| POLYMERS Vol.64 No.5 |
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COVER STORY
Spices for Intelligent Polymer Materials |
| COVER STORY: Highlight Reviews |
| Control of Optical Anisotropy for Polymer Film with Additives | Masayuki YAMAGUCHI |
| <Abstract> Optical anisotropy of a polymer film is controlled by a small amount of low-molecular weight compounds. Intermolecular orientation correlation between polymer chains and additive molecules, called Nematic interaction, is responsible for the modification. A thinner retardation film, a retardation film with extraordinary wavelength dispersion, and a film with three-dimensional refractive index control can be designed by applying this phenomenon. Moreover, the orientation correlation occurs even at the solution-cast method, which is used to erase the out-of-plane retardation of a solution-cast film. Since most low-molecular weight compounds are miscible with a polymer matrix due to the contribution of mixing entropy, this technique will be widely available to modify the optical anisotropy in polymer films. Finally, a method to use form birefringence is also introduced, in which an additive phase is extracted by an organic solvent after stretching. The film with elongated micro-pores shows extraordinary wavelength dispersion with high glass transition temperature. Keywords: Polymer Blend / Orientation / Polymer Processing / Birefringence / Additive / Retardation Film |
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| Filler Technology to Provide Diversity in Clay-Polymer Nanocomposites | Kenji TAMURA, Hiroshi SAKUMA |
| <Abstract> It is well known that clay-polymer nanocomposites reveal excellent mechanical, gas barrier properties and flamability at low weight fractions of inorganic components. Important factors in achieving excellent performance from clay-polymer nanocomposites are mainly the dispersion state of clay, interfacial interaction of clay/polymer and morphology of the dispersed particles. Despite extensive work, there have been few reports about controlling the morphology (such as particle shape and size) of the nanocomposites. Although morphology control is still difficult, it is a pivotal technique used to study how morphology affects nanocomposites properties. Here, our attention is focused on the clay components of nanocomposites, the controlling dispersion of inorganic plateletes using natural mica and mixed layer minerals. Keywords: Clay / Mica / Nanocomposite / Morphology / Aspect Retio / Mixed Layer Mineral / Staging |
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| COVER STORY: Topics and Products |
| Dye Sensitization of Polymer Solar Cells | Hideo OHKITA |
| <Abstract> Polymer solar cells have attracted much attention because of their advantages such as lightweight, flexible, colorful, and lowcost. However, the power conversion efficiency (PCE) is still lower than that of conventional silicon solar cells. For further improvement in the PCE, many more photons should be harvested from solar light. In this article, we show a new approach to improving the light-harvesting efficiency of polymer solar cells. To harvest more photons, we have incorporated a near-IR dye (SiPc) with bulky axial ligands into polymer solar cells based on binary blends of poly(3-hexylthiophene) (P3HT) and a fullerene derivative (PCBM). As a result, the photocurrent is clearly enhanced because of the additional dye absorption. Interestingly, almost all the dyes are located at the P3HT/PCBM interface. This is partly because the surface energy of SiPc is in between those of P3HT and PCBM. These findings indicate that dye location in blend films can be controlled even by solution processes on the basis of careful materials design. Keywords: Polymer Solar Cells / Dye / Sensitization / Near-IR / Interface / Surface Energy |
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| Fuctionalization of Commodity Polymers by Introducing Guest Molecules into the Crystalline Region | Fumitoshi KANEKO |
| <Abstract> In order to functionalize commodity polymers, functional chemical compounds have been doped into the amorphous region. In contrast, there had been few attempts to introduce them into the crystalline region, though some advantages are expected for such polymer-crystalline-region-based composite materials. However, recent studies on syndiotactic polystrene (sPS) have revealed that sPS forms co-crystal structures with many chemical compounds. The range of guest molecules has expanded by exploiting the guest exchange phenomenon of sPS co-crystals; in particular, it was found that some additives to the new guest promote the guest exchange process significantly and incorporates bulky molecules easily into the crystalline region. A wide range of chemical species, dye, organic radicals, crown ether and even polymeric compounds, such as polyethylene glycols, have been included in sPS co-crystals. Anisotropy in the properties due to guest molecules can be adjusted by controlling the orientation of crystalline regions. Keywords: Syndiotactic Polystyrene / Cocrystal / Guest Exchange / Clathrate / Functionalization / Crystalline Region |
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| Conductive Polymer Composite with Small Amount of CNTs | Seisuke ATA |
