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Single-walled carbon nanotubes were dispersed in an aqueous medium using surfactants and filtered to make entangled networks, called buckypaper (BP), and the Raman spectra of BP samples revealed the degree of entanglement and residual surfactant content. The temperature dependence of the G-band peak shift in the BP was found to depend on the reduction in residual surfactant and nanotube oxidation. The electrical conductivity was improved after removing the surfactant and increasing the nanotube alignment, although the temperature dependence of electrical resistivity still followed a variable range hopping conduction behavior. The mechanical properties were affected by the degree of entanglement, alignment, and residual surfactant content, and tensile properties were found to improve with the reduction in surfactant and enhancement of alignment. [ABSTRACT FROM AUTHOR]

Buckypaper is a free-standing carbon nanotube (CNT) sheet used to improve handling and manufacturability of CNT-based nanocomposites. To enhance the mechanical properties and manufacturing efficiency of buckypaper, polymeric binders, such as poly(vinyl alcohol) (PVA), are often added into the CNT network during the manufacturing process. This paper describes a physics-based model to predict the elastic modulus of PVA-enhanced buckypaper and a statistical approach to calibrate and adjust the model based on physical experiments. Compared to the physics-based model alone, the hybrid model can provide more accurate predictions for the Young's modulus of PVA-enhanced buckypaper and give a 95 % confidence interval on the prediction. One of the inputs for this model, the average length of carbon nanotubes, was calibrated using maximum likelihood estimation (MLE). The bias of this model was adjusted by estimating a bias function. Both the calibration parameter and adjustment function were estimated from a set of experimental measurements. The improvement in making a prediction was validated by comparing the performance of the physics-based model, statistical model, and statistics-enhanced physics model at a new experiment point. The hybrid model provides a more accurate prediction than either the physics-based model or statistical model does. This model calibration technique provides an effective tool for nanomanufacturing process design and material property prediction. [ABSTRACT FROM AUTHOR]

Process monitoring and quality control is essential for continuous manufacturing processes of carbon nano- tube (CNT) thin sheets or buckypaper. Raman spectroscopy is an attractive inline quality characterization and quantification tool for nanomanufacturing because of its nondestructive nature, fast data acquisition speed, and ability to provide detailed material information. However, there is signal-dependent noise buried in the Raman spectra, which reduces the signal-to-noise (S/N) ratio and affects the accuracy, efficiency, and sensitivity for Raman spectrum-based quality control approaches. In this paper, a signal analysis model with signal-dependent noise for Raman spectroscopy is developed and validated based on experimental data. The wavelet shrinkage method is used for denoising and improving the S/N ratio of raw Raman spectra. Based on the validated signal-noise relationship, a novel generalized wavelet shrinkage approach is introduced to remove noise in all wavelet coefficients by applying individual adaptive wavelet thresholds. The effectiveness of this method is demonstrated using both simulation and experimental case studies of inline Raman monitoring of continuous buckypaper manufacturing. The proposed method allows for a significant reduction of Raman data acquisition time without much loss of S/N ratio, which inherently enables Raman spectroscopy for inline monitoring and control for continuous nanomanufacturing processes. [ABSTRACT FROM AUTHOR]

This article demonstrates novel fabrication of the first interdigital 3D microsupercapacitors (MSC) using area-selective atomic layer deposition (ASALD). A unique ASALD process was developed to selectively deposit pseudocapacitive titanium oxide and nitride layers on one or both interdigitated vertically aligned carbon nanotube (VACNT) electrodes to form asymmetric or symmetric 3D MSC devices. This work compliments and expands on our previously published article exploring ALD of thin conformal coatings of TiO 2 and TiN on VACNTs for 3D MSCs. Further, we demonstrate the first use of Aerosol Jet Printing, a recently developed additive manufacturing technique, to enable ASALD patterning of 3D MSC devices by direct writing of PMMA inhibitors on and adjacent to relatively thick nanostructured electrodes. The synthesis, characterization, and performance evaluation of ASALD TiN-TiO 2 -VACNT 3D MSCs described herein provides a novel approach for manufacturing of new nanocomposite based electrochemical energy storage microdevices that could be integrated as an on-chip power source for portable electronics. Results indicated the symmetric ASALD TiN(100)-TiO 2 (100)-VACNT MSC (6.55 mF cm−2) exhibited nearly two orders of magnitude (94×) improvement in specific capacitance compared to the uncoated VACNT MSC (0.07 mF cm−2), significantly improving energy density (3.28 mWhr cm−2) while maintaining high power density (2.34 mW cm−2). • First interdigital 3D MSC fabricated using area-selective atomic layer deposition. • First use of Aerosol Jet Printing to enable ASALD patterning of 3D MSC devices. • ASALD TiN(100)-TiO 2 (100) coating enabled 94x greater C sp vs. bare VACNT MSC. [ABSTRACT FROM AUTHOR]

