Soft Actuator

Abstract

To provide a soft actuator that has flexibility, can operate at high speed and with high output, and can have a large area.SOLUTION: A soft actuator includes electrode layers and an active layer between the electrode layers. The electrode layers each include a conductive material. The active layer includes a crystalline dielectric polymer. The electrode layers and / or the active layer includes hydrophilic functional group-containing carbon particles.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] This invention relates to a soft actuator. [Background technology]

[0002] Actuators are manufactured using MEMS (inorganic semiconductor) technology and motor drive (Non-Patent Document 1).

[0003] Furthermore, soft actuators using organic materials have been proposed (Non-Patent Literature 2). Soft actuators are useful for applications in active braille and haptic devices. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Xingdong Lv, et al., A novel MEMS electromagnetic actuator with large displacement, Sensors and Actuators A, 221 (2015) 22-28 [Non-Patent Document 2] Philipp Rothemund, et al., A soft, bistable valve for autonomous control of soft actuators, Science Robotics, 3, (2018) 1-10 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, actuators manufactured using MEMS (inorganic semiconductor) technology and motor drive systems, while offering high output, have been hampered by their rigidity and small operating area.

[0006] Furthermore, while conventional actuators using organic materials are flexible, their output, or displacement, is smaller compared to those using inorganic materials, making it inherently difficult to achieve both high speed and high output performance simultaneously.

[0007] This invention has been made in view of the above circumstances, and aims to provide a soft actuator that is flexible, capable of high-speed and high-power operation, and can be scaled up to a large area. [Means for solving the problem]

[0008] The gist of this invention is as follows: (1) A soft actuator comprising an electrode layer and an active layer between the electrode layers, The electrode layer includes a conductive material, The active layer comprises a crystalline dielectric polymer. At least one of the electrode layer and the active layer includes carbon particles having hydrophilic functional groups. Soft actuator. (2) The soft actuator according to (1) above, wherein the carbon particles are graphene oxide, carbon nanotubes, or a combination thereof. (3) The soft actuator according to (2) above, wherein the active layer contains the carbon nanotube. (4) The soft actuator according to (2) or (3) above, wherein the electrode layer contains graphene oxide. (5) The soft actuator according to any one of (1) to (4) above, wherein the active layer contains 0.01 to 0.1 mass% of the carbon particles. (6) The soft actuator according to any one of (1) to (5) above, wherein the electrode layer contains 0.0005 to 0.5 mass% of the carbon particles. (7) 10mm 2 A soft actuator according to any of (1) to (6) above, having the above area. (8) A soft actuator comprising an electrode layer and an active layer between the electrode layers, The active layer includes a crystalline dielectric polymer and carbon particles having hydrophilic functional groups. Soft actuator.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a soft actuator that is flexible, can operate at high speed and with high output, and can be further enlarged in area.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a photograph of the appearance of a plurality of soft actuators fabricated on a polyethylene naphthalate (PEN) substrate. [Figure 2] FIG. 2 is an example for explaining a laser displacement meter for measuring the displacement amount of an actuator and a laser irradiation portion of the actuator. [Figure 3] FIG. 3 is a schematic diagram for explaining a method of measuring the displacement amount of an actuator. [Figure 4] FIG. 4 shows the results of measuring the displacement amount when an electric field of 10 to 100 MV / m is applied to the actuator fabricated in Comparative Example 1 at every 10 MV / m. [[ID=二十七]] [Figure 5] FIG. 5 shows the results of measuring the displacement amount when an electric field of 10 to 100 MV / m is applied to the actuator fabricated in Example 1 at every 10 MV / m. [Figure 6] FIG. 6 shows the results of measuring the displacement amount when an electric field of 10 to 100 MV / m is applied to the actuator fabricated in Example 2 at every 10 MV / m. [Figure 7] FIG. 7 shows the results of measuring the displacement amount when an electric field of 10 to 100 MV / m is applied to the actuator fabricated in Example 3 at every 10 MV / m. [Figure 8] FIG. 8 is a hysteresis curve of the measured electric field (MV / m) and the residual polarization value (μC / cm2) for the actuators fabricated in Examples 1 to 3 and Comparative Example 1. [Figure 9]FIG. 9 is a graph showing the relationship between the electric field amount and the displacement amount measured for the actuators fabricated in Examples 1 to 3 and Comparative Example 1. [Figure 10] FIG. 10 is a graph showing the relationship between the displacement amount and the residual polarization value measured for the actuators fabricated in Examples 1 to 3 and Comparative Example 1. [Figure 11] FIG. 11 is an atomic force microscope (AFM) image of the dielectric film of P(VDF-TrFE) alone formed in Example 1. [Figure 12] FIG. 12 is an atomic force microscope (AFM) image of the dielectric film in which single-walled carbon nanotubes are mixed with P(VDF-TrFE) formed in Example 2. [Figure 13] FIG. 13 is an atomic force microscope (AFM) image of the electrode film of PEDOT:PSS alone formed in Example 2. [Figure 14] FIG. 14 is an atomic force microscope (AFM) image of the electrode film in which graphene oxide is mixed with PEDOT:PSS formed in Example 1. [Figure 15] FIG. 15 is an optical microscope image of the dielectric film of P(VDF-TrFE) alone formed in Example 1. [Figure 16] FIG. 16 is an optical microscope image of the dielectric film in which single-walled carbon nanotubes are mixed with P(VDF-TrFE) formed in Example 2. [Figure 17] FIG. 17 is an optical microscope image of the electrode film of PEDOT:PSS alone formed in Example 2. [Figure 18] FIG. 18 is an optical microscope image of the electrode film in which graphene oxide is mixed with PEDOT:PSS formed in Example 1. [Figure 19] FIG. 19 is a graph showing the relationship between the applied frequency and the actually measured frequency measured for the actuators fabricated in Example 1 and Comparative Example 1. [Figure 20] FIG. 20 is a graph showing the relationship between the applied frequency and the displacement amount measured for the actuators fabricated in Example 1 and Comparative Example 1. [Figure 21] FIG. 21 is a cross-sectional SEM image of the actuator fabricated in Example 3. [Figure 22] Figure 22 is a schematic cross-sectional view of an example of a soft actuator having a capacitor structure including electrode layers and an active layer between the electrode layers. [Modes for carrying out the invention]

