Three-dimensional morphological chirality induction using high magnetic fields in membrane tubes prepared by a silicate garden reaction

Using a vertical superconducting magnet (max. 15 T), we studied magnetic field effects on membrane tube morphology prepared by a silicate garden reaction. At zero field, semipermeable membrane tubes grew upward when metal salts were added to a sodium silicate aqueous solution. In the presence of a magnetic field (15 T, downward) right-handed helical membrane tubes grew along a glass vessel's inner surface when magnesium chloride and copper sulfate were added. Referring to membrane tubes by the names of metal cations used in their preparation, in the case of Mg(II) and Zn(II) membrane tubes, the left-handed helical tubes grew when the field direction was reversed upward. The left-handed helical Mg(II) membrane tubes grew in the magnetic field when a glass rod was placed in a vessel. Mg(II) and Zn(II) tubes, separate from a vessel wall, grew in a twisted shape in the magnetic field. In situ observation of the solution's motion during the reaction revealed that the Lorentz force on the outflow from the opened top of the hollow membrane tube induced convection of the solution near the tube exit, engendering chiral growth of the membrane tubes. Relative orientation of the outflow and a boundary (a vessel wall or glass rod surface) helped to determine the convection's direction.     

Hollow polyelectrolyte multilayer tubes: mechanical properties and shape changes

In this paper, novel hollow polyelectrolyte multilayer tubes from poly(diallyldimethylammonium chloride) (PDADMAC), poly(styrene sulfonate) (PSS), and poly(allylamine hydrochloride) (PAH) were prepared: Readily available glass fiber templates are coated with polyelectrolytes using the layer-by-layer technique, followed by subsequent fiber dissolution. Depending on the composition of the polymeric multilayer, stable hollow tubes or tubes showing a pearling instability are observed. This instability corresponds to the Rayleigh instability and is a consequence of an increased mobility of the polyelectrolyte chains within the multilayer. The well-defined stable tubes were characterized with fluorescence microscopy, confocal laser scanning microscopy, and atomic force microscopy (AFM). The tubes were found to be remarkably free of defects, which results in an impermeable tube wall for even low molecular weight molecules. The mechanical properties of the tubes were determined with AFM force spectroscopy in water, and because continuum mechanical models apply, the Young's modulus of the wall material was determined. Additionally, scaling relations for the dependency of tube stiffness on diameter and wall thickness were validated. Because both parameters can be experimentally controlled by our approach, the deformability of the tubes can be varied over a broad range and adjusted for the particular needs.     

The intermediate frequency modes of single- and double-walled carbon nanotubes: a Raman spectroscopic and in situ Raman spectroelectrochemical study

The intermediate frequency modes (IFM) of single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) were analyzed by Raman spectroscopy and in situ Raman spectroelectrochemistry. The inner and outer tubes of DWCNTs manifested themselves as distinct bands in the IFM region. This confirmed the diameter dependence of IFM frequencies. Furthermore, the analysis of inner tubes of DWCNTs allowed a more-precise assignment of the bands in the IFM region to features intrinsic for carbon nanotubes. Although the inner tubes in DWCNTs are assumed to be structurally perfect, the role of defects on IFM was discussed. The dependence of IFM on electrochemical charging was also studied. In situ spectroelectrochemical data provide a means to distinguish the bands of the outer and inner tubes.     

Growth of single-layer carbon tubes assisted with iron-group metal catalysts in carbon arc

Single-layer (SL) carbon tubes were produced by arc evaporation of graphite rods containing iron-group metals (Fe, Co, Ni, Fe/Co, Co/Ni, Fe/Ni) under He and Ar gas. Transmission electron microscopy (TEM) revealed that these elemental and binary metals, excluding Fe which need a special atmosphere (a mixture of Ar and CH₄), showed catalytic activity producing SL tubes under pure inactive gases. Fe/Ni alloy was the most effectual catalysts for producing SL tubes. The highest abundance of SL tubes in raw soot was estimated to be ～ 10% from TEM observation. Smoke particles directly caught on TEM grids near an evaporation source during arcburning were also investigated, and it was suggested that small metal particles were first formed in the gas phase and then SL tubes grew from them.     