This paper reports on a study of carbon nanotube (CNT) thin film, or buckypaper (BP), integrated into carbon fiber (CF) prepreg composites to create hybrid composite materials with high CNT content. The autoclave process of manufacturing hybrid composite laminates was investigated to gain an understanding of nano/micro dual-scale resin flow characteristics. The study found that resin bleeding along the through-thickness direction was inhibited due to extra-low permeability and high resin absorbing capacity of the BP. Resin matrix-impregnated BP layers were much thicker than dry pristine BP due to high resin absorbency and swelling effects. The BP/unidirectional carbon fiber (UD-CF) hybrid composites with local fiber volume fraction of 61.46 vol% in CF ply and local CNT volume fraction of 26.57 vol% in BP layer, had a tensile strength of 2519 ± 101 MPa and modulus of 149 ± 18 GPa. The dramatic improvements in both in-plane and through-thickness electrical conductivities demonstrate potential for both structural and multifunctional applications of the resultant hybrid composites. [ABSTRACT FROM AUTHOR]

Buckypapers are thin sheets produced from Carbon NanoTubes (CNTs) that effectively transfer the exceptional mechanical properties of CNTs to bulk materials. To accomplish a sensible tradeoff between effectiveness and efficiency in predicting the mechanical properties of CNT buckypapers, a multi-fidelity analysis appears necessary, combining costly but high-fidelity physical experiment outputs with affordable but low-fidelity Finite Element Analysis (FEA)-based simulation responses. Unlike the existing multi-fidelity analysis reported in the literature, not all of the input variables in the FEA simulation code are observable in the physical experiments; the unobservable ones are the latent variables in our multi-fidelity analysis. This article presents a formulation for multi-fidelity analysis problems involving latent variables and further develops a solution procedure based on nonlinear optimization. In a broad sense, this latent variable-involved multi-fidelity analysis falls under the category of non-isometric matching problems. The performance of the proposed method is compared with both a single-fidelity analysis and the existing multi-fidelity analysis without considering latent variables, and the superiority of the new method is demonstrated, especially when we perform extrapolation. [ABSTRACT FROM AUTHOR]

This paper presents a new method for quantifying uncertainty in the predictions of a nanomaterial computational model to account for variability in the constituent nanostructure properties and characterization measurements. The stiffness of a buckypaper-polymer composite is predicted using a micromechanics model. The model requires from the user as inputs the nanostructure properties, including the diameter, length, and curvature distribution of the carbon nanotubes which shows large variability. The current characterization techniques used to describe these dimensions are subject to considerable measurement error. We propose a constrained nonlinear programming approach for quantification of raw material variability and its impact on the property prediction of buckypaper-polymer composites. The uncertainty quantification method is useful for decision making to predict probability that the quality characteristic of the final part will satisfy design constraints. A case study based on data from a real buckypaper manufacturing process was used to illustrate the approach. It is shown that modeling the correlation between nanostructure properties using a multivariate distribution rather than independent univariate distributions is important to accurately quantify the effect of these properties on the final-part property. [ABSTRACT FROM AUTHOR]

