JP2005224027A - Actuator element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an actuator element that operates stably in air, can be driven at low voltage and is satisfactory in response and cycling durability. <P>SOLUTION: In this air actuator element, at least two electrodes 2 insulated from each other, are formed on the surface of a conductor 1, formed of a composite of carbon nanotubes, doped with metal ions and a solid polyelectrolyte; and the actuator element can be bent or deformed, by applying a potential difference between the electrodes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrochemical actuator element. Here, the electrochemical actuator element is an actuator element that uses an electrochemical process such as an electrochemical reaction or charge / discharge of an electric double layer as a driving force.

  In the fields of medical equipment, industrial use, personal robots, and micromachines, there is an increasing need for actuators that are small, light, and flexible.

  When the actuator is miniaturized in this way, friction and viscous force become more dominant than inertial force. Therefore, a mechanism that uses inertial force such as a motor or engine to change energy into motion is used as power for the small actuator. It was difficult. For this reason, electrostatic attractive force type, piezoelectric type, ultrasonic type, shape memory alloy type, and polymer expansion / contraction type have been proposed as operating principles of small actuators.

  However, these small actuators have problems such as limited operating environment, insufficient responsiveness, complicated structure, and lack of flexibility. Applications are also limited.

  In order to overcome these problems and expand the application of small actuators to a wider range, it can be driven at low voltage, fast response, flexible, easy to downsize and light weight, Polymer actuators that operate with low power have been developed. Among these, those using redox expansion and contraction in the electrolyte of an electroconductive polymer such as polypyrrole and polyaniline (electroconductive polymer actuator), and consisting of an ion exchange membrane and a junction electrode, In a water-containing state, by dividing the ion exchange membrane by applying a potential difference to cause the ion exchange membrane to bend and deform, it can be roughly divided into those that can function as actuators (ion conductive polymer actuator, see Patent Document 1). Two types are known.

  Among these, the electroconductive polymer actuator has advantages such as low voltage drive, large expansion and contraction, and large generated pressure, but the response speed is slow and the most effective method for producing polypyrrole is electropolymerization. It has been pointed out that there is a problem in repeated durability in principle because the response is due to ion doping and dedoping based on the redox reaction.

  On the other hand, both conventional electron conductive polymer actuators and ion conductive polymer actuators have been used mainly in aqueous electrolyte solutions because an electrolyte is required for their operation. Since the ion conductive polymer actuator does not exhibit sufficient ion conductivity unless the ion exchange resin is swollen with water, it is basically used in water. In order to use this actuator in the air, it is necessary to prevent water evaporation. For this reason, a resin coating method has been reported, but with this method, it is difficult to completely coat, the coating can be broken even by slight gas generation due to electrode reaction, and the coating itself has a deformation response. It has not been put into practical use because of its resistance. Also, instead of water, high-boiling organic solvents such as propylene carbonate are also used, but this also has the same problem, and the problem is that the ionic conductivity is not as great as water and the response is poor. There is.

  Thus, since the conventional actuator is driven only in a limited environment mainly in the electrolyte solution, its application is extremely limited. Therefore, the development of actuator elements that are driven in the air is indispensable for the practical application of small actuators to a wide range of applications.

For the purpose of applying the actuator to air operation, an example in which an electron conductive polymer is pasted on both sides of an ion exchange resin, or a conductive polymer is pasted on a gel film containing a high-boiling organic solvent such as propylene carbonate. There is an example in which the expansion and contraction of the electrode is used as an actuator element. These examples also have the problem of drying of the solvent and the problem of low ion conductivity, as in the case of the ion conductive polymer actuator, and are not an essential solution.
Japanese Patent Laid-Open No. 4-275078

  An object of the present invention is to provide an actuator element that operates stably in air, can be driven at a low voltage, has quick response, and has good repeated durability.

  As a result of intensive studies, the present inventors have found that a composite of a carbon ion-doped carbon nanotube and a solid polymer electrolyte is used as an active layer having electrical conductivity and stretchability, so that it can be operated in the air. The present inventors have found that an actuator element can be obtained and have completed the present invention.

