Daiki Hoshino

Fabrication and Characterization of a Polypyrrole Soft Actuator Having Corrugated Structures

Recently, polypyrrole has attracted much attention, because it has a high electroconductivity and can be used in a soft actuator. We have recently succeeded in increasing the expansion and contraction ratio of a polypyrrole film by fabricating a Au/polypyrrole stacked structure, whose polypyrrole film was formed on a Au thin film coated on an acrylic board as working electrode for galvanostatic electropolymerization. Here, we propose a new soft actuator with a corrugated polypyrrole film whose backside is covered by a Au film. The corrugated Au/polypyrrole actuator was fabricated by forming a polypyrrole film on a corrugated acrylic board covered by a Au thin film and successively removing the acrylic board in acetone. Consequently, the expansion and contraction ratio of the actuator increased to 11.6%, while the actuator without the corrugated structures was 8.1%.

Fabrication of Bi-Directional Bending Organic Actuators Consisting of Stacked Polypyrrole Films With Different Expansion and Contraction Ratios

An organic conductor, polypyrrole has been extensively studied as one of the prospective soft actuator materials. In this paper, simple bimorph actuators consisting of an electropolymerized polypyrrole (PPy) film and an adhesive tape were fabricated. It turned out that those actuators nonuniformly bent depending on the distance between the actuator and the counter electrode. Then, a structure consisting of polypyrrole/both-side adhesive tape/polypyrrole, whose two polypyrrole films have different extension/contraction ratios, has been fabricated, and it was found that the actuator exhibited more uniform bending deformation which was nearly independent of the distance between the actuator and the counter electrode.

A Novel Thiophene-Fused Polycyclic Aromatic with a Tetracene Core: Synthesis, Characterization, Optical and Electrochemical Properties

FeCl3-mediated oxidative cyclization was successfully used to construct an extended thiophene-pendant pyrene skeleton and synthesize a novel thiophene-fused polycyclic aromatic (THTP-C) with a tetracene core. The identity of the compound was confirmed by 1H-NMR, 13C-NMR, MS, and elemental analysis. Meanwhile, a single crystal of THTP-C was obtained and analyzed by X-ray single-crystal diffraction. THTP-C has a “saddle” shaped π-conjugated 1-D supramolecular structure, and favors highly ordered self-assembly by π-π interactions as evidenced by its concentration-dependent 1H-NMR spectra in solution. The optical properties of THTP-C were investigated by ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy and its electrochemical properties were investigated by cyclic voltammetry (CV). The relatively large band gap (2.86 eV), low EHOMO level (−5.64 eV) and intermolecular π-π interactions imply that THTP-C has a high stability against photo-degradation and oxidation, and may be a promising candidate for stable hole-transporting materials.

Dynamic Behaviors of Polypyrrole Actuators in Electrolyte Solution Mixed with 2-Propanol

It has been previously reported that dynamic behaviours of polypyrrole (PPy) soft actuators were improved when they were driven in aqueous solutions of an electrolyte, lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) containing an optimised amount of 2-propanol. In this work, the influences of the potential sweep rate on electrochemical and creep strains of PPy actuators in aqueous LiTFSI electrolyte solutions with 2-propanol concentrations of 0 and 20% were investigated under the load stress of 0.3 MPa. The electrochemical strain rates in the 0% and 20% 2-propanol solution were found to be approximately 0.1% s−1 and 0.25% s−1, respectively, and they are nearly independent of the sweep rate between 10 and 25 mV s−1. These results suggest that TFSI anion penetration into the PPy films might be limited by the interactions between the PPy surface and the TFSI anions. The creep rate was more rapidly increased as time elapsed in the electrolyte solution containing 2-propanol than that in the electrolyte solution without 2-propanol, which was due to the swelling of PPy film in the electrolyte.

Effect of 2-Propanol Concentration in Electrolyte Solution on Polypyrrole Actuator Performance

Organic soft linear actuators made of conducting polymers such as polypyrrole (PPy) films are of special interest for application in microelectromechanical systems (MEMS) because they generate large electrochemomechanical stress and strain. In this work, a PPy actuator was fabricated by galvanostatic electropolymerization. The electrochemical deformation behaviors of the PPy actuator were investigated in aqueous solutions of an electrolyte, lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), containing different concentrations of 2-propanol. Marked improvement of the electrochemical strain from 3 to 12% was achieved when the actuator was driven by a potential between -1 and 1 V in the LiTFSI electrolyte containing 20 to 40% of 2-propanol under a load stress of 0.3 MPa. Possible mechanisms for these behaviors were discussed.