Compared with the ordinary vertically aligned carbon nanotube (VACNT) arrays, the carbon nanotubes in spinnable VACNT arrays have better alignment, higher density, and narrower diameter distribution. The synthesis of spinnable VACNT arrays is sensitive to the reaction condition and the repeatable prepared of spinnable VACNT arrays still need improvement. In this paper, spinnable VACNT arrays were grown by chemical vapor deposition from C2H2/Ar using Fe coated on Si wafers as a catalyst. With the aim of improving the yield and reproducibility of spinnable VACNT arrays, the reaction conditions were systematically investigated. The growth kinetics of VACNT arrays was also investigated. The rate of growth of VACNT arrays can reach 465 μm/min at the initial growth stage and the activation energy of VACNT array growth is determined to be 112.2 kJ/mol. Meanwhile, a collective growth model for the evolution of spinnable VACNT arrays is also proposed. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have been recognized as a potential superior reinforcement for high-performance, multifunctional composites. However, non-uniform CNT dispersion within the polymer matrix, the lack of adequate adhesion between the constituents of the composites, and lack of nanotube alignment have hindered significant improvements in composite performance. In this study, we present the development of a layer-by-layer assembly method to produce high mechanical performance and electrical conductivity CNT-reinforced liquid crystalline polymer (LCP) composites using CNT sheets or buckypaper (BP) and self-reinforcing polyphenylene resin, Parmax. The Parmax/BP composite morphology, X-ray diffraction, mechanical, thermal, and electrical properties have been investigated. SEM observations and X-ray diffraction demonstrate alignment of the CNTs due to flow-induced orientational ordering of LCP chains. The tensile strength and Young's modulus of the Parmax/BP nanocomposites with 6.23 wt % multi-walled carbon nanotube content were 390 MPa and 33 GPa, respectively, which were substantially improved when compared to the neat LCP. Noticeable improvements in the thermal stability and glass transition temperature with increasing CNT content due to the restriction in chain mobility imposed by the CNTs was demonstrated. Moreover, the electrical conductivity of the composites increased sharply to 100.23 S/cm (from approximately 10−13 S/cm) with the addition of CNT BP. These results suggest that the developed approach would be an effective method to fabricate high-performance, multifunctional CNT/LCP nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

SUMMARY Hybrid buckypapers (HBP) were developed and showed potential as efficient fire-retardant materials by implementing multiple fire retardance mechanisms. The fabrication of HBP was performed using multi-walled carbon nanotubes (MWCNTs) and magnesium hydroxide (Mg(OH)2) nanoparticles. The Mg(OH)2 nanoparticles were well dispersed throughout the CNTs network, as revealed by scanning electron microscopy and Energy Dispersive X-ray spectroscopy. Thermogravimetric analysis and differential scanning calorimetry both confirmed the decomposition of magnesium hydroxide in the HBPs and heat absorption under elevated temperatures. Our initial results indicated that when used as a skin layer, the HBP has the potential to significantly improve the fire-retardant properties of epoxy carbon fiber composites. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Carbon nanotube field emission backlight (CNT-BLU) is promising to replace traditional backlighting devices in liquid crystal display (LCD) industry. This study reports a laser irradiation process to enhance field emission properties of buckypaper, a thin sheet of high-loading carbon nanotube network. The scanning laser treated the selected region of buckypaper to activate CNT emitters. The improvement of phosphorescence luminance intensity, uniformity, and the reduction of turn-on field were achieved by adjusting machining parameters of laser power, laser lens motion speed, laser resolution, laser beam size, and pattern orientation. Design of experiment and response surface methodology provided ways to rapidly search the feasible laser parameter setting for processing buckypaper field emitters and improving field emission properties within fewer experimental runs. 25−1 Fractional fracotrial design presented the initial models of five repsponses. In addition, the face-centered central composite design is applied since the 25−1 factional factorial design showed curvature significance. It assisted to give the scientifical insight of the following conclusions. High-energy laser treatment damages and burns the CNTs into carbon oxide materials; furthermore, it loses the effective CNTs. Low-energy laser treatment performs CNT activation and produced low field emission performance. In this study, we succeeded to apply statistical analysis methods to understand the physics and mechanics of laser-activated buckypaper field emission and, furthermore, improve, optimize, and demonstrate performance by material selection, process development, and characterization. [ABSTRACT FROM AUTHOR]

Nanocomposite piezoelectric powders comprising polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) were synthesized using a novel process, which combines ultrasonication and solvent-nonsolvent mixture-induced crystallization at very low temperatures ≤10 °C. The morphological and thermal properties of these composite powders were extensively studied. Scanning electron microscopy characterization showed that these composite powders have polymer particles with an average diameter of 150 nm. Fourier transform infrared spectroscopy, differential scanning calorimetry and wide-angle x-ray scattering analyses confirmed that at CNT concentrations of 0.05–20 wt% this process introduces the β-phase in both PVDF/single-walled CNT (SWCNT) and PVDF/multiwalled CNT (MWCNT) composite powders. Both types of composite powders (PVDF-multiwalled and PVDF-single-walled nanotubes) have shown piezoelectric response at different voltages up to 1% loading of multiwalled nanotubes (MWCNTs) and 0.5% loading of single-walled nanotubes (SWCNTs) in composites. [ABSTRACT FROM PUBLISHER]

