Masa Aki Kakimoto

One-Step Direct-Patterning Template Utilizing Self-Assembly of POSS-Containing Block Copolymers.

We report the self-assembly of organic-inorganic block copolymers (BCP) in thin-films by simple solvent annealing on unmodified substrates. The resulting vertically oriented lamellae and cylinders are converted to a hard silica mask by a single step highly selective oxygen plasma etching. The size of the resulting nanostructures in the case of cylinders is less than 10u2009nm.

THERMAL AND OPTICAL STABILITIES OF PHOTOISOMERIZABLE POLYIMIDE LAYERS FOR NEMATIC LIQUID CRYSTAL ALIGNMENTS

We have investigated the thermal and optical stabilities of the photoalignment layers for nematic liquid crystals (LCs). For the photoalignment layers, three kinds of photoisomerizable polymer systems were studied; a polyamic acid doped with azobenzene molecules, a side-chain-substituted polyamic acid with azobenzene units, and a main-chain-substituted polyamic acid with azobenzene units. Photoinduced anisotropy was produced by illumination with linearly polarized near-UV light from a mercury lamp, and evaluated by measuring polarized UV absorption spectra and optical birefringence. The nematic LC-alignment properties were investigated using the photoalignment layers processed under various thermal and optical conditions. It was observed that the main-chain polyimide system exhibited good unidirectional LC alignment and excellent thermal (300°C for 1 h) and optical stabilities. Moreover, we suggest a new procedure, in which the photoillumination process is carried out before the thermal imidization process, to achieve a stable photoalignment layer.

Organic Macromolecular High Dielectric Constant Materials: Synthesis, Characterization, and Applications

Hyperbranched and dendritic architectures have been targeted for various applications such as sensing, drug delivery, optical limiting, and light harvesting. One interesting development in this area has focused on utilizing the existence of long-range delocalization in hyperbranched structures to achieve high dielectric constants. In this Feature Article, we will review the creation and development of this concept, and we highlight our recent research progress in this aspect. In particular, we discuss (1) synthetic methods for a particular group of hyperbranched polymers; (2) detailed optical and electronic characterization of this group of hyperbranched polymers, revealing the design criteria for achieving a good combination of high dielectric constant and minimum loss in such materials; and (3) the importance and potential applications of these materials.

Electrochemical Oxygen Reduction Activity of Carbon Nitride Supported on Carbon Black

Electrochemical oxygen reduction via nonprecious, Fe/N/C catalysts has potential to reduce the cost and increase acceptance of hydrogen-powered polymer electrolyte membrane fuel cells. However, because these materials are a complex mixture of carbon, nitrogen, and iron, the nature of the active site is still much debated. By using carbon nitride as an ideal, nitrogen-rich, iron-free catalyst we shed light on the role of carbon-nitrogen bonding in electrochemical oxygen reduction. Carbon nitride was synthesized on a carbon black support via a simple solvothermal process. The resulting material was pyrolyzed and characterized via a variety of techniques. Electrochemical testing revealed that carbon nitride pyrolyzed at 1000°C displayed the best oxygen reduction activity, with an onset potential of 0.90 V and a low selectivity to H 2 O 2 formation, indicating a 4-electron oxygen reduction pathway. Due to small amounts of Fe contamination in this series of samples, an Fe-free sample was prepared without the carbon black support, resulting in similar electrochemical properties. The enhanced activity is tentatively attributed to enriched quaternary nitrogen in the material at this temperature, as suggested by X-ray photoelectron spectroscopy.

Preparation of polyimide Langmuir-Blodgett films possessing a triphenylamine unit and their application to photodiodes

Abstract Photoconductive devices (photodiodes) were constructed by the deposition of polyimide LB multilayer films which possessed different chemical structures, i.e., a triphenylamine unit as an electron donor (D), tetraphenylporphyrin as a sensitizer (S), and aromatic polyimide as an electron acceptor (A). Two types of photodiodes with E/D/S/A/ and E/A/S/D systems were prepared on a semitransparent gold electrode (E). The dependence of each number of D, S, and A layers on the photocurrent behavior was examined to discuss the electron transfer in each layer.

