SILICON OXYCARBIDE NANOCOMPOSITE LAMINATES REINFORCED WITH CARBON NANOTUBES OF HIGH DEGREE OF ALIGNMENT AND ULTRAHIGH PACKING DENSITY

Growth of primary motor neurons on horizontally aligned carbon nanotube thin films and striped patterns

Higher concentrations of long carbon nanotubes (CNTs) that are aligned and functionalized can improve the mechanical properties of CNT composites. For this purpose, pristine/random CNT sheets were mechanically stretched at different strains of 40 %, 60 % and up to 80 %. The higher degree of CNT alignment was confirmed by scanning electron microscope (SEM) images and the degree of alignment was quantified by X-ray scattering and polarized Raman spectroscopy. The highest degree of alignment of 0.93 was achieved by using this method. Aligned CNT sheets were functionalized and CNT/bismaleimide (BMI) composites were fabricated. The mechanical properties of the composites were improved with a higher degree of alignment achieving a modulus of 252 GPa and tensile strength of over 1.4 GPa for an 80% stretched CNT/BMI composite. To understand the internal CNT packing and the CNT/resin interface, thin composite cross sections that are perpendicular to the alignment direction were prepared using focused ion beam (FIB) with a lift-out process. Using a high-resolution transmission electron microscopy (HRTEM), relatively large diameter CNTs (> 5 nm) cross sections and double-walled CNT bundles were observed. An increased number of densely packed and collapsed CNT structures were also observed with higher stretch ratio, which confirmed the CNT alignment and dense packing along the stretch direction. The CNT/resin interface was also analyzed by electron energy loss spectroscopy (EELS). Carbon K-edge peak was used to identify the functionalization of CNT, and a ratio of 1s-* to 1s-* transition was mapped by a scanning TEM. A decreased */* transition ratio was observed at the edge of CNT packing and could be related to the reduced sp2 bonding after functionalization. This leads efficient load transfer between CNT and resin, thus higher mechanical properties.

Applications of carbon nanotubes (CNTs) in flexible and complementary metal-oxide-semiconductor (CMOS)-based electronic and energy devices are impeded due to typically low CNT areal densities, growth temperatures that are incompatible with device substrates, and challenges in large-area alignment and interconnection. A scalable method for continuous fabrication and transfer printing of dense horizontally aligned CNT (HA-CNT) ribbon interconnects is presented. The process combines vertically aligned CNT (VA-CNT) growth by thermal chemical vapor deposition, a novel mechanical rolling process to transform the VA-CNTs to HA-CNTs, and adhesion-controlled transfer printing without needing a carrier film. The rolling force determines the HA-CNT packing fraction and the HA-CNTs are processed by conventional lithography. An electrical resistivity of 2 mOmega . cm is measured for ribbons having 800-nm thickness, while the resistivity of copper is 100 times lower, a value that exceeds most CNT assemblies made to date, and significant improvements can be made in CNT structural quality. This rolling and printing process could be scaled to full wafer areas and more complex architectures such as continuous CNT sheets and multidirectional patterns could be achieved by straightforward design of the CNT growth process and/or multiple rolling and printing sequences.

Poly(vinylidene fluoride) based nanocomposites: the preparation, structures, and properties

The objective of this research is to design, fabricate, and demonstrate scalable manufacturing processes, aerospace-quality and advanced structural and multifunctional properties of nanocomposites using commercially available carbon nanotube (CNT) yarns and sheets and aerospace qualified resin matrix. The goal is to achieve extra-high modulus, and adequate interfacial shear property with scale-up sample sizes (4"×4"×0.1"). Different from current low CNT content (<5 wt%) composites and micrometer-scale sample size efforts, we will study and demonstrate effective approaches to manufacture aerospace-quality structural composite materials of ~60 wt% CNT concentration and achieve sizable demonstration samples with a high degree of alignment and packing for potential structural applications. We have developed a unique manufacturing process to produce highly aligned, and high concentration CNT yarn composites by stretch-assist CNT filament winding, heatassisted multiple-step stretching and curing under tension processes, which are potentially easy to scale-up and are low cost with utilization of commercially available CNT materials. CNT purification was also performed to eliminate residual catalyst and amorphous carbon and to facilitate the removal of manufacturing added chemicals during CNT synthesis. CNT surface treatment, such as chemical functionalization and plasma etching were further studied to improve the CNT and resin interfacial bonding. Cytec 5250-4 BMI resin and an autoclave process were used to produce the large size test panels. Tensile testing and three-point bending tests were conducted, as well as SEM failure analysis. This is the first attempt to scale-up manufacturing of high CNT loading and alignment test panels and conduct ASTM standard level tests.

