Concentric lamella structures of symmetric diblock copolymers confined in cylindrical nanopores

We applied a real-space self-consistent field theory to investigate the concentric lamella structures of symmetric diblock copolymers confined in the cylindrical nanopores with the preferential surfaces. The symmetric diblock copolymers are selected to locate in the very weak and strong segregation regions where the lamellae obviously exhibit the “soft” and “rigid” characteristics, respectively. For the soft lamellae, the cylindrical confinement induces the soft concentric lamella structure with the same thickness as the bulk lamellar period, except that the thickness of the innermost layer depends on the confinement degree. For the rigid lamellae, the cylindrical confinement not only induces the rigid concentric lamella structure having the linear dependence on the confinement degree, but also results in several novel morphologies, such as the connective concentric lamella and the broken concentric lamella structures. The results are quantitatively discussed in a wide range of confinement degree and can be reasonably understood based on symmetry breaking and structural frustration. In addition, our results are quantitatively compared to the available observations from the simulations and experiments, which are in good agreements and may be helpful to experimentally fabricate the ordered nanostructures on the large scale.     

Domain nucleation dictates overall nanostructure in composites of block copolymers and model nanorods

The detailed nanostructure of composites formed from block copolymers and nanoparticles is known to depend sensitively on the preferred morphology of the block copolymer, on the shapes of the particles, and on interactions between the two components. But it can also depend on the kinetics of self-assembly in the polymer, and there are circumstances under which the kinetics of morphologically selective domain nucleation and growth determine the overall nanostructure of the composite. To study the mechanism of morphological seeding in block-copolymer nanocomposites, we have combined cylinder phases of polystyrene-block-polyisoprene diblock (as a solution in dibutylphthalate) and poly(styrene-block-isoprene-block-styrene) triblock (as a blend with homopolystyrene) copolymers with gold nanorods of different diameters and surface treatments. Polarized optical microscopy and transmission electron microscopy on these composites demonstrate that the nanorods selectively nucleate coaxial domains of copolymer cylinders (i.e., domains of cylinders aligned along the same axis as the nanorod). These single nucleation events occur regardless of nanorod diameter and surface character, and determine the order of most of the surrounding polymer. Mesoscale modeling of the nucleation process, performed with nanorods of different diameters and with different polymer-surface interactions, illustrates the mechanism by which copolymer-dispersed nanorods with different sizes and surface chemistry can template the organization of cylindrical copolymer domains.     

Assembly of one-dimensional polymer nanostructure arrays by photolithographic approaches

In this work, large area polymer nanostructure arrays with different patterns were successfully obtained by photolithographic approach and wetting anodic aluminum oxide (AAO) templates. First of all, the AAO templates with patterns were produced by photolithographic approach. Then the AAO/pattern membrane was used as a secondary template to fabricate polymer nanostructure arrays by solution-wetting and melt-wetting methods. The morphology of the polymer nanostructures has been characterized using scanning electron microscopy and transmission electron microscopy. The different factors have been discussed in the process of experiments.     

One-pot microwave synthesis of SnSe and Lanthanum doped SnSe nanostructure with direct Z scheme pattern for excellent photodegradation of organic pollutants

A novel nanostructure photocatalytic material was fabricated using Lanthanum doped SnSe by one-pot microwave method is reported to newest. Photocatalytic performance efficiency of pristine SnSe and Lanthanum doped SnSe nanostructures were investigated to degrade organic pollutants from wastewater. The crystal structure, morphology, and optical properties of the nanostructure were investigated using powder X-ray diffraction, field emission scanning electron microscope, UV–Vis, and PL spectral studies. Nano rods/spheres for pure SnSe were altered significantly leading to higher amounts of nanorods due to La doped and increase in concertation leads higher formation of nanorods. Increased in structure and morphology played a vital role in photocatalytic activity. Nanostructure exhibits enhanced physicochemical properties and showed an excellent synergetic effect demonstrating the effect of La (1, 3, and 5%) concentrations in SnSe nanostructure. The optical energy gap has a reducing trend due to the increment of doping concentration. The individual elements oxidation states were justified from X-ray photoelectron spectroscopical studies. Thermal stability and phase changes of the nanostructure before and after doping of La were evaluated through TGA/DTA analysis. From the photocatalytic measurement rare-earth (La) doped samples expressed higher catalytic nature than the pure SnSe. It was observed that the higher atomic element La had a significant role to produce a large number of electron-hole pair recombination and defective structure in the host lattice.     

