Synthesis and self‐organization properties of copolyurethanes based on perylenediimide and naphthalenediimide units

A series of perylene and naphthalene diimide‐containing random copolyurethanes with different ratios of perylene/naphthalene diimide content was synthesized and characterized. Copolymerization improved the solubility of these rigid aromatic diimides, and the copolymers were soluble in common organic solvents like chloroform, tetrahydrofuran, and so forth. The absorption spectra of perylene‐based copolymers showed a red‐shifted peak at a wavelength of 557 nm corresponding to J‐type aggregates. For naphthalene copolymers, the quenching of fluorescence at higher naphthalene incorporation suggested the presence of aggregates because of the extensive π‐π stacking of the aromatic core. FTIR spectroscopic analysis showed that the hydrogen bonding tendency of the polymer decreased with increase in perylene/naphthalene incorporation. The fluorescence spectra of the perylene polymers were exactly a mirror image of the absorption spectra. The fluorescence spectra of the naphthalene polymers at higher naphthalene incorporation showed a red‐shifted excimer like emission peak, which was assigned as static excimers based on their excitation spectra. These polymers could exhibit two types of secondary interaction modes, namely, hydrogen bonding (via urethane linkage) and π‐stacking (via aromatic perylene or naphthalene units) thus highlighting the importance of polymer design in inducing self‐organization at both low and high incorporation of the rigid bisimide moieties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1224–1235, 2009     

Site-selective direct photochemical deposition of copper on glass substrates using TiO2 nanocrystals

Deposition of copper thin films was achieved by a photocatalytic reaction of site-selectively adsorbed TiO(2) nanocrystals for direct fabrication of copper circuit patterns on glass substrates. The nanocrystal monolayers absorbed on hydrophobic surface templates serve as an effective photocatalyst, producing metallic copper and formic acid via oxidation of methanol in solution. The formic acid generated has also been suggested to serve as an electron donor that accelerates copper deposition through a UV-mediated autocatalytic reaction, even after nanocrystals are embedded into the grown copper films. The thickness of the deposited copper films was easily controlled by varying the UV irradiation time, irradiation power, and initial concentration of methanol as a hole scavenger. The process presented herein provides an effective methodology for resist-free, direct metallization of insulating substrates.     

Novel silver nanostructures from silver mirror reaction on reactive substrates

Novel silver clusters have been prepared by simply carrying out the silver mirror reaction on certain reactive substrates. Leaflike fractal silver microstructures and perpendicularly aligned silver nanosheets were produced on a commercially available copper foil and sandpaper-rubbed copper foil, respectively. The surface features of copper foils and the chemical state of Cu atoms play important roles in regulating the morphological structures of the resulting silver clusters. Silver nanoclusters with various morphologies ranging from the leaflike to flowerlike hierarchical structures can be produced from the silver mirror reaction on commercially available copper foils after being treated with a dilute aqueous HCl solution under different conditions. The aqueous solution of silver nanosheets shows an optical absorption spectrum with a broad light-scattering peak at about 350 nm, compared to a corresponding surface plasmon absorption band around 430 nm for silver nanoparticles from the conventional silver mirror reaction on glass.     

Energy-efficient electrodeposition of metal-based nanostructures through simultaneous deposition at both the cathode and the anode

To meet the energy and environmental requirements, an effective strategy is demonstrated to enable electrochemistry to be energy-efficient for deposition of metal-based nanoparticles, based on careful design of the surface/interface reactions of metal precursors in such a way that the deposition can be induced at both the anode and the cathode.     

Self-assembly of aluminium-salen coupled nanostructures from encoded modules with cleavable disulfide DNA-linkers

DNA-directed coupling of organic modules by formation of stable aluminium-salen complexes, makes possible the subsequent reductive cleavage of disulfide linkers and release of the two oligonucleotide chains attached to each building-block.     

