Jun Matsui

Characterization of the molecular environment of polymer Langmuir-Blodgett films using a pyrene fluorescent probe

The molecular environment of polymer Langmuir−Blodgett (LB) films with different alkyl chain length, poly(N-dodecyl acrylamide) (pDDA) and poly(tert-pentyl acrylamide) (ptPA), which are copolymerized with a small amount of 1-pyrenylmethyl acrylate (PyMA) comonomer as a luminescent probe, was investigated by means of the surface pressure (π)−area (A) isotherms, UV−vis spectroscopy, and fluorescence spectroscopy. The pyrene ring orients perpendicular to the p(DDA/PyMA) layer in both the monolayer at the air/water interface and LB multilayers, while the pyrene moiety of p(tPA/PyMA) takes a parallel orientation to its layer plane. The pyrene residue is more exposed to its surroundings in p(tPA/PyMA) LB films and therefore sensitive to solvent polarity. The measurement of fluorescence anisotropy confirmed that the pyrene was densely packed in the LB films. These findings suggest that the molecular orientation of luminescent molecules can be controlled when the length of side chains is changed by only several a...

Langmuir-Blodgett films composed of amphiphilic double-decker shaped polyhedral oligomeric silsesquioxanes.

New amphiphilic polyhedral oligomeric silsesquioxanes (POSSs) were synthesized, and their monolayer behavior on a water surface and Langmuir-Blodgett (LB) film formation were studied. Two kinds of amphiphilic POSS molecules, which have two or four di(ethylene glycol) units (2OH-DDSQ and 4OH-DDSQ, respectively), were synthesized by direct hydrosilylation of di(ethylene glycol) vinyl ether with double-decker shaped polyhedral oligomeric silsesquioxanes (DDSQs). Surface pressure (π)-area (A) isotherms and Brewster angle microscope (BAM) measurements indicated that both amphiphilic DDSQs form a stable monolayer at the air-water interface. In addition, 4OH-DDSQ can be deposited on a solid substrate by the LB technique. Atomic force microscope (AFM) images of a one-layer 4OH-DDSQ film showed a homogenous uniform surface on a hydrophilic silicon substrate, whereas nanometer scale dots were formed on a hydrophobic silicon substrate. Multilayer deposition on a hydrophobic substrate resulted in an increase of dot size with increasing deposition number of layers. Moreover, homogenous multilayer films with a few voids were obtained on a hydrophilic substrate. The results indicate that 4OH-DDSQ is a good candidate for preparing hybrid nanoassemblies.

Helicity-Selective Photoreaction of Single-Walled Carbon Nanotubes with Organosulfur Compounds in the Presence of Oxygen

This report describes a helicity-selective photoreaction of single-walled carbon nanotubes (SWNTs) with disulfide in the presence of oxygen. The SWNTs were characterized using absorption, photoluminescence (PL), Raman, and X-ray photoelectron spectroscopy, scanning electron microscopy, and current-voltage (I-V) measurements. Results showed remarkable helicity-selective (metallic SWNTs/semiconducting SWNTs and diameter) functionalization of SWNTs. The reaction rate decreases in the order of metallic SWNTs > semiconducting SWNTs and small-diameter SWNTs > large-diameter SWNTs. Control experiments conducted under various experimental conditions and ESR and femtosecond laser flash photolysis measurements revealed that the helicity-selective reaction proceeds via a photoinduced electron transfer reaction. The PL and I-V measurements showed that the photoreaction is effective not only to control SWNT conductivity but also for the band gap modulation of semiconducting SWNTs.