[0011] This disclosure relates to a soft actuator comprising an electrode layer and an active layer between the electrode layers, wherein the electrode layer comprises a conductive material, the active layer comprises a crystalline dielectric polymer, and at least one of the electrode layer and the active layer comprises carbon particles having hydrophilic functional groups.

[0012] This soft actuator is flexible because its main component, the active layer (driving layer), is primarily composed of a crystalline dielectric polymer. By incorporating carbon particles with hydrophilic functional groups into at least one of the electrode layer (primarily composed of a conductive material) and the active layer (primarily composed of a crystalline dielectric polymer), a soft actuator that operates at higher speeds and outputs than conventional actuators can be obtained. Furthermore, this soft actuator can be manufactured using a coating process and is easily scaled up to large areas. This soft actuator is suitably used in haptic devices that replicate human touch.

[0013] Crystalline dielectric polymers are crystalline materials that can be formed by a coating process, and then, after a heat treatment process, their crystal orientations become aligned. When a dielectric film is formed by mixing a crystalline dielectric polymer with carbon particles having hydrophilic functional groups and coating it, and then a dielectric layer is formed through a firing process, the crystal orientations of the crystalline dielectric polymer in the dielectric layer become more aligned. The more aligned the crystal orientations of the crystalline dielectric polymer, the easier it is for the crystals to move in the same direction when an electric field is applied, thus improving the output of the actuator, i.e., increasing the amount of displacement. In this application, the film containing the crystalline dielectric polymer before heat treatment is called the dielectric film, and the film containing the crystalline dielectric polymer after heat treatment is called the dielectric layer.

[0014] Conductive materials can also be formed by a coating process, and an electrode layer can be obtained through a heat treatment process. When a conductive material is mixed with carbon particles having hydrophilic functional groups, an electrode film is formed by a coating process, and then a heat treatment process is performed to form an electrode layer adjacent to the active layer, the crystal orientation of the crystalline dielectric polymer in the dielectric layer becomes more aligned, improving the output of the actuator, i.e., increasing the amount of displacement. Although not bound by theory, when a conductive material is mixed with carbon particles having hydrophilic functional groups and an electrode film is formed by a coating process, the carbon particles with hydrophilic functional groups are present on the surface of the electrode film, and it is thought that during the heat treatment process, the hydrophilic functional groups of the carbon particles interposed at the interface with the dielectric film act on the crystalline dielectric polymer of the dielectric film, improving the crystallinity of the crystalline dielectric polymer. In this application, the film containing the conductive material before heat treatment is called the electrode film, and the film containing the conductive material after heat treatment is called the electrode layer.

