Conductive nanofilms and dielectric elastomer actuators using them

Abstract

To provide an electric conductive nano thin film with excellent flexibility while securing electric conductivity, and good elasticity in a thickness and a surface direction, and good conformability to body curvature and shape deformation, and a dielectric elastomer actuator using the film.SOLUTION: The electric conductive nano thin film according to the present invention includes an elastomer layer, and a carbon nanotube layer stacked on at least one side thereof, wherein a film thickness is less than 1,000 nm. The dielectric elastomer actuator according to the present invention comprises the electric conductive nano thin film as an electrode.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a conductive nano thin film and a dielectric elastomer actuator using the same.

Background Art

[0002] In recent years, many reports have been made on the development of tactile devices that present a sense of touch or detect contact with an object by applying a mechanical stimulus to human sensory receptors to wearable devices. Generally, since these devices use a substrate or a fixing jig that is harder and thicker than the skin, they have low followability to body curves and shape deformations, and there is an urgent need to improve the followability to curves by reducing the bending rigidity of the device, that is, improving the flexibility.

[0003] If a conductive ultra-thin film with low bending rigidity can be produced as a self-supporting electrode film, a wearable biological device with high followability to body curves and less sense of restraint can be realized.

[0004] A dielectric elastomer actuator (DEA) is a technology that uses a rubber-like polymer (elastomer) as a material. It has a simple structure in which the elastomer is sandwiched between electrodes that can be stretched and contracted. By applying a potential difference between the upper and lower electrodes, the electrostatic force (Coulomb force) generated causes both electrodes to attract each other. As a result, the elastomer contracts in the thickness direction and expands in the plane direction. Applications to devices such as robots used as artificial muscles, sensors, and power generation have been studied (Non-Patent Documents 1 to 3).

[0005] Non-Patent Document 2 discloses a conductive thin film formed on the surface of a polydimethylsiloxane (PDMS) sheet with a film thickness of 1.4 μm by the Langmuir-Schaefer method using a mixed solution of a conductive polymer (polythiophene) and multi-walled carbon nanotubes (MWCNT).

[0006] Non-patent document 3 discloses a conductive thin film formed by using chemically modified single-walled carbon nanotubes to create a molecular layer on the surface of a 6.5 μm thick PDMS sheet using the Langmuir-Schaefer method. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Journal of the Japan Society for Precision Engineering Vol.80, No.8, 713-717(2014). [Non-Patent Document 2] X. Ji et al., Sensors and Actuators B 261 135-143(2018). [Non-Patent Document 3] Ji et al., Sci. Robot. 4, eaaz6451(2019). [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, as described in Non-Patent Document 2, using a conductive polymer in the electrode film reduces flexibility, limiting the expansion and contraction of the PDMS in the thickness and surface directions, and resulting in reduced conformability to body curves and shape deformations. Similarly, as described in Non-Patent Document 3, when the PDMS is a thick film on the micron scale, there are further issues that need to be improved in terms of flexibility. In particular, for applications in dielectric elastomer actuators, there has been a need for conductive nanofilms that are highly flexible while ensuring good conductivity.

[0009] This invention has been made in view of the above circumstances, and aims to provide a conductive nanofilm that is highly flexible while ensuring conductivity, and exhibits good stretchability in the thickness direction and surface direction, as well as good conformability to curved surfaces and shape deformation of the body, and a dielectric elastomer actuator using the same. [Means for solving the problem]

[0010] To solve the above problems, the inventors conducted diligent research and, as a result, attempted to form a carbon nanotube layer as a conductive layer on an elastomer sheet with a thickness of nanoscale. They confirmed that it possesses self-supporting properties, and found that such a conductive nanofilm with a thickness of less than 1000 nm has excellent flexibility while ensuring good conductivity, thus completing the present invention. For example, when used as a dielectric elastomer actuator, it exhibits large displacement and shrinkage rates in response to applied voltage, enabling operation at low voltages.

[0011] In other words, the following invention is disclosed. [1] A conductive nanofilm comprising an elastomer layer and a carbon nanotube layer laminated on at least one of its surfaces, with a film thickness of less than 1000 nm. [2] The conductive nanofilm of [1] having a Young's modulus of 50 MPa or more and 200 MPa or less.

