Tetsuo Saji

Simple Method for Preparing Superhydrophobic Paper: Spray-Deposited Hydrophobic Silica Nanoparticle Coatings Exhibit High Water-Repellency and Transparency

Superhydrophobic and transparent coatings are deposited onto paper by spraying alcohol suspensions of SiO(2) nanoparticles. Superhydrophobicity depends on the aggregation states of nanoparticles, which are determined by the type of alcohol used in the suspensions. The superhydrophobicity of the paper is maintained after touching the paper with a bare finger.

Polarographic studies on bipyridine complexes: I. Correlation between reduction potentials of iron(II), ruthenium(II) and osmium(II) complexes and those of free ligands

Summary A linear relationship between the reduction half-wave potential of a transition metal complex and of its free ligand is predicted, when it is assumed that the electron added to the complex in electrochemical reduction occupies a molecular orbital mainly composed of a ligand π*-orbital. This relationship is found to hold for the complexes ML32+, ML3+ and ML3 (M=iron, ruthenium, osmium; L=2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 5,5′-dimethyl-2,2′-bipyridine). When the central metal is iron, the linear relationship is extended to the terpyridine complexes, i.e. Fe(terpy)22+ and Fe(terpy)2+, where terpy is 2,2′,2″-terpyridine. The assumed electronic configuration is supported spectroscopically in two cases. However, the relation does not hold in the cases where the added electron occupies a metal t2g-orbital. This finding suggests that the electronic configuration of a transition metal complex in a low oxidation state be determined polarographically.

Composite coatings of nickel and ceramic particles prepared in two steps

Abstract A simple technique has been proposed in order to disperse a high vol.% of ceramic particles into a nickel matrix in two steps. A uniform film of ceramic particles was first electrophoretically deposited on an iron plate. Nickel was then electrodeposited in the second step onto the substrate covered with the film of these ceramic particles. Using 5 g/dm 3 of particles in the electrophoretic bath, the two-step method enabled us to incorporate 63 and 67 vol.% of Al 2 O 3 and BN particles, respectively, into the nickel matrix. Similarly, using a mixture of 5 g/dm 3 of BN and 2.5 g/dm 3 of Al 2 O 3 particles in the electrophoretic bath, the proposed two-step method enabled us to incorporate 55.5 and 6.2 vol.% of BN and Al 2 O 3 particles, respectively, into the nickel matrix. In the present investigation, the wear resistance of the coatings was examined under dry sliding conditions using the ball-on-disk configuration. For the reference, an iron plate was coated with the Ni/BN and Ni/Al 2 O 3 composites in a single step. The content of BN and Al 2 O 3 particles in these coatings were 18 and 8.4 vol.%, respectively. The wear experiments showed that, regardless of the method of preparation, the Ni/BN composite coatings had a better wear-resistant performance than the Ni/Al 2 O 3 coatings. However, all three composite coatings prepared by the two-step method showed substantially better wear resistance than those prepared by the single-step method. It has been assumed here that the better anti-wear performance of the composite coatings prepared by the two-step method is due, not only to the higher volumetric content of the particles, but also to the manner in which these particles were incorporated within the metal matrix.

Electron-transfer rate constants for redox systems of Fe(III)/Fe(II) complexes with 2,2′-bipyridine and/or cyanide ion as measured by the galvanostatic double pulse method

Abstract The formal standard rate constants for the redox systems, Fe(bipy) 3 3+ /Fe(bipy) 3 2+ ,Fe(bipy) 2 (CN) 2 − /Fe(bipy) 2 (CN) 2 , Fe(bipy)(CN) 4 − /Fe(bipy)(CN) 4 2− and Fe(CN) 6 3− /Fe(CN) 6 4− (bipy=2,2′-bipyridine), in aqueous solution and N,N-dimethylformamide solution are measured with the aid of the galvanostatic double pulse method. The standard rate constant decreases as the number of the coordinated 2,2′-bipyridine decreases. It is in accordance with the trend in the homogeneous rate constants for these systems and is interpreted on the basis of the extension of ligand π-orbitals. This finding may be evidence for the mechanistic similarity of the electrochemical electron-transfer reaction of a redox system to the corresponding homonuclear electron-exchange reaction occurring in solution phase. An empirical relation between rate constants for both kinds of reactions is discussed. It is noted that the maximum electrochemical rate constant is limited at a value much smaller than the one theoretically allowed.

Electrochemical detection of C60 6? at low temperature

Low temperature cyclic voltammetry (CV) in water-free N,N-dimethylformamide (DMF)–toluene (2:3) mixture containing 0.1 mol dm–3 tetraethylammonium hexafluorophosphate (TEAH) showed a complete set of six one-electron reversible waves for C60, providing evidence for the existence of C606–.

