Wide Length Distribution Research Articles

Crystallization of single-walled carbon nanotubes from a dilute solution

Single-walled carbon nanotubes (SWNTs) with lengths of several hundred nanometers were crystallized from dilute solutions, and slender lath-shaped SWNT crystals were obtained. The SWNTs were oriented along the long axis of the lath-shaped crystal, and the obtained crystals were two-dimensional crystals comprising hexagonally close-packed SWNTs. A relatively long SWNT acted as a crystalline nucleus. The length of the SWNT used for crystallization affected the morphology and growth rate of the crystals. Higher crystallization temperature shortened the time to precipitation, and the diffusion of SWNTs dominated the crystal growth of SWNT crystals. Because the short SWNTs were rigid with a wide length distribution, their tube ends were inevitably included in the crystals, resulting in crystal defects, such as lattice curvature and edge dislocations. These defects were directly observed by high-resolution electron microscopy. The mechanism for the crystallization of the SWNTs was proposed based on the observed morphologies, crystal defects, and crystallization process.

Synthesis, characterization and oxidizing strength of a nano-structured hypervalent iodine(v) compound: iodylbenzene nanofibers

In this study, disproportionation of freshly synthesized iodosylbenzene in boiling distilled water in the presence of triethylene glycol monomethyl ether was used to prepare ribbon-like iodylbenzene nanostructures with a wide length distribution (250 nm up to several microns) and a width in the range of 100–200 nm.

Nanostructured Fat Crystal and Solid Fat Content Effects on the Physical Properties of Water-in-Oil Semisolid Fat Blends.

The effect of nanostructured fat crystals on oil migration properties in water-in-oil-type emulsified semisolid fats was investigated. Model emulsions containing 4 different semisolid fats (palm oil, partially hydrogenated palm oil, partially hydrogenated soybean oil, and milk fat) and 1 bulk fat blend were prepared with rapidly cooling crystallization. The length of the nanoplatelets was observed by cryo transmission electron microscopy, the crystal thickness was calculated by small-angle X-ray diffraction, and the solid fat content (SFC) was determined. Although the interfacial surface of the dispersed water droplets did not influence nanoplatelet size, oil migration in the emulsified samples was lower than in the bulk fat. The crystal sizes in samples with partially hydrogenated soybean oil involving elaidic acid were larger, in contrast to that of milk fat, involving low to medium chain length fatty acids, which had smaller crystal sizes and showed wide length distribution. The length of the platelets and SFC were related to the oil migration value. These results suggest that the oil binding ability of fat products, such as margarine, is influenced by the nanostructure, which is related to fatty acid composition and interfacial structure.

Methylmercury in fish from the southern Baltic Sea and coastal lagoons as a function of species, size, and region.

Methylmercury (MeHg) is a highly toxic compound that traverses the blood-brain barrier with deleterious effects to the central nervous system. Exposure is generally through the ingestion of contaminated fish. Fish are a main source of MeHg. Goals and methods: The aim of this study was to determine the dependence of MeHg concentrations on fish species and age, the percentage of MeHg in total mercury (THg) and risk assessment depending on the size of fish. Assays of THg and MeHg were performed on the muscle tissues of 18 species of fish. The investigations indicated there were differences in the mercury concentrations depending on fish size. THg and MeHg concentrations in the muscles of fish species that have a wide length distribution were strongly, positively correlated with fish length. However, concentrations of MeHg were strongly, positively correlated with those of THg in all the fish species investigated. Variation in the percentage share of MeHg in THg in the muscles of fish of large sizes was also noted within species, but this correlation was not noted in small-sized fish. The dose of MeHg in small-sized fish species was estimated and the risk posed to consumer health was assessed using mean MeHg concentrations determined for different fish species. For species of fish that occur within a wide length distribution, the dose of MeHg should be assessed separately in different length classes. Fish consumption of small-sized species poses no health risk.