This article proposes an improved surrogate model for the prediction of the elastic modulus of carbon nanotube–reinforced-nanocomposites. By statistically combining micromechanical modeling results with limited amounts of experimental data, a better predictive surrogate model is constructed using a two-stage sequential modeling approach. A set of data for multi-walled carbon nanotube–bismaleimide nanocomposites is used in a case study to demonstrate the effectiveness of the proposed surrogate modeling procedure. In the case study, the theoretical composite modulus is computed with micromechanical models, and the experimental modulus is measured through tensile tests. Both theoretical and experimental composite moduli are integrated by using a statistical adjustment method to construct the surrogate model. The results demonstrate an improved predictive ability compared to the original micromechanical model. [ABSTRACT FROM AUTHOR]

In this research, networks of single-walled carbon nanotubes (SWNTs) were used to host activated carbon (aC) microparticles to fabricate freestanding composite electrodes without the use of polymer binders. The aC-SWNT composite electrodes with up to 50 wt. % aC showed specific surface areas approaching 1000 m/g and electrical conductivities >36 S/cm. The composite electrodes possessed the properties of both pure SWNT electrodes (e.g. low ohmic drop and rapid ion diffusion) and activated carbon particles (e.g. high specific capacitance). With an interconnected mesoporous microstructure and high electrical conductivity, the CNT networks provide an attractive alternative to polymer binders for forming freestanding electrodes for electrical energy storage devices. Here we show that micron-sized particles can be supported in this framework to utilize the performance enhancement and robustness provided by CNTs. Symmetric electrochemical capacitors fabricated with the electrodes in 6 M potassium hydroxide (KOH) aqueous electrolyte maintained specific capacitances of more than 45 F/g after 30,000 constant-current charge-discharge cycles with a current of 3.6 mA/cm. [ABSTRACT FROM AUTHOR]

There are documented advantages to using carbon nanotubes (CNTs) in composites for various property enhancements. However, to date, only limited studies have been conducted on using of longer CNTs over 1mm in length. This study used long multiwalled carbon nanotubes (LMWCNTs) and their longer extended networks to test multiple properties in thermal conductivity, electrical conductivity, mechanical strength, and modulus and then compared these properties to those of shorter multi-walled carbon nanotubes (SMWCNTs). For carbon fiber-reinforced composites, the longer graphite paths from LMWCNTs in the matrix were expected to improve all properties. The longer networks were expected to allow for more undisturbed phonon transportation to improve thermal conductivity. This in turn relates to improved electrical conductivity and better mechanical properties. However, results have shown that the LMWCNTs do not improve or decrease thermal conductivity, whereas the shorter MWCNTs provide mixed results. LMWCNTs did show improvements in electrical, mechanical, and physical properties, but compared to shorter MWCNTs, the results in other certain properties varied. This perplexing outcome resides in the functioning of the networks made by both the LMWCNTs and shorter MWCNTs. [ABSTRACT FROM AUTHOR]

• First study to demonstrate ALD coatings in a full-cell microsupercapacitor device. • Simple and scalable fabrication process for TiN-TiO 2 -VACNT 3D microsupercapacitor. • TiN(100)-TiO 2 (100) coating improved VACNT device specific capacitance by 74 times. • TiN(300)-TiO 2 (100) coating improved VACNT IDE specific capacitance by 240 times. • Performance attributed to O 2 vacancies in N 2 -doped TiON formed during CV cycling. This work demonstrates the use of ALD coatings in a full-cell 3D microsupercapacitor (MSC) device for the first time. The novel device design described herein has potential to be exploited for rapid and scalable manufacturing of on-chip MSCs integrated with other electronic devices in standard semiconductor fabs or foundries. In this study, atomic layer deposition (ALD) was used to deposit conformal pseudocapacitive coatings of titanium oxide (TiO 2) and titanium nitride (TiN) onto CVD-grown vertically aligned carbon nanotubes (VACNTs) to increase the area-specific capacitance (by 240× and 74× at 0.1 Vs−1 versus the as-deposited VACNT electrode and full-cell VACNT device, respectively) and thus energy density for microscale energy storage applications. The study indicated that combining TiO 2 and TiN ALD layers resulted in a multilayered composite coating rich in oxygen vacancies with enhanced capacitance relative to a single TiO 2 or TiN layer due to a dynamic surface chemistry that developed during charge-discharge cycling. A key component of this multilayered coating was the formation of titanium oxynitride (TiON) which we attributed to the improved performance. Further, we demonstrated that controlling the thickness and stoichiometric ratio of the TiN-TiO 2 composite coating was key to enabling functionality and optimizing the symmetric 3D MSC device performance. [ABSTRACT FROM AUTHOR]