That is, the present invention provides a conductor for an air actuator element and an air actuator element as shown below.
Item 1. A conductor for an aerial actuator element comprising a composite of a metal ion-doped carbon nanotube and a solid polymer electrolyte.
Item 2. An aerial actuator element in which at least two electrodes are formed in an insulated state on the surface of the conductor according to Item 1, and can be bent and deformed by applying a potential difference between the electrodes.

  The “air actuator element” in the present invention means an actuator element operable in air.

  Hereinafter, the present invention will be described in detail.

  The carbon nanotube used in the present invention is a carbon-based material having a shape in which a graphene sheet is wound into a cylindrical shape, and is roughly classified into a single-walled nanotube (SWNT) and a multi-walled nanotube (MWNT) from the number of components of the peripheral wall thereof. Also, various types are known, such as being divided into a chiral type, a zigzag type, and an armchair type due to the difference in the structure of the graphene sheet. Of these, single-walled nanotubes are preferably used in the present invention. A suitable example of carbon nanotubes for practical use is HiPco (manufactured by Carbon Nanotechnology Inc.), which can be relatively mass-produced using carbon monoxide as a raw material. Of course, it is limited to this. is not.

The carbon nanotube used in the present invention is doped with metal ions. Examples of the metal ions include lithium ions, cesium ions, potassium ions, rubidium ions, and the like that can be doped by an electrochemical process or a vacuum process, in addition to iron ions included in the manufacturing process of carbon nanotubes. It is considered that the responsiveness of the actuator element can be changed by doping different kinds of ions by these methods. The doping amount of metal ions is preferably 5 to 25% by weight.

  Examples of the solid polymer electrolyte used in the present invention include fluorine ion exchange resins (for example, perfluorosulfonic acid resins such as Nafion), and polymer electrolyte gels such as polyacrylic acid. In order to form a composite with carbon nanotubes, it is necessary to prepare a dispersion with carbon nanotubes. Examples of the solvent used for preparing the dispersion include a low molecular weight linear alcohol such as methanol, and an aqueous activator such as Triton X-100. Therefore, a solid polymer electrolyte polymer or a precursor thereof that can be dissolved in these solvents can be used.

  The formation of the composite (conductor) is performed, for example, by dispersing carbon nanotubes in a solid polymer electrolyte solution using ultrasonic waves, and spreading (casting) the obtained dispersion (cast solution). . The concentration of the solid polymer electrolyte in the casting solution is preferably 0.5 to 5% by weight, more preferably 1 to 3% by weight. The amount of carbon nanotubes in the casting solution is preferably 0.2 to 1 mg / ml, more preferably 0.4 to 0.6 mg / ml. After casting, the solvent may be dried, and then heat treatment (annealing) may be performed as necessary. The heat treatment is effective in promoting crystallization of the solid polymer and increasing elasticity. The heat treatment temperature is preferably 100 to 160 ° C, more preferably about 150 ° C. The thickness of the film-like composite (conductor) thus obtained is preferably 10 to 300 μm, and more preferably 20 to 200 μm. The ratio (weight ratio) between the carbon nanotube and the solid polymer electrolyte in the composite (conductor) is preferably carbon nanotube: solid polymer electrolyte = 1: 0.03-0.07. : Solid polymer electrolyte = 1: 0.04 to 0.06 is more preferable.

  An actuator element is obtained by bonding an electrode to the composite (conductor) made of the carbon nanotube and the solid polymer electrolyte obtained as described above. For the joining of the electrodes, it is possible to use methods such as vapor deposition methods of metals and carbon, sputtering methods, electroless plating methods, coating methods, press methods, printing methods and the like. Of these, the simplest and most effective is the joining of noble metals by sputtering. The thickness of the electrode is preferably 10 to 50 nm.

