Estimation of ion dimension doped in conducting polymers electrochemically
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MRS Advances © 2017 Materials Research Society DOI: 10.1557/adv.2017.639
Estimation of ion dimension doped in conducting polymers electrochemically Keiichi Kaneto, Fumito Hata, and Sadahito Uto Department of Biomedical Engineering, Osaka Institute of Technology, 5-16-1, Ohmiya, Asahi-ku, Osaka, 535-8585, Japan
ABSTRACT
Electroactive conducting polymers are suitable for soft actuators (artificial muscles). The actuation is induced by electrochemical oxidation of conducting polymer (film) in an electrolyte solution, due to insertion of bulky counter ions (dopant ions). The magnitude of deformation (strain) depends on the size of dopant ions and the degree of oxidation. It is worthwhile to know the relationship between the magnitudes of deformation and ion size. An electrodeposited Polypyrrole film was electrochemically cycled in aqueous electrolytes of NaCl, NaBr, NaNO3, NaBF4 and NaClO4. The strain of film during electrochemical oxidation and reduction was precisely measured using a laser displacement meter and a handmade apparatus. From the strain and electrical charges inserted in the film during oxidation, the volumes and radii of dopant ions were estimated, assuming the isotropic expansion of the film. The estimated anion radii of Cl-, Br-, NO3-, BF4- and ClO4- were 235, 246, 250, 270 and 290, respectively. The results were discussed taking the crystallographic and hydrated ion radii in literatures into consideration.
INTRODUCTION In welfare era of decreasing birthrate and aging population, human friendly robots are demanded. Such robots should be driven by softactuators and move smoothly and quietly. Softactuators are desired to have large strain, high contraction force (stress), quick response, easily control, and flexible, tough and long durability. Materials for softactuators are electroactive polymers (EAPs) [1], which are ionic polymer and metal composite (IPMC) [2], conducting polymers [3-6], dielectric elastomers [7], hydrogels, polymer gels [8] and carbon nano tube (CNT) [9]. Since the actuation of these EAPs is driven by a voltage application, the response time and strain can be controlled by the waveform and magnitude of the applied voltage. Among various EAPs, conducting polymers are a potential candidate for the softactuator [3-6,10], since the large strain and stress are generated by a low voltage application of several volts. The large strain of about 40% has been reported in polypyrrole actuators [10], which is larger than the strain of 25% in skeletal muscle.
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The strain of conducting polymers is generated by the ion (dopant) doping upon the electrochemical oxidation [3-5]. The strain depends on the bulkiness of ions and the morphology of conducting polymers [10,11,12]. However, the detailed structure and size of ions in oxidized conducting po
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