Quad-band terahertz absorber with single-sized metamaterial design formed by a perforated rectangular resonator on a gold substrate with a dielectric gap in between is investigated. The designed metamaterial structure enables four absorption peaks, of which the first three peaks have large absorption coefficient while the last peak possesses a high Q (quality factor) value of 98.33. The underlying physical mechanisms of these peaks are explored; it is found that their near-field distributions are different. Moreover, the figure of merit (FOM) of the last absorption peak can reach 101.67, which is much higher than that of the first three absorption modes and even absorption bands of other works operated in the terahertz frequency. The designed device with multiple-band absorption and high FOM could provide numerous potential applications in terahertz technology-related fields. [ABSTRACT FROM AUTHOR]

Abstract: Simultaneous measurements of Raman scattering and photoluminescence (PL) prove to be a powerful method for quantifying the bundling states of single-walled carbon nanotube (SWCNT). This paper presents physical analysis and experimental evidence to establish that the G-band normalized photoluminescence, which is determined from the simultaneously acquired Raman scattering and PL emission spectra, can serve as a good indicator for quantifying the degree of exfoliation of SWCNT dispersions. Without introducing the complications of sampling geometry and instrumental correction, this indicator directly relates to the intrinsic physical properties of a given SWCNT sample, namely, the absorption cross-section, differential Raman scattering cross-section, and PL quantum yield of SWCNT. An inverse linear relationship between the G-band normalized 267cm−1 RBM intensity and the PL emission intensities for SWCNT dispersions with different degrees of exfoliation was experimentally observed, indicating this can be used for quantitative characterization of the degree of exfoliation for a given SWCNT sample. An in-depth analysis of the indicators of the degree of exfoliation in various as-sonicated SWCNT dispersions highlights a two-stage exfoliation mechanism of SWCNT bundles under sonication. [Copyright &y& Elsevier]

Abstract: In this study, a modified bi-mode finitely extensible non-linear elastic (FENE) dumbbell model was introduced to investigate the concentration-dependent and shear-rate-dependent viscosity of carbon nanotubes (CNTs) dispersed polymer solutions. It is called bi-mode because the aggregated CNTs and free CNTs are considered as two different types of CNTs with different mobility. The diffusion coefficient was simulated by classical molecular dynamics (MD) simulation and input into the FENE models. For the steady shear flow, the coupled Fokker–Planck equations and the corresponding stress tensors were solved numerically. The influence of CNT diameter and CNT mass on the shear viscosity was discussed. In addition, the bi-mode FENE dumbbell simulation can be applied to investigate the shear viscosity under different shear rates and increase of shear viscosity with time evolution. With the model, the influence of the anisotropy parameter, finite extensibility parameter was investigated. The shear-rate-dependent viscosity profile of resin solutions with different CNT concentrations was also predicted and validated with experimental rheological behavior. The simulation model can provide qualitative prediction of rheological behavior of CNTs dispersed resin. [Copyright &y& Elsevier]

Abstract: A mechanical method was used to shorten carbon nanotubes (CNTs) for improving dispersion without reducing their thermal conductivity. Single walled carbon nanotubes (SWCNTs) were mechanically cut to produce short and open-ended fullerene pipes. These shortened SWCNTs were then used in polymer composites. Both atomic force microscopy and scanning electron microscopy characterizations suggested that nanotube shortening significantly improved CNT dispersion. Thermal conductivity of composites containing short CNTs were found to be much better than those containing pristine CNTs. [Copyright &y& Elsevier]