[0012] [3] The conductive nanofilm according to [1] or [2], wherein the ratio of the thickness T2 of the carbon nanotube layer to the thickness T1 of the elastomer layer is 0.01 or more and 1.85 or less. [4] A conductive nanofilm from any one of the above [1] to [3], wherein the carbon nanotube is a single-walled carbon nanotube. [5] A self-supporting conductive nanofilm of any one of the above [1] to [4]. [6] A dielectric elastomer actuator comprising one of the conductive nanofilms described in [1] to [5] above as an electrode. [7] The dielectric elastomer actuator of [6], which is a laminate in which one or more conductive nanofilms and one or more elastomer substrates are alternately laminated. [Effects of the Invention]

[0013] According to the conductive nanothin film of the present invention, by applying a carbon nanotube layer as a conductive layer to the elastomer layer, excellent flexibility is ensured while ensuring conductivity, and the film can stretch and contract in the thickness and surface directions, and has good followability to body curves and shape deformations. The dielectric elastomer actuator of the present invention can be driven at a low voltage by laminating the conductive thin film and the dielectric layer.

Brief Description of the Drawings

[0014] [Figure 1] Photographs of self-supporting nanothin films with a tape frame, where (a) is an SBS sheet and (b) is a SWCNT-SBS sheet. [Figure 2] Graphs showing (a) the state of stretching the wrist with the SWCNT-SBS nanothin film attached, (b) the state of bending the wrist, (c) each photograph of the attached part, and (d) the resistivity dependence on the number of bending cycles in a bending test. [Figure 3] Photograph of (a) the SWCNT-SBS nanothin film connected to the forearm and (b) the result of sEMG measurement using the SWCNT-SBS nanothin film. [Figure 4] Graph showing the dependence of the Young's modulus and sheet resistance value on the thickness of the SWCNT layer in the SWCNT-SBS nanothin film. [Figure 5] Figure showing the schematic configuration of a laminated dielectric elastomer actuator using the SWCNT-SBS nanothin film, together with the displacement measurement scheme using a microscope. [Figure 6] Graph showing the dependence of the displacement and contraction strain of a laminated dielectric elastomer actuator using SWCNT-SBS nanothin films with different thicknesses on the applied voltage. [Figure 7] Photographs showing (a) a laminated dielectric elastomer actuator using the SWCNT-SBS nanothin film and (b) the state of attaching it to the index finger. [Figure 8] Graph showing the dependence of the displacement and contraction strain of a laminated dielectric elastomer actuator using PDMS layers with different thicknesses on the applied voltage. [Figure 9] It is a graph showing the dependence of the applied voltage at a displacement of about 8 μm on the thickness of the PDMS layer in a laminated dielectric elastomer actuator. [Figure 10] It is a graph showing the dependence of the displacement and the shrinkage strain of a laminated dielectric elastomer actuator with different substrate rigidities on the applied voltage.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, specific embodiments of the present invention will be described.

[0016] In the present invention, for the film thickness of the conductive nano-thin film, and the thicknesses of the carbon nanotube layer and the elastomer layer, the average value determined by the step difference between the support substrate and the film to be measured using a measuring instrument such as a cross-sectional profiler is considered.

[0017] The conductive nano-thin film of the present invention includes an elastomer layer and a carbon nanotube layer laminated on at least one surface thereof.

[0018] The conductive nano-thin film of the present invention has a film thickness of less than 1000 nm. Preferably 800 nm or less, more preferably 700 nm or less, still more preferably 600 nm or less, particularly preferably 500 nm or less, and most preferably 200 nm or less. The lower limit of the film thickness is not particularly limited, but is preferably 50 nm or more. When the film thickness is small, it is excellent in flexibility, has good stretchability in the thickness direction and the plane direction, and good followability to body curved surfaces and shape deformations. When the film thickness is appropriate, it has self-supporting properties and can ensure strength.

[0019] The material of the elastomer layer in the conductive nano-thin film of the present invention is not particularly limited. Polymers having elasticity, such as thermoplastic or thermosetting elastomers, can be used.

[0020] Specifically, examples include styrene-based elastomers, silicone-based elastomers, olefin-based elastomers, urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, acrylic elastomers, and rubber-modified epoxy resins. These may be used individually or in combination of two or more types.

[0021] Examples of styrene-based elastomers include styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-propylene-styrene block copolymer (SEPS, a hydrogenated version of SIS), styrene-ethylene-propylene block copolymer (SEP, a hydrogenated version of styrene-isoprene block copolymer), and styrene-isobutylene-styrene block copolymer (SIBS).