Facile Fabrication of Colored Superhydrophobic Coatings by Spraying a Pigment Nanoparticle Suspension

Superhydrophobic coatings were prepared by spraying a pigment nanoparticle suspension. By changing the type of pigment nanoparticles, the colors of the coating could be controlled. The particle size of the pigments, which determines the surface structure of the coatings, played an important role in exhibiting superhydrophobicity. The spray-coating process is applicable to a variety of materials (e.g., copper, glass, paper, coiled wire, and tied thread), and the superhydrophobicity was repairable.

Composite Plating of Ni/SiC Using a Cationic Surfactant with an Azobenzene Group

A high volume percentage of SiC was uniformly codeposited into a nickel matrix by electrodeposition of nickel from a Watts bath containing particles in suspension which were dispersed with the aid of a cationic surfactant ~AZTAB! containing an azobenzene group. Studies show that AZTAB compared to other surfactants so far reported enhances the codeposition of SiC. It is proposed that this enhancement in the codeposition of the particles is related to the reduction of AZTAB at the cathode surface during the deposition of nickel. The effects of particle loading, current density, and temperature on the extent of codeposition were also studied. At the optimum condition, the maximum volume percentage of the codeposited SiC in the nickel matrix was 62.4%. The industrial performance of metal matrix composites with a SiC-dispersed phase is growing in importance due to the high degree of hardness and wear resistance. However, the magnitude of these properties depends on the volume percentage of SiC. In an attempt to increase the incorporation of SiC particles in such composite the use of various additives and surfactants in an electrolytic bath has been explored by many researchers. 1-4 Ehrsam 5 claimed that the oleyl dimethyl amine oxide surfactant yields a disperseion of about 48 vol % SiC into a nickel matrix. However, this required a much larger amount ~ 600 gd m 23 ! of SiC in the plating bath. Helle 6 proposed that a fluorocarbon surfactant could promote the codeposition of SiC up to 50 vol %. Recently, we demonstrated that a nonionic surfactant containing an azobenzene group loses its amphiphilic function upon reduction, and this phenomenon was applied to the electroless plating of organic pigment films on base metals. 7 In this paper, we report composite plating of Ni/SiC using a cationic surfactant containing an azobenzene group ~AZTAB, Fig. 1!, which enabled us to increase the content of SiC particles in the composite. Experimental Synthesis of AZTAB.—The cationic surfactant ~AZTAB! was synthesized by azo-coupling of n-p-ethylaniline with phenol, followed by ethylation with 1,2-dibromoethane and quaternization with trimethylamine as previously described. 8 The yellow powder of AZTAB was dissolved in water and filtered. An excess volume of acetone was added to the filtrate, and the mixture was shaken vigorously. Then, liquid was evaporated by vacuum distillation. The resultant mass was dried in air and dissolved in ethanol. Finally, it was recrystalized in diethyl ether. Plating procedure.—All plating experiments were performed in a beaker ~4 cm diam, capacity of about 75 mL!. The composition and the operating conditions of the bath are shown in Table I. To 50 mL of the nickel bath, AZTAB was first dissolved and SiC particles added. This bath was sonicated for 5 min and then stirred for 30 min prior to use to ensure uniform adsorption of the surfactant on the particles. The a-type SiC particles labeled as 1 mm particle size ~Soekawa Chemicals, Japan! were used without purification. The actual distribution of the particle size in the plating bath was not examined. However, a trace amount of the SiC powder was studied by spraying the powder on a conducting adhesive tape and a thin film of gold was coated over these particles. It was then examined using a scanning electron microscope ~SEM!. The particles thus observed were about 1-5 mm ~Fig. 7a!. The substrate was a copper plate and a nickel plate was used as the anode. These electrodes were cleaned by polishing with the metal polishing reagent Pikal ~Nihon Maryo-Kogyo Co., Ltd.! followed by sonicating with acetone and chloroform for 5 min. The active geometry of the cathode was 0.03 3 1 3 1.5 cm and that of the anode was 0.05 3 2 3 2 cm on either sides. These electrodes were held vertically at a distance of 2 cm apart, parallel to each other. During the electrolysis, the bath was continuously stirred at a constant speed with a magnetic stirrer in order to enhance the dispersion of the SiC particles in the bath. Analysis of deposits.—After electrolysis, the deposits were rinsed subsequently in distilled water and acetone. Ultrasonic cleaning in acetone was applied for 10 min on each sample in order to remove loosely adsorbed SiC particles from the surface. Finally it was rinsed with acetone and dried in air. The morphology of the surface and cross section of the coatings were examined using a SEM and the amount of codeposits and SiC was determined using an energy dispersive X-ray ~EDX! microanalyzer coupled to the SEM at a magnification of 100 times and an accelerating voltage of 15 kV. The ZAF ~factors of atomic number Z, absorption A, and fluorescence correction F ! corrected EDX data were used to determine the atomic percentages of nickel and silicon from the intensity of the respective Ka lines. The amount of codeposits was examined at three different locations of each coating and the average volume percentage of these deposited elements was calculated. The volume percentage of Si thus calculated is represented here as the total content of SiC in the coatings. The reproducibility of the coating was examined by analyzing the ten replicas of the coating prepared under the same optimum condition.

