Hidenori Okuzaki

A polypyrrole rotor driven by sorption of water vapour

Abstract The polypyrrole films containing perchlorate were electrochemically synthesized and the bending and recovery motion of the film obtained have been investigated. The principle of motion was based on a reversible sorption of water vapour on one side of the film, causing an expansion of the film surface. On the basis of this phenomenon, we have devised a polypyrrole rotor driven by sorption of water vapour, producing a continuous rotation at a speed of 21 cm min −1 .

Mechanical properties and structure of the zone‐drawn poly(L‐lactic acid) fibers

The zone-drawing (ZD) method was applied three times to the melt-spun poly(L-lactic acid) (PLLA) fibers of low molecular weight (Mv = 13,100) at different temperatures under various tensions. The mechanical properties and superstructure of the ZD fibers were investigated. The resulting ZD-3 fiber had a draw ratio of 10.5, birefringence of 37.31 × 10−3, and crystallinity of 37%, while an orientation factor of crystallites remarkably increased to 0.985 by the ZD-1. The Youngs modulus and tensile strength of the ZD-3 fiber respectively attained 9.1 GPa and 275 MPa, and the dynamic storage modulus was 10.4 GPa at room temperature.

Adsorption-induced bending of polypyrrole films and its application to a chemomechanical rotor

We have discovered that polypyrrole films undergo rapid and intensive bending in the solid state. Bending was induced by the reversible and anisotropic adsorption of various substances in the vapor state. The speed and direction of bending largely depended on the adsorbate used. By using this phenomenon, we have devised an experimental “chemomechanical rotor” capable of transducing a chemical free energy change directly into a continuous rotation.

Characteristics of water in polypyrrole films

Polypyrrole films containing different dopant ions were electrochemically synthesized and the interaction between polypyrrole and water was evaluated by means of sorption isotherm, cluster function and d.s.c. It was found that the water sorbed in the polypyrrole behaved as a non-freezing bound water which was rather isolated and prevented from clustering over the whole experimental range of the relative water vapour pressure from 0.1 to 0.95. This might be associated with the nature of the conductive polymers having a π-conjugated system where the delocalization of carbonium charges would lower the ionic polarity and hydrophilicity of the polymeric chains.

Adsorption‐induced chemomechanical behavior of polypyrrole films

We have discovered that electrochemically synthesized polypyrrole films undergo quick and intensive bending in ambient air without the use of heat, ions, or an electric field. The principle of motion was based on a reversible van der Waals adsorption of water or polar organic molecules onto the film, which distinguished it from other systems owing to electrochemical doping and undoping. The motion of film largely depended on the kind of adsorbate used: water vapor molecules caused rapid bending of the film to the opposite side. In contrast, when polar organic molecules were used as an adsorbate, the bending of film occurred to the same side, namely, the direction of bending was just opposite to that observed for water vapor. On the basis of this phenomenon, we have devised a novel actuator which moves by a spontaneous rotation. Further, an experimental polypyrrole engine has been made, which used a polypyrrole belt as working substance and adsorbate as fuel. When water and iodomethane were used as the adsorbates, the belt rotated at a speed of 22 cm min -1 .

Electro-responsive polypyrrole film based on reversible sorption of water vapor

Polypyrrole films containing tetrafluoroborate were electrochemically synthesized and electrically driven motion of the film was investigated. It was found that application of dc voltage brought about reversible contraction of the film in ambient air, where the contraction increased with increasing applied voltage and ambient relative humidity (RH). The degree of contraction was 1.2% under 2 V (25°C, 50% RH), while the value decreased at voltages higher than 5 V. In contrast, the film in a vacuum underwent elongation by the electric field. The results allowed us to consider that the apparent strain of the film under the electric field was expressed by two processes: one was the contraction due to the desorption of water vapor and the other was the thermal expansion of polymer chains both caused by Joule heating. Under isometric conditions, the film generated contractile stress of 4.8 MPa under 2 V, which was four orders of magnitude larger than its own weight.

Electrically Driven Polypyrrole Film Actuator Working in Air

The polypyrrole (PPy) films containing tetrafluoroborate ions were electrochemically synthesized and electrically driven motion of the film was investigated. The application of dc voltage brought about reversible contraction of the film in air, where the degree of contraction increased with increasing both applied voltage and ambient humidity. The contraction of the film was associated with desorption of water vapor due to the Joule heating, which was different from electrochemical doping and dedoping. The degree of contraction attained 1.2% under 2 V, where the initial speeds of contraction and expansion of the film were 4.4 and 1.8% min-1, respectively. Under loading conditions, the power density increased with increasing load and the value attained 0.78 W kg- (6 V.W) under the load of 60 g (4 MPa). The energy efficiency, defined as the ratio of work done by the PPy film to the electric energy, was calculated as 6.6 x 10-3%.

Mechanical properties and structure of zone-drawn poly(p-phenylene vinylene) films

The zone-drawing (ZD) method was applied to poly(p-phenylene vinylene) (PPV) precursor films under various applied tensions and heater temperatures. The ZD precursor films were successively converted to PPV by heat treatment, and the structure and mechanical properties of the resulting ZD-PPV films were investigated. It was found that the draw ratio, orientation function, crystallinity and apparent crystallite size of the ZD-PPV films were 8.0, 0.74, 65.2% and 47.5 A, respectively. The mechanical properties were improved by the ZD, and the dynamic storage modulus of the ZD-PPV film reached 33.7 GPa at room temperature and held at 11.5 GPa even at 300°C.

Electrical and mechanical properties of the zone-drawn polypyrrole films

The zone-drawing method (ZD) was applied to electrochemically synthesized polypyrrole films containing tosylate (PPy/TsO) and the mechanical and electrical properties of the resulting films were investigated. It was found that the electrical conductivity of the zone-drawn film reached 365 S cm -1 in the drawing direction, which was 4.7 times that of the original film. The tensile properties of the zone-drawn film were improved and Youngs modulus and strength at break increased to 4.32 GPa and 90.1 MPa from 0.53 GPa and 40.4 MPa of the as-synthesized film, respectively. The dynamic storage modulus (E) increased by the zone-drawing over a whole experimental temperature range and attained 7.0 GPa at room temperature and 4.0 GPa even at 200°C.

Viscoelastic properties and structure of the zone-drawn polyaniline films

The zone-drawing method was applied to chemically synthesized polyaniline cast films of emeraldine base under various applied tensions and drawing temperatures. The changes in the microstructure and viscoelastic properties of the resulting films were investigated. It was found that the microstructure was strongly affected by the drawing temperature (Td). The crystallinity, crystallite size, and orientation factor of crystallites, respectively, attained 42%, 23 A, and 0.975 for the film zone-drawn at Td = 170°C, whereas a further increase in the Td brought about a decrease of these values. The viscoelastic measurements indicated that the dynamic storage modulus attained 12 GPa at room temperature and was 5 GPa at 280°C for the film zone-drawn at Td = 210°C, which was comparable to that of the typical engineering plastics.