[0022] Silicone elastomers are mainly composed of organopolysiloxanes, such as polydimethylsiloxanes, polymethylphenylsiloxanes, and polydiphenylsiloxanes. They may also be partially modified with vinyl groups, alkoxy groups, etc. Thin films of organopolysiloxanes can be obtained, for example, by treating a main component containing a siloxane compound with a curing agent to polymerize and / or crosslink it. Depending on the type of main reactive group of the main component, if the main component has a hydrosilyl group as its main reactive group, a compound having an alkenyl group can be used as the curing agent, and if the main component has an alkenyl group as its main reactive group, a compound having a hydrosilyl group can be used as the curing agent.

[0023] Examples of olefin-based elastomers include copolymers of α-olefins having 2 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 1-hexene, and 4-methylpentene. Specific examples include ethylene-propylene copolymer (EPR), ethylene-propylene-diene copolymer (EPDM), copolymers of α-olefins with non-conjugated dienes having 2 to 20 carbon atoms, such as dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylenenorbornene, ethylidenenorbornene, butadiene, and isoprene, and carboxylated NBR obtained by copolymerizing butadiene-acrylonitrile copolymer with methacrylic acid.

[0024] Examples of urethane elastomers include those composed of structural units consisting of a hard segment made of a low molecular weight glycol and diisocyanate, and a soft segment made of a high molecular weight (long chain) diol and diisocyanate.

[0025] Examples of polyester elastomers include those obtained by polycondensation of dicarboxylic acids or their derivatives and diol compounds or their derivatives, and in particular, those obtained by copolymerizing a polyester structure with a polyether structure.

[0026] Examples of polyamide elastomers include polyether block amide types and polyether ester block amide types, which use polyamide for the hard segment and polyether or polyester for the soft segment.

[0027] Acrylic elastomers primarily consist of acrylic acid esters, with ethyl acrylate, butyl acrylate, methoxyethyl acrylate, and ethoxyethyl acrylate being commonly used. Glycidyl methacrylate and allyl glycidyl ether can also be used as crosslinking monomers. Furthermore, copolymerization with acrylonitrile and ethylene is also possible. Specifically, examples include acrylonitrile-butyl acrylate copolymers, acrylonitrile-butyl acrylate-ethyl acrylate copolymers, and acrylonitrile-butyl acrylate-glycidyl methacrylate copolymers.

[0028] Examples of rubber-modified epoxy resins include those obtained by modifying some or all of the epoxy groups of bisphenol F type epoxy resin, bisphenol A type epoxy resin, salicylaldehyde type epoxy resin, phenol novolac type epoxy resin, or cresol novolac type epoxy resin with terminally carboxylic acid-modified butadiene-acrylonitrile rubber, terminally amino-modified silicone rubber, etc. Among these, styrene-based elastomers and silicone-based elastomers can be preferably used.

[0029] The elastomer layer may contain other components, such as known additives, as long as they do not impair the effects of the present invention. Examples of known additives include antioxidants, weather stabilizers, heat stabilizers, lubricants, nucleating agents, ultraviolet absorbers, colorants, surfactants, and fillers. These may be used individually or in combination of two or more.

[0030] The thickness of the elastomer layer depends on the total thickness of the conductive nanofilm and the carbon nanotube layer, but is preferably 750 nm or less, more preferably 500 nm or less, and even more preferably 200 nm or less. It is also preferably 30 nm or more. A small thickness provides excellent flexibility, good stretchability in the thickness direction and surface direction, and good conformability to body curves and shape deformation. A moderate thickness provides self-supporting properties and ensures strength.

[0031] In the conductive nanofilm of the present invention, the carbon nanotube layer becomes a conductive layer and functions as an electrode film or the like. Examples of materials constituting the carbon nanotube layer include single-walled carbon nanotubes (SWCNTs), which have a structure of a single graphene sheet, multi-walled carbon nanotubes (MWCNTs), which are composed of multiple graphene sheets, fullerene tubes, bucky tubes, graphite fibrils, etc. These may be chemically modified to increase their affinity for solvents, or they may be concentrated from a mixture of metallic carbon nanotubes and semiconducting carbon nanotubes.

[0032] Among these, single-walled carbon nanotubes are preferred due to their excellent flexibility as conductive nanofilms, their ability to stretch and contract in the thickness and surface directions, and their good conformability to curved surfaces and shape deformations of the body. The carbon nanotube layer may contain other components, such as carbon nanotube dispersants, to the extent that they do not impair the effects of the present invention.

[0033] The thickness of the carbon nanotube layer depends on the total thickness of the conductive nanofilm and the thickness of the elastomer layer, but is preferably 250 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. It is also preferably 10 nm or more. When the carbon nanotube layer is laminated on both sides of the elastomer layer, the thickness here is the sum of the carbon nanotube layers on both sides. A small thickness provides excellent flexibility, good stretching and contraction in the thickness direction and surface direction, and good conformability to body curves and shape deformation. An appropriate thickness ensures conductivity.

