JP2013106491A - Polymer actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability of a polymer actuator.SOLUTION: A polymer actuator 1 comprises: an electrolyte layer 20; and electrode layers 11 and 12 disposed adjacent to the electrolyte layer 20. In the inside of the electrode layers 11 and 12, the polymer actuator 1 comprises gap parts in which at least one of the gap parts exists at a boundary surface with the electrolyte layer 20.

Description

  The present invention relates to a polymer actuator.

A polymer actuator using a conductive polymer is generally composed of a plurality of electrode layers and an electrolyte layer interposed therebetween (for example, Patent Document 1). Polymer actuators have advantages such as low drive voltage and high energy density, and are being studied with the expectation of application to artificial muscles and the like.
JP 2006-50780 A

  In particular, a polymer actuator composed of an electrode layer containing a conductive polymer and an electrolyte layer having ionic conductivity causes ions to move between the electrode layers through energization between the opposing electrode layers, so that the ions The electrode layer on the entering side expands and the electrode layer on the ion escape side contracts, causing a bending action. At this time, stress is generated at the interface between the electrode layer and the electrolyte layer due to a difference in expansion and contraction between the electrode layer and the electrolyte layer, and peeling occurs at the interface between the electrode layer and the electrolyte layer when the actuator is repeatedly operated. This is a cause of lowering the durability of the molecular actuator.

  Accordingly, an object of the present invention is to improve the durability of a polymer actuator when it is repeatedly operated.

  In order to achieve the above object, the polymer actuator of the present invention comprises an electrolyte layer and an electrode layer provided adjacent to the electrolyte layer, and a void portion at the interface with the electrolyte layer in the electrode layer. It is characterized by having.

  The void in the electrode layer in contact with the electrolyte layer has an action of relaxing stress due to a difference in expansion and contraction between the electrode layer and the electrolyte layer when the polymer actuator is driven. Furthermore, since the void portion has at the interface with the electrolyte layer, peeling of the electrolyte layer and the electrode layer is suppressed, and an effect of improving durability when the actuator is repeatedly operated is obtained.

  As a desirable mode, the volume ratio which the space part accounts in the electrode layer increases toward the electrolyte layer provided adjacent. This has a large effect of relaxing the stress at the interface between the electrode layer and the electrolyte layer due to the large number of voids on the surface of the electrode layer adjacent to the electrolyte layer. Since there are few parts and there are many electrode layers, electrical conductivity is high, and the displacement amount as an actuator can be obtained largely.

  Moreover, the volume ratio in the said electrode layer of the said space | gap part is 4 volume% to 50 volume%. When the volume ratio is 4% by volume to 50% by volume, a larger displacement can be obtained in terms of conductivity in the electrode layer, which is preferable as an actuator.

  According to the present invention, the peeling between the electrode layer and the electrolyte layer is improved by reducing the stress generated by the expansion and contraction difference between the electrode layer and the electrolyte layer when the polymer actuator is driven, and the polymer actuator is operated repeatedly. When durability is improved.

FIG. 1 is a cross-sectional view showing an embodiment of a polymer actuator. FIG. 2 is a cross-sectional view showing an embodiment of a gap in the electrode layer.

  DESCRIPTION OF SYMBOLS 1 ... Polymer actuator, 11, 12 ... Electrode layer, 20 ... Electrolyte layer, 30 ... Gap part, 41, 42 ... Connection terminal

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a cross-sectional view showing an embodiment of a polymer actuator. A polymer actuator 1 shown in FIG. 1 is composed of a pair of opposed electrode layers 11, 12 and an electrolyte layer 20 sandwiched between the pair of electrode layers 11, 12. Inside the electrode layers 11 and 12, a gap 30 is provided. Connection terminals 41 and 42 are respectively attached to the outer sides of the electrode layers 11 and 12, and these are connected to a circuit including a variable voltage power source. In the polymer actuator 1, for example, when a high potential is applied to the connection terminal 41 from the connection terminal 41 by energization, displacement occurs in the direction of the arrow A.