Carbon nanotube (CNT) has attracted of great interest as advanced nanoreinforcements in new kinds of polymer nanocomposites because of the combination of its unique extraordinary properties with high aspect ratio and small size (Ebbesen, 1997; Dresselhaus et al., 2001; Schadler et al., 1998; Ajayan, 1999; Bokobza, 2007; Paul & Robesson, 2008). In particular, excellent mechanical strength, thermal conductivity, and electrical properties of CNT have created a high level of activity in materials research and development for potential applications such as fuel cell, hydrogen storage, field emission display, chemical or biological sensor, and advanced polymer nanocomposites (Iijima, 1991; De Heer et al., 1995; Wong et al, 1997; Fan et al., 1999; Kim & Lieber, 1999; Liu et al., 1999; Kong et al., 2000; Ishihara et al., 2001; Alan et al., 2003; Wu & Shaw, 2005). This feature has motivated a number of attempts to fabricate CNT/polymer nanocomposites in the development of highperformance composite materials (Kim et al., 2006; Kim et al., 2007; Kim et al., 2008; Kim, 2009; Kim et al., 2009; Kim et al., 2010). In this regard, much research and development have been performed to date for achieving the practical realization of excellent properties of CNT for advanced polymer nanocomposites in a broad range of industrial applications. However, because of high cost and limited availability, only a few practical applications in industrial fields such as electronic and electric appliances have been realized to date. The CNT consisting of concentric cylinder of graphite layers is a new form of carbon and can be classified into three types (Dresselhaus et al., 2001; Iijima, 1991; Shonaike & Advani, 2003): single-walled CNT (SWCNT), double-walled CNT (DWCNT), and multi-walled CNT (MWCNT). SWCNT consists of a single layer of carbon atoms through the thickness of the cylindrical wall with the diameters of 1.0-1.4 nm, two such concentric cylinders forms DWCNT, and MWCNT consists of several layers of coaxial carbon tubes, the diameters of which range from 10 to 50 nm with the length of more than 10 μm (Dresselhaus et al., 2001; Iijima, 1991; Shonaike & Advani, 2003). The graphite nature of the nanotube lattice results in a fiber with high strength, stiffness, and conductivity, and higher aspect ratio represented by very small diameter and long length makes it possible for CNTs to be ideal nanoreinforcing fillers in advanced polymer nanocomposites (Thostenson et al., 2001). Both theoretical and experimental approaches suggest the exceptional mechanical properties of CNTs ~100 times higher than the strongest steel at a fraction of the weight (Goze et al., 1999; Yao et al., 2001;

Carbon nanotubes (CNTs) have been attracted by the researchers for their extraordinary properties and wide applications in various fields. Among numerous types of CNTs, the horizontally aligned CNTs (HACNTs) has shown many advantages due to its nano-structural features and proper arrangements. HACNTs open new opportunity in the field of microwave, nanoelectronics, and heat dissipation system. This article reports the study on the post-growth processing technique (mechanical) to transform vertically aligned carbon nanotubes (VACNTs) array into HACNTs mat. The above technique has been named as micromechanical rolling (M2R) that uses a rotating rigid cylinder to bend and align the individual nanotubes in the VACNTs array. The process yielded remarkably arranged (horizontal) nanotubes with a resultant smooth surface. Various process parameters such as tool rotational speed, lateral speed, and step size were investigated in this study to achieve the smooth surface of HACNTs array. It was observed that the minimum surface roughness of Ra = 4 nm was achieved with 2000 rpm of the tool’s rotational speed, 1 mm min−1 of lateral speed and 1 μm of step size.