Polypyrrole Actuator Operating Characteristicsin Electrolyte Solution Mixed with Methanol

In this work, a PPy actuator was fabricated by galvanostatic electropolymerization. The electrochemical deformation behaviors of the PPy actuator were investigated in aqueous solutions of an electrolyte, lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), containing different concentrations of methanol. Marked improvement of the actuating strain of approximately 9% was achieved when the actuator was driven by a potential between –1 and 1 V in the LiTFSI electrolyte containing 40 to 50% of methanol under a load stress of 0. 3 MPa. On the other hand, the actuator functioned in the electrolyte solutions containing more than 60% of methanol showed rapid decrease of the actuating strain and the electrochemical creep after repeated actuations. Possible mechanisms for these behaviors were discussed.

Novel Thienyl-dibenzothiophene Oligomers End-capped by Hexylphenyl Groups as Potential Organic Semiconductor Materials

Novel thienyl-dibenzothiophene oligomers end-capped by hexylphenyl groups, 2,8-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene (28HPTDBT) and 3,7-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene (37HPTDBT), have been synthesized using Stille cross-coupling reactions. Newly synthesized oligomers were investigated by Ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopy, cyclic voltammogram, and thermal analysis. Strong intermolecular π-π interactions, appropriate energy band gaps and low HOMO energy levels imply that the two oligomers are promising candidate materials for durable organic electronic devices.

Influence of Electrochemical Actuations on Mechanical Properties of PPy Actuators in Electrolyte Solutions Mixed with 2-propanol or Methanol

Changes in Youngs modulus, tensile strength, and tensile strain at break of polypyrrole (PPy) actuators after electrochemical actuations were investigated. The actuators made of 150 μm-thick PPy films with an area of 5 × 20 mm2 were fabricated using electropolymerization. The actuators were functioned in aqueous lithium bis(trifluoromethansulfonyl)imide (LiTFSI) electrolyte solutions containing 0% or 20% of 2-propanol or methanol. Actuating strains of the actuators functioned in the electrolyte solutions containing 2-propanol or methanol were larger than the electrochemical strain of the actuator functioned in the electrolyte solution without 2-propanol or methanol. However, notable increase in the Youngs modulus and reduction in the tensile strength and the tensile strains at break were observed after actuations in the electrolyte solution containing 0% or 20% of 2-propanol or methanol.

Synthesis and Characterization of Novel Pyrene Derivatives Containing Thienyl Groups

New thiophene modified pyrene derivatives 4,5,9,10-tetra(2-thienyl)-2,7-di-tert-butylpyrene (TTP) and 4,5,9,10-tetra(2-(5-hexyl)thienyl)-2,7-di-tert-butylpyrene (THTP) have been designed and synthesized by Friedel-Crafts alkylation reaction, bromination, Stille Coupling reaction of pyrene, and so on. The optical band gaps of the TTP and THTP determined from the absorption onsets were 3.21 and 3.10 eV, respectively. The energy levels for highest occupied molecular orbital (EHOMO) were determined from their cyclic voltammograms to be −5.84 and −5.68 eV, respectively. The relatively large band gaps and low EHOMO levels imply that these materials have high stability against photo-degradation, and may be promising candidates for stable hole-transporting materials.

Characterization of Pyrrole Copolymer Soft Actuators Prepared by Electrochemical Polymerization Pyrrole and Diethyl 3,4-pyrroledicarboxylate

Polypyrrole (PPy) actuators, which expand and contract by doping and dedoping ions in an electrolyte solution, have been reported to have a large strain under a large stress. However, many of these actuators exhibited notable electrochemical creep (swelling) after repeated electrochemical actuations. Here, actuator films were prepared by electrochemical polymerization of pyrrole and diethyl 3,4-pyrroledicarboxylate with different mol ratios. The actuating strain of the film actuators prepared from a solution of pyrrole and diethyl 3,4-pyrroledicarboxylate with 97:3 mol ratio showed significant reduction of the electrochemical creep with minimal reduction of the actuating strain.