Preparation and catalytic activity of Pd and bimetallic Pd-Ni nanowires.

This article describes the preparation and catalytic property of Pd and Pd-Ni nanowires with network structure. A soft template with network structure formed by long-chain amidoamine derivative (C18AA) was essential to preparing Pd and Pd-Ni nanowires because of the preparation of only spherical nanoparticles using octadecylamine, which does not form a network structure as a soft template, instead of C18AA. Furthermore, this soft-template method demands a slow reduction rate for the metal ion, the same as the general preparation method for novel metal nanowires. The distinguishing features of the present method is that the nanowires are a few nanometers in diameter and there are no byproducts such as nanoparticles. In addition, the bimetallic Pd-Ni nanowires show very high catalytic activity for the hydrogenation of p-nitrophenol as compared to Pd nanowires, Pd nanoparticles, and Pd-Ni nanoparticles.

Preparation of silica-coated ultrathin gold nanowires with high morphological stability.

We demonstrated a preparation method of silica-coated straight ultrathin Au nanowires (NWs). Water-dispersive ultrathin Au NWs capped with a long-chain amidoamine derivative (C18AA) were used for silica coating. The Au NWs were partially covered with 3-mercaptopropanoic acid by the ligand exchange method, and silica coating of the Au NWs was carried out by the hydrolysis of tetraethoxysilane (TEOS) at pH > 6.7 because the shape of the Au NWs was changed under acidic conditions. The thickness of the silica layer depended on the concentration of TEOS, and the layer was able to decrease to 6-10 nm thick. We also demonstrated that the silica-coated Au NWs had high morphological stabilities against external stimuli such as a TEM electron beam, heat, and pH compared with the bare Au NWs.

Thermal-sensitive viscosity transition of elongated micelles induced by breaking intermolecular hydrogen bonding of amide groups.

A heat-induced viscosity transition of novel worm-like micelles of a long alkyl-chain amidoamine derivative (C18AA) bearing intermolecular hydrogen-bonding group was investigated by cryo-TEM, FT-IR, and rheological measurements. At lower temperature, C18AA forms straight elongated micelles with a length on the order of micrometers due to strong intermolecular hydrogen-bonded packing of the amide groups, although the micelles rarely entangle and have low value of zero-shear viscosity. The straight elongated micelles likely became flexible and underwent a morphological transition from straight structure to worm-like structure at a certain temperature, which caused a drastic increase in viscosity due to entanglement of the micelles. This morphological transition was caused by a defect of intermolecular hydrogen bonding between the amide groups on heating. Furthermore, addition of LiCl, which acts as hydrogen-bond breaker, also promoted the viscosity transition, leading to a lowering of the transition temperature.

High organogelation ability and soft-templating for ultrathin Au nanowires of long-chain amidoamine derivatives.

Two kinds of long-chain amidoamine derivatives (C13A2AA and C17A2AA) bearing three amide moieties and terminal amine moieties were synthesized and their gelation abilities in apolar solvents were compared with the previously reported amidoamine gelator containing two amide moieties (C18AA). The derivatives acted as organogelators in the same organic solvents. XRD and FT-IR measurements revealed that C13A2AA and C17A2AA formed lamellar-like aggregates in the organogels, in which amide moieties were in the strong intermolecular hydrogen bonding state. In addition, C17A2AA was found to have an outstanding capacity as a soft template for Au nanowires, allowing the successful preparation of Au NWs at a low (0.3 wt%) concentration of [C17A2AA].

Room-temperature synthesis of two-dimensional ultrathin gold nanowire parallel array with tunable spacing.

A series of long-chain amidoamine derivatives with different alkyl chain lengths (CnAA where n is 12, 14, 16, or 18) were synthesized and studied with regard to their ability to form organogels and to act as soft templates for the production of Au nanomaterials. These compounds were found to self-assemble into lamellar structures and exhibited gelation ability in some apolar solvents. The gelation concentration, gel-sol phase transition temperature, and lattice spacing of the lamellar structures in organic solvent all varied on the basis of the alkyl chain length of the particular CnAA compound employed. The potential for these molecules to function as templates was evaluated through the synthesis of Au nanowires (NWs) in their organogels. Ultrathin Au NWs were obtained from all CnAA/toluene gel systems, each within an optimal temperature range. Interestingly, in the case of C12AA and C14AA, it was possible to fabricate ultrathin Au NWs at room temperature. In addition, two-dimensional parallel arrays of ultrathin Au NWs were self-assembled onto TEM copper grids as a result of the drying of dispersion solutions of these NWs. The use of CnAA compounds with differing alkyl chain lengths enabled precise tuning of the distance between the Au NWs in these arrays.