[0034] The conductive nanofilm of the present invention preferably has a Young's modulus of 50 MPa to 200 MPa. A Young's modulus within this range exhibits excellent flexibility, allowing for good expansion and contraction in the thickness and surface directions, as well as good conformity to curved surfaces and shape deformations of the body.

[0035] The conductive nanofilm of the present invention preferably has a ratio of the thickness T2 of the carbon nanotube layer to the thickness T1 of the elastomer layer of 0.01 to 1.85, more preferably 0.05 to 1.85. When the carbon nanotube layer is laminated on both sides of the elastomer layer, the thickness of the carbon nanotube layer here refers to the sum of the carbon nanotube layers on both sides. A small ratio results in excellent flexibility, good stretchability in the thickness and surface directions, and good conformability to body curves and shape deformations. A moderately large ratio ensures conductivity.

[0036] The conductive nanofilm of the present invention is not particularly limited in its sheet shape or size. It may be adapted to the intended use, for example, to bio-attachable electrodes, wearable bio-devices such as tactile devices, dielectric elastomer actuators, etc. The carbon nanotube layer may be partially formed within the plane of the elastomer layer, or for example, the carbon nanotube layer may be patterned within the plane of the elastomer layer.

[0037] The conductive nanofilm of the present invention is not particularly limited in its manufacturing method, but can be manufactured using known film-forming methods such as the roll-to-roll method using a gravure coater. For example, using a gravure coater, an aqueous solution of polyvinyl alcohol (PVA) to serve as a sacrificial layer is applied to a polyethylene terephthalate (PET) film, and then dried to form a PVA layer. Next, a solution to form an elastomer layer, such as a tetrahydrofuran solution of SBS, is applied to this PVA layer and dried to form a second layer. This creates a laminated film in which the first and second layers are laminated. Furthermore, a solution to form a carbon nanotube layer, such as an aqueous dispersion of SWCNTs, is applied and dried to form a third layer. This creates a laminated film in which the first, second, and third layers are laminated. Then, paper tape is applied to the surface where the third layer has been formed to outline the desired shape, and by peeling it off from the edge, the three-layer film containing the first, second, and third layers is peeled off from the PET film while being held by the paper tape. The three-layer film held by the obtained paper tape is suspended on pure water with the PVA surface in contact with it. This dissolves only the first PVA layer, yielding a conductive nanofilm consisting of the elastomer layer and carbon nanotube layer held by the paper tape. The paper tape holding this conductive nanofilm can be cut into the desired shape and used, and may be attached to a separate substrate as needed.

[0038] The conductive nanofilm of the present invention is self-supporting, and by applying a carbon nanotube layer as a conductive layer to an elastomer layer, a conductive nanofilm with excellent flexibility while ensuring good conductivity can be obtained. Therefore, it can be suitably used in wearable biodevices such as bio-adhesive electrodes and tactile devices, dielectric elastomer actuators and artificial muscles using them, robots, soft robotics technology, and the like.

[0039] The dielectric elastomer actuator of the present invention is equipped with the conductive nanofilm described above as an electrode. The dielectric elastomer actuator comprises at least one elastomer substrate and at least one pair of electrode films sandwiching this elastomer substrate. A stretchable conductive nanofilm of the present invention is used as at least one electrode film.

[0040] The dielectric elastomer actuator of the present invention works by applying a voltage to electrode films sandwiching an elastomer substrate, thereby creating a potential difference between the upper and lower electrode films. The resulting electrostatic force (Coulomb force) attracts both electrode films, causing the elastomer substrate to contract in the thickness direction and expand in the planar direction.

[0041] The elastomer substrate is in sheet form and is not particularly limited in terms of material, but examples include the example of an elastomer layer of a conductive nanofilm. Among these, silicone-based elastomers are preferably used.

[0042] The thickness of the elastomer substrate is not particularly limited, depending on the number of layers stacked alternately with the electrode film, but is preferably 1 to 1000 μm, and more preferably 10 to 300 μm.

[0043] In a preferred embodiment, the dielectric elastomer actuator is a laminate in which one or more conductive nanofilms of the present invention and one or more elastomer substrates are alternately laminated. This laminate is flexible, has high affinity to curved surfaces of the body, and can be driven at low voltage.