[0015] Hydrophilic functional groups present on the surface of carbon particles readily form hydrogen bonds with crystalline dielectric polymers. When a crystalline dielectric polymer and carbon particles are deposited together and then heat-treated, a crystalline dielectric polymer with more aligned crystal orientations can be obtained. The hydrophilic functional groups are preferably hydroxyl groups, carboxyl groups, or amino groups, and more preferably hydroxyl groups or carboxyl groups. Since carbon particles generally have hydrophilic functional groups on their surface, an effect of improving the crystallinity of the crystalline dielectric polymer can be obtained. Desired hydrophilic functional groups may be imparted to the surface of the carbon particles or the amount of hydrophilic functional groups on the surface of the carbon particles may be increased by subjecting the carbon particles to conventional oxidation treatments, plasma treatments, etc. The number of hydrophilic functional groups on the carbon particles is preferably 0.01 to 1 mmol / g. The presence and number of hydrophilic functional groups on the surface of carbon particles can be measured by acid-base titration (Boehm method), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), or thermal generated gas mass spectrometry (TPD / MS).

[0016] The carbon particles preferably have a maximum particle size smaller than the thickness of the active layer, and more preferably a maximum particle size smaller than the thickness of the active layer and / or electrode layer containing the carbon particles. By having the carbon particles have the above preferred maximum particle size, it is possible to improve the crystallinity of the active layer while suppressing short circuits caused by the carbon particles penetrating the active layer. The carbon particles preferably have a maximum particle size of 1 to 75%, more preferably 2 to 50%, and even more preferably 3 to 25% of the thickness of the active layer. The maximum particle size of the carbon particles refers to the maximum size of all particles observed in a 1500 × 1500 μm field of view by high-resolution optical microscope observation of the surface or cross-section of the electrode layer or active layer.

[0017] The carbon particles preferably have an average particle size of 0.1 to 10,000 nm, more preferably 1 to 1,000 nm, and even more preferably 10 to 100 nm. By having the carbon particles have the above preferred fine average particle size, it is possible to further improve the crystallinity of the active layer while suppressing short circuits in the active layer. The average particle size of the carbon particles refers to the average value of the dimensions of 10 randomly selected particles observed in a 150 × 150 μm field of view using a high-resolution optical microscope on the surface or cross-section of the electrode layer or active layer. The dimensions of a single carbon particle can be calculated as the average value of the longitudinal dimension, which shows the maximum dimension of the particle in the observed image, and the dimension in the direction perpendicular to it.

[0018] The average and maximum particle sizes of carbon particles may be adjusted by grinding them using a mortar and pestle, removing coarse particles using a sieve, etc.

[0019] Carbon particles can be graphite, carbon black, graphene, graphene oxide, carbon nanotubes, fullerenes, etc., or combinations thereof. Graphene oxide and carbon nanotubes are generally preferred because they contain many hydrophilic functional groups such as carboxyl groups, eliminating the need for special treatment to acquire these hydrophilic functional groups.

[0020] The electrode layer preferably contains 0.0005 to 0.5 mass%, more preferably 0.001 to 0.1 mass%, and even more preferably 0.005 to 0.05 mass% of carbon particles. By including carbon particles within the above preferred range in the electrode layer, the crystallinity of the active layer can be improved while ensuring the insulating properties of the active layer.

[0021] The active layer preferably contains 0.01 to 1% by mass, more preferably 0.03 to 0.5% by mass, and even more preferably 0.05 to 0.1% by mass of carbon particles. By including carbon particles within the above preferred range in the active layer, the crystallinity of the active layer can be improved while ensuring the insulating properties of the active layer.

[0022] Carbon particles are contained in at least one of the electrode layer and the active layer, preferably in both the electrode layer and the active layer. The carbon particles contained in the electrode layer and the active layer may be the same or different.

[0023] The carbon particles contained in the electrode layer are preferably graphene oxide. Graphene oxide has many hydrophilic functional groups, particularly hydroxyl and carboxyl groups, which makes it easier to improve the crystallinity of the electrode layer.

[0024] Graphene oxide preferably has an average particle size of 1 to 1000 nm, more preferably 10 to 500 nm, and even more preferably 20 to 1000 nm. Graphene oxide with the above average particle size exhibits good dispersibility when incorporated into the electrode layer, and can significantly improve the crystallinity of the active layer.

[0025] The carbon particles contained in the active layer are preferably carbon nanotubes. Since carbon nanotubes have many hydrophilic functional groups and a small average particle size, their inclusion in the active layer greatly contributes to improving the crystallinity of the active layer while ensuring its insulating properties.