| <Abstract> In this article, we report the ability of carbon nanotubes as a conductive filler of polymer composites. CNTs are well-known as high conductive, high thermal conductive and high mechanical strength materials. Therefore, CNTs are believed to be the most suitable conductive fillers for polymer composites. We report that the solubility parameter is an important parameter that determines the degree of a long super growth carbon nanotube (SG-SWNT) dispersion in the rubber matrix, and thus the conductivity or other properties of the SG-SWNT-polymer composites. This finding explains why fluorinated rubber/SG-SWNT composites, with a solubility parameter matching that of SG-SWNT, shows the highest conductivity compared with other rubber at a same amount of CNT loading. Based on this finding, we speculate that the addition of a small amount of fluorinated rubber into the rubber matrix acts as a unified and practical technology to improve the conductivity of the SG-SWNT/rubber composite for a various kinds of rubber matrices. Keywords: Carbon Nanotube |
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| Design of Stimuli-Responsive Hydrogels Consisting of Cylindrical Inorganic Polymer | Kazuhiro SHIKINAKA |
| <Abstract> In this paper, stimuli-responsive hydrogels prepared from a rigid cylindrical inorganic polymer ‘imogolite’ and a dicarboxylic acid are described. Due to the network structure of imogolites connected by hydrogen bonding, the hydrogel exhibited thixotropy in response to mechanical shock that could be liquefied and re-solidified reversibly by shaking and standing, respectively, within subseconds. After flow-orienting and subsequent standing the sol-state mixture, the uniaxial alignments of imogolite nanotubes in the centimeter scale were realized in the recovered gel. The degree of orientation of imogolite was noticed to be dependent on the flow velocity of the sol-state mixture. The self-standing interpenetrated network (IPN) gels were also prepared by the in situ polymerization of the uniaxially oriented gels that were pre-impregnated by vinyl monomer and a cross-linker. The confinement of the imogolite nanotubes with the uniaxial orientation induced some anisotropic physical properties to the gels such as anisotropic birefringence and mechanical strength. Keywords: Nanotubes / Colloids / Gels / Thixotropy / Self-assembly |
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| Highly Sensitive Photopolymers Based on Cascade Chemistry | Koji ARIMITSU |
| <Abstract> A system that amplifies the first stage of a photochemical reaction by connecting several thermochemical reactions is called “cascade chemistry”. Cascade chemistry will enable us to create highly sensitive photopolymers, such as photoresists and UV curing materials. We have developed compounds that generate organic acids and bases autocatalytically, denoted as either acid amplifiers or base amplifiers, because the number of acid or base molecules can be boosted in a nonlinear manner as a result of the autocatalytic decomposition of the amplifier. Our effort has been focused on the development of these amplifiers, and on how to combine these acid or base amplifiers with photoacid or photobase generator systems, because a small concentration of photogenerated acidic or basic species may be amplified. This results in a marked enhancement of the subsequent acid- or base-catalyzed reaction to provide novel photopolymer systems with a high sensitivity. Keywords: Cascade Chemistry / Photopolymers / Photoresists / UV Curing / Acid Amplifiers / Base Amplifiers / High Sensitivity |
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| Polymer Science and I: A Personal Account |
| I am an Optimist | Eriko SATO |
| <Abstract> At the turning points of my researcher life, I have kept making an optimistic decision, and this is why I am still enjoying research now. I truly feel grateful for having been given a good research environment and valuable experiences, which enhanced my personal and professional development much better than my expectations. |
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| Front-Line Polymer Science |
| Smart Polymers for Cell Mechanobiology | Mitsuhiro EBARA |
| <Abstract> Cell responsiveness to their surrounding mechanical cues has been the subject of a number of researchers. Especially, mechanical and topographical properties of the substrate are critical parameters in stem cell maintenance and differentiation. In spite of a considerable amount of ongoing research, however, current efforts are centered on rather static patterns. Therefore, the scientific community has recently shown increased interest in developing surfaces with tunable abilities. The present review aims to bring together the exciting design of smart polymers and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments, which have been considered to be critical parameters in cell fate determination. The untapped potential of smart polymers makes them one of the most exciting interfaces of materials science and cell mechanobiology. Keywords: Smart Polymers / Shape-Memory Polymers / Mechanobiology / Dynamic Sbstrates |
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