Tailoring the carbon nanostructures grown on the surface of Ni-Al bimetallic nanoparticles in the gas phase

A gas-phase, one-step method for producing various aerosol carbon nanostructures is described. The carbon nanostructures can be selectively tailored with either straight, coiled, or sea urchin-like structures by controlling the size of Ni-Al bimetallic nanoparticles and the reaction temperature. The carbon nanostructures were grown using both conventional spray pyrolysis and thermal chemical vapor deposition. Bimetallic nanoparticles with catalytic Ni (guest) and non-catalytic Al (host) matrix were reacted with acetylene and hydrogen gases. At the processing temperature range of 650-800 °C, high concentration straight carbon nanotubes (S-CNTs) with a small amount of coiled carbon nanotubes (C-CNTs) can be grown on the surface of seeded bimetallic nanoparticle size <100 nm, resulting from consumption of the melting Al matrix sites; sea urchin-like carbon nanotubes (SU-CNTs) of small diameter (～10±4 nm) can be grown on the bimetallic nanoparticle size >100 nm, resulting from the significant size reduction of the available Ni sites due to thermal expansion of molten Al matrix sites without consumption of Al matrix. However, at the processing temperature range of 500-650 °C, C-CNTs can be grown on the bimetallic nanoparticle size <100 nm due to the presence of Al matrix in the bimetallic nanoparticles; SU-CNTs of large diameter (～60±13 nm) can also be grown on the bimetallic nanoparticle size >100 nm due to the isolation of Ni sites in the Al matrix.     

Self-assembly of catecholic macroinitiator on various substrates and surface-initiated polymerization

A catechol-containing macroinitiator has been designed for the surface-initiated atom transfer radical polymerization (SI-ATRP) from various substrates at ambient temperature. Temperature-sensitive poly(N-isopropyl acrylamide) (PNIPAM) brushes were successfully grafted from a range of substrates surfaces, including metals and polyimides, via SI-ATRP using the resulting macroinitiator, which were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle measurements, and atomic force microscopy (AFM). Effects of the temperature response behavior of PNIPAM brushes on the water contact angles and the impedance of the modified surfaces were also exhibited. The self-assembled film of macroinitiator and the resulting polymer brushes were both stable to soaking of basic solvents, and the brushes did not show any exfoliation or delamination even after 2 h of ultrasonic test. The advantages of the macroinitiator in strong interactions with surfaces and high stability and convenience make it possible to modify the native materials with polymer brushes in a convenient and nondestructive way. Importantly, the macroinitiator is compatible with microcontact printing, and patterned polymer brushes on Ti plate were demonstrated by microcontact printing of BrDOPAMA and the following SI-ATRP.     

Self-assembly and stability of double rosette nanostructures with biological functionalities

The syntheses of calix[4]arene dimelamines that are functionalized with alkyl, aminoalkyl, ureido, pyridyl, carbohydrate, amino acid and peptide functionalities, and their self-assembly with barbituric acid or cyanuric acid derivatives into well-defined hydrogen-bonded nanostructures are described. The thermodynamic stability of these hydrogen-bonded assemblies was studied by CD spectroscopy in mixtures of CHCl3 and MeOH. The stability of the assemblies depends on several steric factors and the polarity of the functional groups connected to the assembly components.     

Self-assembly of amphiphiles with terthiophene and tripeptide segments into helical nanostructures

We previously reported a class of tripeptide amphiphiles known as peptide lipids that self-assemble into one-dimensional nanostructures with superhelical twisting. The pitch of this supramolecular twisting is controlled directly through sterics in the molecular structure of hydrophobic segments. In this work we study the supramolecular behavior of these nanoscale helices by substituting with a terthiophene conjugated segment of potential electronic interest and also through variations in the stereochemistry of the tripeptide. This terthiophene peptide lipid was shown to self-assemble into one-dimensional helical nanofibers with a regular diameter of 9±1 nm and helical pitch of 65±6 nm, and also found to form hierarchical double- and triple-stranded helices, which could be associated with terthiophene J-aggregate interactions among fibers. For stereochemical effects, we compared four diastereomers in the tripeptide sequence using l-glutamic acid and l- and d-alanine residues to probe their ability to control supramolecular organization. Interestingly, we found by atomic force microscopy that the LLD diastereomers formed cylindrical nanofibers without any twisting, whereas LDD diastereomeric segments self-assembled into helical nanofibers with a pitch of 40±6 nm. LDL diastereomeric segments formed, on the other hand, aggregates without any regular shape. We propose that these profound effects of chirality with amino acid sequence are related to changes in the β-sheet sub-structure within the nanofibers.     

