Cylindrical Nanostructures Research Articles

Pharmacokinetics of CNT-based Drug Delivery Systems

Carbon nanotubes (CNT) are allotropes of carbon with a cylindrical nanostructure. They have recently aroused great interests as drug carriers, but their pharmacokinetic profiles which determine their potentials in clinical application are yet to be fully understood. Therefore, this overview attempts to outline the processes of absorption, distribution, metabolism and excretion (ADME) that govern the pharmacokinetics of CNT. In addition, the molecular mechanisms of intracellular internalization and drug release are also discussed.

Surface plasmon modes of infinite cylindrical metallic nanostructures

The surface modes as well as their dispersion relations for surface plasmons (SPs) in some infinite cylindrical metallic nanostructures including wires, cavities, and tubes are investigated theoretically by using plasmon hybridization (PH) theory. We discuss that how the dispersion curves of SP modes for nanotubes depend on the geometry parameters, revealing that hybridization strength between inner and outer SPs strongly relies on the wall thickness of tube. In addition, in the long-wavelength limit, these geometry-dependent properties for nanotubes behave in an extremely similar fashion as that of nanorings.

Magnetic properties of multisegmented cylindrical nanoparticles with alternating magnetic wire and tube segments

The magnetic properties in multisegmented cylindrical nanostructures comprised of nanowire and nanotube segments are investigated numerically as a function of their geometry. In this work we report systematic changes in the coercivity and remanence in these systems. Besides, we have found the ideal conditions for a magnetic configuration with two antiparallel domains that could be used to help to stabilize magnetic nanoparticles inside ferromagnetic multisegmented cylindrical nanoparticles. This magnetic behavior is due to the fact that the tube segment reverses its magnetization before the wire segment, allowing the control of the magnetic domain walls motion between two segments. In this way, these magnetic nanoobjects can be an alternative to store information or even perform logic functions.

Cylindrical Nanostructure of Rigid-Rod POSS-Containing Polymethacrylate from a Star-Branched Block Copolymer.

A nanostructure consisting of rectangular polyhedral oligomeric silsesquioxane (POSS) nanodomains packed into a hexagonal lattice was observed in POSS-containing A2B star-branched polymers. The A2B star-branched polymers, which comprised polystyrene (A) and bulky POSS-containing poly(methacrylate) (PMAPOSS) (B) units, were synthesized by anionic polymerization and addition reaction. The self-assembled structures of the A2B star-branched polymers were studied via transmission electron microscopy (TEM) and small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). It was found that a rectangular nanostructure was packed into a hexagonal arrangement of nanodomains for a PMAPOSS volume fraction of 40 vol. % in the star-branched polymer. In addition, the cylinder-like nanostructure of bulky POSS observed, which is not observed in the case of PS-b-PMAPOSS diblock copolymers, was formed owing to the curvature effect, which is the result of the branched architecture of the copolymer.

Graphene-layered steps and their fields visualized by 4D electron microscopy

Enhanced image contrast has been seen at graphene-layered steps a few nanometers in height by means of photon-induced near-field electron microscopy (PINEM) using synchronous femtosecond pulses of light and electrons. The observed steps are formed by the edges of graphene strips lying on the surface of a graphene substrate, where the strips are hundreds of nanometers in width and many micrometers in length. PINEM measurements reflect the interaction of imaging electrons and induced (near) electric fields at the steps, and this leads to a much higher contrast than that achieved in bright-field transmission electron microscopy imaging of the same strips. Theory and numerical simulations support the experimental PINEM findings and elucidate the nature of the electric field at the steps formed by the graphene layers. These results extend the range of applications of the experimental PINEM methodology, which has previously been demonstrated for spherical, cylindrical, and triangular nanostructures, to shapes of high aspect ratio (rectangular strips), as well as into the regime of atomic layer thicknesses.