[0044] This laminate can be manufactured, for example, by alternately laminating the conductive thin film of the present invention and an elastomer substrate which is a dielectric layer in a dry process. The number of layers is not particularly limited, but when considering a unit consisting of one conductive thin film and one elastomer substrate, it is preferably 1 to 1000 layers, more preferably 4 to 50 layers.

[0045] The dielectric elastomer actuator of the present invention may be laminated on a substrate. A hard substrate such as glass or a soft substrate such as elastomer can be used as the substrate. Using a soft substrate reduces the constraints on the actuator drive region (electrode overlap region) in contact with the substrate, suppressing in-plane deformation of layers in contact with or near the substrate, and consequently reducing displacement in the film thickness direction. This enables operation at a lower voltage.

[0046] The dielectric elastomer actuator of the present invention can change shape by applying a voltage to the electrode film. The voltage can be applied using a power source such as DC. The power source may be one that modulates the magnitude of the voltage, and may be equipped with means for controlling the voltage in that manner. The method of electrical connection between the electrode film of the dielectric elastomer actuator and the power source is not particularly limited, but in the case of a laminate in which conductive nanofilms and elastomer substrates are alternately laminated, for example, one of adjacent conductive nanofilms can be extended in one direction and the other in the opposite direction, and the extended portions can be connected to wiring with a conductive semi-solid material, thereby connecting one to the anode terminal and the other to the cathode terminal. The applied voltage is not particularly limited, but one example is in the range of 400 to 5000V.

[0047] Figure 5 shows a schematic configuration of an example of the dielectric elastomer actuator of the present invention. This dielectric elastomer actuator (laminated DEA1) is a laminate in which multiple conductive nanofilms 2 of the present invention and multiple or more elastomer substrates (silicone rubber sheets 3) are alternately laminated. The laminated DEA1 is provided on a glass substrate 4. One of the adjacent conductive nanofilms 2,2,... is extended in one direction, and the extended portion is connected to a wiring with a conductive semi-solid material as electrode 5a, and connected to the anode terminal of the power supply 6 via the wiring. The other of the adjacent conductive nanofilms 2,2,... is extended in one direction, and the extended portion is connected to a wiring with a conductive semi-solid material as electrode 5b, and connected to the cathode terminal of the power supply 6 via the wiring. In the stacked DEA1, applying a voltage to electrodes 5a and 5b with a silicone rubber sheet 3 in between creates an electrostatic force (Coulomb force) that generates a potential difference between the upper and lower conductive nanofilms 2,2 acting as a pair of electrode films. This attracts both electrode films, causing the silicone rubber sheet 3 to contract in the thickness direction and displace its shape in the film thickness direction.

[0048] Although the present invention has been described above based on embodiments, the present invention is not limited to these embodiments, and various modifications are possible without departing from the spirit of the invention. [Examples]

[0049] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0050] <Example 1> Fabrication of SWCNT-SBS nanosheets Using the gravure coating method, a conductive nanofilm (SWCNT-SBS nanofilm, hereinafter referred to as nanosheet or sheet) was fabricated by coating a thin layer of single-walled carbon nanotubes (SWCNTs) onto a styrene-butadiene-styrene (SBS) elastomer with an elongation of approximately 300% at cleavage.

[0051] Using a role-to-role gravure coating system (tabletop Mini-Labo test coater, Yasui Seiki), a 5 wt% PVA (Mw22000 Kanto Chemical) aqueous solution was applied to a polyethylene terephthalate (PET) film roll at a microgravure roll (MG) rotation speed of 30 rpm and a substrate feed rate (LS) of 0.8 m / min. A PVA thin film was then obtained on the PET by drying at 80°C using the system's heater. On the obtained PVA thin film, 1, 5, and 10 wt% SBS (Mw280000 Sigma-Aldrich) THF solutions were applied at an MG rotation speed of 30 rpm and an LS of 1.3 m / min (0.8 m / min for 10 wt%). The 1 wt% solution was dried at 80°C, and the 5 and 10 wt% solutions were dried at 40°C using the heater. Furthermore, 1 g / cm³ 3 A water dispersion of SWCNTs (Sigma-Aldrich) was applied to an SBS thin film at an MG rotation speed of 30 rpm and a LS of 0.8 m / min, and dried at 80°C with a heater.

[0052] After film formation, the PVA / SBS / SWCNT sheet was peeled off using the tape frame method (N. Sato et al., Soft Matter, 12 (45), 9202-9209 (2016)), and the PVA layer was removed in a deionized water bath to obtain a self-supporting SWCNT-SBS nanofilm. The SWCNT-SBS nanofilm was attached to a glass substrate, and the film thickness of the SWCNT-SBS nanofilm was measured using a cross-sectional profiler (DektakXT Bruker).

