitors fabricated from 40% volumetric fraction (Vf) of A-CNTs as the electrodes with the thickness of 0.8mm exhibit a power density of 25kWL−1 (50kWkg−1), which is much higher than that of the A-CNTs electrodes with similar thickness fabricated by other methods and that of activated carbon electrodes. [Copyright &y& Elsevier]

In situ X-ray synchrotron radiation computed tomography (SRCT) of carbon fiber composite laminates reveals the first-ever qualitative and quantitative comparisons of 3D progressive damage effects introduced by two mechanical enhancement technologies: aligned nanoscale fiber interlaminar reinforcement and thin-ply layers. The technologies were studied individually and in combination, using aerospace-grade unidirectional prepreg standard-thickness ('std-ply') and thin-ply composite laminates. The relatively weak interlaminar regions of the laminates were reinforced with high densities of aligned carbon nanotubes (A-CNTs) in a hierarchical architecture termed 'nanostitching'. Quasi-isotropic double edge-notched tension (DENT) laminates were tested and simultaneously 3D-imaged via SRCT at various load steps, revealing a progressive 3D network of damage micro-mechanisms that were segmented according to modality and extent. For load steps of 0%, 70%, 80%, and 90% of baseline ultimate tensile strength (UTS), intralaminar matrix cracking and fiber/matrix interfacial debonding are found to be the dominant damage mechanisms, common to all laminate types. For both std-ply and thin-ply, nanostitched laminates had qualitatively and quantitatively similar matrix damage modality and extent compared to the baseline laminates through 90% UTS, including relatively few delaminations, despite an ~9% increase in std-ply nanostitched UTS over the std-ply baseline. Complementary finite element-based modeling of damage predicts greater delamination extent in std-ply vs. thin-ply laminates that manifests only between 90% and 100% UTS, offering an explanation for the observed positive nanostitch effect in the std-ply, which is known to be more susceptible to delamination formation and growth than the thin-ply laminates. Thin-ply, with and without nanostitch, intrinsically suppresses matrix damage, as expected from past work and evidenced here by 6.5X less overall matrix damage surface area vs. std-ply baseline laminates averaged over all load steps. These findings contribute new insights from high-resolution experimental mapping of composite damage states that can guide and inform mechanical enhancement approaches and improved damage models. [ABSTRACT FROM AUTHOR]

• Measurements of thermal diffusivity and conductivity of single-walled carbon nanotube (SWCNT) forests with biaxial mechanical densification. • Anomalous increase of thermal diffusivity with increase in volume fraction beyond threshold. • New thermal conduction path for densified forest of single-walled carbon nanotubes. Needs of a material for thermal management in reduced-sized electronic devices drive single-walled carbon nanotubes (SWCNTs) to be one of the most promising candidates due to their excellent thermal properties. Many numerical and experimental studies have reported on understanding thermal properties of the SWCNT for thermal device applications. In the present study, thermal diffusivity and conductivity of SWCNT forests in the axial direction with various volume fractions of SWCNTs were measured by laser flash analysis technique and the same properties of an individual SWCNT were derived. The volume fraction was controlled up to 25 vol% by biaxial mechanical densification which maintains SWCNT alignment. While the thermal diffusivity of SWCNT forests was almost constant, it increased when the volume fraction was higher than 17 vol%, suggesting that some SWCNTs, which did not serve as a thermal path in the case of lower volume fraction, were connected with the other SWCNTs. Through the increase of inferred thermal conductivity equivalent to an individual SWCNT after 17 vol%, we also realized that the enhancement of volume fraction of SWCNT forest diminished thermal boundary resistance in good agreement with the tendency inferred from the reported numerical data. [ABSTRACT FROM AUTHOR]