Electroactive polymer based devices and methods of making

Abstract

The present application illustrates an electroactive polymer (EAR)-based device (10, 20) comprising: a dielectric layer (13, 23) arranged between two electrode layers (12, 14), the dielectric layer (13, 24) consisting of a stretchable material, the two electrode layers (12, 14) comprising a carbon-based electrically conductive material forming the stretchable layer and a solid oxidant material, the EAP-based device further comprises an additional dielectric layer (11, 15) of the stretchable material arranged on each of the two electrode layers (11, 13) and configured with the dielectric layers (13, 23) to seal each of the two electrode layers (12, 14) therein.

Description

Technical Field

[0001] This invention relates to a device based on an electroactive polymer. The invention further relates to a method for manufacturing an EAP-based device, the use of such a device, and a method for self-cleaning such a device. Background Technology

[0002] Electromechanical power conversion systems using devices based on electroactive polymers (EAP) are disclosed, for example, in WO 2010 / 146457.

[0003] This EAP-based device comprises a dielectric elastomer layer. Electrode layers are arranged on the surface of the dielectric elastomer layer. The EAP-based device can be considered as a variable capacitor whose capacitance varies with the amount of deformation applied to the EAP material layer. Due to external force, the electroactive polymer material can be stretched, which causes the distance between the electrode layers to decrease. When the external force decreases and the electroactive polymer layer relaxes, this distance increases again.

[0004] Energy can be harvested from EAP-based devices by applying charge to the electrode layer with substantially maximum deformation and removing charge with minimal deformation.

[0005] Electrode layers made of metal exhibit plastic deformation and cracking at relatively low tensile rates under elastomeric carrier layers, and deteriorate severely during a relatively low number of tensile cycles. For this reason, carbon-based electrodes exhibiting enhanced tensile properties have emerged as candidates for fabricating EAP-based device layers.

[0006] However, despite the enhanced tensile properties of carbon-based electrodes, localized defects such as bubbles or contamination can exist within the dielectric layer, creating small openings or thinning regions. When exposed to an electric field, dielectric breakdown will occur at low field strengths, causing pinhole defects across the dielectric layer thickness, and particularly causing shortcuts, rendering EAP-based devices unable to harvest energy. Consequently, the devices fail within a timeframe far shorter than their design life. Therefore, the object of the present invention is to provide an EAP-based device having a carbon-based electrode layer, which has improved lifetime and electrical performance during exposure to mechanical cycles with relatively high deformation. Summary of the Invention

[0007] According to a first aspect of the invention, an EAP-based device is disclosed, comprising: a dielectric layer disposed between two electrode layers, the dielectric layer being composed of a stretchable material; the two electrode layers comprising a carbon-based conductive material and a solid oxidant material forming the stretchable layer; the EAP-based device further comprising an additional dielectric layer of the stretchable material disposed on each of the two electrode layers and configured together with the dielectric layer to seal each of the two electrode layers therein. The EAP-based device of the present invention includes composite electrode layers made of strong oxidants and carbon materials, which impart both stretchability and excellent conductivity. Each dielectric layer of the EAP-based device is also stretchable and surrounded by an electrode layer on each side, thereby forming a stack with alternating dielectric and electrode layers to form a capacitor. Due to their high conductivity and stretchability, the electrodes will efficiently conduct current and can be repeatedly stretched together with the dielectric layers. Therefore, the EAP-based device can be used in various flexible electronic components, such as actuators or sensors, and electrical devices. When connected to power electronic devices, EAP-based devices can be used as variable capacitors to harvest energy.

