JP2006353034A - Polymer actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer actuator that quickly expands and contracts with certainty at a low voltage. <P>SOLUTION: The polymer actuator includes a gel-electrode composite 6, 16 constructed by disposing an internal electrode 2, 12 in hydrogel 3 containing polymer, having one or more kinds of functional groups that interact with a polyvalent cation or hydrogel 3, whose volume is changed by the concentration of a metal ion, and electrolyte 1 containing polyvalent cations or metal ions. A pair of external electrodes 4a, 4b are disposed outside the gel-electrode composite and the electrolyte 1. By applying a potential between the internal electrode 2, 12 and the pair of external electrodes 4a, 4b, the concentrations of the polyvalent cations or metal ions are thereby varied, to cause change in the volume of the hydrogel 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer actuator using a stimulus-responsive high-strength hydrogel.

  Conventionally, practical application of robots has attracted attention in various fields such as care support, dangerous work, and entertainment. A robot applied to these uses is required to have a large number of joints (movable parts) and to perform complicated movements.

Conventionally, a magnetic rotation motor, a piezoelectric element, a hydraulic drive cylinder, and the like have been put to practical use as actuators for driving the movable part, and electromagnetic motors have been used in most cases.
However, a drive mechanism using an electromagnetic motor has the disadvantages that various engines such as a transmission mechanism and a speed reduction mechanism are necessary, and that the main constituent material is made of metal and therefore its weight increases. Since the actuator weight becomes a load when the movable part is operated, if a heavy actuator is used, a large output is required. On the other hand, a large output actuator is large and heavy.
In addition, when using a magnetic rotary motor, a speed reducer for adjusting to the required rotational speed and torque is required, and the performance of the gear used for this speed reducer is gradually deteriorated due to wear. Therefore, there is a problem that it is difficult to ensure reliability.
An ultrasonic motor capable of obtaining high torque at low speed does not require a speed reducer, but it is also made of a metal material, so that its weight increases and the same problem as described above occurs.

In view of the problems as described above, in recent years, a polymer actuator made of a polymer material that is light and flexible and has begun to attract attention in order to realize a small and lightweight high-performance robot.
For example, for example, an ICPF actuator (K. Oguro, Y. Kawakami, H. Takenaka, J. Micromachine Soc., 5, 27 (1992) ), Conductive polymer actuators that change volume by doping / de-doping ions with electrolyte or solid electrolyte (RHBaughman, Synth. Met., 78,339 (1996)), and applying voltage between electrodes Polymer piezoelectric elements (R. Pelrine, R. Kornbluh, Q. Pei, Science, 287, 836 (2000)) etc. that are deformed by the above have been proposed.

However, the ICPF actuator is limited to a bending operation and has a problem that the generated force is weak.
Further, the conductive polymer actuator has a problem that the displacement is small and the piezoelectric element needs to be applied with a very large voltage in order to drive.

On the other hand, in recent years, there have been proposals for hydrogel actuators (for example, Y. Osada, H. Okuzaki, H. Hori, Nature, 355, 242 (1992)) with large volume changes in response to chemical or electrochemical stimuli. Has been made.
The above-mentioned hydrogel actuator, particularly a polymer hydrogel actuator to which a water-swelling polymer gel is applied, utilizes the fact that the polymer hydrogel changes in volume in response to changes in temperature, ionic strength, pH, etc. is there.
The displacement amount in the hydrogel actuator is as large as 30 to 50%, and the generated force is also 0.2 to 0.4 MPa, so that performance comparable to that of living skeletal muscle can be exhibited.

However, among the above materials, the temperature-responsive type material has a practical problem that it is difficult to precisely control the operation during heat dissipation when used for a small robot or the like.
In addition, in an actuator using a pH-responsive gel, the gel / electrode composite structure in which the electrode is embedded in the hydrogel, the acidic polymer gel on one electrode side and the basic polymer on the other electrode side As a pair of gels, it has been confirmed that a linear expansion and contraction operation similar to that of a living skeletal muscle can be obtained by electrical control and electrical drive.
Furthermore, as an electrode material for inducing a change in pH, for example, palladium, a hydrogen storage alloy, and the like have been proposed, but it is difficult to induce a sufficiently large pH change practically in these, In addition, hydrogen gas is generated by recombination of hydrogen atoms on the electrode surface, and all of the hydrogen occluded by the hydrogen occlusion alloy cannot be discharged, making it difficult to use it repeatedly over a long period of time. is doing.