Polarographic studies on bipyridine complexes: III. Polarography of tris(2,2′-bipyridine) complexes of chromium(I), chromium(0), vanadium(0), titanium(0) and molybdenum(0)

Abstract Polarograms and cyclic voltammograms for tris(2,2′-bipyridine) complexes of V(0), Cr(0), Cr(I), Ti(0) and Mo(0) in N,N-dimethylformamide are reported. The reversible half-wave potentials for the following redox systems in lower oxidation states are determined: Cr(−I)/Cr(−II), Cr(−II)/Cr(−III), V(I)/V(0), V(0)/V(−I), V(−I)/V(−II), V(−II)/V(−III), Ti(0)/Ti(−I), Ti(−I)/Ti(−II), Mo(−I)/Mo(−II) and Mo(−II)/Mo-(−III). On the basis of the half-wave-potential shift caused by the methyl substitution of ligands, it is concluded that each excess electron of the reductant species of the redox systems, V(bipy)3−/V(bipy)32−, Cr(bipy)3/Cr(bipy)3−, Cr(bipy)3−/Cr(bipy)32− and Cr(bipy)32−/Cr(bipy)33− (bipy=2,2′-bipyridine), occupies a ligand π*-orbital and that of the V(bipy)32+/V(bipy)3+ and V(bipy)3+/V(bipy)3 systems a metal t2g-orbital. The apparent π-character of the excess electron of the redox systems Cr(bipy)3+/Cr(bipy)3 and V(bipy)3/V(bipy)3− is discussed. It is pointed out that the relative electron affinities of trisbipyridine complexes can be determined from the half-wave potential data. The lowest π*-orbitals of V(bipy)3−, Cr(bipy)3 and Fe(bidy)32+ become higher in this order. This suggests that the electrostatic interaction between a π*-electron and the residual charge on the central metal ion predominantly accounts for the observed π*-level shift.

One-step electrophoretic deposition for the preparation of superhydrophobic silica particle/trimethylsiloxysilicate composite coatings.

SiO(2) particle/silicone resin (trimethylsiloxysilicate (TMSS)) composite coatings were prepared by electrophoretic deposition (EPD), and their wettability was examined. SiO(2) coatings prepared by EPD baths without TMSS were hydrophilic, while superhydrophobicity was observed for SiO(2)/TMSS composite coatings. IR spectra and EDS analyses revealed that not only SiO(2) particles but also TMSS electrophoretically moved toward a cathode; as a result, hydrophilic SiO(2) particles turned into superhydrophobic composite coatings by one-step EPD. SEM and AFM images of the superhydrophobic SiO(2)/TMSS composite coatings showed the presence of both nanometer- and micrometer-sized roughness in their surfaces. Particle size of SiO(2) had a great influence on the wettability of the composite coatings. The superhydrophobic SiO(2)/TMSS composite coatings showed excellent water repellency; they repelled running water continuously. In addition, by controlling the amount of deposited SiO(2) particles and TMSS, transparent superhydrophobic SiO(2)/TMSS composite coatings were prepared.

Formation of Copper Phthalocyanine Thin Films by Electrolysis of Surfactants with Ferrocenyl Moiety

Recently, the authors presented a novel technique for electrochemical formation of an organic thin film by disruption of micellar aggregates formed by cationic surfactants having a ferrocenyl moiety (MD method). They reported the preparation of metal-free high concentration of free FPEG not adsorbed on the CuPc particles. The agreements of absorption spectra and x-ray diffraction patterns among CuPc powders, their micellar solutions, and their films indicate that the crystalline form of CuPc is maintained throughout the film preparation processes. The results of the study presented in this paper demonstrate that the MD method is a convenient method to prepare a thin film of CuPc which has a desired crystalline form.