[0026] The carbon nanotubes preferably have a length of 1 to 1000 nm, more preferably 10 to 500 nm, and even more preferably 50 to 200 nm. The carbon nanotubes also preferably have an aspect ratio of 0.1:100 to 10:100, more preferably 0.3:100 to 5:100, and even more preferably 0.5:100 to 2:100. The average particle size of the carbon nanotubes can be calculated as the average value in the longitudinal and transverse directions. When carbon nanotubes of the above preferred shape are incorporated into the active layer, they have good dispersibility and can ensure better insulation of the layer.

[0027] The carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes, and are preferably single-walled carbon nanotubes.

[0028] The electrode layer thickness is preferably 50 to 2000 nm, more preferably 100 to 1000 nm, and even more preferably 250 to 750 nm. Having the electrode layer with the above preferred thickness allows for a better balance of flexibility, low resistance, and excellent surface smoothness in the actuator, which is a multilayer device.

[0029] The thickness of the active layer is preferably 0.1 to 100 μm, more preferably 0.5 to 30 μm, and even more preferably 1 to 10 μm. Having the above preferred thickness of the active layer allows for better film formation when manufacturing the actuator, which is a multilayer device, and also facilitates voltage application (actuator driving).

[0030] This actuator can be manufactured using a coating process and can be easily scaled up to a large area. Preferably, the actuator is 10 mm in diameter. 2 More than 100mm 2 More preferably 300 mm 2 More preferably 3000mm 2 It has the above area. The upper limit of the area of ​​this actuator is not particularly limited, but for example, 100,000 mm² 2Even a moderate area is acceptable. The actuator with the above preferred area may be divided into smaller pieces of actuator having a smaller area.

[0031] The conductive material used in the electrode layer is not particularly limited as long as it is a material that improves the crystallinity of the dielectric layer by mixing with carbon particles having hydrophilic functional groups and is flexible when the electrode layer is formed, but conductive polymers or metal particles are preferred.

[0032] Examples of conductive polymers include polythiophene, polyaniline, polypyrrole, polyacetylene, polycarbazole, polyvinylpyridine, poly(n-vinylcarbazole), polyfluorene, polyphenylene, poly(p-phenylenevinylene), poly(pyridinevinylene), polyquinoxalines, polyquinolines, their derivatives, and mixtures thereof. Among these, polythiophene, polyaniline, polypyrrole, their derivatives, and mixtures thereof can be used due to their high conductivity, and PEDOT:PSS, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS), is particularly preferred because it disperses more easily with carbon particles in polar solvents.

[0033] The metal particles can be Au particles, aluminum particles, silver particles, etc. Preferably, the metal particles have an average particle size of 20 nm or more, 50 nm or more, 100 nm or more, 200 nm or more, or 500 nm or more, and 1000 nm or less, 800 nm or less, 600 nm or less, 500 nm or less, or 300 nm or less. Metal particles having the above preferred average particle size are preferred because they are more easily dispersed together with carbon particles in a polar solvent.

[0034] The crystalline dielectric polymer used in the active layer is a crystalline piezoelectric material whose crystal orientation aligns after being formed by a coating process and then subjected to a heat treatment process. Mixing in carbon particles further enhances the alignment of the crystal orientation. The more aligned the crystal orientation, the easier it is for the material to move in the same direction when an electric field is applied, resulting in a large uniaxial driving force dependent on the applied electric field, improving the actuator's output and thus increasing the amount of displacement.

[0035] The crystalline dielectric polymer used in the active layer preferably has a relative permittivity of 4 to 12, more preferably 5 to 11, and even more preferably 6 to 10. Having the above preferred relative permittivity of the crystalline dielectric polymer makes it possible to obtain actuators that are faster and have higher output.

[0036] The crystalline dielectric polymer used in the active layer preferably has a weight-average molecular weight Mw of 200,000 to 700,000, more preferably 300,000 to 600,000, and even more preferably 400,000 to 500,000. Having the above preferred molecular weight of the crystalline dielectric polymer improves its ferroelectric properties, thereby further increasing the output of the actuator.

[0037] The crystalline dielectric polymer used in the active layer is not particularly limited as long as it is a crystalline polymer that has piezoelectric properties, whose crystallinity is improved when mixed with carbon particles having hydrophilic functional groups, and which is flexible when a dielectric layer is formed. Examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)), and polyvinylidene fluoride-tetrafluoroethylene copolymer.

[0038] This soft actuator has a capacitor structure including electrode layers and active layers between the electrode layers. Figure 22 shows a schematic cross-sectional view of an example of a soft actuator 10 having a capacitor structure including electrode layers 1 and active layers 2 between the electrode layers 1. This soft actuator may have two or more electrode layers and one or more active layers, and may have multiple active layers sandwiched between electrode layers. This soft actuator may also have a substrate 3 as illustrated in Figure 22.