By the way, conventionally, regarding a driving method of a mechanochemical material responsive to ion concentration change, copper ions are oxidized and reduced at one electrode and a reaction not involving copper ions is generated at the other electrode. There has been proposed a technique for changing the concentration of copper ions so that the hydrogel that interacts with the copper ions expands and contracts (for example, see Patent Document 1).
This technology can perform oxidation / reduction of copper ions at a potential lower than that in which electrolysis of water occurs, so that an actuator can be obtained in which expansion and contraction of hydrogel is repeatedly performed without causing gas generation. Has advantages.

JP-A-1-41673

However, the actuator disclosed in Patent Document 1 has a problem that a large amount of electricity is required and the response speed is slow because the copper ion concentration of the entire electrolyte must be changed. .
In addition, since there is a large difference in the ion concentration between the vicinity of the electrode and a position away from the electrode by a predetermined distance, there is a problem that the expansion / contraction behavior of the hydrogel becomes non-uniform.

  Therefore, in the present invention, in view of the problems of the prior art as described above, a polymer actuator capable of obtaining a high-speed and stable displacement at a low potential is provided.

  In the present invention, a gel / electrode complex comprising a hydrogel containing a polymer having one or more functional groups that interact with a polyvalent cation, and an internal electrode present in the hydrogel, An electrolyte aqueous solution containing a valent cation, and a pair of external electrodes are disposed on the outside of the gel / electrode complex and the aqueous electrolyte solution, and the pair of external electrodes, the internal electrodes, So that the polyvalent cation is reduced or oxidized to cause a change in the polyvalent cation concentration, thereby causing a change in volume of the hydrogel constituting the gel / electrode composite. Provided is a polymer actuator.

  Further, in the present invention, a gel / electrode composite composed of a stimuli-responsive hydrogel that causes a volume change with a change in metal ion concentration, and an internal electrode dispersed in the hydrogel, An aqueous electrolyte solution containing metal ions, and a pair of external electrodes are disposed on the outside of the gel / electrode composite and the aqueous electrolyte solution, and the external electrode of the pair, the internal electrode, By applying a potential between the metal ions, the metal ions are reduced, the metal ion concentration is reduced, the volume of the hydrogel constituting the gel / electrode complex is changed, and the metal ions are A polymer actuator is provided which is in a reduced state and is electrically connected between the electrodes to conduct.

  According to the present invention, a polymer actuator capable of rapidly and reliably transmitting a change in the ionic concentration of the electrolyte solution to the entire stimulus-responsive hydrogel and causing a high-speed and uniform volume change in the entire hydrogel was obtained. .

  Hereinafter, specific embodiments of the polymer actuator of the present invention will be described with reference to the drawings, but the present invention is not limited to the examples shown below.

[First embodiment]
In FIG. 1, the schematic block diagram of an example of the polymer actuator of this invention is shown.
The polymer actuator 10 comprises a gel / electrode complex 6 composed of a hydrogel 3 responsive to changes in ion concentration, a coiled internal electrode 2 disposed in the hydrogel, and a polyvalent cation. And a pair of external electrodes 4a and 4b are arranged on the outer side of the gel / electrode complex 6 and the electrolyte solution 1, and the electrolyte solution 1 leaks on the outermost periphery. In order to prevent volatilization, the flexible resin 5 is assumed to be disposed.

The electrolyte solution 1 is a solution containing a polyvalent cation, and in the polymer actuator 10 of the present invention, the gel / electrode complex 6 and the electrolyte solution coexist.
When the polyvalent cation is a metal ion, when the metal ion is reduced on the surface of the internal electrode 2 by energization, the ion concentration in the vicinity of the internal electrode 2 decreases. On the other hand, when the reduced metal is oxidized, the ion concentration near the internal electrode 2 increases. Such a change in the metal ion concentration causes the hydrogel to expand / contract.

