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[en] A study was conducted on the effect of multiwalled carbon nanotubes (MWNT) on the course of free-radical grafting of trans-ethylene-1,2-dicarboxylic acid (TEDA) onto linear low-density polyethylene (LLDPE) and ethylene-propylene copolymer (cPP), containing ethylene units * 7 wt%, using the reactive extrusion process. The extrusion reactor was the material cylinder of the twin-screw extruder TSSK.-35/40 (screw diameter = 35 mm; L/D = 40; 10 independent heating zones). It was found that small amounts of MWNT (0.01-0.3 wt%) influence noticeably the monomer grafting onto macromolecules of LLDPE and cPP, as well as the structure, functionalized products' mechanical properties, strength and high elasticity properties of their melts. The extent of MWNT influence depends on their concentration and PO-structure. It is show that the monomers grafting efficiency can be raised with MWNT >= 0.1 wt% inhibit the secondary process of macromolecular cross-linking; in the case of cPP which mostly undergoes degradation during functionalization, the secondary reactions accelerate catalytically. (authors)
[en] A nonlinear current induced in carbon nanotubes with metallic conductivity and in graphene nanoribbons by an alternating electric field with a subnanosecond width of the leading edge in the presence of a static electric field has been theoretically studied. The parameters of the static electric field for simple carbon nanotubes coincide with the parameters of nanosecond electric pulses
[ru]Теоретически изучается нелинейный ток, индуцированный в углеродных нанотрубках (УНТ) с металлическим типом проводимости и в графеновых нанолентах переменным электрическим полем, с субнаносекундной шириной переднего фронта при наличии постоянного электрического поля. Для простых УНТ параметры постоянного электрического поля совпадали с параметрами наносекундных электрических импульсов
[en] Full text: Single-walled carbon nanotubes (SWNTs) has physically and chemically superior properties. Although SWNTs are generally hydrophobic, SWNTs can be dispersed in aqueous solution by forming complexes with DNA (DNA-SWNTs). Nanobiosensors using optical responses of DNA-SWNT complexes such as near-infrared photoluminescence (PL) of SWNTs have been proposed by many research groups. On the other hand, it is known that the optical responses of SWNTs are affected by chirality of SWNTs although the chirality effects in the nanobiosensing with DNA-SWNT complexes have not been well understood. If we understand and regulate the chirality effects, it is expected that more sophisticated nanobiosensing techniques can be established. In this study, we investigated the chirality effects on PL from DNA-SWNT surfaces in absence and presence of fluorescent dyes. We previously reported attachments of fluorescent dyes to DNA-SWNT surfaces for functionalization. SWNTs were dispersed with single stranded DNA (ssDNA) or double stranded DNA (dsDNA). Excitation wavelengths for PL measurements were 550 to 750 nm. PL of SWNTs were measured from 850 to 1600 nm (every 1 nm). When rhodamine B solution (RB) or uranine solution (UR) was added to DNA-SWNT suspension as fluorescent dyes, molar ratio of the fluorescent dyes to carbon atom in the samples were adjusted to 1:200. Normalized PL intensities before and after addition of dyes were plotted for several different chiralities of SWNTs. For normalization, PL of (9, 4) chirality was defined as 1. The data indicated average values of independent three experiments. PL intensity was decreased in all the chiralities when RB or UR were added to the DNA-SWMT suspension, however, quenching ratios were different due to chirality of SWNTs and combinations of types of DNA and dyes. In the case of ssDNA-SWNT complexes with RB, quenching ratios of (8,6), (8,3), (8,4), (7,5), (7,6), and (9,4) were 5%, 3%, 4%, 10%, 10%, and 10%, respectively. Based on this result, we propose categorization of the six chiralities. In group (a) ((8,6), (8,3), and (8,4)), the quenching ratios were low (average quenching ratios of the three chiralities = 4%). In the groups (b) ((7,5), (7,6), and (9,4)), those were relatively higher (average quenching ratios of the three chiralities = 10%). In ssDNA-SWNT with UR, average quenching ratios of groups (a) and (b) were 3% and 3%, respectively. In the case of dsDNA-SWNT with RB, the ratios of (a) and (b) were 3% and 3%, respectively. In these samples, there was no difference between groups (a) and (b). In dsDNA-SWNT with UR, the ratios of (a) and (b) were 2% and 0%, respectively. In this combination, group (a) indicated slightly higher quenching ratios. Our results revealed that each chirality of SWNTs involves its specific optical responses. The different responses originated from chirality are probably useful to establish nanobiosensing techniques using DNA-SWNT complexes. (author)