Proton-conducting electrolyte film of double-decker-shaped polyhedral silsesquioxane containing covalently bonded phosphonic acid groups

As described in this paper, phosphonic-acid-containing double-decker-shaped polyhedral silsesquioxane (PHOS-DDSQ) was synthesized and the proton conductivity of the PHOS-DDSQ cast film was studied under humid and non-humid conditions. To synthesize PHOS-DDSQ, double-decker-shaped polyhedral silsesquioxane (DDSQ) was initially reacted with di(ethylene glycol) (DEG) vinyl ether using hydrosilylation reaction to attach four DEG units to one DDSQ (4DEG-DDSQ). Subsequently, a phosphate esterification of hydroxyl groups in 4DEG-DDSQ was carried out using POCl3. NMR, XPS, and MALDI-TOF MS spectra and titration measurements revealed that the phosphate esterification connected two DEG units to form a crown-ether-like structure. This structure prevents hydrolysis of the phosphate ester bond. PHOS-DDSQ showed high thermal stability, with decomposition temperature exceeding 220 °C, because of its inorganic DDSQ core. A uniform film of PHOS-DDSQ can be fabricated by drop casting. The cast film showed high proton conductivity (0.12 S cm−1) under humid conditions, which is comparable to that of a Nafion® membrane. Moreover, the cast film offered good proton conductivity under non-humid conditions (3.6 × 10−4 S cm−1 at 170 °C). The conductivity and thermal stability indicate that PHOS-DDSQ is a good candidate for use as a proton-conductive membrane in hydrated type fuel cells as well as fuel cells operated at intermediate temperatures (100–200 °C) under non-humid conditions.

Multi-Walled Carbon Nanotube Ultrathin Film Using a Liquid-Liquid Interface: Effect of Alcohol Type to the Film Property

Ultrathin film of multi-walled carbon nanotubes (MWCNTs) was fabricated using a liquid–liquid interface. Water dispersible MWCNTs, which were synthesized using an anodic aluminum oxide film as a template were used as a water phase. Hexane solution was added to the water dispersion as an oil phase. The MWCNTs were assembled at the liquid–liquid interface by adding 10 vol% of alcohol (methanol, ethanol, and 2-propanol) to the MWCNTs water dispersion/hexane solution. The assembled film was transferred to a solid substrate and the effect of alcohol type to the film properties was discussed.

Assembly of Fullerene Nanoparticles Using a Liquid–Liquid Interface

Fullerene (C60) nanoparticles were assembled in two-dimension using a liquid–liquid interface. C60 nanoparticles dispersed in ethyl lactate/water solution were added to a glass vessel. Then, hexane was added to the dispersion solution to create the liquid–liquid interface. C60 nanocrystals were assembled at the interface, when ethanol was added to the water dispersion–hexane solution. The assembled film was transferred onto a solid substrate and the film morphology was observed by a scanning electron microscope (SEM) and atomic force microscope (AFM).

Electrochemical charging and photochemical discharging in heterodeposited polymer nanosheet assembly