Thermally modulated nanostructure of poly(ε-caprolactone)–POSS multiblock thermoplastic polyurethanes

A series of multiblock polyurethanes with alternating sequence structures of a poly(ε-caprolactone) (PCL) segment of 2600 or 3600 g/mol and a polyhedral oligomeric silsesquioxane (POSS) segment with multiple POSS moieties (TPU2.6k_1-x or TPU3.6k_1-x, respectively; the molar ratio of PCL:POSS is 1: x; x = 2, 3, or 4) were synthesized through two-step polymerization to assure quantitative conversion of reactants. Differential scanning calorimetry and simultaneous wide- and small-angle X-ray scattering measurements were performed to study the nanostructures of those samples. The multiblock and alternating sequence structures provided nano-confined environments for PCL and POSS domains, which significantly suppressed crystallinity of the PCL phase, while nano-sized crystallites were formed in the POSS phase. The samples in series TPU2.6k and TPU3.6k were also proven to display either lamellar, cubic, or cylindrical hexagonal phase-separated nanostructures depending on the molecular weight of the PCL segment, as well as the PCL/POSS ratio. It was also found that repeated thermal cycling under a nitrogen atmosphere low enough in temperature not to alter molecular weight caused larger and more ordered PCL and POSS crystalline structure to form for the TPU3.6k series. Apparent reconfiguration of the PCL and POSS moieties along the backbone by exchange reactions associated with reversibility of urethane bonds led to increases in PCL and POSS block lengths in the TPU chains. We envision an opportunity of future research and applicability in the areas of tailored toughness and rigidity in biodegradable polymer coatings, devices with enlarged data storage capacity, drug delivery systems and tissue engineering.

Theoretical description of cylindrical nano-structures, including pores in semiconductors

Cylindrical and prismatic nano-structures (nano-wires and pores) with circular and hexagonal cross-section are studied using mirror boundary conditions to solve the Schrödinger equation in effective mass approximation. In comparison with “quantum billiard” problem, the solution using mirror boundary conditions allows to obtain the results in a much simpler way. It is possible to use even and odd mirror boundary conditions depending on the sign of the wave-function equated in the original and the image points, respectively. The even mirror boundary conditions provides non-vanishing wave-function at the boundary, corresponding to weak confinement allowing quantum tunneling. The odd mirror boundary conditions set wave-function to zero at the boundary, corresponding to a strong confinement. We report on spatial distributions of probability density in cross-section of a cylindrical and prismatic nano-structures, presenting the formulas for the energy of the corresponding quantum states.

Application of carbon nanotube in wireless sensor network to monitor carbon dioxide

Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Over the years, new discoveries have led to new applications, often taking advantage of their unique electrical properties, extraordinary strength and efficiency in heat conduction. Since industrialisation, human activities have resulted in steadily increasing concentrations of the greenhouse gases. Excess amount of carbon dioxide (CO2) in living environment is toxic and unsuitable for human consumption. Thus, a need exists for accurate, inexpensive, long-term monitoring of environmental contaminants using sensors that can be operated on site. Over the past decade, many wireless sensor network (WSN)-based monitoring applications have been proposed. This article reviews the developments of sensing elements to monitor CO2 in the environment. The cylindrical carbon molecules have novel properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential sensing element in wireless sensor technology. They exhibit extraordinary strength and unique electrical properties, and are efficient thermal conductors. The unique properties of CNT makes it a potential sensing element in the WSN technology.

Quantum mechanical description of Electronic transitions in Cylindrical nanostructures, including pores in semiconductors

Papers in the Appendix were published in electronic format as Volume 1534

Biomimetic zinc chlorin–poly(4-vinylpyridine) assemblies: doping level dependent emission–absorption regimes