  The electrode layers 11 and 12 contain a conductive polymer. Examples of the conductive polymer include polythiophene, polypyrrole, polyaniline, polyacetylene, and the like. Among them, polypyrrole is preferable because it is easy to manufacture and has a stable conductivity with respect to the surrounding environment as a conductive polymer. The conductive polymer is preferably doped with a dopant.

  FIG. 2 is a cross-sectional view showing an embodiment of the gap portion 30 contained in the electrode layers 11 and 12. At least one of the gaps 30 is provided at the interface between the electrode layers 11 and 12 and the electrolyte layer 20. When driving a polymer actuator formed by laminating an opposing electrode layer and an electrolyte layer, a bending operation is performed by one side of the opposing electrode layer expanding and one side contracting. At this time, stress is generated at the interface between the electrode layer and the electrolyte layer, which causes peeling. The presence of the void at the interface between the electrode layer and the electrolyte layer makes it possible to relieve the stress generated at the interface between the electrode layer and the electrolyte layer.

  The gap portion 30 provided at the interface between the electrode layers 11 and 12 and the electrolyte layer 20 has an opening where the adjacent electrolyte layer 20 is exposed in the gap portion. The gap 30 has a shape that is longer in the direction along the adjacent electrolyte layer than in the thickness direction of the electrode layer, so that the electrode layer can be formed thick, so that the generated stress for moving the actuator itself is large. More preferable in terms.

  It is more preferable that the ratio of the voids in the electrode layers 11 and 12 is 4% by volume to 50% by volume. If it is less than 4% by volume, the stress relaxation effect is small, and if it is 50% by volume or more, the electrical conductivity in the electrode layer is lowered, and a large amount of displacement tends not to be obtained. Furthermore, it is more preferable that it is 20 volume% or more and 40 volume% or less in the point that a displacement amount is large and generated force is large.

  It is preferable that the volume ratio which the said space part accounts in an electrode layer increases toward the electrolyte layer provided adjacently. As a result, the gap between the electrolyte layer and the electrolyte layer is increased, and the stress relaxation effect is greater. Can keep.

  Here, the void portion is a portion where no conductive polymer exists in the electrode layer in this example, and may contain a gas or a liquid such as an electrolytic solution.

  Moreover, the porosity is a ratio of the volume which the space | gap part in an electrode layer occupies, and is measured with the following method. (1) The polymer actuator of this embodiment is cleaved, a sample with the cross section of the electrode layer exposed is cut out, and the electrode layer is imaged with a scanning electron microscope. (2) Binarization processing is performed on the imaged electrode layer image. Then, the ratio of the area of the void portion with respect to the electrode layer is calculated. (3) The above measurement is performed at any five locations per sample of the polymer actuator, and the average value of the five locations is calculated as the value of the porosity.

  More preferably, the gap 30 in the electrode layers 11 and 12 has no opening in the gap on the surface not adjacent to the electrolyte layer. Since the electrolyte layer is exposed at the opening of the gap, the effect of relaxing the stress at the interface between the electrode layer and the electrolyte layer is great. In addition, when there is an opening in the gap on the surface not adjacent to the electrolyte layer, the electrode layer on the surface of the polymer actuator becomes discontinuous, which is not preferable in that foreign matter is mixed in from the outside.

  A preferable film thickness of the electrode layers 11 and 12 is 1 to 50 μm, and a more preferable film thickness is 10 to 30 μm. If it is thin, the rigidity tends to be low and the generated stress tends to be small, and if it is thick, the electrode layer itself hinders displacement, which is not preferable because a large amount of displacement cannot be obtained.

  The electrolyte layer 20 is not particularly limited as long as it has ion conductivity and flexibility. Examples include solid polymer electrolytes containing ionic substances, gel electrolytes, or porous membranes containing electrolytes or ionic liquids. A porous membrane containing a liquid or an ionic liquid is preferred.

  The porous film is not particularly limited as long as it is a flexible film that can contain an electrolytic solution or an ionic liquid. Specifically, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polyamide, polyimide Examples thereof include porous resin membranes such as polyester, glass paper, and nonwoven fabric. A resin porous membrane is preferable from the viewpoint of obtaining a larger displacement amount as an actuator.