In the development of nanotube reinforced polymer composites, one of the fundamental issues that scientists and engineers are confronting is the nanotube/polymer interfacial bonding, which will determine load transfer capability from the polymer matrix to the nanotube. In this paper, the interfacial bonding of single-walled nanotube (SWNT) reinforced epoxy composites was investigated using a combination of computational and experimental methods. The interfacial bonding was predicted using molecular dynamics (MD) simulations based on a cured epoxy resin model, which was constructed by incorporating three-dimensional cross-links formed during curing reaction. Based on the pullout simulations, the interfacial shear strength between the nanotube and the cured epoxy resin was calculated to be up to 75 MPa, indicating that there could be an effective stress transfer from the epoxy resin to the nanotube. In the experiments, single-walled nanotube reinforced epoxy composites were fabricated, characterized and analyzed. The uniform dispersion and good interfacial bonding of the nanotubes in the epoxy resin resulted in a 250–300% increase in storage modulus with the addition of 20–30 wt% nanotubes. These experimental results provided evidence of stress transfer in agreement with the simulation results. [Copyright &y& Elsevier]

Abstract: Two SWCNT dispersion processing techniques – microfluidization and ultrasonication– were examined using an ultracentrifuge method and simultaneous Raman scattering and photoluminescence spectroscopy. It was demonstrated that the extremely high energy dissipation rate in microfluidization facilitates the high throughput dispersion of SWCNT bundles. However, the efficiency of SWCNT bundles being separated into individual tubes in this process is much lower compared to ultrasonication, in which the energy dissipation rate is very low. This suggests that the types of flow field rather than the energy dissipation rate play a critical role in the separation of bundles into single SWCNTs. [Copyright &y& Elsevier]

A new nanocomposite manufacturing process, Dual-material aerosol jet printing (DMAJP), was developed to fabricate polyimide (PI)/carbon nanotube (CNT) nanocomposite with tailorable and controllable intra-part varying CNT loading. This process mixes the aerosols of CNT ink and a solution of PI precursor to achieve a homogenous dispersion of CNTs in the PI matrix. The mixing ratio of the two aerosols determines the CNT loading in the nanocomposite, which can be used to control the conductivity of the film. Thickness, nanostructure, and conductivity of the nanocomposites fabricated under different process conditions were investigated. The high degree with which the printed PI/CNT nanocomposite film may be tailored was demonstrated through three examples: a film with different CNT loadings at designated regions; a film with a built-in circuit; and a film with a through-thickness conductive channel. DMAJP is a facile, versatile, and potentially scalable manufacturing process for the next generation of smart nanocomposites. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on highly sensitive aligned carbon nanotube network (CNTN)-based strain sensors produced by aerosol jet printed electrodes and polyimide substrates. Two types of sensing mechanisms were revealed. Type A sensors, whose electrodes were directly printed on the CNTNs and embedded in epoxy resin, take advantage of the intrinsic piezoresistive properties of highly oriented carbon nanotube bundles and exhibited large positive gauge factor. Type B sensors, whose electrodes were printed on the polyimide substrate, utilize the effects of applied strains on the contact resistances between layers of the CNTN structure and between CNTN and the electrodes, exhibited large negative gauge factors. Type A and B sensors achieved positive and negative gauge factors up to 20 and 40 in magnitude, respectively. The high performance and flexible nature of the sensors, combined with the capability of scalable manufacturing processes, exhibits promising application potentials. [Copyright &y& Elsevier]

Abstract: Poly (methyl methacrylate) (PMMA) and multi-walled carbon nanotubes (MWCNTs) nanocomposites were synthesized and foamed by supercritical carbon dioxide. Morphology and tensile properties of both solid and foamed nanocomposites were investigated. Moderate improvement in the tensile properties was observed in the solid nanocomposites, which depended on carbon nanotube (CNT) dispersion and polymer–CNT interaction. The CNTs had significant influences on the foam cell morphology. Moreover, the convoluted effects of CNT dispersion, polymer–CNT interaction and foam structure differences led to significant difference in foam properties. Nanocomposite foam with concurrent increases in tensile strength (∼40%), tensile modulus (∼60%) and strain at break (∼70%) was successfully prepared with the use of 0.5% functionalized CNTs that were well dispersed. The foam showed a ductile failure under tension that involved extensive pore deformation and collapsing, and formation and coalescence of microvoids that were largely responsible for the significantly improved tensile toughness. By contrast, foam properties were reduced in the presence of poorly dispersed CNTs that weakly adhered to the matrix. [Copyright &y& Elsevier]

