Carbon nanotube-based polymer composites: A trade-off between manufacturing cost and mechanical performance

A methodology was devised to evaluate the newly-developed carbon nanotube reinforced polymer composites by means of mechanical performance and manufacturing cost. Glass fibre reinforced-epoxy composite plates were produced having different parameters: (a) three manufacturing processes, (b) geometrical dimensions, (c) carbon nanotubes concentration in the epoxy resin and finally (d) modified resin infusion temperature. Tensile coupons were machined out of the manufactured plates and their quasi-static mechanical properties were evaluated. Three cost models were developed to assess plates and tensile coupons manufacturing cost for each different case. Optimal values were evaluated for major manufacturing parameters, driving force being the mechanical properties of interest (quality) as well as their low manufacturing cost. It is demonstrated that the added cost to manufacture such nano-reinforced composites is attributed to increase strength on the expense of ductility; the main benefit of the carbon nanotube-based polymer composites seems to be their ability to be monitored. Almost 20% added cost is paid to attain this new function of piezo-resistivity for the RTM process, while this amount further increases for the non-automated processes such as the Hand Lay-up.     

International collaboration: Will it be keeping alive East European research?

International scientific collaboration is very sensitive to political and economic changes in a country or a geopolitical region. Collaboration in research is reflected by the corresponding coauthorship of the published results which can be analysed with the help of bibliometric methods. Based on data from theScience Citation Index (SCI), the change of annual international coauthorship patterns ofBulgaria, Czechoslovakia, Hungary, Poland andRomania have been analysed for the periods 1981–1985 and 1984–1993, respectively. It is shown that international collaboration was not developing similarly in the countries under study. Whilst scientific communities of Hungary and Poland have already been opening in the early 80s, the international collaboration of the other East-European countries was still dominated by COMECON relations till 1989. As expected, since 1990 an increasing scientific collaboration with highly developed countries can be observed in all five countries. At the same time, scientific collaboration with the former communist countries shows a clear decline. The great share of international co-authorship links is some countries reflect various tendencies part of which are interpreted with the help of a cardiologic model.     

An assessment of the science and technology of carbon nanotube-based fibers and composites

This paper examines the recent advancements in the science and technology of carbon nanotube (CNT)-based fibers and composites. The assessment is made according to the hierarchical structural levels of CNTs used in composites, ranging from 1-D to 2-D to 3-D. At the 1-D level, fibers composed of pure CNTs or CNTs embedded in a polymeric matrix produced by various techniques are reviewed. At the 2-D level, the focuses are on CNT-modified advanced fibers, CNT-modified interlaminar surfaces and highly oriented CNTs in planar form. At the 3-D level, we examine the mechanical and physical properties CNT/polymer composites, CNT-based damage sensing, and textile assemblies of CNTs. The opportunities and challenges in basic research at these hierarchical levels have been discussed.     

Elucidating the electro-catalytic oxidation of hydrazine over carbon nanotube-based transition metal single atom catalysts

Elucidating the reaction mechanism of hydrazine oxidation reaction (HzOR) over carbon-based catalysts is highly propitious for the rational design of novel electrocatalysts for HzOR. In present work, isolated first-row transition metal atoms have been coordinated with N atoms on the graphite layers of carbon nanotubes via a M-N₄-C configuration (MSA/CNT, M=Fe, Co and Ni). The HzOR over the three single atom catalysts follows a predominant 4-electron reaction pathway to emit N₂ and a negligible 1-electron pathway to emit trace of NH₃, while their electrocatalytic activity for HzOR is dominated by the absorption energy of N₂H₄ on them. Furthermore, FeSA/CNT reverses the passivation effect on Fe/C and shows superior performance than CoSA/CNT and NiSA/CNT with a recorded high mass activity for HzOR due to the higher electronic charge of Fe over Co and Ni in the M-N₄-C configuration and the lowest absorption energy of N₂H₄ on FeSA/CNT among the three MSA/CNT catalysts.

     

Sugar coated ceramic nanocarriers for the oral delivery of hydrophobic drugs: formulation, optimization and evaluation

In order to enhance the delivery of poorly-soluble drugs, we have explored aquasomes (three-layered, ceramic core based, oligosaccharide coated nanoparticles) as potential carriers for the delivery of model hydrophobic drug piroxicam (log P = 3.1). Ceramic nanoparticles were prepared using two techniques; namely, co-precipitation by refluxing and co-precipitation by sonication. Core preparation was finally done using sonication approach; based on the higher % yield (42.4 ± 0.4%) and shorter duration (1 day) compared to the reflux method (27.4 ± 2.05%, 6 days). Lactose loading onto ceramic core was achieved using adsorption. Colorimetric analysis of lactose coating was done using Anthrone method. Optimization of process variables namely, incubation time and core to coat ratio (for sugar loading) was carried out. Optimum time of incubation was 3 h and the core to coat ratio was 4:1. The drug loading was achieved by incubating the sugar loaded cores in different concentrations of piroxicam solution and it was found that 1.5% w/v piroxicam was optimal. Structural characterization using Fourier-Transform Infra Red Spectroscopy (FTIR) confirmed the presence of sugar coating onto the core. Morphological evaluation using transmission electron microscopy (TEM) revealed spherical nanoparticles (size 56.56 ± 5.93 nm for lactose coated core and 184.75 ± 13.78 nm for piroxicam loaded aquasomes) confirming the nanometric dimensions.     