Self-assembly of vertically aligned gold nanorod arrays on patterned substrates

Nanorods standing at attention! A self-assembly technique based on convective and capillary forces was used for the direct fabrication of standing arrays of gold nanorods on lithographically predefined areas. The hexagonal close-packed structure of gold nanorods creates an ideal substrate for surface-enhanced Raman spectroscopy.     

Electrochemical growth of nickel hollow nanostructures on copper substrates

We have shown hollow Ni nanonodules with outer diameters of 80-200 nm and wall thicknesses of 5-25 nm could be prepared by electrochemical deposition in the NiCl2 + dimethyl sulfoxide + C2H4O3 + H2O system, and the products were high purity. In particular, Ni hollow nanonodule structures or highly assembling Ni hollow nanostructures can be selected by varying the compositions of the solvent mixture. Apart from the hollow grain size, the wall thickness can also easily be controlled by varying the electrochemical parameters, salt concentration, and deposition time. The typical coercivity of Ni hollow nanostructures with particle sizes of about 100-150 nm was much bigger than that of the bulk Ni.     

Site-selective patterning of organic luminescent molecules via gas phase deposition

In this paper, we present a bottom-up approach to pattern organic luminescent molecules with a feature size down to sub-100 nm over wafer-sized areas. This method is based on the selective gas deposition of organic molecules on self-organized patterned structures, which consist of an organic monolayer with two different phases rather than different materials. The site selectivity is controllable by deposition rate and the pattern features. The reason for the site selectivity may be due to the nucleation and diffusion behaviors of the deposited organic molecules on different monolayer phases.     

Effect of silver deposition on tio for photocatalytic oxidation of benzene in the gas phase

Summary Deposition of Ag on TiO₂ surface by photodeposition method improved the photooxidation rate of benzene in air by inhibiting the build-up of intermediate compounds on the catalyst surface. Although the reaction rate decreased with the increase in benzene concentration, the decrement of reaction rate became smaller by Ag deposition. The selectivities to CO₂ and CO were 95 and 5%, respectively, which were almost independent of Ag loading and benzene conversion.     

Growth of anisotropic gold nanostructures on conducting glass surfaces

In this paper, we describe a method for the growth of gold nanowires and nanoplates starting from a bilayer array of gold seeds, anchored on electrically conducting indium tin oxide (ITO) substrates. This is based on a seed-mediated growth approach, where the nanoparticles attached on the substrate through molecular linkages are converted to nanowires and nanoplates at certain cetyltrimethylammonium bromide (CTAB) concentration. Our modified approach can be used to make nanowires of several tens of micrometers length at a lower CTAB concentration of 0.1 M. The length of the nanowires can be varied by adjusting the time of the reaction. As the concentration of CTAB was increased to 0.25 M, the nanoparticles got converted to nanoplates. These Au nanoplates are (111) oriented and are aligned parallel to the substrate.     

Cell adhesion and locomotion on microwell-structured glass substrates

The purpose of this study was to investigate the effect of microstructured material surface on cell adhesion and locomotion in real-time. ArF excimer laser direct-writing ablation was used to fabricate microwell patterns with precise control of size and spacing on glass. The influence of the ablation process parameters (laser fluence, pulse number and repetition rate) on the micromachining quality (depth, width, aspect ratio and edge effects) of the microwells was established. Human fibroblast cells, as an example of anchorage-dependent cells, were seeded onto the microstructured glass substrate and time-lapse microscopy was used to study cell adhesion and locomotion. The interaction with microstructured materials resulted in fibroblast cell repulsion and the cells exhibited a higher locomotion speed (75.77±3.36 μm/h) on the structures in comparison with plane glass control (54.01±15.53 μm/h). Further studies are needed to firmly establish the potential of microstructuring, for example, in elongating the life spans of implantable devices.     