Synthesis of Aliphatic Polyurea Films by Vapor Deposition Polymerization and Their Piezoelectric Properties

Aliphatic polyurea 9 films were prepared by vapor deposition polymerization of the monomers 1,9-diisocyanatononane and 1,9-diaminononane on a glass substrate cooled to various temperatures below 0° C. When the temperature of the substrate was low, the residence time of deposited monomers was sufficiently long to allow addition polymerization. The piezoelectric constant of poled films depended on the poling electric field and the poling temperature. Three relaxation processes were observed at -150° C (γ), -50° C (β) and 100–140° C (α) in the measurement of the temperature dependence of the elastic and dielectric constants. The thermal molecular motins at these three relaxations influenced the crystallization, poling process and thermal stability of piezoelectric activity.

Patterned surfaces in self-organized block copolymer films with hexagonally ordered microporous structures

A novel fabrication of the patterned surfaces in the polymer films was demonstrated by using the selforganizing character of the block copolymers of polystyrene-b-oligothiophenes and polystyrene-b-aromatic amide dendron. Hexagonally arranged open pores with a micrometer-size were spontaneously formed by casting the polymer solutions under a moist air flow. The amphiphilic character of the block copolymers played the crucial role as a surfactant to stabilize the inverse emulsion of water in the organic solvent, and subsequently the aggregated structure of the hydrophilic oligothiophene or aromatic amide dendron segments remained on the interiors of the micropores. The chemical composition on the top of the surface of the microporous films was characterized by energy-filtering transmission electron microscopy (EFTEM) or a time-of-flight secondary ion mass spectrometer (ToF-SIMS). The characterizations clearly indicated that the patterned surfaces in the self-organized block copolymer films with the hexagonally ordered microporous structures were fabricated in a single step.

Synthesis, end-functionalization and characterization of hyperbranched polysiloxysilanes from AB3 type monomer

Hyperbranched polysiloxysilanes (HBPSs), with a variety of terminal functional groups (vinyl, epoxy, carboxyl and hydroxyl), were synthesized by the self-polymerization of an AB3 type monomer of tris(dimethylvinylsiloxy) silane, with subsequent end-functionalizations, such as epoxidation and radical addition reaction, respectively. The ratio of the α- and β-addition linkages in the HBPS polymerized by hydrosilylation of the AB3 monomer was found to be approximately 1 to 3. The thermal stability and solubility were affected by the terminal functional groups.

Adsorption of hyperbranched polysiloxysilane modified with triethoxy group onto the silicon wafer

Triethoxysilyl functionalized hyperbranched polsiloxysilanes at the focal (FT-HBPSs) and terminal (TT-HBPSs) positions were synthesized to investigate adsorption behavior onto a silicon wafer surface. The surface of the silicon wafer adsorbed with the HBPSs was characterized by X-ray photoelectron spectroscopy, atomic force microscopy (AFM), static and dynamic water contact angle measurements. The AFM images indicated the formation size of dot-like structures were approximately 200 nm. The presence of vinyl terminal groups of FT-HBPSs permitted conversion of the surface from a non-polar hydrocarbon to a polar hydroxylated or carboxylated structures. After the polarity was changed, the surface properties were also studied using the above surface analysis techniques. The dynamic contact angle measurement indicated that the silicon wafer surface modified by FT-HBPSs was more hydrophilic in water than TT-HBPS. This behavior can be explained by the difference of connecting points between HBPS and the silicon wafer surface.

Observation of Cross Sections of Plasma-Polymerized Films of Benzene and Naphthalene by Electron Spectroscopic Imaging

Plasma-polymerized films of benzene and naphthalene were prepared by direct current (D.C.) glow discharge. The chemical structures of the films were characterized by IR and Raman spectroscopy, electron energy loss spectroscopy (EELS), and electron spectroscopic imaging (ESI). With increasing D.C. voltage, the hydrogen-free carbon films consisting of sp2 bonded carbon tended to change to sp3 bonded carbon. Successive plasma-polymerization with different D.C. voltages for benzene and naphthalene on poly(ethylene terephthalate) (PET) film yielded double-layer films consisting of sp2 and sp3 bonded carbons, respectively. Observation of cross section of the film by ESI yielded clear images of the heterostructure.