Effect of amide moieties for hydrogelators on gelation property and heating-free pH responsive gel-sol phase transition.

Two long-chain amidoamine derivatives (C13A2AOH and C17A2AOH) bearing three amide moieties were synthesized and their gelation ability and pH responsivity were compared with a similar, previously reported amidoamine derivative gelator with two amide moieties. C13A2AOH and C17A2AOH gels prepared in water and organic solvents acted as ambidextrous low molecular mass gelators. X-ray diffraction and Fourier transform infrared spectroscopy analyses revealed that C13A2AOH and C17A2AOH formed lamellar-like aggregates in the gels, where the amide moieties were in a strong intermolecular hydrogen-bonding state. The gelation ability, i.e., the molar ratio of solvent to gelator, was significantly dependent on the length of the alkyl chain and the number of amide moieties. In addition, the C13A2AOH and C17A2AOH hydrogels exhibited highly pH-responsive gel-sol transitions. The gel-sol transition for the hydrogels was induced by protonation of the ternary amine and the transition was completely reversible by regulating only the pH without heating.

Neuron-shaped gold nanocrystals and two-dimensional dendritic gold nanowires fabricated by use of a long-chain amidoamine derivative.

We report the synthesis of two-dimensional (2D) dendritic Au nanowires (DNWs) with diameters of 100-200 nm in an aqueous solution of long-chain amidoamine derivative (C18AA), which acted as both capping and reducing agent, and the preparation of large 2D DNWs with diameters of 400-700 nm by seeded growth of the original DNWs. The seeded growth method in the presence of C18AA enables the fabrication of novel neuron-shaped Au nanostructures consisting of two DNWs dangling from both ends of an ultrathin Au nanowire.

Double-stimuli responsive O/W emulsion gel based on a novel amidoamine surfactant.

A heat-induced O/W emulsion gel that undergoes a phase transition from sol to gel on heating was formed from the addition of aqueous HCl to a toluene solution of a long-chain amidoamine derivative (C18AA). The heat induced O/W emulsions are highly sensitive to temperature, and the sol-gel transition temperature could be simply controlled by adjusting the C18AA concentration. Interestingly, the sol-gel transition of the O/W emulsions was also very sensitive to pH. Thus, we have successfully prepared a novel double-stimuli responsive gel based on O/W emulsions consisting of C18AA and HCl.

Novel thermo-responsive coloring phenomena in water/surfactant/oil emulsions.

Emulsions comprising a dual-surfactant system of a long-chain amidoamine derivative and a quaternary ammonium salt developed an iridescent color at a specific temperature region. The emulsions underwent phase inversion on heating from an O/W emulsion to a W/O emulsion, passing through a periodical lamellar structure which developed a characteristic interference color. Interestingly, the color and the coloring temperature can be independently controlled by adjusting the concentration of surfactants, respectively.

Water-dispersible ultrathin Au nanowires prepared using a lamellar template of a long-chain amidoamine derivative.

Straight ultrathin Au nanowires (NWs) with diameters less than 2 nm were synthesized using the lamellar structure of C18AA in an organogel and its selective adsorption for specific gold surfaces. In addition, the potential to form a bilayer structure with interdigitated hydrocarbon chains enabled the production of water-dispersible Au NWs without morphological change.

Reversible phase transfer and fractionation of Au nanoparticles by pH change.

The reversible transfer of Au nanoparticles between water and chloroform phases by pH change was achieved by using a long-chain amine derivative. Further, we demonstrated that the phase transfer method was very effective for the fractionation of Au nanoparticles according to their crystal facet distinction.

Changes in viscosity behavior from a normal organogelator to a heat-induced gelator for a long-chain amidoamine derivative.

A long-chain amidoamine derivative (C18AA) acts as a normal organogelator in toluene, but changes to a heat-induced gelator, exhibiting a phase transition from sol to gel on heating upon addition of aqueous LiCl to the toluene gel. The thermal response of the heat-induced gel of C18AA was highly sensitive.

Characterization of colloidal crystal film of polystyrene particles at the air-suspension interface.

An aqueous suspension of polystyrene (PS) particles gave rise to a distinct color when a water-soluble volatile solvent, such as methanol or acetone, was added and left to evaporate. The color was caused by the formation of a colloidal crystal film of PS particles at the air-suspension interface. The colloidal crystal formation was possibly induced by the shear flow of particles and condensation of the suspension due to evaporation of the solvent. The colloidal crystal was estimated to consist of about 120 layers of PS particles. PS particles in the colloidal crystals formed a periodic array among the dispersion media, and the interparticle distance of the particles depended on the conductivity of the suspension. Further, the color of the colloidal crystal film as observed by the naked eye was complementary to the direct reflection peak.