[0008] Furthermore, the electrode layers of EAP-based devices contain solid oxidants, enabling them to self-clean. Upon electrical breakdown, the oxidant-containing electrode layer decomposes, thereby isolating that area from the current and cleaning the electrode in the breakdown region: oxygen integrated in the electrode as a solid is vaporized by the energy delivered by the breakdown and reacts with the carbon material of the electrode layer to form carbon oxide molecules. This removes the volume of the electrode layer near the damaged section of the dielectric layer, thus isolating the short-circuited section from the rest of the EAP-based device. Therefore, the EAP-based device of this invention quickly returns to a working state. The oxygen present in the oxidant can only interact with the electrode layer during breakdown, when it is released from the electrode layer itself by the energy generated by the breakdown, whereas the electrode layer was originally sealed by the dielectric layer to isolate it from ambient air. Therefore, the self-cleaning device has increased lifetime and can operate under high electric fields.

[0009] In an embodiment, the EAP-based device further includes a package that seals the electrode layer and dielectric layer to isolate them from ambient air. By providing the package, any contact with ambient air before breakdown is minimized, providing a substantially oxygen-free, preferably oxygen-free environment for the electrode layer. Therefore, it is ensured that the electrode layer does not come into contact with air before breakdown, which improves self-cleaning.

[0010] In the embodiments, the encapsulation is made of polymeric materials such as silicone (polysiloxane), epoxy resin, or polyurethane. The polymeric material, and particularly silicone, as the outer layer provides excellent protection against shock and stress for EAP-based devices. Furthermore, silicone can withstand extreme temperatures far above 200°C and as low as -60°C without deformation. EAP-based devices are adaptable to a wide range of environments.

[0011] In embodiments, the electrode layers and dielectric layers are encapsulated under vacuum or in a nitrogen atmosphere. These layers can also be encapsulated under nitrogen overpressure. By providing an oxygen-deficient atmosphere to the electrode stack within the package, control over the self-cleaning process is enhanced, where no oxygen partial pressure exists in EAP-based devices prior to dielectric breakdown.

[0012] In this embodiment, a carbon-based conductive material is mixed with a solid oxidant material. Instead of a surface layer comprising an oxidant, a composite electrode layer comprising a mixture of the oxidant and the carbon-based conductive material is included, which promotes the release of oxygen-containing components and vaporization of the electrode layer, thereby creating an isolation region at the site of breakdown.

[0013] In embodiments, the solid oxidant material comprises one or more compounds selected from the group consisting of permanganates, nitrates, dichromates, perborates, and chlorates. Selecting one or more of the solid oxidant materials used to fabricate the electrode layer allows the electrode layer to decompose sufficiently upon dielectric breakdown without requiring additional energy input.

[0014] In embodiments, the solid oxidant material comprises sodium or potassium as a cation of one or more of these compounds. For example, potassium nitrate (KNO3) at a concentration equal to or less than about 10 wt% in the electrode layer provides self-cleaning for EAP-based devices in substantially oxygen-deficient environments. In embodiments, this concentration does not exceed about 10 wt% and the electrode layer has a thickness of less than about 5 micrometers.

[0015] In an embodiment, the EAP-based device further includes at least one stack on at least one additional dielectric layer, the stack having alternating electrode layers comprising a carbon-based conductive material and a solid oxidant material, and a dielectric layer of a stretchable material, the dielectric layer of the stack being configured together with the additional dielectric layer to seal the electrode layers of the stack therein. Such a multilayered device provides multiple capacitors connected in parallel, and thus allows for increased energy harvesting while maintaining self-cleaning properties.

[0016] In an embodiment, the carbon-based conductive material of the electrode layer comprises nanoparticles of at least one of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, or graphene. Such carbon-based conductive materials can provide electrode patterns, including at least one of film electrodes, wire electrodes, or mesh electrodes, thereby providing high flexibility and enhanced deformability of the electrode layer.

[0017] In this embodiment, the stretchable material of the dielectric layer is selected from the group consisting of silicone, rubber, and thermoplastic polyurethane (TPU). Such dielectric layers provide high stretchability, stability, reliability, and high-temperature resistance.

[0018] In this embodiment, the electrode layer further comprises an additive, such as a silane-based coupling agent. An example of a suitable silane-based coupling agent is 3-aminopropyltriethoxysilane. The additive provides enhanced adhesion between the electrode layer and the dielectric layer and improves the mechanical uniformity of the composite electrode layer.