In addition, when redoxing a metal in an aqueous solution, the redox potential of the metal must be smaller than the potential at which electrolysis of water occurs.
Examples of metal ions having such characteristics include ions of copper, iron, lead, tin, nickel, zinc, aluminum, and the like. These may be used alone or in a mixture. Among these, copper having a small redox potential is particularly suitable.
Furthermore, in addition to the metal ion species that are oxidized and reduced on the surface of the internal electrode 2, a salt containing a monovalent cation having a redox potential that is not oxidized or reduced when the actuator is driven is mixed in the electrolytic solution 1. preferable. Furthermore, it is desirable that the counter anion of this cation is monovalent.

Next, the internal electrode 2 will be described.
The internal electrode 2 has a function of changing the ion concentration in the electrolyte solution 1 because the ions in the electrolyte solution 1 are oxidized and reduced on the electrode surface by applying a potential between the pair of external electrodes. It is what.
The internal electrode 2 is made of a material having a higher redox potential than that of the ionic species, for example, copper ions, contained in the electrolytic solution 1.
In addition, when used in an aqueous solution, a material having a large oxygen overvoltage is preferable, and specific materials include gold, platinum, carbon black, ketjen black, carbon nanotube, fullerene, polyacetylene, polypyrrole, polythiophene, poly-1, Examples thereof include 6-heptadiyne, poly-p-phenylene, polyphenylene vinylene, and the like. These may be used alone, or may be a mixture containing these materials.
In addition, although the shape of the internal electrode 2 is a coil shape in the polymer actuator 10 of FIG. 1, as described later, for example, it may be a particle shape, a filler shape, or the like.

Next, the hydrogel 3 will be described.
The stimulus-responsive hydrogel 3 is contained in the electrolyte solution 1 and has a functional group in the molecule that forms a coordinate bond, an ionic bond, and the like with the ions that are oxidized and reduced on the surface of the internal electrode 2. It shall be.
Specifically, hydrogel which has a carboxyl group, a sulfonic acid group, a phosphoric acid group etc. is mentioned, for example. These may be used alone, or may be a mixture of two or more or a copolymer.

  The polymer actuator 10 having the configuration shown in FIG. 1 has an internal electrode 2 disposed in a hydrogel 3 that is responsive to changes in ion concentration. Between the internal electrode 2 and a pair of external electrodes 4a and 4b. By causing a potential difference to occur, the ion concentration changes in the vicinity of the internal electrode 2, and the change in ion concentration is uniformly and reliably transmitted to the entire hydrogel 3, and the hydrogel 3 expands / contracts quickly and accurately.

[Second Embodiment]
Next, another example of the polymer actuator of the present invention will be described with reference to FIG.
A polymer actuator 20 shown in FIG. 2 includes a gel / electrode complex 16 composed of a hydrogel 3 that is responsive to changes in ion concentration, and particulate internal electrodes 12 dispersed therein. It comprises an electrolytic solution 1 containing a polyvalent cation, for example, a divalent copper ion, and a pair of external electrodes 4a and 4b are disposed on the outside of the gel / electrode composite 16 and the electrolytic solution 1. It is assumed that a flexible resin 5 is disposed on the outermost periphery in order to prevent leakage and volatilization of the electrolytic solution 1.

  In addition, about the electrolyte solution 1 and the hydrogel 3, the thing similar to the polymer actuator shown and demonstrated in FIG. 1 is applicable.

  In the polymer actuator 20, a particle-shaped internal electrode 12 is disposed in a hydrogel 3 that is responsive to changes in ion concentration, and a potential difference is generated between the internal electrode 12 and the pair of external electrodes 4a and 4b. As a result, the ion concentration changes in the vicinity of the internal electrode 12, the change in ion concentration is transmitted to the entire hydrogel 3, and the hydrogel 3 expands and contracts uniformly.