Bioassisted synthesis of catalytic gold/silica nanotubes using layer-by-layer assembled polypeptide templates

We report the bioassisted synthesis of gold nanoparticle/silica (Au NP/silica) tubes using layer-by-layer (LBL) assembled poly(L-lysine)/poly(L-tyrosine) (PLL/PLT) multilayer films deposited on the polycarbonate (PC) membrane pores as both mediating agents and templates. The novelty of this approach is the in situ synthesis of Au NP/silica tubes using PLL/PLT multilayer films for sequential growth of Au NPs and silicas. The experimental data revealed that the buildup of the LBL multilayer films was mainly driven by the formation of hydrogen bond and the polypeptide macromolecular assemblies adopted mainly β-sheet conformation. The as-prepared Au NP/silica tubes possessed promising catalytic activity toward the reduction of p-nitrophenol. The synthesis conditions such as the concentration of gold precursor and polypeptide molecular weight were found to influence the gold weight ratio and particle size in the tubes and the catalytic properties of the Au NP/silica tubes. This approach provides a facile, robust, and green method to obtain nonaggregated metal nanoparticles immobilized in porous oxide network at ambient conditions. Using the synergy between biomimetic or bioassisted synthesis of nanostructured materials and LbL assembly technique, a variety of structures such as films, tubes, and capsules comprising of multiple compositions can be obtained.     

Comparison of uncoated, pyro-coated and totally pyrolytic graphite tubes for the HGA-500 electrothermal atomiser

The analytical performance of three uncoated electrographite tubes, three pyro-coated electrographite tubes, one tantalum carbide (TaC) coated electrographite tube, and three totally pyrolytic graphite (TPG) tubes has been evaluated and compared. A test programme was devised to determine the useful operational lifetime of each tube, and assess the influence of tube age on the sensitivity of lead, manganese and vanadium measurements by atomic absorption spectrometry. The TPG tubes were found to be more durable than the other types studied, but the lifetime advantage depended on the thickness of the pyrolytic graphite. The best TPG tube, of 720 μm wall-thickness, lasted 2.5 times longer than the pyro-coated tubes, and 5 times longer than the uncoated electrographite tubes.The TPG tubes gave slightly poorer AAS sensitivity for lead, equivalent sensitivity for manganese, and 4 times better sensitivity for vanadium than the pyro-coated electrographite tubes. Also, with TPG, signal magnitude was more consistent throughout the lifetime of a tube. For each of the test elements studied, poorest sensitivity was encountered with the TaC-coated electrographite tube.     

Fire behaviour of hybrid filament-wound single and adhesively bonded composites tubes under static pressure

The present work aims to experimentally investigate the fire behaviour of water-filled E glass reinforced thermoset resin hybrid filament-wound composites tubes under static pressure. Heretofore, fire endurance tests have been conducted on single and adhesively bonded tubes manufactured by CTRA Company. Furthermore, internal pressure tests until failure have been performed on the burnt single and burnt joined tubes in order to quantify their abilities to contain the fluid after being exposed to heat flux. A comparison between the pressure behaviour of exposed to fire (burnt) and non-exposed tubes (single and joined) was also inspected. The identification of the fire-induced damage mechanisms of the tubes was performed through optical microscopy, Scanning Electron Microscopy (SEM) and X-ray tomographic observations. Finally, the thermal analysis was carried-out on burnt specimens in order to better understand the multiphysical phenomenon taking place during the fire endurance tests. The experimental results have revealed that the combustion process of both single and joined tubes was described in four steps namely tube heating, resin degradation, ignition and flame decay. Moreover, it was found that no leakage was witnessed on the tubes (single and joined) outer surfaces during the fire endurance tests. The comparison between the pressure behaviour of the burnt single tube and the burnt joined one has proved that the single tube is much resistant under internal pressure loading than the burnt joined tube. Finally, the fire-induced damage included matrix cracking and delamination between the tube plies which was noticed from microscopic observations.     