Electrochemical synthesis of nickel hexacyanoferrate nanoarrays with dots, rods and nanotubes morphology using a porous alumina template

Transition metal hexacyanoferrate (MeHCF) have attracted extensive attention because of their outstanding properties including, electrocatalysis, molecular magnetism, biosensing and ion-exchange. This paper describes an approach for fabrication of ordered nanoarrays of Ni hexacyanoferrate (NiHCF) structures with different morphologies such as dots, rods and tubes in order to advance their properties and applications. The method is based on the conversion of Ni into NiHCF nanostructures by electrochemical oxidation in the presence of hexacyanoferrate ions, using nanoporous anodic alumina oxide (AAO) as a template. The structure and morphology of formed Ni and NiHCF nanoarrays were confirmed by scanning electron microscopy (SEM), showing agreement with the pore structures of the AAO template. The electrocatalytic activity of NiHCF nanorod array electrodes showed high catalytic properties for the detection of hydrogen peroxide and the potential to be used as a platform for direct biosensing applications. The ion-exchange ability of fabricated NiHCF nanostructures (nanorods and nanotubes) toward alkali cations such as Na⁺ has been successfully confirmed.     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Growth of ZnO nanostructures: Cones,rods and hallow-rods,by microwave assisted wet chemical growth and their characterization

ZnO nanostructures were grown by microwave assisted wet-chemical growth, at different microwave powers and for different growth durations. The grown nanostructures were analysed for their morphological, structural, compositional and optical characteristics. The total microwave power per growth run (product of microwave power and growth duration, with units in watt-min), has a linear relationship with most of the characteristics of the grown ZnO nanostructures. It is shown that by altering the microwave power per growth run, the morphology of the individual ZnO nanostructure can be changed from cones with hexagonal cross section, to faceted hexagonal nanorods, to hollow hexagonal nanorods. It is observed that, while the fast growth rate along the high energy polar faces (0001) and (000ī) of ZnO is the reason behind the formation of one dimensional ZnO structures (cones and rods), the process of formation of hallow ZnO rods is due to further etching/material-removal from the tip of the rods, at high microwave power conditions at long growth durations.     

Fabrication of nanostructure via self-assembly of nanowires within the AAO template

The novel nanostructures are fabricated by the spatial chemical modification of nanowires within the anodic aluminum oxide (AAO) template. To make the nanowires better dispersion in the aqueous solution, the copper is first deposited to fill the dendrite structure at the bottom of template. During the process of self-assembly, the dithiol compound was used as the connector between the nanowires and nanoparticles by a self-assembly method. The nanostructures of the nano cigars and structure which is containing particles junction are characterized by transmission electron microscopy (TEM). These kinds of novel nanostructure will be the building blocks for nanoelectronic and nanophotonic devices.      

Effect of the morphology of solution‐grown ZnO nanostructures on gas‐sensing properties

Despite the great potential of zinc oxide (ZnO) nanostructures as a sensing material for high‐performance gas sensors, the correlation between the morphology of ZnO nanostructure and its gas‐sensing performance has not been systematically investigated yet. In this work, ZnO nanostructures with controlled morphologies were synthesized by low‐temperature solution route and chemical bath deposition method. Thin film gas sensors were fabricated from the nanostructures and the sensor performance such as the response, recovery time, and stability was examined for several gases. It is demonstrated that the gas‐sensing performance of a ZnO nanostructure sensor is strongly influenced by its morphology. One dimensional ZnO nanocones are highly promising for practical application to gas sensors, due to their large surface area per unit mass and unique conical structure.     

Fabrication and optical characterization of poly(2,5‐di‐n‐butoxyphenylene) nanofibril arrays

Anodic aluminum oxide (AAO) membrane can be used as template for the synthesized nanostructures. In this article, we have prepared the AAO membrane by using electrooxidation of aluminum substrate in phosphoric acid, and fabricated poly(2,5‐di‐n‐butoxyphenylene) (BuO–PPP) nanofibril arrays by oxidative coupling polymerization of 1,4‐di‐n‐butoxybenzene (DBB) within the pores of the AAO template membrane. The detailed molecular structure of the polymer nanofibrils was characterized by using infrared and ¹H nuclear magnetic resonance spectra, and estimated to consist of almost equal fractions of 1,4‐ and 1,3‐ linkages. We have used transmission electron microscopy, scanning electron microscopy, and atom force microscopy to confirm the morphologies and images of the AAO template membrane and the fabricated nanometer scale of BuO–PPP nanofibril arrays. The experimental results demonstrated that the pores of the AAO membrane were regular and uniform, and parallel each other, and the BuO–PPP chains in the narrowest template‐synthesized nanofibrils were oriented parallel to the porous axes of the AAO membrane and perpendicular to the surface of the aluminum substrate. The polymer chain orientation was partially responsible for the enhanced conductivity. The ultraviolet absorption spectrum of the BuO–PPP nanofibril arrays shown that the polymer contains a better extended π‐conjugation system along poly‐(p‐phenylene) backbone, which resulted in longer wavelength shift of the absorption band, the absorption maxima were located at 258 nm (E₁ absorption band) and 332 nm (E₂ absorption band), respectively. Photoluminescence spectrum of the BuO–PPP nanofibril arrays exhibited a blue emission. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 425–430, 2004     