  The actuator element thus obtained can obtain a displacement of about 0.2 to 0.5 times the element length within a few seconds when a DC voltage of 3 to 10 V is applied between the electrodes. In addition, the actuator element can operate flexibly in a completely dry state (in the air) or in a swollen state in water.

The operating principle of the actuator element of the present invention in a completely dry state (in the air) is that, as shown in FIG. 1, when a potential difference is applied to the electrodes 2 and 2 formed on the surface of the conductor 1 in a mutually insulated state, It is considered that this is because stress is generated when metal ions (for example, Fe ⁺⁺ ) contained between the layers in the carbon nanotube undergo an oxidation-reduction reaction on the electrode 2.

  The actuator element of the present invention operates stably in air and can be driven at a low voltage. In addition, it is easy to manufacture, can be easily downsized, has a quick response, operates flexibly, and has good repeated durability.

  Next, the present invention will be described in more detail with reference to examples.

Example 1
Single-walled carbon nanotube (“HiPco” manufactured by Carbon Nanotechnology Inc., Fe content 14% by weight) (hereinafter also referred to as SWNT) 25 mg, 5% Nafion solution (manufactured by Aldrich, low molecular weight linear alcohol and 25 ml of water (10% mixed solvent) and 25 ml of reagent-grade methanol are weighed in a beaker and mixed, and then subjected to ultrasonic irradiation for 10 hours or more in an ultrasonic cleaner to prepare a mixed dispersion of SWNT and Nafion. Prepared. This dispersion was cast into a glass petri dish and left for more than one day in a draft to remove the solvent. After removing the solvent, heat treatment was performed at 150 ° C. for 4 hours. After the formed SWNT and Nafion composite film is peeled off from the petri dish, it is cut into a size of 3 cm × 2 cm, and gold is sputtered on both sides of the composite film using a sputtering machine for sample preparation of a scanning electron microscope. Joined. The conditions were 10 mA per side for 30 minutes.

  The joined body film produced as described above was cut into a 1 mm × 15 mm strip and the deformation response was evaluated (Examples 2 to 6). Moreover, the joined body film was cut into a disk shape having a diameter of 10 mm, and the voltage-current characteristics were evaluated (Example 7).

Example 2
FIG. 2 is a diagram showing an outline of the displacement measuring apparatus. Evaluation of responsiveness was performed by grasping a 3 mm end portion of a joined sample piece cut into a 1 mm × 15 mm strip with a holder with an electrode, applying a voltage in the air, and using a laser displacement meter, 10 mm from the fixed end. The displacement of the position of was measured.

  FIG. 3 shows a case where a bonded sample piece having a thickness of 35 μm manufactured by the method of Example 1 was vacuum-dried for 1 hour, and then 0.1 Hz, 7 Vp. -P. It is the figure which applied the square wave voltage and measured the response of displacement. “Displacement” on the vertical axis means “displacement”, “Time” on the horizontal axis means “time”, and “sec” means “second”. Even in a completely dry state, a large (displacement amount of 2 mm or more) and fast (within 0.5 second) response was observed in air.

Example 3
A bonded sample piece similar to that in Example 2 was applied to 1 Hz, 6 Vp. -P. FIG. 4 shows the displacement response measured by applying the square wave voltage. Similar to Example 2, even in a completely dry state, a large (displacement amount of 2 mm or more) and fast (within 0.5 second) response was observed in the air.

Example 4
After a 27 μm-thick bonded body sample piece produced by the same method as in Example 1 was vacuum-dried for 1 hour, displacement measurement was performed in the same manner as in Example 2. FIG. 5 shows that 12 Vp. -P. It is the figure which plotted the intensity | strength (peak to peak, peak to peak) of the displacement when the square wave voltage of (2) was added and the frequency was changed. “Frequency” on the horizontal axis means “frequency”. A resonance peak was observed at 19 Hz. The response was observed up to 30 Hz.