[0053] Figure 1 shows the appearance of SBS nanofilms (sheets) and SWCNT-SBS nanofilms (sheets) fabricated using a 1 wt% SBS solution. The film thicknesses were 33 nm and 94 nm (SWCNT layer thickness 61 nm), respectively, indicating their potential use as self-supporting sheets. For reference, the currently reported film thickness of self-supporting SBS nanosheets is 212 nm. (N. Sato et al., Soft Matter, 12 (45), 9202-9209(2016).)

[0054] <Example 2> Measurement of resistivity of SWCNT-SBS nanosheets The SWCNT-SBS nanothin film prepared in Example 1 was attached to the wrist, and the change in resistance value when bending motions were repeatedly examined. This investigated the adhesion and conformability to curved surfaces of the body, as well as the properties of the SWCNT-SBS nanothin film as a bio-adhesive electrode.

[0055] A SWCNT-SBS nanofilm was attached to the back of the wrist, and the number of repeated wrist flexion and extension movements was performed. The change in resistance value was measured. Photographs of the measurement are shown in Figures 2(a) to (c), and the measurement results are shown in Figure 2(d). The resistance value was measured using the following method: A polyimide film with gold sputtering was attached to the inside of the left wrist with double-sided tape and used as a collecting electrode (Figure 2(c)). The SWCNT-SBS nanosheet was attached with the SWCNT side facing the collecting electrode, covering this collecting electrode. The collecting electrode was connected to an LCR meter (HIOKI, IM3533), and a bending test was performed from 0 to 250 times, with the resistance value sampled every 10 times. The initial resistance value was approximately 2.7 kΩ, and the resistance value increased with increasing number of repetitions. i / R0 increased and remained almost constant after more than 100 cycles. The resistance value at the 250th cycle did not exceed twice the initial resistance value, indicating that conductivity was maintained.

[0056] <Example 3> Surface electromyography measurement of SWCNT-SBS nanofilm We performed electromyography measurements to investigate the effectiveness of SWCNT-SBS nanofilms as wearable biodevice electrodes.

[0057] The SWCNT-SBS nanofilms prepared in Example 1 were folded in half and attached to two locations on the brachioradialis muscle of the right forearm. Electromyography (sEMG) was measured using a surface electromyography (sEMG) recording device (Mwatch, Wada Aircraft Technology Co., Ltd.). During the measurement, the subject repeatedly gripped and released a baseball at approximately 2-second intervals.

[0058] Furthermore, sEMG was measured on the brachioradialis muscle of the right arm using a SWCNT-SBS nanofilm (Figure 3(a)). As reference data, the results measured using a commercially available gel pad electrode (Vitrode F150M Nihon Kohden) are shown in Figure 3(b). The amplitude change of the electromyogram measured with the SWCNT-SBS nanosheet was smaller compared to that of the commercially available electrode, but it was found to be suitable for use as a bio-adhesive electrode.

[0059] <Examples 4-8> Changes in sheet resistance and Young's modulus with respect to film thickness of SWCNT-SBS nanofilm and SWCNT layer thickness. In Example 1, SWCNT-SBS nanofilms and SBS nanofilms were fabricated by changing the SBS concentration, SWCNT concentration, number of SWCNT coatings, gravure roll speed, and heating temperature as shown in Table 1. The total film thickness, SWCNT layer thickness, ratio of the total SWCNT layer thickness T2 to the SBS layer thickness T1, sheet resistance, and Young's modulus were measured. The sheet resistance was measured using the method described above (the resistance value of a roll-shaped SWCNT-SBS nanosheet was measured using the four-probe method with an LCR meter (HIOKI, IM3533), and the sheet resistance was defined as the value obtained by multiplying the resistance value by a correction factor π / ln2). The Young's modulus was measured using the following method. First, a nanosheet was peeled off into a rectangle of 2 cm x 4 cm using a jig made by processing masking tape into a frame shape, and attached to the chuck of a tensile testing machine. Immediately before starting the measurement, the tape frame was cut with scissors to a width of 2.4 cm around the chuck of the tensile testing machine (Shimadzu Corporation, EZ-TEST), and the measurement was started at a scanning speed of 10 mm / min. The results are shown in Table 1.