Preparation of Highly Crystalline TiO<Subscript>2</Subscript> Nanostructures by Acid-assisted Hydrothermal Treatment of Hexagonal-structured Nanocrystalline Titania/Cetyltrimethyammonium Bromide Nanoskeleton

Highly crystalline TiO₂ nanostructures were prepared through a facile inorganic acid-assisted hydrothermal treatment of hexagonal-structured assemblies of nanocrystalline titiania templated by cetyltrimethylammonium bromide (Hex-ncTiO₂/CTAB Nanoskeleton) as starting materials. All samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of hydrochloric acid concentration on the morphology, crystalline and the formation of the nanostructures were investigated. We found that the morphology and crystalline phase strongly depended on the hydrochloric acid concentrations. More importantly, crystalline phase was closely related to the morphology of TiO₂ nanostructure. Nanoparticles were polycrystalline anatase phase, and aligned nanorods were single crystalline rutile phase. Possible formation mechanisms of TiO₂ nanostructures with various crystalline phases and morphologies were proposed.     

Cylindrical phase of diblock copolymers confined in thin films. A real-space self-consistent field theory study

We have used real-space self-consistent field theory to search possible morphology of an asymmetric AB diblock copolymer thin film confined between two homogeneous hard walls. The volume fraction of the A block is fixed to be f=0.3, as expected, a cylindrical phase is stable without confinement (in the bulk). Our simulation reveals that under confinement, in addition to parallel and perpendicular cylinders, other phases, such as flat lamellae, perforated lamellae, undulated cylinders and undulated lamellae, are also stable due to the block-substrate interactions. Three new structures, i.e. undulated lamellae, undulated cylinders and parallel cylinders with non-integer period, are observed to be stable with suitable film thickness and block-substrate interaction. By systematically varying the film thickness and the interaction parameters between the two blocks, phase diagrams are constructed for typical block-substrate interactions. We compare the phase diagrams for weak and strong substrate preference and discuss the effects of confinement and substrate preference on the stability of various structures.     

Block copolymer nanoshells

With the help of cell dynamics simulation we investigate morphology of thin block copolymer film around a nanoparticle. The obtained structures include: parallel, perpendicular, mixed and perforated lamellae, parallel and perpendicular cylinders and spheres. Analogy and difference with planar films are discussed. Our simulation suggests that novel porous nanocontainers can be formed by the coating of a sacrificial nano-bead by a block copolymer layer with a well controlled nanostructure.     

pH Dependent Molecular Self-Assembly of Octaphosphonate Porphyrin of Nanoscale Dimensions: Nanosphere and Nanorod Aggregates

Self-assembled nanostructures of zwitterionic octaphosphanatoporphyrin 1, of either nanoparticles or nanorods, depending on small changes in the pH, is demonstrated based on the J-aggregates. Porphyrin 1 self-assembled into nanosphere aggregates with a diameter of about 70-80 nm in the pH range 5-7, and nanorod aggregates were observed at pH 8.5. Hydrogen bonding, π-π stacking and hydrophilic interactions play important roles in the formation of this nanostructure morphology. Nanostructures were characterized by UV/Vis absorbance, fluorescence, atomic force microscopy (AFM) and transmission electron microscopy (TEM). This interesting pH dependent self-assembly phenomenon could provide a basis for development of novel biomaterials.     

Microstructures of lamella-forming diblock copolymer melts under nanorod-array confinements

The microstructures of lamellae-forming diblock copolymer melts confined in nanorod arrays are investigated using the real-space self-consistent field theory. The nanorod array leads to the incomplete confinement at each direction so that the confinement-dimension is fractional between zero and two. This incomplete confinement can yield a rich variety of mixture microstructures by varying its fractional confinement-dimension, such as the mixture of concentric lamellae and parallel lamellae and the mixture of the concentric lamellae and cylinders, as well as a series of continuous network mixtures. By comparing with the available simulations and experiments, these novel microstructures can be understood based on the symmetry competition and structural frustration that originated from the incomplete confinement. Our theoretical predictions may be helpful to the design of nanomaterials.     