  The electrolytic solution contains an anion as an electrolyte. As the anion, bistrifluoromethanesulfonylimide ion, tetrafluoroborate ion, hexafluorophosphate ion, or the like can be used as a dopant ion. The anion may be an electrolyte salt that forms a counter ion with a cation such as Li +, Na +, or K +. The dopant ion is preferably a bistrifluoromethanesulfonylimide ion from the viewpoint of obtaining a larger displacement as an actuator.

  The solvent contained in the electrolytic solution is not particularly limited as long as the solvent can dissolve the electrolyte. Examples of the solvent include water, acetone, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, propylene carbonate, ethylene carbonate, gamma butyrolactone, and the like. These solvents can be used alone or as a mixed solvent.

  Examples of the ionic liquid contained in the porous membrane include imidazolium salts, pyridium salts, and quaternary ammonium salts.

  The ionic liquid may be used alone or as a mixture of the ionic liquid and the solvent.

  The electrolyte layer 20 may include a metal thin film having a thickness of about 0.1 μm on the surface corresponding to the interface with the electrode layer for the purpose of imparting conductivity to the porous film.

  As an example of the method for producing the polymer actuator of the present embodiment, a metal thin film is formed on both surfaces of a porous film by sputtering to form an electrolyte layer 20, and this is used as a working electrode to conduct electropolymerization of a conductive polymer to form an electrode Layers 11 and 12 are formed. At this time, voids are formed in the electrode layers 11 and 12. Thereafter, the polymer actuator is manufactured by impregnating the electrolyte layer with an electrolytic solution or an ionic liquid.

  The metal thin film can be formed of a metal such as gold, platinum, or nickel by a method such as sputtering or vapor deposition.

  A known electrolytic solution can be used for the electrolytic polymerization of the conductive polymer because a known electrolytic polymerization method can be used. Electropolymerization can be carried out at a current density of 0.01 to 20 mA / cm 2 and a reaction temperature of −70 to 80 ° C.

  The said electrolyte solution for superposition | polymerization consists of a conductive polymer monomer, the dopant ion contained in a conductive polymer, and a solvent. As the conductive polymer monomer, pyrrole that is easy to produce and is stable as the conductive polymer is preferable. Examples of the dopant ion include bistrifluoromethanesulfonylimide ion, tetrafluoroborate ion, hexafluorophosphate ion, and the like, but bistrifluoromethanesulfonylimide ion capable of obtaining a large displacement as an actuator is preferable. These dopant ions may form a salt with a cation. As a solvent, what is necessary is just a solvent which melt | dissolves or is compatible with the said conductive polymer monomer and dopant ion. Examples include solvents such as tetrahydrofuran, gamma butyrolactone, ethyl acetate, propylene carbonate, ethylene carbonate, ethylene glycol, and acetonitrile, and these solvents may be used alone or as a mixed solvent.

  The polymerization electrolyte may contain known additives such as a plasticizer and a crosslinking agent.

  The void portion 30 inside the electrode layers 11 and 12 can be formed by containing a gas in the electrolyte layer during electrolytic polymerization. Specifically, the electrolyte layer is put into an inert gas tank such as nitrogen or argon pressurized to 0.2 to 0.5 MPa, and the electrolyte layer is filled with an inert gas. Thereafter, the electrolyte layer filled with the inert gas is immersed in the polymer electrolyte and subjected to electrolytic polymerization, so that the inert gas flows into the electrode layer from the inside of the electrolyte layer, and a gap is formed at the interface between the electrode layer and the electrolyte layer. Can be formed. The amount of voids can be controlled by depressurizing and reducing the amount of inert gas contained in the porous membrane when the electrolyte layer filled with inert gas is immersed in the polymerization electrolyte. is there.

  Alternatively, after the electrolyte layer is immersed in the polymer electrolyte, the electrode layer is filled with an inert gas by bubbling an inert gas such as nitrogen or argon on the surface of the electrolyte layer, and then subjected to electrolytic polymerization. A void can also be formed inside.

