| POLYMERS Vol.63 No.11 |
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COVER STORY
Smart Progress on Science and Technology of Carbon-Based Thermoelectric Materials |
| COVER STORY: Highlight Reviews |
| Toward Computational Simulation Aided Screening for High Performance Thermoelectric Material Search | Yoshihiro ASAI |
| <Abstract> Heat problems such like heat generation, heat transport and heat dissipation have become important targets of first principle computer simulation in terms of Non-equilibrium Green Function (NEGF) theory. While such theory has been primarily applied to the field of nanoelectronics, thermoelectric material research would become another successful target of the theory. We will review the present status of theory/computer simulation approaches to thermoelectric material research by comparing this new direction with the standard classical Boltzmann equation approach. We will also discuss organometallic molecular multilayer, which exhibits long-range charge migration with small β where β is the exponent of the length dependent conductance. Narrow band formed close to the Fermi level of the electrode due to the introduction of the central metallic atom helps the small β as well as simultaneous enhancement of the Seebeck coefficient and the conductance. Thickness dependent and the metallic atom specific thermoelectric figure of merit ZT are discussed based on the first principle NEGF result. Keywords: Thermoelectric Figure of Merit / First Principle Non-Equilibrium Green Function (NEGF) Method |
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| Recent Progress of Organic and Hybrid Thermoelectric Materials | Naoki TOSHIMA |
| <Abstract> Thermal management is very important for the life of human beings. In fact most energy content of fossil fuel is lost as waste heat without use. Organic thermoelectric materials can be used for recovering such electric energy from waste heat in a low grade. Here we review recent progress in the development of organic thermoelectric materials. The research on organic thermoelectric materials started in 1999 by using conducting polyaniline. Relatively good thermoelectric performance (ZT=0.1) was achieved for stretched polyphenylenevinylene derivatives in 2007. Now polythiophene derivatives (PEDOT) with high electrical conductivity were found to have a high thermoelectric performance by controlling the oxidation level and dopant concentration. Much effort has been concentrated on the development of organic-inorganic hybrid thermoelectric materials, too. Hybridization of PEDOT with semiconducting and metallic nanomaterials, as well as multi-walled, single-walled and double-walled carbon nanotubes, was extensively investigated. The hybrid materials of PEDOT and double-walled carbon nanotubes was found to have the highest performance at the present. Keywords: Organic Thermoelectric Materials / Conducting Polymers / PEDOT / Hybrid Materials / CNT / Thermoelectric Figure-of-Merit / Electrical Conductivity / Thermal Management |
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| Development of Nanostructured Thermoelectric Materials | Hiromichi OHTA |
| <Abstract> Nano-structure control is the key for the realization of high-performance thermoelectric materials. The effectiveness of nano-structure control was theoretically predicted by Dresselhaus (MIT) et al. in 1993. After that, materials with high ZT values (>2) have been reported one after another. There are two approaches of nano-structure control for the realization of high-performance thermoelectric materials. One is to enhance the thermopower by utilizing quantum electron confinement effect. The other one is to reduce the thermal conductivity based on the “phonon-glass electron-crystal” concept (Slack, 1995). In this article, state-of-the-art nano-structure control techniques are reviewed using several examples. Keywords: Nano-Structure Control / Quantum Confinment Effect / Superlattices / Two-Dimensional Electron Gas (2DEG) / Phonon-Glass Electron-Crystal / Lattice Thermal Conductivity |
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| COVER STORY: Topics and Products |
| Separation of Single-wall Carbon Nanotubes Towards High Efficiency Thermoelectric Devices | Hiromichi KATAURA |
| <Abstract> Because 50% of used energy is wasted as heat in Japan, utilizing waste heat could greatly contribute preventing global warming and energy saving. Thin film, flexible, and high performance at low temperature thermoelectric devices are desirable for that purpose. Very recently, Maniwa et al. revealed that semiconducting SWCNT separated from pristine mixture has very large Seebeck coefficient at room temperature, while metallic SWCNT shows low value. This surprising difference can be explained by well- known Mott’s equation. We have demonstrated a thermocouple device constructed from junctions of metallic and semiconducting SWCNTs. Because SWCNT is robust, flexible, chemically inactive, and highly conductive, SWCNT can be a candidate material for high efficiency thin film thermoelectric devices. Low cost and large scale metal / semiconductor separation method of SWCNT was developed in NEDO project. Supply of low price semiconducting SWCNT could be possible in near future. Keywords: Thermoelectric Device / Carbon Nanotube / Separation / Seebeck Coefficient |