To develop biomimetic dye–polymers for photonics, two different types of Zn chlorin–poly(4-vinylpyridine) (P4VP) assemblies were prepared by varying Zn pyro-pheophorbide a methylester (ZnPPME) and Zn 31-OH-pyro-pheophorbide a methylester (Zn-31-OH-PPME) doping levels. 1H NMR spectroscopy and diffusion ordered NMR spectroscopy (DOSY) studies revealed that a coordinative interaction between Zn chlorin and P4VP was predominant in solution (d5-nitrobenzene). Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) characterization of bulk samples of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) doped with variable amounts of Zn chlorin showed that the pigment doping transformed the native cylindrical block copolymer nanostructures to lamellar morphologies. The result indicates that the pyridine moiety–Zn chlorin coordination is stronger than the aggregation tendency between the pigment molecules even in the solid state. UV-Vis absorption spectroscopy studies of a Zn chlorin–P4VP thin film showed characteristic monomeric chlorin spectra, while steady-state fluorescence spectroscopy displayed quenching of fluorescence and time-resolved studies indicated shortening of fluorescence lifetimes with an increasing chlorin doping level. Notably, time-resolved fluorescence spectroscopy revealed that the lifetime decay changed from monoexponential to biexponential above 0.5 wt% (ca. 0.001 equiv.) loadings. The Förster analysis implies that excitonic chlorin–chlorin interactions are observed in the thin films when the distance between the pigment molecules is approximately 50 Å. The Zn chlorin–P4VP solid films emit strongly up to 1 wt% (ca. 0.002 equiv.) doping level above which the chlorin–chlorin interactions start to linearly dominate with an increase of doping level, while with 10 wt% (ca. 0.02 equiv.) loading less than 10% of fluorescence remains. Doping levels up to 300 wt% (0.5 equiv.) can be used in absorbing materials without the formation of chlorin aggregates. These defined optical response regions pave the way for photonic materials based on biopigment assemblies.

Hierarchically assembled theranostic nanostructures for siRNA delivery and imaging applications.

Dual functional hierarchically assembled nanostructures, with two unique functions of carrying therapeutic cargo electrostatically and maintaining radiolabeled imaging agents covalently within separate component building blocks, have been developed via the supramolecular assembly of several spherical cationic shell cross-linked nanoparticles clustered around a central anionic shell cross-linked cylinder. The shells of the cationic nanoparticles and the hydrophobic core domain of the anionic central cylindrical nanostructure of the assemblies were utilized to complex negatively charged nucleic acids (siRNA) and to undergo radiolabeling, respectively, for potential theranostic applications. The assemblies exhibited exceptional cell transfection and radiolabeling efficiencies, providing an overall advantage over the individual components, which could each facilitate only one or the other of the functions.

Spatial and Orientation Control of Cylindrical Nanostructures in ABA Triblock Copolymer Thin Films by Raster Solvent Vapor Annealing

We present a spatially resolved approach for the solvent vapor annealing (SVA) of block copolymer thin films that permits the facile and relatively rapid manipulation of nanoscale ordering and nanostructure orientation. In our method, a localized (point) SVA zone is created through the use of a vapor delivery nozzle. This point annealing zone can be rastered across the thin film using a motorized stage to control the local nanoscale structure and orientation in a cylinder-forming ABA triblock copolymer thin film. At moderate rastering speeds (∼100 μm/s) (i.e., relatively modest annealing time at a given point), the film displayed ordered cylindrical nanostructures with the cylinders oriented parallel to the substrate surface. As the rastering speed was decreased (∼10 μm/s), the morphology transformed into a surface nanostructure indicative of cylinders oriented perpendicular to the substrate surface. These perpendicular cylinder orientations also were created by rastering multiple times over the same region, and this effect was found when rastering in either retrace (overlapping) or crossed-path (orthogonal) geometries. Similar trends in nanostructure orientation and ordering were obtained from various nozzle diameters by accounting for differences in solvent flux and annealing time, illustrating the universality of this approach. Finally, we note that our "stylus-based" raster solvent vapor annealing technique allows a given point to be solvent annealed approximately 2 orders of magnitude faster than conventional "bell jar" solvent vapor annealing.

Biomimetic Mineralization: The Role of Nanoscale Architecture in Supramolecular Templating of Biomimetic Hydroxyapatite Mineralization (Small 14/2012)

When 3D peptide amphiphile assemblies with flat and cylindrical morphologies are used as templates for mineralization, the nanoscale architecture is found to play a significant role in orienting hydroxyapatite in a bone-like fashion. Cylindrical nanostructures facilitate mineral orientation parallel to the long axis of the 1D assembly while flatter, ribbonlike architectures nucleate randomly oriented mineral. Macroscopically aligned constructs of the cylindrical nanostructures further demonstrate the ability to orient hydroxyapatite across length scales. This work by S. I. Stupp and co-workers emphasizes the importance of template morphology.