Theoretical study of boron nitride nanotubes with defects in nitrogen-rich synthesis

On the basis of calculations using the density functional theory, it is shown that BNNT synthesis could produce tubes deprived of one (B1 hole) or two (B2 hole) boron atoms under the condition where nitrogen atoms exist in excess throughout this study. The relative populations of various isomers of defective tubes will depend on the chirality of the tube. Interestingly, calculations show that B2 holes are much more favored than B1 holes, particularly in armchair tubes. Electronic properties are modified in such a way that the band gap is decreased through the introduction of defect states inside the gap. Magnetic properties will also be dependent on the chirality. The majority of armchair tubes with B2 holes will be nonmagnetic, while the majority of zigzag tubes with defects will exhibit magnetism. Contrary to the case of defect-free BNNT, the defective tubes are expected to be easily subject to reduction by accommodating excess electrons in the presence of Li atoms. In addition, the defect sites will show a higher affinity toward hydrogenation than the defect-free sites.     

Gold tubes membrane with novel morphology replicated from ZnO template

Gold tubes membrane with novel morphology was fabricated on glass substrate by electroless plating gold on ZnO crystals array, and then annealing and removing the ZnO template by acid erosion. The morphology and size of the gold tubes membrane were decided by ZnO template. Hexagonal gold tubes membrane and double-wall gold tubes membrane were obtained, which enjoys some potential usage in electrode modification or chemical separation due to their huge surface area and unique geometric structure. SEM images show that those gold tubes in membrane are hollowed hexagonal columns with a closed head and an open bottom. Further researches found that two main factors determined the success of replication: the gold seeds (4-5 nm in diameter) immobilized on ZnO surface through APTMS (3-Aminopropyl-trimethoxysilane) before gold electroless plating and the annealing condition after electroless plating.     

Synthesis, characterization, and electrochemical application of Ca(OH)2-, Co(OH)2-, and Y(OH)3-Coated Ni(OH)2 tubes

We report on the synthesis, characterization, and electrochemical application of Ca(OH)2-, Co(OH)2-, and Y(OH)3-coated Ni(OH)2 tubes with mesoscale dimensions. These composite tubes were prepared via a two-step chemical precipitation within an anodic alumina membrane under ambient conditions. The morphology and structure of the as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) equipped with energy dispersive spectroscopy (EDS). The results showed that the size of the tubes was of mesoscale dimension and the proportion of the tube morphology was about 95%. The as-prepared composite tubes were further investigated as the positive-electrode materials of rechargeable alkaline batteries. Electrochemical measurements revealed that the Ni(OH)2 tubes coated with Ca(OH)2, Co(OH)2, and Y(OH)3 exhibited superior electrode properties including high discharge capacity, excellent high-temperature and high-rate discharge ability, and good cycling reversibility. The mechanism analysis suggests that both the coated layers and the unique hollow-tube structures play an indispensable role in optimizing the electrochemical performance of nickel hydroxide electrodes.     

Aqueous Dispersions of Thin Multiwalled Carbon Nanotubes

Aqueous dispersions of thin multiwalled carbon nanotubes stabilized by surface-active substance Triton X-100 were studied. The concentration of tubes depended on the surfactant: tubes weight ratio and reached 1.67 g/l at ratios of (2.0–2.3): 1.0. The diameter and length distributions of nanotubes were different in the dispersions and precipitates. A functional relation between the diameter and the ratio between the length and diameter was found for nanotubes in colloidal solution: the thickest tubes had the smallest length, and the length of the thinnest tubes was maximum.     

Synthesis of carbon tubes with mesoporous wall structure using designed silica tubes as templates

Hollow silica tubes with mesoporous wall structure were synthesized through the sol-gel reactions of tetraethoxysilane and n-octadecyltrimethoxysilane (TEOS/C18-TMS) on the surface of ammonium dl-tartrate crystals. Novel hollow carbon tubes with mesoporous walls and rectangular-shaped channels were fabricated using the silica tubes as templates.     

Ti and Ni tubes combined in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for the determination of copper in biological samples