[0019] According to a second aspect of the invention, a method for manufacturing a device based on an electroactive polymer (EAP) is disclosed, the method comprising: providing two or more dielectric layers composed of a stretchable material in a processing volume; disposing an electrode layer made of a carbon-based conductive material on at least one of the two or more dielectric layers, wherein the electrode layer comprises the carbon-based conductive material; covering an exposed surface of at least one of the electrode layers with another dielectric layer made of the stretchable material; adding a solid oxidant material to the carbon-based conductive material of the electrode layer; and, when the electrode layer is disposed on at least one of the two or more dielectric layers, the method is characterized in that it further comprises: maintaining a substantially oxygen-free atmosphere or vacuum in the processing volume; and configuring the dielectric layer to seal one of the electrode layers therebetween. By introducing the oxidant into the carbon material, a self-cleaning electrode layer with high conductivity and compliance is provided.

[0020] In an embodiment, the step of arranging the electrode layer on at least one of the two or more dielectric layers includes spraying a carbon-based dispersion containing a solid oxidant and an additive that promotes adhesion between the electrode layer and the at least one dielectric layer. By utilizing spraying, a (composite) electrode layer with a thickness of less than one micrometer can be fabricated. The thin electrode layer allows for optimal electrode resistivity in the range of several hundred ohms. The dispersion can be readily prepared by diluting a powder or sheet of a carbon-based material in a solvent, further adding an oxidant and dissolving it therein. The mixture is uniformly stirred to obtain a mixed electrode dispersion containing the oxidant. The electrode dispersion is uniformly coated onto one side of the dielectric substrate until the solution evaporates. During solvent evaporation, a carbon / oxidant composite electrode with a uniformly distributed oxidant is formed. This fabrication of the composite electrode is simple and easy to control. In doing so, a carbon / oxidant composite electrode with a uniformly distributed oxidant can be formed. Finally, the adhesion between the electrode layer and the dielectric layer is improved.

[0021] According to a third aspect of the invention, the use of EAP-based devices as described in the first aspect or manufactured according to the second aspect is disclosed. In particular, the stacked electroactive polymer, comprising a deformable dielectric and an oxygen-containing electrode, can be used in a power converter system to convert the mechanical energy of repeatedly moving parts into usable electricity, wherein the EAP-based device is coupled to a power extraction unit. Due to its deformability, the electrode can be used in sheet form or wound into a spiral shape. For example, such a power converter system relates to wave energy converters.

[0022] According to a fourth aspect of the invention, a method for self-cleaning an EAP-based device manufactured according to the first aspect or the third aspect is disclosed. The method includes releasing gaseous oxygen from an electrode layer into a sealed space of the EAP-based device formed by a package, wherein the released gaseous oxygen reacts with a carbon-based material of the electrode to produce, for example, oxygen-based components such as carbon dioxide and / or carbon monoxide. Oxygen participates in the self-cleaning process. Successful self-cleaning of the carbon-based electrode requires oxygen and produces combustion. This allows for successful isolation of dielectric regions damaged during breakdown and allows continued system operation. The repeatability of the self-cleaning process is also guaranteed. Attached Figure Description

[0023] Embodiments of EAP-based devices and methods for manufacturing and using such electrodes will be described in detail with reference to the accompanying drawings by way of non-limiting example. In the drawings: Figure 1 Cross-sectional views of a conventional electroactive polymer structure are shown in both the strained state (solid line) and the unstrained state (dashed outline) during the application of voltage.

[0024] Figure 2A schematic diagram illustrating the problems of existing technologies using conventional electroactive polymer structures is shown.

[0025] Figure 3A A cross-sectional view of a device based on an electroactive polymer according to the present invention is shown.

[0026] Figure 3B A cross-sectional view of a device based on an electroactive polymer according to the present invention is shown.

[0027] Figure 4 A flowchart of a method for manufacturing a device based on an electroactive polymer according to the present invention is shown.