Improving mechanical and electrical properties of oriented polymer-free multi-walled carbon nanotube paper by spraying while winding

Carbon nanotubes (CNTs) can be produced from floating catalyst synthesis to form random networks. However, the CNTs must be aligned and closely packed to eliminate molecular and microscale defects to reach levels of mechanical performance similar to carbon fiber systems. Previous research has shown that strain-induced alignment methods using bismaleimide (BMI) infiltration can effectively modify randomly oriented CNT networks. The BMI resin lubricates the network decreasing the friction between the CNT bundles and assists with load transfer between CNT bundles during the stretching process. This process yields unique CNT collapsing, self-assembling behaviors, and graphitic crystal packing at the nanoscale. In this study, the CNTs’ alignment degree was measured by Raman spectroscopy and X-ray scattering. Alignment degree analysis results showed a considerable increase at 40% stretch ratio with a plateau at 60% stretch ratio. An 80% stretch ratio achieved the highest alignment degree of 0.93 with noticeable graphitic crystal packing. Both scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) images of the CNT sheet surfaces and cross-sections show that as the stretch ratio increased, the CNTs started to align along the stretching axis and self-assembled into large bundles. Additionally, HRTEM analysis indicated that the CNTs exhibited collapsing and self-assemblage to form graphitic crystal packing. Tensile testing on the aligned CNT/BMI composite samples measured an increase in tensile properties. The ultimate tensile strength (UTS) and Young's modulus reached maximums of 1.58 GPa at 70% stretch ratio and 252 GPa at 80% stretch ratio, respectively. The high alignment degree and graphitic packing improved load transfer throughout the CNT network, and consequently, better mechanical performance in the CNT composites were achieved. Furthermore, this alignment process proved its scalability and potential to transcend into industrial-scale applications that utilize CNT material systems.

Microstructure evolution and self-assembling of CNT networks during mechanical stretching and mechanical properties of highly aligned CNT composites

The assembly of single-walled carbon nanotubes (CNTs) into high-density horizontal arrays is strongly desired for practical applications, but challenges remain despite myriads of research efforts. Herein, we developed a non-destructive soft-lock drawing method to achieve ultraclean single-walled CNT arrays with a very high degree of alignment (angle standard deviation of ~0.03°). These arrays contained a large portion of nanometre-sized CNT bundles, yielding a high packing density (~400 µm-1) and high current carrying capacity (∼1.8 × 108 A cm-2). This alignment strategy can be generally extended to diverse substrates or sources of raw single-walled CNTs. Significantly, the assembled CNT bundles were used as nanometre electrical contacts of high-density monolayer molybdenum disulfide (MoS2) transistors, exhibiting high current density (~38 µA µm-1), low contact resistance (~1.6 kΩ µm), excellent device-to-device uniformity and highly reduced device areas (0.06 µm2 per device), demonstrating their potential for future electronic devices and advanced integration technologies.

Carbon nanotubes (CNTs) are a potential new component to be incorporated into existing aerospace structural composites for multifunctional (mechanical, electrical, thermal, etc.) property enhancement. Although CNT properties are extraordinary when measured individually, they tend to degrade by a large factor when integrated in system (often in polymer matrices). Mechanisms and effectiveness of nano-scale CNT implementation into macro-scale structural composites are not well understood. Non-mechanical aspects of these composites are the focus of this work. As a CNT hybridized fiber polymer composite, fuzzy fiber reinforced plastic (FFRP) is developed using a scalable fabrication method that achieves uniform CNT distributions for thermal and electrical conductive networks without requiring intensive mixing which can damage CNTs. At small CNT volume fractions (~0.58% Vf), characterization shows significant enhancement in electrical conduction (x10 6 -10 8 ) but limited enhancement in thermal conduction (x1.9). In addition, aligned-CNT polymer nanocomposites (A-CNT-PNCs) are being characterized as a representative volume element (RVE) of the FFRP. Experimentally obtained data on consistent A-CNT-PNC samples sets provide engineering knowledge and to achieve effective utilization of CNTs' multifunctional properties. Theoretical studies, both analytical and numerical, have been recently developed, suggesting interface effects may be a key to explaining the above limitations, including electron tunneling/hopping or phonon scattering at CNT-CNT and CNT-polymer interfaces. Multiple test techniques and property extraction methods for A-CNT-PNCs are developed and/or employed for cross-comparison. Applications of nano-engineered composites enhanced with CNTs can include lightning protection layers, electromagnetic interference shields, thermal management layers, and thermoelectrical sensor layers for airplane structures.