This study presents an evaluation of Cu determination in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) using Ni and Ti metal tube atomizers. The TS-FF-AAS system was equipped with Ti tubes inserted inside Ni tubes (called Ni/Ti), and also different configurations of Ti tube atomizers placed on an oxidizing air/acetylene flame. This new arrangement combining both tubes permitted an increased sensitivity (approximately 4 times) when it was compared with single Ni or Ti tubes. This high sensitivity is due to the formation of TiO₂ inside the Ti tubes (shown by X-ray diffractometry and microanalyses), improving the Cu atomization through the corresponding oxide. The estimated gaseous phase temperatures for the tubes (Ni, Ti and Ni/Ti) were of the same magnitude (varied from 1400 to 1800 °C). Tests with concomitants (Na, K, Ca and Mg) showed similar behavior of Ni and Ni/Ti tubes. The differences between Ni and Ni/Ti tube atomizers for Cu sensitivity were not related to differences between the tube atomizers' internal volumes. The method accuracy was verified using certified reference materials (CRM's) of biological samples prepared with a closed-vessel microwave system using diluted HNO₃. A 2 µg L^− 1 Cu detection limit was obtained using a Ni/Ti tube atomizer. The recoveries for Cu from the CRM's were about 100%. Finally, the use of a Ti tube inside a Ni tube increased the Ti tube lifetime.     

Fast growth of TiO2 nanotube arrays with controlled tube spacing based on a self-ordering process at two different scales

In the present work, we introduce a technique to achieve rapid growth of self-ordered anodic nanotubes with a well-defined tube-to-tube spacing (spaced tubes) and single-wall morphology. By optimizing the anodization conditions (electrolyte, temperature, etc.), the growth rate of spaced tubes can be ≈ 25 times faster than in conventional approaches while maintaining a tube-to-tube spacing of ≈ 100 nm. We show that the origin of the tube-to-tube spacing is self-ordering of nanotubes on two different scales – the primary large tubes are embedded in a matrix of secondary, very short nanotubes with a small diameter. Preferential etching of the small tubes during anodic growth leaves behind an ordered array of spaced individual tubes with a well-defined tube-to-tube spacing.     

End-cap effects on vibrational structures of finite-length carbon nanotubes

Vibrational structures of C60-related finite-length nanotubes, C(40+20n) and C(42+18n) (1 < or = n < or = 4), in which n is, respectively, the number of cyclic cis- and trans-polyene chains inserted between fullerene hemispheres, are analyzed from density functional theory (DFT) calculations. To illuminate the end-cap effects on their vibrational structures, the corresponding tubes terminated by H atoms C(20n)H20 and C(18n)H18 (1 < or = n < or = 5) are also investigated. DFT calculations show a broad range of vibrational frequencies for the finite-size nanotubes: high-frequency modes (1100-1600 cm(-1)) containing oscillations along tangential directions (tangential modes), medium-frequency modes (700-850 cm(-1)) whose oscillations are located on the edges or end caps, and low-frequency modes (300-600 cm(-1)) involving oscillations along the radial directions (radial modes). Broadening of the calculated frequencies is due to the number of nodes in the standing waves of normal modes in the finite-size tubes. In the capped tubes, calculated vibrational frequencies are insensitive to the number of chains (n), whereas in the uncapped tubes, most vibrational frequencies change significantly with an increase in tube length. The discrepancy in the size dependency is reasonably understood by their C-C bonding networks; the capped tubes have similar bond-length alternation patterns within the polyene chains irrespective of n, whereas the uncapped tubes have various bond-deformation patterns. Thus, DFT calculations illuminate that the edge effects have strong impacts on the vibrational frequencies in the finite-size nanotubes.     

Dispersion of nitric acid-treated SWNTs in organic solvents and solvent mixtures

The dispersion of pristine and nitric acid-treated single-wall carbon nanotubes (SWNTs) has been studied in organic solvents and solvent mixtures using optical absorption, as a function of settling time. The extinction coefficients of both the pristine and acid-treated tubes at 500-nm wavelength was measured to be 25.5 (mg/L)(-1) cm(-1) in various solvents. The dispersibility of nitric acid-treated tubes increased with the solvent's hydrogen-bonding ability and reached 27 mg/L in ethanol and 35 mg/L in water. Nitric acid-treated tubes could also be dispersed in butanol/toluene and xylene/ethanol mixtures, which are known to be poor solvents for the pristine SWNTs.     