Deposition of thin mesoporous silica films on glass substrates from basic solution

Transparent thin (ca. 100 nm) films of silica-surfactant mesostructured materials were deposited on borosilicate glass plates and soda-lime glass tubes from aqueous solutions containing tetraethoxysilane, alkyltrimethylammonium chloride, ammonia, and methanol. By calcination in air, the films became mesoporous (BET surface area of 700-900 m2 g-1) with pore diameter 2.0-2.8 nm.     

Self-assembly of Co-based nanosheets into novel nest-shaped nanostructures: Synthesis and characterization

We report the first observation of the formation of novel Co-based three-dimensional (3D) self-assembly hollow nanostructures, i.e., nest-shaped nanospheres composed of sheet-like particles, via reduction of cobalt salt with sodium tetrahydroboride in cetyltrimethylammonium bromide (CTAB)-cyclohexane-NH4F aqueous solutions. It was found that the cyclohexane has a significant influence on the formation of the nest-shaped Co-based nanospheres, because when the experiments are carried out in the absence of cyclohexane, only sheet-like particles are formed. NH4F plays also an important role in the formation of the hollow nanostructures because without this salt mainly solid spherical structures, composed of sheet-like particles, instead of nest-shaped structures are obtained. The nanostructures are mainly formed by Co, but also a minor amount (17%) of Co2B is present in the final compounds. The structures are characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and field-emission scanning electron microscopy (FESEM). A possible mechanism for the formation of the novel Co-based nanostructures is proposed.     

Focused electron beam-induced deposition of iron- and carbon-containing nanostructures from triiron dodecacarbonyl vapor

Iron-based nanocomposites are of substantial interest, in particular, from the viewpoint of their magnetic properties. Preliminary results are reported on the deposition of nanostructures from triiron dodecacarbonyl vapor by the action of a focused electron beam. It was found that depending on deposition conditions, the resistivity of applied lines varied from 4 × 10^–2 to 10³ cm, decreasing rapidly with an increase in the electron beam current. The effective activation energy of conductivity varied from 3–5 kJ/mol for low-resistance lines to 15–25 kJ/mol for high-resistance lines. The results obtained were discussed in terms of the assumption that the deposited lines are nanocomposite materials made from iron (iron oxide or carbide) nanoparticles distributed in an amorphous carbon matrix. A change in the resistance of one of the deposited lines (with an initial resistance of about 8 M) in a medium of certain vapors and gases was determined.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 93–96.Original Russian Text Copyright © 2005 by Bruk, Zhikharev, Grigorev, Spirin, Kalnov, Kardash.This revised version was published online in April 2005 with a corrected cover date.     

The effect of pressure on gas permeation through semicrystalline polymers above the glass transition temperature

A method is proposed to analyze the effect of pressure on permeation of gases through semicrystalline polymers above the glass transition temperature. The method utilizes similarities in molecular diameters of the gases and differences in their solubilities. Two polymers, polyethylene and polypropylene, and a series of gases are chosen for an application of the method, and the effect of pressure on the permeabilities for 10 gases is measured in the pressure range 1–130 atm at 25°C. For polymers, the logarithm of the permeability coefficient is linear in the pressure for each gas, with negative slope for slightly soluble gases (He, Ne, H₂, N₂, O₂, and Ar) and positive slope for highly soluble gases (CH₄, Kr, CO₂, and N₂O). Analyzing these slopes by the method proposed permits contributions of hydrostatic pressure and concentration to the pressure dependence of permeation to be evaluated. On the basis of the results, the mechanism of gas permeation in rubbery films under high pressures is discussed.