[0028] Figure 5A The chemical process during dielectric breakdown in the EAP-based device according to the present invention is illustrated schematically.

[0029] Figure 5B The self-cleaning of the EAP-based device according to the present invention is illustrated schematically.

[0030] The electrodes and their features are shown schematically and are not drawn to scale. The drawings are for illustrative purposes only and are not intended to limit the scope of the claims. In the drawings, identical or similar elements are indicated by the same reference numerals or numbers. Detailed Implementation

[0031] Figure 1 A cross-sectional view of a conventional electroactive polymer layer structure 1 is shown in both a strained state (solid line) and an unstrained state (dashed outline) under an applied voltage (not shown). Structure 1 includes a dielectric elastomer layer 3 sandwiched between two stretchable electrode layers 2 and 4. The electroactive polymer layer structure can be used as a variable capacitor. If a deformation F is applied to the electroactive polymer layer structure 1 in a direction included in the layer plane, the dielectric elastomer layer 3 is stretched and the electrodes 2 and 4 are forced to follow the stretched dielectric elastomer, thus the dielectric and electrodes are in a strained state and the thickness of the electrodes decreases.

[0032] Figure 2 This schematically illustrates a problem with the prior art regarding the use of a conventional electroactive polymer layer structure 1 as a variable capacitor. The electroactive polymer structure 1 shown includes a bulk volume V within a dielectric elastomer layer 3. 缺陷 The volume V of this body 缺陷The structure contains defects, such as defect 5. When structure 1 is under strain and unstrained conditions, a voltage V is applied between the two electrodes 2 and 4 to accumulate positive charges (+) or negative charges (-) in the dielectric layer near the electrodes 2 and 4 connected to the power electronic device. Under small spacing distance d in the strained state or under high applied voltage V, the electric field E (the magnitude of E is equal to the ratio of V to d) depending on the spacing distance d between the electrodes may exceed the dielectric strength of the material. In this case, within the defect bulk volume V... 缺陷 A discharge A is generated, in which the layer structure subjected to the discharge melts or vaporizes. A pinhole P is created through the thickness of the structure, thereby damaging the material and creating a path for a short-circuit current that affects the capacitance of the structure.

[0033] Figure 3A A cross-sectional view of an EAP-based device 10 according to the present invention is shown. The EAP-based device 10 includes three electrode layers 12, 14, 16 and four dielectric layers 11, 13, 15, 17. The electrode layers and dielectric layers form a stack, wherein the electrode layers are positioned on opposite surfaces of the dielectric layers. Both the electrode layers and dielectric layers are made of a stretchable material, such that they can be repeatedly strained and unstrained without fracture and / or plastic deformation. In particular, the electrode layers are made of a carbon-based conductive material, which further contains a solid oxidant. The dielectric layers 11, 13, 15, 17, placed around the electrode layers 12, 14, 16, seal the electrode layers to isolate them from ambient air. In another embodiment, layers 16, 17 (shown in dashed lines) are optional, or the device may include an additional stack of the same layers as layers 16, 17 on either side of the EAP-based device, wherein each electrode layer is sealed to isolate it from ambient air by two dielectric layers surrounding it.

[0034] Figure 3B A cross-sectional view of an EAP-based device 20 according to another embodiment of the present invention is shown. The EAP-based device 20 includes two electrode layers 12, 14 and three dielectric layers 11, 13, 15. The EAP-based device further includes an encapsulation 18. The electrode layers form a stack together with the dielectric layers, wherein the electrode layers are positioned on opposite surfaces of the dielectric layers. Both the electrode layers and the dielectric layers are made of a stretchable material, allowing them to be repeatedly strained and unstrained without fracture and / or plastic deformation. In particular, the electrode layers are made of a carbon-based conductive material, which further contains a solid oxidant. The dielectric layers 11, 13, 15, placed around the electrode layers 12, 14, seal the electrode layers to isolate them from ambient air. The encapsulation 18 seals the stack of dielectric and electrode layers and ensures a substantially oxygen-free environment. In another embodiment, the EAP-based device may include additional layers, such as… Figure 3A Layers 16 and 17. In any case, the stack always alternates between dielectric and electrode layers, wherein each electrode layer within the package 18 is sealed to the ambient air by two dielectric layers surrounding it.