[en] It is shown that the interplay between curvature and interfacial Dzyalonshinsky–Moriya interaction (DMI) is a pathway to ultrafast domain wall (DW) dynamics in ferromagnetic nanotubes. In this work, we theoretically study the effect that interfacial DMI has on the average velocity of a vortex DW in thin ferromagnetic nanotubes grown around a core composed of heavy atoms. Our main result shows that by delaying the Walker breakdown instability, the DW average velocity is of the order of 103 m s−1, which is greater than usual values for these systems. The remarkable velocities achieved through this configuration could greatly benefit the development of spintronic devices. (paper)
[en] Nanotubes are miniature materials with significant potential applications in nanotechnological, medical, biological and material sciences. The quest for manufacturing methods of nano-mechanical modules is in progress. For example, the application of carbon nanotubes has been extensively investigated due to the precise width control, but the precise length control remains challenging. Here we report two approaches for the one-pot self-assembly of RNA nanotubes. For the first approach, six RNA strands were used to assemble the nanotube by forming a 11 nm long hollow channel with the inner diameter of 1.7 nm and the outside diameter of 6.3 nm. For the second approach, six RNA strands were designed to hybridize with their neighboring strands by complementary base pairing and formed a nanotube with a six-helix hollow channel similar to the nanotube assembled by the first approach. The fabricated RNA nanotubes were characterized by gel electrophoresis and atomic force microscopy (AFM), confirming the formation of nanotube-shaped RNA nanostructures. Cholesterol molecules were introduced into RNA nanotubes to facilitate their incorporation into lipid bilayer. Incubation of RNA nanotube complex with the free-standing lipid bilayer membrane under applied voltage led to discrete current signatures. Addition of peptides into the sensing chamber revealed discrete steps of current blockage. Polyarginine peptides with different lengths can be detected by current signatures, suggesting that the RNA-cholesterol complex holds the promise of achieving single molecule sensing of peptides. .
[en] By using density functional theory calculations, the chemical functionalization of finite-sized (5,0) and (6,0) carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) by different carbonyl derivatives -COX (X = H, CH3, OCH3, OH, and NH2) is studied in terms of geometrical and electronic structure properties. Also, the benefits of local reactivity descriptors is studied to characterize the reactive sites of the external surface of the tubes. These local reactivity descriptors include the electrostatic potential VS(r) and average local ionization energy ⧶S(r) on the surfaces of these nanotubes. The estimated ⧶S(r) values show that the functionalized CNTs tend to activate the surface toward electrophilic/radical attack. Results show that the chemical functionalization of CNTs leads to the reduction of VS(r) values and therefore enhances the surface reactivity. On the other hand, BNNTs resist chemical functionalization due to the negligible decrease in the VS,min and ⧶S,min values. Generally, in contrast to BNNTs, the chemical functionalization of CNTs can considerably improve their surface reactivity. To verify the surface reactivity pattern based on the chosen reactivity descriptors, the reaction energies for the interaction of an H+ ion or hydrogen radical with external surface of the functionalized CNTs and BNNTs are calculated. A general feature of all studied systems is that stronger potentials are associated with regions of higher curvature. (author)
[en] The emergence of new nanotechnologies involves the spreading of nanoparticles in various fields of human life. Nanoparticles in general and, more specifically, carbon nanotubes have been adopted for many practical approaches i.e.: coatings for medical devices, food process industry and drug delivery. Humans will be increasingly exposed to nanoparticles but the susceptibility of nanostructured materials to microbial colonization in process of manufacturing and storage has not been thoroughly considered. Therefore, the microbiological quality control of nanoparticles plays a pivotal role. Different analytical methods have been attempted for detecting bacterial population contaminating a surface, but no one can be considered fully appropriate. Here, BioTimer Assay (BTA) and conventional sonication followed by colony forming units method (S-CFU) were applied for microbiological quality control of single-walled carbon nanotubes (SWCNTs)-coated surfaces experimentally contaminated with Streptococcus mutans and Pseudomonas aeruginosa. Our results demonstrated that S-CFU is unreliable to actually determine the number of bacteria, contaminating abiotic surfaces, as it does not detach all adherent bacteria and kills part of the bacterial population. Instead, BTA is a reliable method to enumerate bacteria colonizing SWCNTs-coated surfaces and can be considered a useful tool for microbiological quality control of nanomaterials for human use.