Abstract: The mechanism of carbon nanotube (CNT) alignment during stretching was examined by the in situ characterization of carbon nanotube networks (CNTNs) under tensile strains using X-ray and Raman scattering techniques. A method of quantifying the inhomogeneous alignment of macroscopic CNTNs is explored based on bulk property measurements of their electrical anisotropy and X-ray diffraction diagrams. The results show that the process of stretch-induced alignment of CNTNs included straightening the waviness of the long nanotube ropes, as well as the self-assembling and denser packing of the nanotubes. For samples at a strain of 40%, the fraction of aligned nanotubes was as high as 0.85. The aligned fraction of CNTs serves as an important parameter for the quality control of the alignment process and numerical simulations of structure–property relationships of CNTNs and their composites. [Copyright &y& Elsevier]

Abstract: The fabrication and electromechanical performance of three layer actuators (carbon nanotube/Nafion/carbon nanotube) with doped Nafion were studied. The Nafion actuators were doped with 1-butyl-3methylimmidazolium tetrafluoroborate (BMI+BF4 −) ionic liquid, which was verified by electrochemical impedance spectroscopy analysis. The three layer actuators were fabricated using a simple method involving a doping and hot-pressing process. Carbon nanotube thin films (buckypaper or BP) were used as the electrode layers for fabricating the actuators. The actuators doped with the ionic liquid generated electromechanical strains up to 0.4%, which was ten times higher than when testing the neat Nafion three layer actuators. The results were promising for manufacturing lightweight, low power smart structures. [Copyright &y& Elsevier]

Abstract: Innovative printing technology enables fine feature deposition (below 10μm) of electronic materials onto low-temperature, non-planar substrates without masks. This could be a promising technology to meet the requirements of present and future microelectronic systems. Silver nanoparticles (NP) ink is widely used for printed electronics; however, its electrical conductivity is low compared to bulk materials. In order to improve the electrical conductivity of printed tracks for the aerosol printing technique, we developed a novel carbon nanotubes (CNTs)/silver NP ink by mechanical stirring and sonication. The produced sample inks with different concentration of CNTs that were printed with a Maskless Mesoscale Material Deposition (M3D) Aerosol Jet® printing system. The dimensions of the printed lines were determined by atomic force microscopy (AFM) and the electrical resistivity was evaluated using the four-point method. Scanning electron microscopy (SEM) was used to characterize the morphology of printed tracks. We found that the CNTs bridged the defects in some printed silver lines, thereby lowering the electrical resistivity by 38%. However, no further improvements were observed with a higher CNT concentration in the silver NP ink samples. We hypothesize that CNT bridges connects the defects thus decreasing the resistivity of printed silver lines when CNT concentration is under the percolation level. However, due to aggregation of CNTs when it is above a concentration threshold, the resistivity of printed silver lines stops decreasing and even increases because of Schottky barrier effect. [Copyright &y& Elsevier]

Abstract: In this study we investigated the effects of inclusion waviness and its distribution to the effective composite stiffness. Different waviness conditions were analyzed: uniform waviness with variable inclusion orientation or aspect ratio, and uniform aspect ratio with variable waviness. The inclusion waviness was found to have a greater effect on tensile moduli and shear modulus for unidirectional composites; however, if the inclusions are either randomly dispersed or partially aligned, the degree of waviness effect was smaller. The elastic moduli were also over-estimated if inclusion aspect ratio or waviness followed symmetric distributions. In addition, the waviness distribution effect was larger when larger inclusion waviness was introduced in a composite. The lack of fiber waviness distribution assumption was found to lead to inaccurate composite stiffness predictions, especially for composite with higher fiber volume fraction. We also demonstrated the inclusion waviness effects on the tensile modulus of carbon nanotube-reinforced composites. The results showed that the disparity between theoretical predictions and experimental data could be due to different inclusion waviness conditions. [ABSTRACT FROM AUTHOR]

Abstract: Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes. [ABSTRACT FROM AUTHOR]