We demonstrate electrochemical charge storage and photochemical release of the charge in heterodeposited polymer nanosheets assemblies. Two kinds of redox polymer nanosheets, those containing ruthenium dipyridyl complex (p(DDA/Rubpy32+)) and ferrocene derivative (p(DDA/Fc)), respectively were heterodeposited onto an ITO electrode using the Langmuir–Blodgett technique. The heterodeposited assembly forms a clear bilayer structure in which p(DDA/Rubpy32+) is located in an inner layer and p(DDA/Fc) in an outer layer. The electrochemical property of the heterodeposited assembly was studied by cyclic voltammetry measurement and compared with their single component film. The cyclic voltammogram of p(DDA/Rubpy32+) monolayer film showed a redox peak of Rubpy32+/3+ reaction around 1.1 V (vs.Ag/AgCl), and that of p(DDA/Fc) monolayer showed a redox peak of Fc0/+1 around 0.4 V. On the other hand, the cyclic voltammogram of the bilayer film showed no oxidation current around 0.4 V, and large oxidation currents were observed from 0.9 V. In the heterodeposited assembly, the p(DDA/Fc) layer was separated from the electrode about 5 nm by the inner p(DDA/Rubpy32+) layers. Therefore the oxidation of Fc moieties occurred by mediation of the inner p(DDA/Rubpy32+) layers, which started around 0.9 V. On the other hand, reduction of Fc+ by scanning the potential to cathodic direction was not observed, because reduction of Fc+ is thermodynamically unable for Rubpy32+. As the results, the outer p(DDA/Fc) layers store charges as Fc+ by one potential cycle (electrochemical charging). Moreover, we demonstrate the Fc+ reduction by using the photoinduced electron transfer from an excited ruthenium complex to Fc+ (photochemical discharging). The repeatability of the charging-discharging process was about 5 times. To improve the repeatability, Prussian blue (PB) nanoparticles were used instead of the p(DDA/Fc) layers. PB nanoparticles were assembled on a solid substrate using a cationic polymer nanosheet, poly(N-dodecylacrylamide-co- N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)acrylamide) (p(DDA/DONH)) as a template. A hybrid heterodeposited assembly was prepared using p(DDA/Rubpy32+) as an inner layer and p(DDA/DONH) templated PB as an outer layer. The hybrid heterodeposited assembly stored and released charges by a similar process with the p(DDA/Rubpy32+)-p(DDA/Fc) heterodeposited polymer nanosheets assembly. The repeatability of the charging-discharging process in the hybrid heterodeposited assembly was increased compared to that in the p(DDA/Rubpy32+)-p(DDA/Fc) heterodeposited assembly due to the high stability of the oxidized form of PB. The high repeatability of the hybrid heterodeposited assembly indicates that the assembly is applicable to molecular-memory and battery.

Dynamic behavior of pyrene fluorescence in highly oriented polymer LB films

Abstract The photophysical properties of the pyrene chromophore in poly( tert -pentylacrylamide- co -1-pyrenylmethyl acrylate) (p( t PA/PyMA)) Langmuir–Blodgett (LB) monolayer were studied. It is found that the emission property of the pyrene is drastically changed by capping with polymer LB films. When the pyrene monolayer was capped with poly( N -dodecylacrylamide) (p(DDA)) LB films, the emission intensity ratio of the excimer to the monomer ( I Ex / I Mon ) was increased with increasing temperature, whereas the I Ex / I Mon value was decreased with increasing temperature in the capping with poly( tert -pentylacrylamide) (p( t PA)) LB film. This interesting effect is discussed on the basis of the time-resolved emission spectroscopy.

Direct deposition of two nanomaterials with the same surface charge using a liquid-liquid interface.

Two negatively charged nanoparticles (SDS-coated SWCNT and polydiacetylene nanocrystals) were sequentially adsorbed onto the same water-hexane interface. The absorbed film can be transferred onto a solid substrate. Repeating the adsorption and transfer process enables assembly of the two nanoparticles in a layer-by-layer growth fashion up to three bi-layers.

Molecular orientation of azobenzene chromophores in ultrathin polymer nanosheets studied by attenuated total reflection spectroscopy.

This paper describes characterization of molecular orientation for azobenzene moieties in a polymer nanosheet. Copolymers of N-[4-(phenylazo)phenyl] acrylamide (PAZoA) with tert-pentyl acrylamide (tPA) were synthesized and the monolayers deposited on tapered quartz waveguides by Langmuir-Blodgett (LB) technique. Spectroscopic properties of the copolymer (p(tPA/PAZoA)) monolayers were monitored by integrated optical waveguide technique on the molecular level. Molecular orientation of the azobenzene was precisely determined by polarized absorption spectra. It was found that the azobenzene groups took a horizontal orientation and distributed uniformly in the p(tPA/PAZoA) monolayer without significant PAZoA aggregation. Photoisomerization process from trans to cis form was also investigated. More than half of the trans form (60-70%) was photoisomerized under unpolarized light irradiation, and the photoisomerization rate was independent on the PAZoA contents. This implies that the microenvironment of PAZoA moieties was almost the same in three different p(tPA/PAZoA) monolayers.