According to the structure of the polymer actuator 20 shown in FIG. 2, when the hydrogel 3 expands, the distance between the particle-shaped internal electrodes 12 increases. Metal ions such as copper ions are reduced and enter between the particles of the internal electrode 12 so that conduction is ensured even in the expansion stage.
The internal electrode 12 is preferably a nanoparticle. When the internal electrode 12 is dispersed inside the hydrogel 3, the surface area can be increased as compared with the case where the internal electrode is coiled as shown in FIG. Become. Therefore, since the ion concentration inside the hydrogel can be changed uniformly and quickly, a hydrogel actuator that performs uniform expansion and contraction at high speed can be obtained.

[Third embodiment]
Next, another example of the polymer actuator of the present invention will be described with reference to FIG.
The polymer actuator 30 shown in FIG. 3 includes a gel / electrode composite 16 composed of a hydrogel 3 that is responsive to changes in ion concentration, and particulate internal electrodes 12 that are dispersed and arranged therein. It comprises an electrolytic solution 1 containing a polyvalent cation, for example, a divalent copper ion, and a pair of external electrodes 4a and 4b are disposed on the outside of the gel / electrode composite 16 and the electrolytic solution 1. It is assumed that a flexible resin 5 is disposed on the outermost periphery in order to prevent leakage and volatilization of the electrolytic solution 1.
Further, it is assumed that an anion exchange membrane 8 is disposed between the gel / electrode composite 16 and the electrolytic solution 1.

  In addition, about the electrolyte solution 1 and the hydrogel 3, the thing similar to the polymer actuator shown and demonstrated in FIG. 1 is applicable.

  In the polymer actuator 30, a particle-shaped internal electrode 12 is arranged in a hydrogel 3 that is responsive to changes in ion concentration, and a potential difference is generated between the internal electrode 12 and the pair of external electrodes 4a and 4b. As a result, the ion concentration, for example, the copper ion concentration, changes in the vicinity of the internal electrode 12, the change in the ion concentration is transmitted to the entire hydrogel 3, and the hydrogel 3 expands / contracts uniformly.

  Also in the case of the polymer actuator 30 in FIG. 3, when the hydrogel 3 expands, the distance between the particle-shaped internal electrodes 12 increases, but at the same time, the metal ions in the electrolytic solution 1 on the internal electrode surface. Is reduced and enters a state of a metal atom and enters between the particles of the internal electrode 12, and conduction is ensured even in the expansion stage.

On the other hand, due to the concentration gradient with the outside of the hydrogel 3, a phenomenon occurs in which the ion concentration change in the vicinity of the internal electrode 12 is gradually canceled.
Therefore, in this example, the anion exchange membrane 8 is disposed so as to be in contact with the surface of the hydrogel 3. Thereby, the passage of metal ions between the outside and the inside of the hydrogel 3 is suppressed, and the change in the ion concentration inside the hydrogel is maintained. That is, there is an advantage that an actuator driven with low power consumption can be obtained.

  Next, an example in which a specific sample of the polymer actuator according to the present invention was prepared and operated will be described.

In this example, a polymer actuator having the configuration shown in FIG. 2 was produced.
Platinum fine particles were applied as the internal electrode 12 for oxidizing and reducing the metal ions contained in the electrolytic solution 1.
As the hydrogel 3 that responds to changes in the ion concentration, a poly (2-acrylamide-2-propanesulfonic acid) gel (AMPS gel) prepared by mixing a crosslinking agent was applied.
As the electrolytic solution 1, a solution prepared by adding sodium sulfate to a 1 mol / l copper (II) sulfate aqueous solution to be 0.05 mol / l was applied.
Monomer of the poly (2-acrylamido-2-propanesulfonic acid) gel: 1.6527 g, n, n-methylenebisacrylimide: 0.118 g, distilled water: 6 ml, and ammonium persulfate are mixed together to prepare a precursor solution. Produced.
As the internal electrode 12, platinum fine particles having a diameter of 0.1 μm were applied. The platinum fine particles were added at a rate of 100 vol% with respect to the gel precursor solution to prepare a mixed solution.