[0039] The substrate that this actuator may incorporate is not particularly limited as long as it is a flexible substrate, and can be a flexible substrate such as polyethylene naphthalate (PEN) or polyimide (PI). The substrate that this actuator may incorporate preferably has a thickness of 10 to 100 μm, more preferably 20 to 80 μm.

[0040] The disclosure also relates to a soft actuator comprising an electrode layer and an active layer between the electrode layers, wherein the active layer comprises a crystalline dielectric polymer and carbon particles having hydrophilic functional groups.

[0041] When the active layer contains a crystalline dielectric polymer and carbon particles having hydrophilic functional groups, the electrode layer is not particularly limited as long as it is made of a material that is conductive and flexible when used to construct the actuator, for example, a metal foil, and may have the electrode layer configuration described above. The metal foil preferably has a thickness of 1 to 500 nm, more preferably 10 to 200 nm. The configuration of the active layer containing carbon particles having hydrophilic functional groups and the overall configuration of the actuator are the same as described above.

[0042] (Method of forming a membrane) The active layer can be formed by preparing a dielectric composition in which hydrophilic functional groups of carbon particles and a crystalline dielectric polymer are dispersed in a polar solvent, and then coating, drying, and heat-treating the dielectric composition. The electrode layer can be formed by preparing an electrode composition in which hydrophilic functional groups of carbon particles and a conductive material are dispersed in a polar solvent, and then coating, drying, and heat-treating the electrode composition. The electrode composition and the dielectric composition can each be in the form of a paste, ink, or the like, which can be applied in the coating process.

[0043] The heat treatment can be carried out, for example, at a temperature of 100°C to 170°C, 110°C to 160°C, 120°C to 150°C, or 125°C to 145°C for 10 minutes to 300 minutes, 20 minutes to 120 minutes, or 30 minutes to 90 minutes.

[0044] A polar solvent is an organic solvent that can dissolve or disperse carbon particles and conductive materials or crystalline dielectric polymers. An organic solution can be prepared by mixing carbon particles and conductive materials or crystalline dielectric polymers in a polar solvent, applied to a substrate, and the organic solvent evaporated to form an electrode film or dielectric film. From the viewpoint of dispersibility, polar solvents such as ketone solvents like acetone, methyl ethyl ketone, and cyclohexanone; ester solvents like ethyl acetate and trimethyl phosphate; ether solvents like tetrahydrofuran and dioxane; N-methyl-2-pyrrolidone (NMP), acetonitrile, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide are preferred.

[0045] The active layer may further contain other materials to the extent that it does not substantially inhibit its function as an active layer, but from the viewpoint of obtaining ferroelectricity, the active layer is preferably formed by mixing only a polar solvent and a crystalline dielectric polymer. The electrode layer may further contain other materials to the extent that it does not substantially inhibit its function as an electrode layer. In forming the electrode layer, the polar solvent may further contain a binder, plasticizer, etc. Examples of binders include natural rubber, polyisoprene rubber, styrene-butadiene rubber, styrene-butadiene thermoplastic elastomer, styrene-isoprene thermoplastic elastomer, polybutadiene thermoplastic elastomer, polybutadiene thermoplastic elastomer, polybutadiene rubber, chloroprene rubber, butyl rubber, halogenated butyl rubber, acrylonitrile butadiene rubber, acrylonitrile-butadiene-isoprene rubber, ethylene-propylene rubber, chlorosulfonated polyethylene rubber, acrylic rubber, urethane rubber, silicone rubber, fluororubber, etc. By including such a binder in the electrode layer, the flexibility of the electrode layer can be improved.

[0046] The polar solvent may contain carbon particles and a conductive material or crystalline dielectric polymer simultaneously, or it may contain carbon particles first, followed by sequentially mixing in the conductive material or crystalline dielectric polymer, or it may contain a polar solvent, a conductive material or crystalline dielectric polymer, followed by sequentially mixing in the carbon particles. For example, when forming an electrode layer, the electrode composition may be prepared by mixing carbon particles with a polar solvent such as N-methyl-2-pyrrolidone (NMP), followed by mixing in a conductive material such as PEDOT:PSS. For example, when forming an active layer, the dielectric composition may be prepared by mixing carbon particles with a polar solvent such as N-methyl-2-pyrrolidone (NMP), followed by mixing in a crystalline dielectric polymer such as P(VDF-TrFE).