Example 5
A bonded sample piece having a thickness of 110 μm produced by the same method as in Example 1 was vacuum-dried for 1 hour, and then the displacement was measured by the same method as in Example 2. FIG. 6 is a graph showing the dependence of the displacement intensity (peak-to-peak) on the voltage value (peak-to-peak) when a 0.1 Hz square wave voltage is applied and the applied voltage intensity is changed. It is. “Voltage” on the horizontal axis means “voltage”. Response is 6 Vp. -P. From 8Vp. -P. To 10 Vp. -P. Until then, the response increased according to the voltage, but was saturated at 10 V or higher.

Example 6
A bonded sample piece having a thickness of 27 μm produced by the same method as in Example 1 was vacuum-dried for 1 hour, and then displacement measurement was performed in the same manner as in Example 2 (Nafion-SWNT). FIG.
1 Hz, 12 Vp. -P. It is the figure which continued applying the square wave voltage of 1 hour, and plotted the time change of the amount of displacement. For comparison, FIG. 7 shows, for comparison, a joined sample piece (Nafion 117) in which gold (Au) is joined to a Nafion 117 (perfluorosulfonic acid resin) film produced by the method described in Japanese Patent Laid-Open No. 11-233504. / Au) also shows the time variation of the displacement measured in the same manner in air (4 Vp.-p. and 12 Vp.-p. applied). In the case of the Nafion 117 / Au film, the amount of displacement decreased rapidly within 10 minutes after the start of measurement, and hardly responded after 1 hour. On the other hand, the device of the present example (Nafion-SWNT) slightly decreased in response, but showed a response of 50% or more of the initial displacement even after 1 hour. This shows that the element of the present invention exhibits a stable deformation response in the air in a dry state.

Example 7
After drying the joined body having a thickness of 110 μm produced by the same method as in Example 1 for 1 hour, it was cut into a disk shape having a diameter of 10 mm, and was sandwiched between holders having a platinum plate of the same size, and a lead wire was taken. Voltage-current characteristics (voltammetry) were measured. The voltage-current characteristic was measured by applying a triangular wave voltage with a frequency of 0.1 Hz. FIG. 8A shows the voltage-current characteristics (voltammogram) when the voltage is changed from −2.5 V to 2.5 V, and FIG. 8B shows that the voltage is changed from −7 V to 7 V. The voltage-current characteristic (voltammogram) is shown. “Current” on the vertical axis means “current”. As can be seen from FIG. 8A, a redox peak current is observed around 0.6V, and the current increases exponentially from 2V to 2.5V. It can be clearly seen from FIG. 8B that the current increases exponentially. From the above results, it can be seen that in this system, there is a current in the redox process in a completely dry state, and thereby a large current flows exponentially from around 2.5V. Considering that the deformation response starts to occur from around 2.5 V and that it occurs stably from 3 V, it is considered that a dry-state response occurs due to this redox process.

It is a figure which shows the operating principle of the actuator element of this invention. It is a figure which shows the outline of a displacement measuring device. It is a figure which shows the responsiveness of the conjugate | zygote sample piece of Example 2. FIG. It is a figure which shows the responsiveness of the conjugate | zygote sample piece of Example 2. FIG. It is a figure which shows the responsiveness of the conjugate | zygote sample piece of Example 4. FIG. It is a figure which shows the responsiveness of the conjugate | zygote sample piece of Example 5. FIG. It is a figure which shows the time change of the responsiveness in the conjugate | zygote sample piece of Example 6. FIG. FIG. 8A is a diagram showing voltage-current characteristics when the voltage applied to the joined body of Example 7 is changed from −2.5 V to 2.5 V, and FIG. It is a figure which shows the voltage-current characteristic when the voltage applied to the junction body of 7 is changed from -7V to 7V.

Explanation of symbols

1 Conductor 2 Electrode

Claims (2)

  A conductor for an aerial actuator element comprising a composite of a metal ion-doped carbon nanotube and a solid polymer electrolyte.   An aerial actuator element, wherein at least two electrodes are formed in an insulated state on the surface of the conductor according to claim 1 and can be bent and deformed by applying a potential difference between the electrodes.

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