Abstract: Single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) membranes (buckypaper) and carbon nanofiber (CNF) paper were incorporated onto the surface of epoxy carbon fiber composites, as proposed fire shields. Their flammability behaviors were investigated by a cone calorimeter. SWCNT buckypaper and CNF paper did not show notable improvement on fire retardancy. However, MWCNT buckypaper acted as an effective flame-retardant shield, reducing the peak heat release rate by more than 60% and reducing smoke generation by 50% during combustion. The pore structures of buckypapers and CNF paper were characterized by scanning electron microscopy (SEM), mercury intrusion porosimetry, and N2 adsorption isotherms. Gas permeability of buckypaper and carbon nanofiber paper was measured. The correlation between buckypaper and CNF paper properties and their fire retardancy was discussed. [Copyright &y& Elsevier]

Abstract: Poly(methyl methacrylate) (PMMA) multi-walled carbon nanotubes (MWCNTs) nanocomposites were synthesized by several methods using both pristine and surface functionalized carbon nanotubes (CNTs). Fourier transform infrared (FTIR) spectroscopy was used to characterize the presence and types of functional groups in functionalized MWCNTs, while the dispersion of MWCNTs in PMMA was characterized using scanning electron microscopy (SEM). The prepared nanocomposites were foamed using carbon dioxide (CO2) as the foaming agent. The cell morphology was observed by SEM, and the cell size and cell density were calculated via image analysis. It was found that both the synthesis methods and CNTs surface functionalization affect the MWCNTs dispersion in the polymer matrix, which in turn profoundly influences the cell nucleation mechanism and cell morphology. The MWCNTs are efficient heterogeneous nucleation agents leading to increased cell density at low particle concentrations. A mixed mode of nucleation mechanism was observed in nanocomposite foams in which polymer rich and particle rich region co-exist due to insufficient particle dispersion. This leads to a bimodal cell size distribution. Uniform dispersion of MWCNTs can be achieved via synergistic combination of improving synthesis methodology and CNTs surface functionalization. Foams from these nanocomposites exhibit single modal cell size distribution and remarkably increased cell density and reduced cell size. An increase in cell density of ∼70 times and reduction of cell size of ∼80% was observed in nanocomposite foam with 1% MWCNTs. [Copyright &y& Elsevier]

Abstract: Single-walled carbon nanotube (SWCNT) buckypaper (BP) was exposed to high temperatures with electrical current-driven thermal heating either in the air or a vacuum. High electrical currents generate Joule heating and then cause breakdown of the BP in the air at over 400°C due to rapid oxidation. In the vacuum, electrical resistive heating can generate temperatures of more than 2000°C for the samples. Structural changes of SWCNTs after electrical current heating were observed using electron microscopy and Raman spectra. After breakdown of BP, the disorder-induced D-band increased and a smaller diameter related radial-breathing mode was reduced in the high temperature region. Structural transformations of SWCNT to other carbon nanostructures were observed after current-driven high-temperature treatment in the vacuum. In addition, surface-enhanced Raman scattering with intensity enhancement more than ten times was observed in the BP with agglomerated Fe or Ti particles. [Copyright &y& Elsevier]

Abstract: A composite’s microstructure significantly influences its overall properties. Orientation and aspect ratio of the fiber are two key parameters that describe the microstructures of a composite with straight short fibers. This paper discusses the effects of fiber orientation and aspect ratio distribution on the overall elastic properties of composites using the Mori–Tanaka’s method in this paper. The results show that using an average aspect ratio of the fibers to estimate overall elastic properties is not appropriate under some conditions. When the aspect ratio of the fibers does not follow a symmetric distribution, the overall elastic properties obtained by the average aspect ratio of the fibers may differ by more than 30% from those obtained by the method considering the aspect ratio distribution. This paper presents a model used to predict the properties of nanotube-reinforced composites. The results obtained by the model were compared with experimental results. [Copyright &y& Elsevier]

Abstract: A carbon nanotube membrane (buckypaper) was incorporated onto the surface of a Polyhedral Oligomeric Silsesquioxanes /glass fiber composite by vacuum-assisted resin transfer molding to improve the flame retardancy. The flammability was investigated with a cone calorimeter. With buckypaper on the surface, the heat release rate, peak heat release rate, smoke production rate and CO yield of the composite were decreased dramatically during the combustion. [Copyright &y& Elsevier]