[0047] In one example, an electrode film can be formed by coating an electrode composition onto a flexible substrate. A dielectric film can be formed by coating and drying a dielectric composition onto a flexible substrate. A laminate of electrode film and dielectric film can be obtained by placing a dielectric film peeled off from the flexible substrate onto the electrode film formed on the flexible substrate. Alternatively, a dielectric film formed on the flexible substrate can be transferred onto an electrode film formed on the flexible substrate, and then the dielectric film can be peeled off the flexible substrate to obtain a laminate of electrode film and dielectric film. A laminate of electrode film and dielectric film with a desired number of layers can be obtained by repeating the same method. The actuator can be manufactured by heat-treating the obtained laminate.

[0048] Alternatively, a dielectric film may be formed on an electrode film formed on a flexible substrate by a coating method to obtain a laminate of electrode film and dielectric film. A similar method may be repeated to obtain a laminate of electrode film and dielectric film with a desired number of layers. The obtained laminate can then be heat-treated to fabricate the actuator.

[0049] The method for coating the electrode film and dielectric film can be any conventional method, such as spin coating, printing (screen printing, inkjet printing, gravure printing, etc.), dispenser coating, spray coating, dip coating, die coating, roll coating, bar coating, blade coating, etc.

[0050] According to the above process, multiple actuators may be fabricated on a substrate, and one or more actuators may be cut out from the substrate. When voltage is applied to the actuators cut out from the substrate, they will operate as actuators. When multiple actuators are fabricated on a substrate, each actuator may be continuous or separated from each other. [Examples]

[0051] (Example 1) (Preparation of electrode composition) Graphene oxide (GO) particles (manufactured by Tokyo Chemical Industry Co., Ltd., G0443) were crushed in a mortar and sieved to prepare graphene oxide particles with an average particle size of 500 nm and a maximum particle size of 5 μm. The graphene oxide particles contained approximately 0.4 mmol / g of hydrophilic functional groups, namely hydroxyl and carboxyl groups.

[0052] A mixture was obtained by mixing 1% by mass of prepared graphene oxide particles with N-methyl-2-pyrrolidone (NMP), a polar solvent. Next, an electrode composition was prepared by mixing the conductive material PEDOT:PSS (Heraeus, Clevios SV4) with the mixture in a mass ratio of (PEDOT:PSS):mixture = 99:1. That is, the content of graphene oxide particles relative to PEDOT:PSS in the prepared electrode composition was 0.01% by mass.

[0053] (Preparation of dielectric composition) A dielectric composition was prepared by mixing N-methyl-2-pyrrolidone (NMP) with P(VDF-TrFE) (Arkema Corporation, FC25).

[0054] (Fabrication of soft actuators) A 50 μm thick PEN substrate (Teijin Limited, Teonex Q65HA) was prepared as a flexible substrate. The prepared electrode composition was applied to the PEN substrate by screen printing and then dried to form an electrode film. The prepared dielectric composition was applied to the formed electrode film by screen printing and then dried to form a dielectric film. Furthermore, the prepared electrode composition was applied to the formed dielectric film by screen printing and then dried to form an electrode film, thereby forming a laminate on the PEN substrate with a three-layer capacitor structure consisting of electrode film / dielectric film / electrode film.

[0055] The formed laminate was heat-treated at 135°C for 1 hour to fabricate a soft actuator comprising a lower electrode layer containing graphene oxide with a thickness of 300 nm, an active layer (driving layer) with a thickness of 4.5 μm, and an upper electrode layer containing graphene oxide with a thickness of 300 nm. The fabricated soft actuator had a thickness of 654.5 μm, a width of 10 mm, a length of 30 mm, and an area of ​​300 mm². 2 Figure 1 shows photographs of the appearance of several soft actuators fabricated on a polyethylene naphthalate (PEN) substrate.

[0056] (Example 2) (Preparation of electrode composition) The electrode composition was prepared in the same manner as in Example 1, except that the electrode layer was formed using only PEDOT:PSS, which was used in Example 1, without using graphene oxide particles.

[0057] (Preparation of dielectric composition) Single-walled carbon nanotube (CNT) particles (Sigma-Aldrich, 900711) were prepared. The single-walled carbon nanotube particles had an average length of 100 nm, an average length of 1 nm, an average particle size of 55.5 nm, and a maximum particle size of 300 nm, and were equipped with hydrophilic functional groups of hydroxyl and carboxyl groups.