A general model for estimating the ordering of mesoporous film by grazing incidence small angle X-ray scattering

The ability to quantifiably characterize the structure of mesoporous membranes over a large sample surface area is inherently crucial to the preparation of well-controlled and functional mesoporous silica films. To estimate the degree of ordering in silica films on a statistical level, grazing incidence small angle x-ray scattering (GISAXS) was used to analyze the nanostructure of silica films with high-ordered mesochannel arrays, and a general analysis model was developed for interpreting the resulting GISAXS patterns. Structural information on the films, including the mesochannel size, orientation, positional distribution factor, subunit number in coherent region, and mesochannel length distribution, were obtained by fitting the model to the experimental data. The GISAXS analysis results showed the gradually decreasing ordering of silica film, which can be attributed to two aspects: the positional deviation from ideal lattice sites in the plane perpendicular to the substrate surface, and the wide length distribution of the mesochannels. The proposed model is expected to be successfully extendable to the analysis of several other types of mesoporous film with different pore morphologies.

Single- and Multi-Wall Carbon Nanotubes Versus Asbestos: Are the Carbon Nanotubes a New Health Risk to Humans?

Carbon nanotubes (CNT), since their discovery, have become one of the most promising nanomaterials in many industrial and biomedical applications. Due to their unique physicochemical properties, interest is growing in the manufacture of CNT-based products and their subsequent marketing. Since their discovery, the prospect of possible undesirable human health effects has been a focus of many scientific studies. Although CNT possess unique physical properties that include (1) nanoscale diameter, (2) a wide length distribution ranging from tens of nanometers to several micrometers, and (3) high aspect ratio, the fibrous-like shape and durability suggest that their toxic properties may be analogous to those observed with other fibrous particles, such as asbestos. The present study provides a summary of published findings on CNT bioactivity, such as the potential of CNT, especially of multi-wall carbon nanotubes (MWCNT), to activate signaling pathways modulating transcription factor activity, induce apoptosis, induce DNA damage, and initiate biological responses. Assessment of risks to human health and adoption of appropriate exposure controls is critical for the safe and successful introduction of CNT -based products for future applications.

From Tunneling to Hopping: A Comprehensive Investigation of Charge Transport Mechanism in Molecular Junctions Based on Oligo(p-phenylene ethynylene)s

The charge transport mechanism of oligo(p-phenylene ethynylene)s with lengths ranging from 0.98 to 5.11 nm was investigated using modified scanning tunneling microscopy break junction and conducting probe atomic force microscopy methods. The methods were based on observing the length dependence of molecular resistance at single molecule level and the current-voltage characteristics in a wide length distribution. An intrinsic transition from tunneling to hopping charge transport mechanism was observed near 2.75 nm. A new transitional zone was observed in the long length molecular wires compared to short ones. This was not a simple transition between direct tunneling and field emission, which may provide new insights into transport mechanism investigations. Theoretical calculations provided an essential explanation for these phenomena in terms of molecular electronic structures.

Morphology and Structure of Poly(p-phenylene Benzobisthiazole) Crystals

The rigid polymer poly(p-phenylene benzobisthiazole) (PBZT) was crystallized from dilute solution. Electron microscopy showed that, on quenching, flat fibrils several nanometers thick were produced. Subsequent heat treatment in a solvent changed the morphology from fibrillar into “segmented ribbon” structure. Isothermal crystallization at a temperature of about 30°C below the dissolution temperature, in general, resulted in aggregation of rod crystals. The polymer chains were oriented normal to the rod crystals. The width of the rod crystal increased with average molecular length, but saturated to a value much smaller than the average molecular length. In the shorter molecular length range, the rod crystals clustered in a fanned-out manner, while with a medium molecular length (ca. 70–120 nm), all rods crystals in a cluster aligned parallel to each other and were of the same length. With longer molecular length (more than ca. 180 nm), the rod growth slowed because of small diffusion constants of molecular chains to the growing face. Based on observation of the morphology and the crystallization process, an isothermal crystallization mechanism is proposed. Because of the rigidity and wide length distribution of polymer chains, the chain ends were inevitably included within the crystals, resulting in crystal defects such as axial shifts, lattice curvatures, and edge dislocations, all of which were observed directly by lattice imaging.

Packing of Cylindrical Particles with a Length Distribution

The packing of cylindrical particles with log‐normal and modified power‐law length distributions has been experimentally studied. The results indicate that the packing density is heavily dependent on the parameters in the two distributions. However, this dependence cannot be predicted by the direct analogy to that for the packing of spherical particles. It is postulated that the packing of nonspherical particles be governed by two factors: the shape effect and the size effect, which respectively correspond to the unmixing and mixing states of a particle mixture and are quantified from the specific volumes of the two states. Analysis of the results suggests that the shape effect is dominant for the packing of cylindrical particles with a wide length distribution.