[0060] [Table 1]

[0061] Figure 4 is a graph showing the dependence of Young's modulus and sheet resistance on the thickness of the SWCNT layer. As the thickness of the SWCNT layer decreases, the sheet resistance decreases, and as the thickness of the SWCNT layer increases, Young's modulus increases, but tends to saturate below 200 MPa.

[0062] <Example 9> 1. Fabrication of a multilayer dielectric elastomer actuator Furthermore, it is an elastomer silicone rubber sheet (Ecoflex) with a low Young's modulus of approximately 100 kPa. TM By combining it with (00-30), we fabricated a multilayer dielectric elastomer actuator (multilayer DEA) that can be driven at low voltage and has high affinity to curved surfaces of the human body.

[0063] Ecoflex TM Solution A and Solution B of 00-30 (Smooth-On, Inc.) were mixed in a 1:1 weight ratio and stirred and defoamed using an Awatori Rentaro (AR-100 THINKYCORPORATION). The resulting precursor solution was spin-coated onto a polystyrene substrate at 500, 1000, and 3000 rpm for 20 seconds (Opticoat MS-B150 MIKASA), and heated on a 70°C hot plate for 1 hour to obtain a silicone rubber sheet.

[0064] A laminated DEA was fabricated by alternately stacking SWCNT-SBS nanofilms obtained in Example 1 and silicone rubber sheets on a glass substrate (Figure 5). The SWCNT-SBS nanofilm (rectangular: 5 × 25 mm) with the PVA layer removed was transferred onto a nylon mesh and attached to a glass substrate or silicone rubber sheet. The same procedure was performed on the silicone rubber sheet (square: 20 × 20 mm) as with the SWCNT-SBS nanofilm. To make the overall thickness of the laminated DEA approximately 1 mm, laminates were fabricated with 50 layers of silicone rubber sheets with a thickness of 12 μm, 10 layers with a thickness of 85 μm, and 4 layers with a thickness of 225 μm.

[0065] 2. Voltage application test of stacked DEA The fabricated multilayer DEA was placed in a wiring fixing jig and connected to the anode and cathode terminals of a high-voltage power supply (M10-HV5000A MCPJapan). The applied voltage was modulated in the range of 400 to 5000V, and the displacement behavior in the film thickness direction at each voltage was recorded using a microscope (L-835 HOZAN, MS-Z35D Asahikogaku). Image analysis was used to calculate the amount of displacement when the voltage was applied (ON) compared to when the voltage was removed (OFF) (Figure 5).

[0066] 2-1. Dependence of Displacement Amount of Multilayer DEA on Film Thickness of SWCNT-SBS Nanofilms with Relevant Voltage To investigate the effect of the elastic force of the electrode film on the deformation behavior of the DEA, a 10-layer laminated DEA was fabricated by combining a silicone rubber sheet with a thickness of approximately 95 μm with SWCNT-SBS nanofilms of different thicknesses (94, 566, and 10500 nm: fabricated using the method described in Example 1) (CNT94, CNT566, CNT10500). Furthermore, a tensile test performed on the 566 nm SWCNT-SBS nanosheet revealed a Young's modulus of 89.1 ± 11.5 MPa. Figure 6 shows the displacement amount with respect to the applied voltage and the shrinkage rate considering the actuator thickness. Interestingly, the displacement amount for CNT94 at an applied voltage of 2000 V was 19 μm, while the displacement amounts for CNT566 and 10500 at the same applied voltage were 7 μm and 3 μm, respectively. This is thought to be because the elastic force increased with increasing electrode film thickness, inhibiting the deformation of the laminated DEA. Furthermore, the applied voltages for displacements of 2-3 μm were 1000, 1700, and 2000 V for CNT94, 566, and 10500, respectively, indicating that the applied voltage decreases as the film thickness decreases.