The mixed solution of the gel precursor solution and the platinum fine particles is poured into a PTFE tube having a diameter of 0.5 mm, both ends of the tube are sealed with silicon stoppers, and left in an oven set at 60 ° C. for 12 hours. did. As a result, a rod-shaped hydrogel 3 (gel / electrode composite 16) having an internal electrode 12 of platinum fine particles was obtained. The gel / electrode composite 16 had a length (L1) of 20 mm in an unloaded state.
One end of the rod-like gel / electrode composite 16 produced as described above was fixed with gold foil, and an electrode terminal was attached.
This gel / electrode composite 16 and a pair of external electrodes 4a, 4b made of a copper plate were immersed in the electrolytic solution 1.
When a voltage of 3.0 V is applied between the electrode terminal fixed to the gel / electrode composite 16 and the pair of external electrodes 4a and 4b, the copper ion concentration in the electrolytic solution 1 changes, and the hydrogel 3 contracted.
The length (L2) after voltage application was 18 mm in an unloaded state, and contraction was confirmed.
The displacement {1- (L2) / (L1)} of the actuator was 0.10, and the time required for this displacement was 10 seconds.

From the above-described embodiments, it was confirmed that the polymer actuator of the present invention can drive the material quickly and reliably by a simple electrical operation.
In addition, by using an electrode that can easily control the ion concentration in the electrolytic solution, it is possible to drive the actuator effectively with a very small operating current.
Moreover, since the internal electrode is made of platinum fine particles, the electrode surface area in the hydrogel 3 becomes extremely large, the ion concentration inside the hydrogel can be changed uniformly and quickly, and high-speed and uniform expansion and contraction can be performed. I was able to.
Even when the hydrogel is in an expanded state, it is confirmed that the copper ions in the electrolytic solution 1 are reduced on the surface of the internal electrode, enter into the state of metal atoms and enter between the platinum fine particles, and the conduction is ensured. It was.

The schematic of the structural example of the polymer actuator of this invention is shown. The schematic of another example of the polymer actuator of this invention is shown. The schematic of another example of the polymer actuator of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte solution 2,12 ... Internal electrode, 3 ... Hydrogel, 4a, 4b ... External electrode, 5 ... Flexible resin, 6, 16 ... Gel / electrode composite 10, 20, 30 …… Polymer actuator

Claims (8)

A gel / electrode composite composed of a hydrogel containing a polymer having one or more functional groups that interact with a polyvalent cation, and an internal electrode present in the hydrogel;
An electrolyte solution containing the polyvalent cation,
On the outside of the gel / electrode composite and the electrolyte, a pair of external electrodes are disposed,
By applying a potential between the pair of external electrodes and the internal electrode, the polyvalent cation is reduced or oxidized to cause a change in the polyvalent cation concentration, and the gel / electrode complex is A polymer actuator characterized by causing a volume change of a constituent hydrogel. A gel / electrode composite comprising a stimuli-responsive hydrogel that undergoes a volume change with a change in metal ion concentration, and an internal electrode dispersed in the hydrogel;
An electrolyte solution containing the metal ions,
On the outside of the gel / electrode composite and the electrolyte, a pair of external electrodes are disposed,
By applying a potential between the pair of external electrodes and the internal electrode, the metal ions are reduced and the concentration of the metal ions is reduced, and the volume of the hydrogel constituting the gel / electrode composite is reduced. A polymer actuator, wherein the polymer ion is changed and is in a state where the metal ions are reduced on the surface of the electrode to electrically connect the electrodes.   The polymer actuator according to claim 1, wherein an anion exchange membrane is provided on the surface of the gel / electrode complex.   4. The polymer actuator according to claim 3, wherein the volume of the hydrogel is changed in accordance with a change in the concentration of polyvalent cations in the hydrogel constituting the gel / electrode composite. .   The polymer actuator according to claim 1, wherein the polyvalent cation is a divalent copper ion.   The polymer actuator according to claim 2, wherein the metal ion is a divalent copper ion.   The material of the internal electrode is at least one of platinum, gold, carbon black, ketjen black, carbon nanotube, fullerene, polyacetylene, polypyrrole, polythiophene, poly-1,6-heptadiyne, poly-p-phenylene, polyphenylene vinylene. The polymer actuator according to claim 1, wherein the polymer actuator is provided. The polymer actuator according to claim 1, wherein the internal electrode is a nanoparticle.

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