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| Flexible Porous Bismuth Telluride Thin Films with Enhanced Figure of Merit Using Micro-Phase Separation of a Block Copolymer | Koji MIYAZAKI |
| <Abstract> We made porous thermoelectric thin films by using a block copolymer as the template. The nano-porous structure was made over a large area by using a phase separation of a block copolymer (PMMA-b-PMAPOSS). The Bismuth telluride was deposited on a porous polymer film. The thermal conductivities of the porous thermoelectric thin films were lower than that of bulk value due to long phonon mean free path, and the non-dimensional figure of merit was enhanced. A prototype thermoelectric module consisting of 20 pairs of p- and n-type strips was fabricated on the porous polyimide substrate. This module produced an output power of 0.1 mW and the output power was 1.5 times greater than that of a module based on flat Bismuth telluride thin films. Keywords: Thermoelectric / ZT Enhancement / Block Copolymer / Porous / Thermal Conductivity / Phonon |
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| Flexible Organic Thermoelectric Materials for Energy Harvesting | Toshiaki AOAI |
| <Abstract> By using a photo acid generator (PAG), photo-induced doping to conductive polymers was investigated. The homogeneous film comprised of conductive polymers and PAGs, such as sulfonium salts, could be prepared without aggregation on coating and gave good conductivity after UV irradiation of the film. With the increase of PAG content and UV dose, the conductivity of the film showed higher values. The photo doping method was also effective for CNT / conductive polymer composites as another organic thermoelectric materials, which produced much higher conductivity and values of more than ZT=0.3. Utilizing the CNT composite materials, a flexible organic thermoelectric module was prepared through mask printing process and showed the possibility for an energy harvesting device. Keywords: Photo Doping / Photo Acid Generator / Organic Thermoelectric / Conductive Polymer / Carbon Nanotube Composite / Flexible Thermoelectric Module |
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| Independent Control of Carrier and Heat Flow in Carbon Nanotube Thermoelectric Composites Using Bio-Nano Junctions | Masakazu NAKAMURA |
| <Abstract> Carbon nanotubes (CNTs) are an attractive material for flexible thermoelectric devices because of their mechanical strength and high electrical conductivity. However, their thermoelectric performance is restricted by the large thermal conductivity. In this work, a novel method to improve performance by inserting bio-based molecules at CNT/CNT junctions is proposed. Thermal conductivity is dramatically suppressed, but electrical conductivity increases by the addition of cage-shaped proteins with semiconducting cores. The Seebeck coefficient can be increased by the selection of core material. By the improvements in all of the three important parameters above, the thermoelectric figure of merit (ZT) increases over 1000-fold. Keywords: Carbon Nanotube / Cage-Shaped Protein / Bio-Nano Junction / Thermoelectricity |
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| Polymer Science and I: A Personal Account |
| Aspiring to Do Excellent Research for People and Society | Yuri KAJIHARA |
| <Abstract> In my college days, I learned not only how to promote my research but also aquired a wide range of knowledge in life. I finally found my enthusiasm to do excellent research for the benefit of people and society. Now as a company reseacher, I aspire that the resin I develop should bring new values to the world. |
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| Front-Line Polymer Science |
| Molecular Simulations of Polymer Crystallization | Takashi YAMAMOTO |
| <Abstract> Computer modeling is acquiring ever increasing significance in the science and technology of polymers. In this article, we review recent advances in computer simulation of polymer crystallization. We here deal with several topics of great relevance, the basic elementary process of polymer crystallization, the characteristic crystallization behavior of polymers having specific molecular structures, the very fast crystallization during deformation and flow, and the crystallization in confined spaces and interfaces with other materials. We here emphasize the great potential of the computer modeling, and the challenges for the future. Keywords: Computer Modeling / Polymer Crystallization / Primary Nucleation / Crystal Growth / Helical Polymers / Comb-Like Polymers / Multi-Scale Modeling |
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