  Further, a filler that can be removed, for example, a glass filler, is sprayed on the surface of the electrolyte layer, and after the electrode layer is formed to a thickness that does not bury the filler, the filler is removed, and an electrode layer is formed on the surface. This can also adjust the structure in which the volume of the opening increases toward the electrolyte layer.

  The present invention is not limited to the embodiments described above, and can be appropriately modified without departing from the spirit of the present invention. For example, in the polymer actuator, only one electrode layer may be provided, or a plurality of electrode layers and electrolyte layers may be alternately stacked. In addition, the shape of the polymer actuator is not limited to a flat plate shape, and can be appropriately changed according to the application.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Element creation>
Example 1
An electrolyte layer was prepared by performing 0.1 μm gold sputtering on both surfaces of a porous polyvinylidene fluoride film (GVWP pore diameter 0.22 μm manufactured by Millipore). This electrolyte layer was left in nitrogen pressurized to 0.2 MPa for 1 hour to fill the electrolyte layer with nitrogen. Next, this electrolyte layer is immersed in an electrolytic solution for electrolytic polymerization, degassed under reduced pressure for 30 minutes in the electrolytic solution to adjust the amount of nitrogen in the electrolyte layer, and then polypyrrole is polymerized for 4 hours by electrolytic polymerization to form an electrode layer. A polymer actuator was prepared in which the porosity of the electrode layer was 4% by volume, the void portion was present at the interface with the electrolyte layer, and the void portion increased toward the electrolyte layer.

Example 2
Except that the vacuum degassing in the electrolytic solution was performed for 20 minutes, the porosity of the electrode layer was 12% by volume in the same manner as in Example 1, and there was a void at the interface with the electrolyte layer. A polymer actuator with increasing voids was created.

Example 3
Except that the pore diameter of the porous polyvinylidene fluoride film was changed to 0.45 μm (HVLP manufactured by Millipore), the porosity of the electrode layer was 25% by volume, and the void at the interface with the electrolyte layer was the same as in Example 2. There was created a polymer actuator in which a void portion increased toward the electrolyte layer.

Example 4
Except for reducing the degassing in the electrolytic solution for 10 minutes, the porosity of the electrode layer was 38% by volume and a void portion was present at the interface with the electrolyte layer by the same method as in Example 3. A polymer actuator was created in which the gap increased toward.

Example 5
Except that the pore diameter of the porous polyvinylidene fluoride membrane was 0.65 μm (DVPP manufactured by Millipore), the porosity of the electrode layer was 50% by volume and the void at the interface with the electrolyte layer was the same as in Example 4. There was created a polymer actuator in which a void portion increased toward the electrolyte layer.

Example 6
Except for 40 minutes of degassing under reduced pressure in the electrolytic solution, the porosity of the electrode layer was 3% by volume and a void portion was present at the interface with the electrolyte layer by the same method as in Example 3. A polymer actuator was created in which the gap increased toward.

Example 7
Except for reducing the vacuum degassing in the electrolytic solution for 5 minutes, the porosity of the electrode layer was 53% by volume and a void portion was present at the interface with the electrolyte layer by the same method as in Example 3. A polymer actuator was created in which the gap increased toward.

Example 8
An electrolyte layer was prepared by performing 0.1 μm gold sputtering on both surfaces of a porous polyvinylidene fluoride membrane (HVLP pore diameter 0.45 μm manufactured by Millipore). This electrolyte layer was left in nitrogen pressurized to 0.2 MPa for 1 hour to fill the electrolyte layer with nitrogen. Next, after immersing this electrolyte layer in an electrolytic solution for electrolytic polymerization, performing degassing under reduced pressure for 20 minutes in the electrolytic solution to adjust the amount of nitrogen in the electrolytic layer, polymerizing polypyrrole for 2 hours by electrolytic polymerization, Nitrogen was bubbled through the solution for 1 minute. Furthermore, polypyrrole is polymerized for 2 hours by an electrolytic polymerization method to form an electrode layer. The porosity of the electrode layer is 32% by volume, there is a void at the interface with the electrolyte layer, and the void decreases toward the electrolyte layer. A molecular actuator was created.