[0058] A dielectric composition was prepared by mixing N-methyl-2-pyrrolidone (NMP) with the same P(VDF-TrFE) used in Example 1, and then mixing it with the prepared single-walled carbon nanotube particles. The mass ratio of single-walled carbon nanotube particles to P(VDF-TrFE) in the prepared dielectric composition was 0.075% by mass.

[0059] (Fabrication of soft actuators) In the same manner as in Example 1, a soft actuator was fabricated on a PEN substrate, which included a lower electrode layer having a thickness of 300 nm / an active layer (driving layer) containing single-walled carbon nanotubes and having a thickness of 4.5 μm / an upper electrode layer having a thickness of 300 nm. The fabricated soft actuator had a thickness of 654.5 μm, a width of 10 mm, and a length of 30 mm, and the area was 300 mm 2 was obtained.

[0060] (Example 3) An electrode composition was prepared in the same manner as in Example 1, a dielectric composition was prepared in the same manner as in Example 2, and in the same manner as in Example 1, on a PEN substrate, a lower electrode layer containing graphene oxide and having a thickness of 300 nm / an active layer (driving layer) containing single-walled carbon nanotubes and having a thickness of 4.5 μm / an upper electrode layer containing graphene oxide and having a thickness of 300 nm was provided to fabricate a soft actuator. The fabricated soft actuator had a thickness of 654.5 μm, a width of 10 mm, and a length of 30 mm, and the area was 300 mm 2 was obtained.

[0061] (Comparative Example 1) In the same manner as in Example 2, an electrode composition was prepared with PEDOT:PSS without containing carbon particles, and in the same manner as in Example 1, a dielectric composition was prepared with P(VDF-TrFE) without containing carbon particles. Then, in the same manner as in Example 1, a soft actuator having a lower electrode layer with a thickness of 300 nm / an active layer (driving layer) with a thickness of 4.5 μm / an upper electrode layer with a thickness of 300 nm was fabricated on a PEN substrate.

[0062] (Displacement Measurement) At a position 2 mm around the fabricated soft actuator, the soft actuator together with the PEN film was cut out. As shown in Figure 2, while irradiating the tip region of the soft actuator with a laser using a laser displacement meter, a probe was applied to the electrodes of the soft actuator to apply a voltage, and the movement of the laser irradiation part of the soft actuator was measured as the displacement amount. As shown in Figure 3, the displacement amount was measured as the absolute value of the difference between the maximum value and the minimum value of the displacement.

[0063] Figure 4 shows the displacement measurements for the soft actuator fabricated in Comparative Example 1 when an electric field ranging from 10 to 100 MV / m was applied at an application frequency of 1 Hz every 10 MV / m. Similarly, Figures 5 to 7 show the displacement measurements for the soft actuators fabricated in Examples 1 to 3 when an electric field ranging from 10 to 100 MV / m was applied at an application frequency of 1 Hz every 10 MV / m.

[0064] (Measurement of residual polarization) The remanent polarization values ​​were measured for the soft actuators fabricated in Examples 1-3 and Comparative Example 1. Figure 8 shows the remanent polarization value (μC / cm²) with the electric field (MV / m) on the horizontal axis. 2 The hysteresis curve with the field strength (MV / m) on the horizontal axis is shown. The remanent polarization values ​​when the electric field is 0 (MV / m) are shown in the table below. It was shown that the remanent polarization value improved by 1.5 to 2.0 times when the active layer, electrode layer, or both contain carbon particles. The soft actuators fabricated in Examples 1 to 3 have large remanent polarization values, suggesting improved actuation performance.

[0065] [Table 1]

[0066] (Drivability evaluation: Relationship between electric field and displacement) The relationship between electric field and displacement was measured for the soft actuators fabricated in Examples 1-3 and Comparative Example 1. Figure 9 shows a graph with the applied electric field (MV / m) on the horizontal axis and the displacement (mm) on the horizontal axis. From the graph in Figure 9, it can be seen that for all the soft actuators fabricated in Examples 1-3 and Comparative Example 1, the displacement increased as the electric field increased up to about 50 (MV / m). However, among them, the actuators fabricated in Examples 1-3 had a larger displacement than the soft actuator fabricated in Comparative Example 1, even at the same electric field.

[0067] (Drivability evaluation: Relationship between residual polarization value and displacement) Figure 10 shows a graph illustrating the relationship between displacement and residual polarization value when an electric field of 100 MV / m is applied to the soft actuators fabricated in Examples 1-3 and Comparative Example 1. Figure 10 summarizes the data from Figures 8 and 9. It can be seen that the displacement of the soft actuators fabricated in Examples 1-3 and Comparative Example 1 increases in proportion to the residual polarization value.