[0067] 2-2. Dependence of Displacement Amount of Laminated DEA on Film Thickness of Silicone Rubber Sheet with Applied Voltage DEAs with silicone rubber sheet thicknesses of 12 μm, 85 μm, and 225 μm were designated Eco12, Eco85, and Eco225, respectively. Figure 7(a) shows the appearance of a DEA (Eco85) fabricated by alternately layering 10 silicone rubber sheets with a thickness of 85 μm and 11 SWCNT-SBS nanofilms with a thickness of 352 nm. Here, the number of layers is 10. As shown in Figure 7(b), it was found that it can be attached to curved surfaces of the body such as the index finger. Figure 8 shows the displacement amount with respect to the applied voltage and the shrinkage rate considering the thickness of the actuator. In Eco225, when an applied voltage of 3000 V, a displacement of 8 μm and a shrinkage rate of 0.9% were observed. On the other hand, when 2000 V was applied to Eco88, a displacement of 9 μm and a shrinkage rate of 0.9% were observed, and when 500 V was applied to Eco12, a displacement of 8 μm and a shrinkage rate of 0.7% were observed. In other words, when comparing with similar displacement and shrinkage rates, it was found that the applied voltage decreased as the film thickness of the silicone rubber sheet decreased (Figure 9). Eco12 was found to exhibit a displacement equivalent to that reported by X. Ji et al. for a 6 μm film thickness (at 450V application, dielectric layer: PDMS elastomer) (X. Ji et al., Adv. Funct. Mater., 2006639(2020).). Furthermore, the bending stiffness of the fabricated DEA was calculated to be 1.09 to 557 nN·m, which is equivalent to the value of 1.47 × 10⁻⁶ for 1 mm thick PDMS. 5 10 3 ~10 5 It was found to be twice as small.

[0068] 2-3. Dependence of Displacement Amount on Substrate in Relation to Applied Voltage of Multilayer DEA DEA layers stacked on a substrate deform primarily in the film thickness direction, but it is thought that in-plane deformation also occurs simultaneously in each layer. In this case, it is expected that the in-plane deformation of layers in contact with or close to a rigid substrate will be suppressed, resulting in a reduction in the displacement in the film thickness direction. Therefore, a 1 mm thick silicone rubber substrate (Ecoflex) is used as a flexible substrate. TMThe dependence of displacement on substrate stiffness was investigated using 00-30 sheets. Figure 10 shows the dependence of displacement on applied voltage in laminated DEAs fabricated on glass substrates and silicone rubber substrates. Interestingly, the DEA fabricated on the glass substrate showed a maximum displacement of 23 μm at 2100 V (shrinkage rate 2.3%), while the DEA fabricated on the silicone rubber substrate reached a maximum displacement of 50 μm (shrinkage rate 4.9%). This is thought to be because making the substrate more flexible reduced the constraint on the actuator drive region (electrode overlap region) in contact with the substrate.

[0069] Based on the above, when a new multilayer DEA was fabricated and the displacement was measured on a measurement jig, it was found that the applied voltage decreased as the film thickness of the dielectric elastomer layer (silicone rubber sheet) and the electrode layer (SWCNT-SBS nanofilm) decreased. In other words, by further investigating the configuration of the multilayer DEA, it is expected that the "low voltage drive" condition required for adhesive devices can be realized. [Explanation of Symbols]

[0070] 1: Stacked DEA 2: Conductive nanofilm 3: Silicone rubber sheet 4: Glass substrate 5a, 5b: Electrode 6: Power supply 7: Microscope 8: Microscope Stage 9: Polystyrene block

Claims

1. A conductive nanothin film, which is an electrode film used as an electrode when attached to an surface, It consists of an elastomer layer and a carbon nanotube layer laminated on at least one of its surfaces. The conductive nanofilm is self-supporting and can be attached to surfaces. The thickness of the elastomer layer is 500 nm or less. The thickness of the carbon nanotube layer is 250 nm or less. A conductive nanofilm in which the elastomer layer is a layer in which at least one selected from styrene-based elastomers and silicone-based elastomers is used as the elastomer.

2. The thickness of the elastomer layer is 200 nm or less. The conductive nanofilm according to claim 1, wherein the thickness of the carbon nanotube layer is 50 nm or less.

3. The conductive nanofilm according to claim 1, wherein the conductive nanofilm has a film thickness of 700 nm or less.

4. The conductive nanofilm according to claim 1, wherein the conductive nanofilm has a film thickness of 200 nm or less.

5. A conductive nanofilm according to any one of claims 1 to 4, wherein the Young's modulus is 50 MPa or more and 200 MPa or less.

6. The thickness T of the elastomer layer 1 The thickness T of the carbon nanotube layer relative to the carbon nanotube layer 2 A conductive nanofilm according to any one of claims 1 to 5, wherein the ratio is 0.01 or more and 1.85 or less.

7. The conductive nanofilm according to any one of claims 1 to 6, wherein the carbon nanotube is a single-walled carbon nanotube.

8. A conductive nanothin film according to any one of claims 1 to 7, which is an electrode film attached to a dielectric layer and used as an electrode.

9. A dielectric elastomer actuator comprising a conductive nanofilm as described in any one of claims 1 to 8 as an electrode.

10. The dielectric elastomer actuator according to claim 9, which is a laminate in which one or more conductive nanofilms and one or more elastomer substrates are alternately laminated.

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