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In-plane permeability of small area (100 × 50 mm) alumina fiber woven fabrics grafted with aligned carbon nanotubes (CNT) was quantified by placing them in series with a glass mat of known permeability during a flow experiment. The methodology was first validated on a reference woven textile. Permeability values matched those obtained by a direct method within a margin of ±15%. Permeabilities of radial-aligned (short CNT, SCNT) and so-called ‘Mohawk’ (long CNT, LCNT) morphologies of the CNT-grafted samples were then measured and compared to the non-grafted alumina, showing a decrease attributed to a change in local textile structure as assessed in previous studies. Unsaturated permeability decreased by 77% after SCNT- and 88% after LCNT-grafting, while saturated permeability further decreased by 90% and 93%, respectively. The high ratio of unsaturated to saturated permeability (in the range of 1.14 – 2.89) implies that capillary wicking contributes largely to the impregnation of CNT-grafted fabrics., Aerospace Manufacturing Technologies

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Aligned carbon nanotube (A-CNT) arrays that were densified via patterning and mechanical instability are placed at the resin-rich ply-ply interface in aerospace-grade advanced composite laminates for z-direction reinforcement. The buckled A-CNT arrays display a wavelike folding shape and maintain such a shape after being transferred between the plies. The buckled A-CNT reinforced laminates were tested under short-beam shear (SBS) and double edge-notched tension (DENT) and are found to have a 7% increase in SBS strength and 25% increase in DENT strength, respectively. Both scanning electron microscope imaging and micro-computed tomography reveal that the buckled A-CNT arrays suppress delamination and force damage into the intralaminar region. Furthermore, they introduce multiscale and mixed mode reinforcement mechanisms. The findings demonstrate good potential for using mechanical instability in nanofiber arrays to densify them and tune their shapes, as well as the promising reinforcement effect from buckling-densified A-CNT arrays. Future work to change the pattern (e.g., patterning feature shape and interspacing between features), as well as synchrotron radiation computed tomography-based in situ testing is planned., National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (award DMR-0819762)

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Aligned carbon nanotube (A-CNT) arrays that were densified via patterning and mechanical instability are placed at the resin-rich ply-ply interface in aerospace-grade advanced composite laminates for z-direction reinforcement. The buckled A-CNT arrays display a wavelike folding shape and maintain such a shape after being transferred between the plies. The buckled A-CNT reinforced laminates were tested under short-beam shear (SBS) and double edge-notched tension (DENT) and are found to have a 7% increase in SBS strength and 25% increase in DENT strength, respectively. Both scanning electron microscope imaging and micro-computed tomography reveal that the buckled A-CNT arrays suppress delamination and force damage into the intralaminar region. Furthermore, they introduce multiscale and mixed mode reinforcement mechanisms. The findings demonstrate good potential for using mechanical instability in nanofiber arrays to densify them and tune their shapes, as well as the promising reinforcement effect from buckling-densified A-CNT arrays. Future work to change the pattern (e.g., patterning feature shape and interspacing between features), as well as synchrotron radiation computed tomography-based in situ testing is planned.

© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim This study is focused on carbon nanostructures (CNS), including both carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), reinforcement of medical-grade polyetheretherketone (PEEK), and in vitro bioactivity for biomedical structural applications. CNS/PEEK scaffolds and bulk specimens, realized via fused filament fabrication (FFF) additive manufacturing, are assessed primarily in the low-strain linear-elastic regime. 3D printed PEEK nanocomposites are found to have enhanced mechanical properties in all cases while maintaining the desired degree of crystallinity in the range of 30–33%. A synergetic effect of the CNS and sulfonation toward bioactivity is observed—apatite growth in simulated body fluid increases by 57% and 77%, for CNT and GNP reinforcement, respectively, doubling the effect of sulfonation and exhibiting a fully-grown mushroom-like apatite morphology. Further, CNT- and GNP-reinforced sulfonated PEEK recovers much of the mechanical losses in modulus and strength due to sulfonation, in one case (GNP reinforcement) increasing the yield and ultimate strengths beyond the (non-sulfonated) printed PEEK. Additive manufacturing of PEEK with CNS reinforcement demonstrated here opens up many design opportunities for structural and biomedical applications, including personalized bioactivated surfaces for bone scaffolds, with further potential arising from the electrically conductive nanoengineered PEEK material toward smart and multifunctional structures.

