Keiichi Kaneto

Artificial muscle: electromechanical actuators using polyaniline films

Abstract Polyaniline films are found to expand and contract by electrochemical oxidation and reduction, respectively. Two polyaniline films are used as cathode and anode muscles. In this system, the proton transfer between the films are essential chemical reaction. Two types of actuators, viz., “Backbone-type” and “Shell-type” actuators have been fabricated. The “Backbone-type” actuator responded to the frequency of more than 44Hz. The “Shell-type” actuator can be operated in free space.

Characteristics of Polythiophene Battery

A secondary battery utilizing polythiophene films as cathode and anode active materials in an electrolyte of TBABF4/MeCN is studied. The cell potential, energy density and maximum power density (based on the weight of cathode and anode films) are observed to be 3.1 V, 93 Wh/kg and 89 kW/kg, respectively, for the dopant concentration of 24 mol%.

Electrical conductivities of multi-wall carbon nano tubes

Electrical conductivities of individual multi-wall carbon nano tubes have been measured using a micro manipulator by two probe method. The nano tubes are 15~50 nm in diameter and longer than 20 μm in length. The resistance of tubes is several kΩ per μm, which gives the average conductivity as 1,000~2,000 S/cm. The current-voltage characteristics at high field are also studied until the dielectric breakdown takes place. It is found that the enormously large current density more than 106 A/cm2 can flow in a piece of individual nano tubes. The temperature dependence of conductivity of the individual nano tube has been also measured. The preliminary result that the tube with low resistance shows metallic behavior and that of high resistance exhibits semiconductive behavior indicates the various helicities for the multi wall nano tubes too.

ESR and Transport Studies in Electrochemically Doped Polythiophene Film

Electron spin resonance (ESR), electrical conductivity and thermoelectric power are studied in electrochemically prepared and doped polythiophene films. The ESR spin density increases by two orders of magnitude up to dopant concentration of ca. 3 mol%, then decreases, while the conductivity increases drastically by more than ten orders of magnitude until this doping level, followed by a rather mild increase. The ESR linewidth decreases sharply from 9 G to 0.4 G upon slight doping with shape change from Gaussian to Lorenzian. The contribution of Pauli-paramagnetism to the spin succeptibility and the positive thermoelectric power of ca. 20 µV/K which depends linearly on the temperature are observed at heavily doped region. These results are discussed in terms of shallow and deep polarons, and formation of bipolaron up to intermediate doping levels and the hole conduction at the metallic regime.

Electrical Properties of Conducting Polymer, Poly-Thiophene, Prepared by Electrochemical Polymerization

Poly-thiophene perchlorate is prepared electrochemically in an electrolyte of 0.5 M AgClO4 and 0.2 M thiophene in acetonitrile. Dark greenish film with the complex of ca. [C4H2S(ClO4)0.26]x is obtained. The electrical conductivity along the film surface is about 0.6 Ω-1cm-1.

Proposal of Electro-Optical Switching and Memory Devices Utilizing Doping and Undoping Processes of Conducting Polymers

New optical switching and memory elements utilizing the spectral change of conducting polymers by electro-chemical doping and undoping are proposed.

Characteristics of Electro-Optic Device Using Conducting Polymers, Polythiophene and Polypyrrole Films

Detailed characteristics of electro-optic elements (color switching and memory) utilizing the spectral change of conducting polymers by electrochemical doping and undoping are studied. The response time of color switching, for example, red↔blue in polythiophene film in the electrolyte of LiBF4/acetonitrile is 30~100 msec under the applied voltages of -2.0↔+4.0 V vs. Li plate. More than 103 cycles of color switch are observed quite reproducibly. Three color states of yellow green, dark brown and blue are demonstrated for polypyrrole film.

Quasi-solid dye sensitised solar cells filled with ionic liquid—increase in efficiencies by specific interaction between conductive polymers and gelators

Photo-energy conversions for quasi-solid dye sensitised solar cells increased when gel electrolytes were combined with conductive polymers as counter electrodes and the conversion surpassed that for DSSCs equipped with conventional Pt counter electrodes.

TFSI-doped polypyrrole actuator with 26% strain

A polypyrrole film, prepared electrochemically from a methyl benzoate solution of tetra-n-butylammonium bis(trifluoromethanesulfonyl)imide (TBATFSI), showed 26.5% strain and 6.7 MPa stress induced electrochemically in aqueous LiTFSI solution.

Alkyl Chain Length Dependence of Field-Effect Mobilities in Regioregular Poly(3-Alkylthiophene)Films

Carrier mobilities have been studied using the field effect in regioregular poly(3-alkylthiphene) (PAT, alkyl=butyl, hexyl, decyl, dodecyl and octadecyl) cast films at a field of around 104 V/cm. It was found that the carrier mobility of poly(3-butylthiophene) is 1.0×10-2 cm2/Vs, which is the largest one to date in the polythiophene family and three to four orders of magnitude larger than that of poly(3-octadecylthiophene). This result indicates that the substituted alkyl chain plays the role of a barrier to carrier migration between π-conjugated main chains, and primarily determines the mobility. The residual carrier densities are 1015 to 1016 cm-3 for all PATs and slightly lower for PATs with shorter alkyl chains. The field-effect mobilities are nearly the same as the values estimated by the time-of-flight method.