Nowadays, global fresh water shortage is becoming the most serious problem affecting the economic and social development. Water treatment including seawater desalination and wastewater treatment is the main technology for producing fresh water. Membrane technology is favored over other approaches for water treatment due to its promising high efficiency, ease of operation, chemicals free, energy and space saving. Membrane filtration for water treatment has increased significantly in the past few decades with the enhanced membrane quality and decreased membrane costs. In addition to high permeate flux and high contaminant rejection, membranes for water treatment require good mechanical durability and good chemical and fouling resistances. Thus, investigation of the mechanical behavior of water treatment membranes with underlying deformation mechanisms is critical not only for membrane structure design but also for their reliability and lifetime prediction.Compared to ceramic and metallic membranes, polymer membranes with smaller pore size and higher efficiency for particle removal are widely used in seawater desalination with a high applied pressure. However, polymer membranes are mechanically weaker and have lower thermal and chemical stability compared to inorganic membranes. Blending of polymers with inorganic fillers is an effective method to introduce advanced properties to polymer based membranes to meet the requirements of many practical applications. The reinforced polymeric membranes with inorganic fillers can provide desirable mechanical strength as well as mechanical stability. Carbon nanotubes (CNTs) have received considerable attention from academic and industries over the last twenty years. In addition to their excellent electrical and thermal properties, CNTs exhibit outstanding mechanical characteristics due to its instinct mechanical strength and high aspect ratio. For the application of water treatment membranes, CNTs could be the excellent channels for water to go through and therefore, CNTs have proven to be excellent fillers in polymer membranes improving the permeability and rejection properties. In literature, it is reported that the mechanical strength of the polymer membranes was improved with the embedding of CNTs due to reinforcement effect of the more rigid CNTs. The mechanical responses of polymer_CNTs composites depended on the interfacial adhesion between the CNTs and the membrane-based polymer as well as the dispersion and distribution of the CNTs within the polymer matrix.In this study, a vertical chemical vapor deposition reactor was designed in order to synthesize CNTs of high aspect ratio using continues injection atomization. Bundles of high purity (99%) and high quality CNTs were produced by this system. The produced CNTs had diameters ranging from 20 to 50 nm and lengths ranging from 300 to 500 micron (corresponded aspect ratios ranging from 6000 to 25000). A novel polysulphone (PSF) based nanocomposite membrane incorporated with the produced high aspect ratio CNTs was then casted via phase inversion method, at a wide range of CNTs loading (0–5 wt. %), in polysulphone-dimethylformamide solutions using the Philos casting system. The poly(vinylpyrrolidone) was used as pore-forming additive. To demonstrate the effect of nanocomposite morphology on the mechanical behavior of the prepared membranes, a set of control samples consisted of PSF membranes embedded with commercial CNTs at the same CNTs loading, were casted at the same conditions. The commercial CNTs had a lengths of 1 μm to 10 μm and outer diameters of 10 nm to 20 nm (corresponded aspect ratios ranging from 50 to 1000), with purity &gt;95% and BET surface area of 156 m2/g.The effects of CNTs content and aspect ratio on morphological, water transport and mechanical properties of the prepared PSF-based porous membranes were investigated. The surface and cross-section morphologies of PSF/CNTs porous membranes were examined using scanning electron microscopy (SEM). The orientation, dispersion and distribution of CNTs within polymer membranes were evaluated for the membrane samples with different CNTs content and CNTs aspect ratio. The average membrane pore size was evaluated by using SEM image analysis software.Uniaxial tensile behavior of the membranes was characterized by means of a universal material testing machine under different testing conditions. Wet specimens were carefully cut from the casted membranes by using a razor blade. Elastic, plastic and failure behaviors of the membranes are analyzed with the impacts of CNTs content and aspect ratio. The macroscopic mechanical behaviors of the membranes are correlated with their strain induced microstructure evolution by using SEM. In this, pore shape evolution, pore and CNTs orientations, neighboring pore interaction, interface between the CNTs and PSF matrix and the failure behavior of the deformed porous membranes were analyzed. The macroscopic stress-strain responses of the membranes were correlated with the microstructure of the studied nanocomposites membranes to provide a better understanding of materials' processing-microstructure-properties relationship.

Producing superior composites by winding carbon nanotubes onto a mandrel under a poly(vinyl alcohol) spray

Carbon nanotubes : their synthesis and integration into nanofabricated structures