© 2021 The Royal Society of Chemistry. The advantageous intrinsic and scale-dependent properties of aligned nanofibers (NFs) and their assembly into 3D architectures motivate their use as dry adhesives and shape-engineerable materials. While controlling NF-substrate adhesion is critical for scaled manufacturing and application-specific performance, current understanding of how this property evolves with processing conditions is limited. In this report, we introduce substrate adhesion predictive capabilities by using an exemplary array of NFs, aligned carbon nanotubes (CNTs), studied as a function of their processing. Substrate adhesion is found to scale non-monotonically with process time in a hydrocarbon environment and is investigated via the tensile pull-off of mm-scale CNT arrays from their growth substrate. CNT synthesis follows two regimes: Mode I ('Growth') and Mode II ('Post-Growth'), separated by growth termination. Within 10 minutes of post-growth, experiments and modeling indicate an order-of-magnitude increase in CNT array-substrate adhesion strength (∼40 to 285 kPa) and effective elastic array modulus (∼6 to 47 MPa), and a two-orders-of-magnitude increase in the single CNT-substrate adhesion force (∼0.190 to 12.3 nN) and work of adhesion (∼0.07 to 1.5 J m-2), where the iron catalyst is found to remain on the substrate. Growth number decay in Mode I and carbon accumulation in Mode II contribute to the mechanical response, which may imply a change in the deformation mechanism. Predictive capabilities of the model are assessed for previously studied NF arrays, suggesting that the current framework can enable the future design and manufacture of high-value NF array applications.

Performance challenges as electronics continue to scale down motivate searches for new interconnect materials. In a recent report in Matter, Lipatov and coworkers demonstrate that MXene may be a candidate for interconnects by measuring conductivity and breakdown current density of Ti[subscript 3]C[subscript 2]T[subscript x].

Separators in energy storage devices such as batteries and supercapacitors are critical elements between the much-researched anodes and cathodes. Here we present a new “structural separator” comprised of electrically-insulating aligned alumina nanotubes, which realizes a structural, or mechanically robust, function in addition to allowing charge transfer. The polymer nanocomposite structural separator is demonstrated in a supercapacitor cell and also as an interface reinforcement in an aerospace-grade structural carbon fiber composite. Relative to a polymeric commercial separator, the structural separator shows advantages both electrically and structurally: ionic conductivity in the supercapacitor cell is doubled due to the nanotubes disrupting the semi-crystallinity in the polymer electrolyte, and the structural separator creates an interface that is 50% stronger in the advanced composite. In addition to providing direct benefits to existing energy storage devices, the structural separator is best suited to multifunctional structural energy storage applications.

We envision the next generation composite materials as hierarchically structured down to the nanoscale. The importance of nanoscale features has been long recognized from studies of naturally occurring composites. Thanks to their hierarchical organization spanning through multiple scales they show exemplary resilience to failure combined with a plethora of different functions. In man-made composites, nanostructure can be introduced through modifications of the matrix, interfaces and fibers. Here we review our research efforts in the field of nano-engineered composites, focusing on the mechanical performance of fiber-reinforced plastics modified with carbon nanotubes. Our research is a combination of experimental and computational studies.

Tomography derived nanoscale 3D morphological information is combined with modeling and simulation to explain anisotropy and scaling of experimental mechanical, thermal, and electrical properties of aligned carbon nanotube polymer composites., National Institute of Standards and Technology (U.S.) (Grant 70NANB10H193), United States. National Aeronautics and Space Administration (Grant NNX17AJ32G), United States. Office of Naval Research (Grant N00014-13-1-0213)

Multilayered multi‐material interfaces are encountered in an array of fields. Here, enhanced mechanical performance of such multi‐material interfaces is demonstrated, focusing on strength and stiffness, by employing bondlayers with spatially‐tuned elastic properties realized via 3D printing. Compliance of the bondlayer is varied along the bondlength with increased compliance at the ends to relieve stress concentrations. Experimental testing to failure of a tri‐layered assembly in a single‐lap joint configuration, including optical strain mapping, reveals that the stress and strain redistribution of the compliance‐tailored bondlayer increases strength by 100% and toughness by 60%, compared to a constant modulus bondlayer, while maintaining the stiffness of the joint with the homogeneous stiff bondlayer. Analyses show that the stress concentrations for both peel and shear stress in the bondlayer have a global minimum when the compliant bond at the lap end comprises ≈10% of the bondlength, and further that increased multilayer performance also holds for long (relative to critical shear transfer length) bondlengths. Damage and failure resistance of multi‐material interfaces can be improved substantially via the compliance‐tailoring demonstrated here, with immediate relevance in additive manufacturing joining applications, and shows promise for generalized joining applications including adhesive bonding. Keywords: Composite interfaces, 3D printing, compliance tailoring, Interface tailoring, multilayered materials, Abu Dhabi National Oil Company (Award EX2016‐000010)