[0035] Figure 4 A flowchart 100 of a method for manufacturing an EAP-based device according to the present invention is shown. In a first step 101, a carbon material dispersion is prepared. For this purpose, an aqueous dispersion of solid carbon material in powder or flake form can be diluted in a solvent such as deionized water. Optionally, the mixture is then ultrasonically stirred. In step 102, a certain amount of solid oxidant is weighed and added to the dispersion solution. Optionally, an additive such as a silane-based coupling agent can be added to the dispersion solution. In step 103, the newly formed dispersion solution is uniformly mixed. In step 104, the dispersion is uniformly coated on one or both sides of a dielectric layer, and then the solvent is evaporated in step 105. In step 104, the dispersion can be coated onto the dielectric layer by spraying or screen printing. Other techniques known to those skilled in the art for coating dielectric layers fall within the scope of the present invention. During solvent evaporation, the oxidant gradually precipitates and is encapsulated by carbon. In step 106, the electrode layer is covered by a dielectric layer deposited on the electrode layer, which seals the electrode layer to isolate it from ambient air. The stack can also be encapsulated to ensure a virtually oxygen-free atmosphere.

[0036] Figure 5A The chemical processes during dielectric breakdown in the EAP-based device 10 according to the present invention are illustrated schematically. Although only a few are shown... Figure 3A The device 10 shown is based on EAP, but the same chemical process will be used in... Figure 3B This occurs in the EAP-based device 20 shown. This also applies to EAP-based devices of the present invention with additional layers, each electrode layer positioned between two dielectric layers and sealed to isolate it from ambient air. Under exposure to an electric field E exceeding the dielectric strength of the dielectric layers, a spark or arc A forms a pinhole P across the entire thickness of the dielectric layer. The electrode layer, made of a composite material containing an oxidant, releases gaseous oxygen under thermal action. The carbon material of the electrode layer reacts with the gaseous oxygen to form carbon monoxide (CO) and / or carbon dioxide (CO2). CH4 may also be released.

[0037] Figure 5B The diagram schematically illustrates the self-cleaning of an EAP-based device according to the present invention, wherein the electrode volume V of electrode layer 12 near the pinholes passing through layers 11 and 13 in the dielectric layer is increased due to oxygen release. 电极 A portion (shown by dashed lines) has vaporized. For clarity, it is not shown in this diagram. Figure 5A The released gas. The damaged portion of the dielectric layer at pinhole P is thus electrically insulated from the rest of the body of the EAP-based device, and the EAP-based device is able to return to its operating state.

[0038] The invention has been described with reference to preferred embodiments. Upon reading and understanding the foregoing detailed description, others will conceive of obvious modifications and variations. It is intended that the invention be construed as including all such modifications and variations, provided they fall within the scope of the appended claims.

Claims

1. A device (10, 20) based on electroactive polymer EAP, comprising: A dielectric layer (13, 23) is arranged between the two electrode layers (12, 14). The dielectric layer (13, 23) is composed of a stretchable material. The two electrode layers (12, 14) comprise a carbon-based conductive material and a solid oxidant material forming the stretchable layer. The EAP-based device further includes an additional dielectric layer (11, 15) of the stretchable material disposed on each of the two electrode layers (11, 13) and configured together with the dielectric layer (13, 23) to seal each of the two electrode layers (12, 14) therein.

2. The EAP-based device according to claim 1, further comprising a package (18) that seals the electrode layers (12, 14) and the dielectric layer (13, 23) to isolate them from ambient air.

3. The EAP-based device according to any one of the preceding claims, wherein, The carbon-based conductive material is mixed with the solid oxidant material.