Comparative Example 1
An electrolyte layer was prepared by performing 0.1 μm gold sputtering on both surfaces of a porous polyvinylidene fluoride film (GVWP pore diameter 0.22 μm manufactured by Millipore). This electrolyte layer is immersed in an electrolytic solution for electrolytic polymerization, and after degassing under reduced pressure for 40 minutes in the electrolytic solution, polypyrrole is polymerized for 4 hours by an electrolytic polymerization method to form an electrode layer, and the porosity of the electrode layer is 0 volume. % Polymer actuators were made.

Comparative Example 2
An electrolyte layer was prepared by performing 0.1 μm gold sputtering on both surfaces of a porous polyvinylidene fluoride film (GVWP pore diameter 0.22 μm manufactured by Millipore). This electrolyte layer was immersed in an electrolytic solution for electrolytic polymerization, degassed under reduced pressure for 40 minutes in the electrolytic solution, and then polypyrrole was polymerized by an electrolytic polymerization method for 1 hour, and then nitrogen was bubbled in the electrolytic solution for 3 minutes. Furthermore, polypyrrole was polymerized for 3 hours by an electrolytic polymerization method to form an electrode layer, and a polymer actuator was prepared in which the porosity of the electrode layer was 35% by volume and the opening of the void was not in the electrolyte layer.

<Measurement of displacement>
The polymer actuator element has a strip shape with a length of 12 mm and a width of 2 mm, impregnated with ionic liquid 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonylimide, and a connection terminal is arranged at a position 2 mm from one end. Then, a voltage was applied with a sine wave having a voltage of ± 1 V and a frequency of 1 Hz to drive the polymer actuator, and the deflection width at the tip of the polymer actuator was measured as an initial displacement. Assuming that a high actuator displacement amount was obtained when the initial displacement amount was 2 mm or more, ◎ was assumed that a sufficient displacement amount was obtained when it was 1 mm or more and less than 2 mm, and ○ was assumed that the initial displacement amount was insufficient.

<Measurement of displacement retention>
In order to evaluate the durability when the operation was repeated, the displacement retention rate was measured. After displacement for 100 hours by the above method, the displacement retention rate was calculated by the following formula.
Initial displacement H0 (mm)
Displacement after 100 hours H1 (mm)
Displacement retention rate = H1 / H0 x 100 (%)
A displacement holding ratio of 80% or more was evaluated as ◎ if sufficient durability was obtained, and less than 80% was evaluated as × because durability was not sufficient.

The evaluation results are shown in Table 1. In each of Examples 1 to 8, as a result of cross-sectional observation, the void in the electrode layer is at the interface between the electrode layer and the electrolyte layer, and the void is present at the interface between the electrode layer and the electrolyte layer. Separation of the electrolyte layer was suppressed, and the displacement retention after 100 hours was 80% or more. Thereby, it was confirmed that durability when repeatedly operated was obtained. Furthermore, in all of Examples 1 to 7, as a result of observation of the cross section, the volume of the void portion increased toward the electrolyte layer. Furthermore, in Examples 1 to 5, the porosity was in the range of 4 to 50% by volume, and the initial displacement was larger. In the cross section of the void at this time, it was observed that the shape was long in the direction along the adjacent electrolyte layer. However, in Comparative Examples 1 and 2, as a result of cross-sectional observation, the void portion in the electrode layer was not at the interface between the electrode layer and the electrolyte layer, and peeling of the electrolyte layer and electrode layer occurred in measuring the displacement amount retention rate.

Claims (3)

An electrolyte layer, and an electrode layer provided adjacent to the electrolyte layer,
A polymer actuator having a void at an interface between the electrode layer and the electrolyte layer.   The polymer actuator according to claim 1, wherein a volume ratio of the gap portion in the electrode layer increases toward the electrolyte layer.   3. The polymer actuator according to claim 1, wherein a volume ratio of the gap in the electrode layer is 4% by volume to 50% by volume.

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