Deep-Ultraviolet–Blue-Light Surface Plasmon Resonance of Al and Alcore/Al2O3shell in Spherical and Cylindrical Nanostructures

The surface plasmon resonance (SPR) properties in the deep-ultraviolet (UV) to blue-light region of Al and Alcore/Al2O3shell in spherical and cylindrical nanostructures have been investigated using the discrete dipole approximation method. Simulation results show that the extremely short resonance wavelength of the Al nanostructures means the SPR is highly sensitive to the particle size and results in significant phase retardation and multipole resonance. Cylindrical Al nanoparticles show multipole resonance peaks with extremely strong intensity and narrow widths that are blue-shifted and then red-shifted with an increase in the cylinder length. An expression of the SPR peak wavelength, λmax, is derived and related to the peak shift. Cylindrical Alcore/Al2O3shell nanostructures are shown to modulate the SPR through changes to the aspect ratio and Al2O3 shell thickness. The results will assist greatly in modulating or optimizing SPR in the deep-UV to blue-light region for multimode optical filter, enhanced...

Weak and strong confinements in prismatic and cylindrical nanostructures

Cylindrical nanostructures, namely, nanowires and pores, with rectangular and circular cross section are examined using mirror boundary conditions to solve the Schrödinger equation, within the effective mass approximation. The boundary conditions are stated as magnitude equivalence of electron's Ψ function in an arbitrary point inside a three-dimensional quantum well and image point formed by mirror reflection in the walls defining the nanostructure. Thus, two types of boundary conditions - even and odd ones - can be applied, when Ψ functions in a point, and its image, are equated with the same and the opposite signs, correspondingly. In the former case, the Ψ function is non-zero at the boundary, which is the case of a weak confinement. In the latter case, the Ψ function vanishes at the boundary, corresponding to strong quantum confinement. The analytical expressions for energy spectra of electron confined within a nanostructure obtained in the paper show a reasonable agreement with the experimental data without using any fitting parameters.

Spin dynamics of magnetic nanostructures investigated by micromagnetic simulations

Micromagnetic simulations were performed to investigate the spin dynamics of cylindrical magnetic nanostructures of various sizes down to 20 nm. The presented simulation technique provides information on the equilibrium states, magnetization precession, and spatial distributions of excited spin wave modes of individual nanostructures. Larger cylindrical nanostructures reveal a flower state magnetization configuration and show rather complex edge and center modes, which depend strongly on the saturation magnetization. This behavior allows controlling the precession frequencies, which is important in microwave-assisted three-dimensional magnetic recording, where layers of different resonance frequency need to be addressed and switched individually.

Carbon Nanotubes in Sample Preparation

The discovery and implementation of new materials in sample preparation have a significant impact on the development of new analytical methods and often on the instrumentation used in chemical analysis. In recent years, nanostructured materials of different chemical composition, such as nanoparticles, nanowires or nanotubes have received increasing attention. Their introduction in almost every stage of chemical analysis has constituted a significant milestone in modern analytical chemistry. Carbon nanotubes (CNTs) are allotropes of carbon that can be obtained as a single-walled (SWCNTs), or multi-walled (MWCNTs) material with a cylindrical nanostructure. Since their discovery in 1991, they have attracted great attention, because of their unique properties, which make them potentially useful in a wide range of scientific fields, from electronics to medicinal chemistry. In analytical chemistry, CNTs can be used as chromatographic solid phase material, and can therefore be directly involved in any step of chemical analysis. More specifically, due to the porous graphite structure of CNTs, they can be used as sorbents in sample preparation techniques, such as Solid Phase Extraction or Solid Phase Microextraction, for the cleaning up and the pre-concentration of a great variety of analytes in different matrices. Many applications can be found in literature regarding the analysis of phenolic compounds, pesticides, pharmaceuticals, inorganic ions, organometallic compounds, etc. in food, in environmental samples, or in biofluids with the use of CNTs. The objective of this review is to summarize the applications of carbon nanotubes in sample preparation over the past decade.