Buckling behavior of carbon nanotube-based intramolecular junctions under compression: Molecular dynamics simulation and finite element analysis

Intramolecular junctions (IMJs) formed by connecting two arbitrary carbon nanotubes (CNTs) can act as functional building blocks in circuits and components of CNT-based electronics devices. While extensive studies have been conducted on the atomic structural as well as electrical properties of IMJs and great advances have been achieved, mechanical response of IMJs under large deformation, which may exert significant effects on their electrical properties, are still not fully explored. In this paper, both molecular dynamics (MD) simulation and finite element (FE) analysis are employed to investigate the buckling behavior of IMJs under axial compression. The strain rate effects are firstly studied in the MD simulations. It is found that the critical compressive strain is not sensitive to the strain rate of relatively low range, but it exhibits a strong dependency upon the strain rate under high speed compression. In particular, a different failure mode may occur under ultra-high loading velocities. Based on the discussion on the strain rate effects, a reasonable loading velocity is suggested to be adopted in the subsequent MD simulations. In this study, the results of both the MD simulations and the FE analyses indicate that the critical compressive strain is dependent upon the length, radial dimensions of the IMJ but insensitive to the chirality of the IMJ. The comparison between the results of the MD simulations and the FE analyses also confirms that the FE analysis is able to provide useful insights into the compressive behavior of CNT-based IMJs with a much less computational cost.     

Evaluations of the effective material properties of carbon nanotube-based composites using a nanoscale representative volume element

Carbon nanotubes (CNTs) possess extremely high stiffness, strength and resilience, and may provide the ultimate reinforcing materials for the development of nanocomposites. In this paper, the effective mechanical properties of CNT-based composites are evaluated using a 3-D nanoscale representative volume element (RVE) based on continuum mechanics and using the finite element method (FEM). Formulas to extract the effective material constants from solutions for the RVE under three loading cases are derived based on the elasticity theory. An extended rule of mixtures, based on the strength of materials theory for estimating the effective Young’s modulus in the axial direction of the RVE, is applied for comparisons with the numerical solutions based on the elasticity theory. Numerical examples using the FEM are presented, which demonstrate that the load carrying capacities of the CNTs in a matrix are significant. With additions of the CNTs in a matrix at volume fractions of only about 2% and 5%, the stiffness of the composite can increase as many as 0.7 and 9.7 times for the short and long CNT cases, respectively. These simulation results are consistent with the experimental ones reported in the literature.     

Technology assessment for clean energy technologies: The case of the Pacific Northwest

This study presents a technology assessment for clean power generation in the Pacific Northwest. Our goal is to incorporate clean production principles into the evaluation process for power alternatives. Two types of technologies are considered: one is for a renewable energy source (wind) and the other is for a traditional, fossil fuel based energy source (coal). The Analytical Hierarchy Process is used to assess the feasibility of both the wind energy and clean burning coal energy technologies. Criteria such as location, cost, feasibility, and availability are used for evaluations. For the wind energy, cost was determined to be the most important criterion when making a technology decision. For the SO₂ emissions technology, the regenerative process was determined to be the best technology to scrub SO₂ emissions from the air. Additionally, efforts towards renewable energy in Oregon should continue. Both federal and state governments offer tax credits that can help mitigate costs and facilitate the adoption of renewable energy options for power companies.     

Composition of the Earth's interior: the importance of early events

The detection of excess 142Nd caused by the decay of 103Ma half-life 146Sm in all terrestrial rocks compared with chondrites shows that the chondrite analogue compositional model cannot be strictly correct, at least for the accessible portion of the Earth. Both the continental crust (CC) and the mantle source of mid-ocean ridge basalts (MORB) originate from the material characterized by superchondritic 142Nd/144Nd. Thus, the mass balance of CC plus mantle depleted by crust extraction (the MORB-source mantle) does not sum back to chondritic compositions, but instead to a composition with Sm/Nd ratio sufficiently high to explain the superchondritic 142Nd/144Nd. This requires that the mass of mantle depleted by CC extraction expand to 75-100 per cent of the mantle depending on the composition assumed for average CC. If the bulk silicate Earth has chondritic relative abundances of the refractory lithophile elements, then there must exist within the Earth's interior an incompatible-element-enriched reservoir that contains roughly 40 per cent of the Earth's 40Ar and heat-producing radioactive elements. The existence of this enriched reservoir is demonstrated by time-varying 142Nd/144Nd in Archaean crustal rocks. Calculations of the mass of the enriched reservoir along with seismically determined properties of the D' layer at the base of the mantle allow the speculation that this enriched reservoir formed by the sinking of dense melts deep in a terrestrial magma ocean. The enriched reservoir may now be confined to the base of the mantle owing to a combination of compositionally induced high density and low viscosity, both of which allow only minimal entrainment into the overlying convecting mantle.     

Simultaneous determination of the size and surface charge of individual nanoparticles using a carbon nanotube-based Coulter counter

A resistive-pulse Coulter counter based on a membrane containing a single multiwall carbon nanotube (MWNT) channel was used to simultaneously determine the size and surface charge of carboxy-terminated polystyrene nanoparticles. The membrane was prepared from an epoxy section containing a MWNT channel mounted on a poly(dimethylsiloxane) (PDMS) support structure. The PDMS support reduced the background noise level by a factor of > 20 compared to the Si/Si3N4 support structure used in our previous study. The lower noise level makes it possible to accurately measure the height and width of resistive-pulse signals resulting from transport of individual particles through the MWNT channel. Particle sizes, calculated from current pulse heights, were comparable to those determined by transmission electron microscope (TEM). The width of the current pulses is a measure of the nanoparticle transport time, and it permits calculation of the electrokinetic surface charge. Different types of polystyrene nanoparticles having nearly the same size, but different electrokinetic surface charge, could be resolved on the basis of the difference in their transport time.