[0068] (Intermolecular force microscopy observation) Figures 11 and 12 show molecular force microscope (AFM) images of the dielectric film formed in Example 1 using only P(VDF-TrFE) after heat treatment, and the dielectric film formed in Example 2 using P(VDF-TrFE) mixed with single-walled carbon nanotubes after heat treatment, respectively. Figures 13 and 14 show molecular force microscope (AFM) images of the electrode film formed in Example 2 using only PEDOT:PSS after heat treatment, and the electrode film formed in Example 1 using PEDOT:PSS mixed with graphene oxide after heat treatment, respectively. Compared to the dielectric film of P(VDF-TrFE) alone, the dielectric film of P(VDF-TrFE) mixed with single-walled carbon nanotubes had thicker fibrous structures and a higher overall density. Similarly, compared to the electrode film of PEDOT:PSS alone, the electrode film of PEDOT:PSS mixed with graphene oxide had thicker fibrous structures and a higher overall density.

[0069] (Observation with an optical microscope) Figures 15 and 16 show optical microscope images of the dielectric film formed in Example 1 using only P(VDF-TrFE) after heat treatment, and the dielectric film formed in Example 2 using P(VDF-TrFE) mixed with single-walled carbon nanotubes after heat treatment, respectively. Figures 17 and 18 show optical microscope images of the electrode film formed in Example 2 using only PEDOT:PSS after heat treatment, and the electrode film formed in Example 1 using PEDOT:PSS mixed with graphene oxide after heat treatment, respectively. More black particles of single-walled carbon nanotubes were observed in the dielectric film of P(VDF-TrFE) mixed with single-walled carbon nanotubes than in the dielectric film of P(VDF-TrFE) alone. Also, more black particles of graphene oxide were observed in the electrode film of PEDOT:PSS mixed with graphene oxide than in the electrode film of PEDOT:PSS alone.

[0070] (Evaluation of high-speed operation) Figure 19 shows the relationship between the applied frequency and the measured frequency for the soft actuators fabricated in Example 1 and Comparative Example 1. Figure 20 shows the relationship between the applied frequency and the amount of displacement for the soft actuators fabricated in Example 1 and Comparative Example 1. The soft actuator fabricated in Comparative Example 1 only tracked up to 50 Hz, but the soft actuator fabricated in Example 1 tracked up to 70 Hz, confirming its high-speed operation.

[0071] (Flexibility evaluation - Electrical properties evaluation while bending) For the soft actuator fabricated in Example 3, the ferroelectric properties were measured both in its original state and when attached to a circular base. The original state (before bending) was defined as Strain 0%, and the actuator was attached to circular bases with different radii of curvature and bent within the strain range of Strain 0 to 1%. The strain was calculated from the radius of curvature of the circular base using the approximate formula: Strain = 2R / d (R is the radius of curvature, d is the substrate thickness). Compared to the ferroelectric properties of 100% at Strain 0%, 90% of the ferroelectric properties were obtained at Strain 1%, indicating that the ferroelectric properties were substantially maintained even when bent.

[0072] (Cross-sectional SEM observation of a soft actuator) Figure 21 shows a cross-sectional SEM image of the soft actuator fabricated in Example 3. The soft actuator 10 includes an active layer 2 between the lower electrode layer 1 and the upper electrode layer 1 on the flexible substrate 3.

[0073] (Example 4) A dielectric composition was prepared in the same manner as in Example 2. The prepared dielectric composition was applied to a PEN substrate by screen printing and then dried to form a dielectric film. The formed dielectric film was heat-treated at 135°C for 1 hour to obtain a dielectric layer (active layer) with a thickness of 4.5 μm. Aluminum layers with a thickness of 30 nm were formed above and below the obtained dielectric layer as electrode layers by resistance heating vacuum deposition to fabricate a soft actuator. When the ferroelectric properties were evaluated, substantially the same properties as in Example 2 were confirmed. [Explanation of symbols]

[0074] 10 Soft Actuators 1 electrode layer 2 Active layer 3 circuit boards

Claims

1. A soft actuator comprising an electrode layer and an active layer between the electrode layers, The electrode layer includes a conductive material, The active layer comprises a crystalline dielectric polymer. The electrode layer comprises graphene oxide having hydrophilic functional groups, and the active layer comprises carbon nanotubes having hydrophilic functional groups. The electrode layer contains 0.0005 to 0.5% by mass of graphene oxide, and the active layer contains 0.01 to 0.1% by mass of carbon nanotubes. Soft actuator.

2. 10mm ２ The soft actuator according to claim 1, having the above area.

Images