POLYMERS　Vol.65　No.2
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COVER STORY
A Milestone Toward Achieving Molecular Alignment
COVER STORY: Highlight Reviews
Molecular Alignment for High-Performance Organic Electronics Jun TAKEYA
<Abstract> Organic single-crystal semiconductors offer the systems of π-conjugated small molecules periodically arranged in a macroscopic length scale. Since molecular alignment is crucial in charge transport with minimized disordered potential, such solids are the most suited both to study fundamental physics of charge transport in the weakly interacting molecular assemblies and to fabricate the best-performing organic devices for printed and flexible electronics. The degree of fundamental intermolecular electronic charge coherence is discussed using the results of Hall effect on various single-crystal transistors under varied temperatures. It turned out that the extent of the coherence depends on molecular systems, so that such an approach gives a prescription to design new molecular compounds because fully coherent materials exhibit high carrier mobility of approximately 10 cm2/Vs, indeed.
Keywords: Organic Semiconductor / Organic Electronics / Organic Transistor / Organic Single-Crystal Transistor / Printed Electronics / Printed LSI / Printed Active Matrix
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Phonon that Influences the Thermal Conductivity of Polymers Yoshitaka TAKEZAWA
<Abstract> The phonon is a quantum of energy or quasiparticle that quantizes the vibration (elastic wave) of the material and is widely handled as a transmission medium of the thermal energy of the insulating materials. Many macromolecules are random structures as viewed in solid-state physics and are hard to discuss on the base of a phonon using quantum theory. However, it is necessary to understand the existence of the phonon for the random macromolecules when we think about a thermal conductive phenomenon from the viewpoint of molecular orientation. I would like to explain the unfamiliar concept of a ‘phonon’ as a thermal conductive phenomenon in a macromolecules.
Keywords: Phonon / Scattering / Thermal Conductivity / Molecular Orientation / Mesogen / Liquid-Crystalline / Epoxy / Polyethylene
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Orientation of Ions Takahiro ICHIKAWA, Hiroyuki OHNO
<Abstract> Ionic liquids have attracted an increasing attention as functional liquids. To date, a variety of approaches have been developed for improving their functions and properties. For endowing them with further and/or additional functions and properties, controlling the orientation of ionic liquids at the molecular level is one of the interesting approaches. In this manuscript, we describe materials design combining ionic liquids and liquid crystals for the orientation of ions. In particular, we introduce some new functions and properties originating from their specific nanostructures and/or their novel interfaces.
Keywords: Ionic Liquids / Liquid Crystals / Ion Conduction / Zwitterions
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COVER STORY: Topics and Products
Control for Orientation of Polymer Crystals Go MATSUBA
<Abstract> We discussed about the structure formation process during shear flow, especially the so-called shish-kebab structure. For this purpose, we developed new type polarized optical microscopy with high-speed camera. We succeeded the formation processes of micro-scaled fibril-like structure in isotactic polypropylene. At first 8 sec, no fibril-like structure could be observed, while after 9 sec we observed increasing of these structure during shear flow. We evaluated the length and width of these structure. The length increases with increasing shear rate and decreasing shear temperature, because the structure formation processes depend on polymer chain relaxation. On the other hand, the width is independent of the shear rate and temperature. To evalutate the nm-scaled structure foramtion processes we carried out in-situ x-ray scattering measurements with synchrotron such as SPring-8 and Photon Factory in Japan. The nm-scaled scature grows up after emerging of micro-scaled fibril-like structure. The nm-structure is due to lamellar-structure with polymer crystal. These suggest that micron-scaled fibril-like structure is caused by precursor of oriented crystalline and higher-ordered structure.
Keywords: Shish-Kebab Structure / Shear Flow / Higher-Ordered Structure / Synchrotron X-ray Scattering
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Mechanochromic Molecules and Materials Shohei SAITO
<Abstract> Molecular alignment is important for the exhibition of molecular functions in bulk materials. The author introduces some examples in which luminescence of materials, particularly mechanochromic luminescence, have been designed based on molecular fluorescence and molecular alignment. The sentences are composed of following three topics, 1) distinct solid-state fluorescences only depending on fluorophore alignment (Angew. Chem., Int. Ed., 51, 714-717 (2012)), 2) discrimination of anisotropic and isotropic stresses by mechanochromism (J. Am. Chem. Soc., 135, 10322-10325 (2013)), and 3) quick and reversible visualization of the stress on a fluorescent polymer film. In the last system, a dynamic fluorophore has been synthesized to realize force-induced fluorescence color change in single molecule (J. Am. Chem. Soc., 135, 8842-8845 (2013) and Chem. Eur. J., 20, 2193-2200 (2014)). The interplay of molecular functions and molecular mechanics becomes more and more important for the creation of fuctional materials, in which the molecular alignment is the key to the synergistic functions.
Keywords: Mechanochromism / Piezochromism / Luminescence / Fluorescence / Molecular Alignment / π Conjugation / High Pressure / Stress Sensor
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Magneto-LC Effects and Magnetoelectric Effect Observed in All-Organic Nitroxide Radical Liquid Crystals Rui TAMURA
<Abstract> For the first time, we prepared all-organic radical liquid crystalline (LC) compounds in which a five-membered cyclic nitroxide unit is incorporated into the central position of the molecule and found the occurrence of a sort of spin glass-like ferromagnetic interactions (average spin-spin exchange interaction constant J > 0) induced by low magnetic fields in the various LC phases. This phenomenon was referred to as “positive magneto-LC effects”. Furthermore, we could observe a “magnetoelectric effect” for the ferroelectric liquid crystalline phase showing the positive magneto-LC effects, by measuring the electric field dependence of paramagnetic susceptibility by means of EPR spectroscopy.
Keywords: Magneto-LC Effects / Magnetoelectric Effect / Nitoxide Radical Liquid Crystals
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Polymer Science and I: A Personal Account
A Misunderstanding Gave Me a Chance to be a Polymer Chemist Hiroaki SHIMOMOTO
<Abstract> After the unexpected encounter with the research area of macromolecules caused by my misunderstanding, I have met a number of great people over the past 10 years. Their continuous guidance and encouragement have made me what I am today.
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Front-Line Polymer Science
Recent Progress in Photoalignment Technology Nobuhiro KAWATSUKI
<Abstract> Photoalignment for LC device applications has received much attention because it has various advantages, such as no-mechanical damage, no-electric charge, and patterning ability, compared to conventional rubbing and stretching techniques. Basically, the axis-selective photoreaction to a photoresponsive thin film using linearly polarized (LP) light source generates photoinduced optical and physical anisotropies of photoreacted materials. Functional materials such as liquid crystals are easily self-organized on the resultant films and photoreacted films show large optical anisotropy in some cases. This mini-review describes recent progress in photoalignment technology for 1) photoalignment for LC molecules and functional materials, 2) molecularly oriented photoalignment technology, and 3) new photoalignment technology.
Keywords: Photoalignment / Photoinduced Orientation / Liquid Crystal / Liquid Crystalline Polymer / LC Display
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