4. The EAP-based device according to any one of the preceding claims, wherein, This solid oxidant material contains oxygen-containing compounds.

5. The EAP-based device according to any one of the preceding claims, wherein, The solid oxidant material comprises one or more compounds selected from the group consisting of: Permanganate, nitrate, dichromate, perborate, and chlorate.

6. The EAP-based device according to claim 5 or the one described in claim 5, wherein, The solid oxidant material contains sodium or potassium as a cation of one or more of the compounds.

7. The EAP-based device according to any one of the preceding claims, wherein, The solid oxidant material has a concentration of 10 wt% or less in the electrode layer, and the electrode layer has a thickness of less than 5 micrometers.

8. The EAP-based device according to any one of the preceding claims, further comprising at least one stack on at least one of the additional dielectric layers (11, 15), the stack having an electrode layer (16) comprising the carbon-based conductive material and the solid oxidant material and a dielectric layer (17) of the stretchable material alternately, the dielectric layer (17) of the stack being configured together with the additional dielectric layers (11, 15) to seal the electrode layer (16) of the stack therein.

9. The EAP-based device according to any one of the preceding claims, wherein, The carbon-based conductive material of the electrode layers (12, 14, 16) comprises nanoparticles of at least one of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

10. The EAP-based device according to any one of the preceding claims, wherein, The stretchable material of these dielectric layers (11, 13, 15, 17) is selected from the group consisting of silicone, rubber, and thermoplastic polyurethane (TPU).

11. The EAP-based device according to any one of the preceding claims, wherein, These electrode layers (12, 14, 16) further contain additives, such as silane-based coupling agents, which are used to promote adhesion between the electrode layer and the dielectric layer.

12. The EAP-based device according to any one of claims 2, 3 to 11—when dependent on claim 2— wherein, The package (18) is made of a polymer material selected from the group consisting of silicone, epoxy resin and urethane.

13. The EAP-based device according to any one of the preceding claims, wherein, These electrode layers (12, 14, 16) and these dielectric layers (11, 13, 15, 17) are encapsulated in a vacuum or in a nitrogen atmosphere.

14. A method for manufacturing a device (10, 20) based on the electroactive polymer EAP, the method comprising: - Provide two or more dielectric layers (11, 13, 15, 17) of stretchable material in the processing volume. - An electrode layer (12, 14, 16) made of a carbon-based conductive material is arranged (104) on at least one of the two or more dielectric layers (11, 13, 15, 17), wherein the electrode layer (12, 14, 16) contains a carbon-based conductive material. - Cover (104) the exposed surface of at least one of these electrode layers (12, 14, 16) with another dielectric layer made of the stretchable material. - Add (102) solid oxidant material to the carbon-based conductive material of these electrode layers (11, 13, 15, 17); When these electrode layers (12, 14, 16) are arranged on at least one of the two or more dielectric layers (11, 13, 15, 17), The method is characterized by further including: The processing volume is kept in a substantially oxygen-free atmosphere or vacuum, and the dielectric layers are configured to seal one of the electrode layers therein.

15. The method for manufacturing an EAP-based device according to claim 13, wherein, The step of arranging the electrode layer (104) on at least one of the two or more dielectric layers (11, 13, 15, 17) includes spraying a carbon-based dispersion containing the solid oxidant and an additive onto at least one of the dielectric layers, the additive promoting adhesion of the electrode layer to the at least one dielectric layer.

16. Use of an EAP-based device manufactured according to any one of claims 1 to 13 or any one of claims 13 to 14.

17. A method for manufacturing an EAP-based device that is self-cleaning and withstands dielectric breakdown according to any one of claims 1 to 12 or any one of claims 14 to 15, the method comprising: - Gaseous oxygen is released from these electrode layers, which contain solid oxidants and carbon-based materials. - Carbon dioxide and / or carbon monoxide are produced by the reaction of the released gaseous oxygen with the carbon-based material of these electrodes.

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