The role of nanoscale architecture in supramolecular templating of biomimetic hydroxyapatite mineralization.

Understanding and mimicking the hierarchical structure of mineralized tissue is a challenge in the field of biomineralization and is important for the development of scaffolds to guide bone regeneration. Bone is a remarkable tissue with an organic matrix comprised of aligned collagen bundles embedded with nanometer-sized inorganic hydroxyapatite (HAP) crystals that exhibit orientation on the macroscale. Hybrid organic-inorganic structures mimic the composition of mineralized tissue for functional bone scaffolds, but the relationship between morphology of the organic matrix and orientation of mineral is poorly understood. Herein the mineralization of supramolecular peptide amphiphile templates, that are designed to vary in nanoscale morphology by altering the amino acid sequence, is reported. It is found that 1D cylindrical nanostructures direct the growth of oriented HAP crystals, while flatter nanostructures fail to guide the orientation found in biological systems. The geometric constraints associated with the morphology of the nanostructures may effectively control HAP nucleation and growth. Additionally, the mineralization of macroscopically aligned bundles of the nanoscale assemblies to create hierarchically ordered scaffolds is explored. Again, it is found that only aligned gel templates of cylindrical nanostructures lead to hierarchical control over hydroxyapatite orientation across multiple length scales as found in bone.

Supramolecularly Engineered Perylene Bisimide Assemblies Exhibiting Thermal Transition from Columnar to Multilamellar Structures

Perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI) was functionalized with ditopic cyanuric acid to organize it into complex columnar architectures through the formation of hydrogen-bonded supermacrocycles (rosette) by complexing with ditopic melamines possessing solubilizing alkoxyphenyl substituents. The aggregation study in solution using UV-vis and NMR spectroscopies showed the formation of extended aggregates through hydrogen-bonding and π-π stacking interactions. The cylindrical fibrillar nanostructures were visualized by microscopic techniques (AFM, TEM), and the formation of lyotropic mesophase was confirmed by polarized optical microscopy and SEM. X-ray diffraction study revealed that a well-defined hexagonal columnar (Col(h)) structure was formed by solution-casting of fibrillar assemblies. All of these results are consistent with the formation of hydrogen-bonded PBI rosettes that spontaneously organize into the Col(h) structure. Upon heating the Col(h) structure in the bulk state, a structural transition to a highly ordered lamellar (Lam) structure was observed by variable-temperature X-ray diffraction, differential scanning calorimetry, and AFM studies. IR study showed that the rearrangement of the hydrogen-bonding motifs occurs during the structural transition. These results suggest that such a striking structural transition is aided by the reorganization in the lowest level of self-organization, i.e., the rearrangement of hydrogen-bonded motifs from rosette to linear tape. A remarkable increase in the transient photoconductivity was observed by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements upon converting the Col(h) structure to the Lam structure. Transient absorption spectroscopy revealed that electron transfer from electron-donating alkoxyphenyl groups of melamine components to electron-deficient PBI moieties takes place, resulting in a higher probability of charge carrier generation in the Lam structure compared to the Col(h) structure.

Structural Parameters for Nanocylinder Microdomains of Polystyrene-polybutadiene- Polystyrene Triblock Copolymer and its Blends with Polystyrene Homopolymer

We illustrate that the redistribution of a compatible homopolymer blended in a certain block copolymer results in a shift of phase boundaries and in the stabilization of well-ordered structures by using polystyrene (PS) homopolymer blended in polystyrenepolybutadiene- polystyrene triblock copolymer (SBS1102) as a model system. The addition of the homopolymer into the asymmetric triblock copolymer increases the periodic orientation normal to the substrate, enabling directed self-assembly of the block copolymers into arrays of highly oriented, high-aspect-ratio cylindrical nanostructures over large areas. Thus, we show that blending a homopolymer with well controlled molecular weight provides an effective ordering process for self-assembly of block copolymers. Keywords: Block copolymer self-assembly, orientation transition of block copolymer nano-cylinders, polystyrene homopolymer blended in polystyrenepolybutadiene-polystyrene triblock copolymer, periodic orientation normal to the substrate, blend microdomain structural parameters