Addition of carbenes to the sidewalls of single-walled carbon nanotubes

The addition of carbenes CX(2) (X=H, Cl) to single-walled carbon nanotubes (SWNTs) was investigated by density functional theory and finite, hydrogen-terminated nanotube clusters or periodic boundary conditions in conjunction with basis sets of up to polarized triple-zeta quality. For armchair [(3,3) to (12,12)] and zigzag tubes [(3,0) to (18,0)], reaction of CH(2) with the C--C bond oriented along the tube axis (A) is less exothermic than with those C--C bonds having circumferential (C) orientation. This preference decreases monotonically with increasing tube diameter for armchair, but not for zigzag tubes; here, tubes with small band gaps have a very low preference for circumferential addition. Axial addition results in cyclopropane products, while circumferential addition produces "open" structures for both armchair and zigzag tubes. The barriers for addition of dichlorocarbene to a (5,5) SWNT, studied for a finite C(90)H(20) cluster, are higher than that for addition to C(60), in spite of similar diameters of the carbon materials. Whereas addition of CCl(2) to [60]fullerene proceeds in a concerted fashion, addition to a (5,5) armchair SWNT is predicted to occur stepwise and involve a diradicaloid intermediate according to B3LYP, PBE, and GVB-PP computations. Addition to C bonds of (5,5) armchair tubes resulting in the thermodynamically more stable insertion products is kinetically less favorable than that to A bonds yielding cyclopropane derivatives.     

Preparation of submicron polypyrrole/poly(methyl methacrylate) coaxial fibers and conversion to polypyrrole tubes and carbon tubes

In an effort to prepare electrically conductive nanofiber and nanotube materials, polypyrrole/poly(methyl methacrylate) coaxial fibers have been prepared using polymer fibers produced from an electrospinning process. Poly(methyl methacrylate) (PMMA) fibers with an average diameter of 230 nm were initially fabricated by electrospinning as core materials. The PMMA fibers were subsequently coated as templates with a thin layer of polypyrrole (PPy) by in-situ deposition of the conducting polymer from aqueous solution. Hollow PPy tubes were produced by dissolution of the PMMA core from PPy/PMMA coaxial fibers. High-temperature (1000 degrees C) treatment under inert atmosphere converted PPy/PMMA coaxial fibers into carbon tubes by complete decomposition of PMMA fiber core and carbonization of the PPy wall. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and FT-IR spectroscopy confirmed the formation of the PPy/PMMA coaxial fibers, PPy tubes, and carbon tubes.     

Molecular dynamics simulation of single wall carbon nanotubes polymerization under compression

Single wall carbon nanotubes (SWCNTs) often aggregate into bundles of hundreds of weakly interacting tubes. Their cross-polymerization opens new possibilities for the creation of new super-hard materials. New mechanical and electronic properties are expected from these condensed structures, as well as novel potential applications. Previous theoretical results presented geometric modifications involving changes in the radial section of the compressed tubes as the explanation to the experimental measurements of structural changes during tube compression. We report here results from molecular dynamics simulations of the SWCNTs polymerization for small diameter arm chair tubes under compression. Hydrostatic and piston-type compression of SWCNTs have been simulated for different temperatures and rates of compression. Our results indicate that large diameter tubes (10,10) are unlike to polymerize while small diameter ones (around 5 A) polymerize even at room temperature. Other interesting results are the observation of the appearance of spontaneous scroll-like structures and also the so-called tubulane motifs, which were predicted in the literature more than a decade ago.     

Point‐to‐Plane Nonhomogeneous Electric‐Field‐Induced Simultaneous Formation of Giant Unilamellar Vesicles (GUVs) and Lipid Tubes

It is well‐known that homogeneous electric fields can be used to generate giant unilamellar vesicles (GUVs). Herein we report an interesting phenomenon of formation of GUVs and lipid tubes simultaneously using a nonhomogeneous electric field generated by point‐to‐plane electrodes. The underlying mechanism was analyzed using finite element analysis. The two forces play main roles, that is, the pulling force (F) to drag GUVs into lipid tubes induced by fluid flow, and the critical force (Fc) to prevent GUVs from deforming into lipid tubes induced by electric fields. In the center area underneath the needle electrode, the GUVs were found because F is less than Fc in that region, whereas in the edge area the lipid tubes were obtained because F is larger than Fc. The diffusion coefficient of lipid in the tubes was found to be 4.45 μm² s^?1 using a fluorescence recovery after photobleaching (FRAP) technique. The method demonstrated here is superior to conventional GUV or lipid tube fabrication methods, and has great potential in cell mimic or hollow material fabrication using GUVs and tubes as templates.