One dimensional nanostructure/nanoparticle composites as photoanodes for dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) show potential as a low cost alternative to silicon solar cells. Power conversion efficiencies exceeding 12% have been achieved for DSCs. Typical DSCs are based on TiO(2) nanoparticle photoanodes, which have numerous grain boundaries, surface defects and trap states as electrons transport from one particle to the other. Such defects and trap states increase back charge transfer (charge recombination) from the photoanode to electrolyte. One dimensional (1D) nanostructures such as nanofibers, nanorods, nanowires, and nanotubes can offer direct and fast electron transport to the electron collecting electrode. However, these 1D nanostructures have a major disadvantage of having insufficient surface area and inefficient dye attachment. To solve this challenge, mixtures of TiO(2) nanoparticles and 1D nanostructures (e.g. nanofibers, nanorods, nanowires, and nanotubes) are used to take advantage of the large surface area of nanoparticles and efficient charge transport of 1D nanostructures. In this article, we review the recent developments in using mixtures of 1D nanostructures and nanoparticles as photoanodes for efficient DSCs. Various randomly oriented and vertically aligned 1D nanostructures and their composites with nanoparticles are discussed. Future increase of efficiency in DSCs using 1D nanostructure/nanoparticle composites will rely on the optimization of diameters of 1D nanostructures, control of ratios of 1D nanostructures and nanoparticles, increase of crystallinity, and reduction of surface defects on the 1D nanostructures. This work will provide guidance for designing and growing appropriate 1D nanostructures, and combining them with nanoparticles at an optimal ratio for efficient DSCs.     

Nanostructure evolution of oriented high-pressure injection-molded poly(ethylene) during heating

High-pressure injection-molded polyethylene (PE) rods are studied by ultra small-angle X-ray scattering from synchrotron during the heating of the polymer. Injection of a cool melt into a cold mold yields highly oriented PE rods with a core-shell structure. Samples from both the core and the shell material are studied. The two-dimensional scattering patterns are evaluated utilizing the multi-dimensional chord distribution function (CDF) analysis. From the obvious evolution of the nanostructure during successive crystallite melting, the sequence of processes occurring during crystallization is elucidated. First, nuclei form one-dimensional lattices with short-range order along the fiber axis. From this row structure, lamellae grow with wide lateral extension. An indication of an intermediate block structure is observed. Finally two steps of insertion crystallization result in two long period halvings. Increase of the mold pressure increases the lateral extension of the inserted lamellae in the shell material. In the core material a uniform row structure is absent. Extended primary lamellae form stacks with decreasing long periods before insertion crystallization takes over. But crystallites inserted in the core material do not form extended lamellae. Each of these steps leaves its footprint in the nanostructure and the corresponding scattering pattern. After CDF interpretation of the heating series, the room temperature pattern can be explained. The strong two-point pattern is associated with the primary lamellae and the intensity ridge extending along the meridian results from irregular insertion of lamellae. When the row structure is observed in the CDF, the fiber pattern exhibits equatorial scattering.Domain roughness generates a strong background scattering, which cannot be separated in one step. For the presented material it is shown that iterative background subtraction eliminates the scattering effects of the imperfect (i.e. inserted) lamellae.     

Fabrication of diameter-modulated and ultrathin porous nanowires in anodic aluminum oxide templates

Anodic aluminum oxide (AAO) membranes with modulated pore diameter were synthesized by pulse anodization in 0.3 M sulfuric acid at 1 °C. For AAO growth, a typical combination of alternating mild anodizing (MA) and hard anodizing (HA) pulses with applied potential pulses of 25 V and 35 V was applied. The control of the duration of HA pulses will provide an interesting way to tune the shape of pores and the structure of AAO channels. It was found that a non-uniform length of HA segments in cross section of AAO is usually observed when the HA pulse duration is shorter than 1.2 s. The pulse anodization performed with longer HA pulses leads to the formation of AAO templates with periodically modulated pore diameter and nearly uniform length of segments. Various diameter-modulated metallic nanowires (Au, Ag, Ni and Ag–Au) were fabricated by electrodeposition in the pores of anodic alumina membranes. A typical average nanowire diameter was about 30 nm and 48 nm for MA and HA nanowire segments, respectively. After a successful dealloying silver from Ag–Au nanowires, porous ultrathin Au nanowires were obtained.     

Relationship among morphology,photoluminescence emission,and photocatalytic activity of Eu-doped ceria nanostructures: A surface-type effect

Herein, we discuss the synthesis of Eu-doped ceria nanostructures via the microwave-assisted hydrothermal method. The morphological analysis showed that Eu-doped ceria nanoparticles, nanorods, nanocubes, and nanopolyhedrons with different sets of exposed facets were obtained. The structural characterization revealed that the samples were crystalline and without secondary phases. The optical analysis showed a decrease in the bandgap energies of the Eu-doped nanostructures compared with pure ceria nanoparticles, and different photoluminescence emissions were found depending on the morphology. The photocatalytic activity of each nanostructure was evaluated, and Eu-doped nanopolyhedrons were the most promising photocatalyst, exhibiting a 60% and 80% increase in RhB discoloration compared to the Eu-doped and pure ceria nanoparticles, respectively. The better performance of the nanopolyhedrons is probably associated with the presence of different exposed facets, such as (111), (200), (220), and (311). The main species involved in the photocatalytic process were holes. The performances of each nanostructure were associated with their different exposed facets, the concentration of oxygen vacancies, and surface defects.