A flexible conductive polymer film electrode material and preparation method thereof

Abstract

The present invention belongs to the field of conductive polymers, and specifically relates to a new type of flexible conductive polymer film electrode material and a preparation method thereof. The flexible conductive polymer film of the present invention is composed of PEDOT:PSS and a polar small molecule containing both a carbon-carbon double bond and a polar functional group; the polar functional group includes a hydroxyl group, a carboxyl group or an amino group; the weight percentage of the polar small molecule in the simplified flexible conductive polymer film is 15%-90%. The present invention achieves a simultaneous improvement in the electrical conductivity and mechanical properties of the conductive polymer film by only mixing one component into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, and can significantly improve the problem of easy leakage of small molecule additives in traditional flexible conductive polymer films.

Description

Technical Field

[0001] The present invention belongs to the field of conductive polymers, and in particular relates to a flexible conductive polymer film electrode material and a preparation method thereof. Background Art

[0002] Human electrophysiological signals (such as electrocardiogram, electromyography, and electroencephalogram) contain a wealth of physiological information. With the development of artificial intelligence (AI), human-centric human-computer interaction systems, including flexible wearable electronics, healthcare, and robotic arm control, can be used for remote monitoring and real-time diagnosis of human health. However, these technologies require accurate and long-term acquisition of human electrophysiological signals. Human-computer interaction interfaces, specifically epidermal electrodes, are ideal platforms for acquiring these signals. Conductive polymer thin film electrodes hold great promise for application due to their easily tunable properties and high long-term stability. PEDOT:PSS is the most widely used and successful conductive polymer. However, because the conductive PEDOT component is encapsulated by a large amount of PSS, it forms a core-shell structure in aqueous solution, limiting the conductive path. Furthermore, due to the rigid conjugated backbone of PEDOT, thin film electrodes prepared from pristine PEDOT:PSS solutions have a conductivity of only approximately 0.2 S / cm and very limited deformability. These low conductivity and poor mechanical properties make them unsuitable for direct application in human-computer interaction interfaces.

[0003] Normally, the common method to achieve high elasticity of PEDOT:PSS films is to blend them with polymer networks. However, simple blending of polymers will destroy the conductive path, hinder the transport of carriers, and reduce the conductivity of the film. Therefore, there is a contradiction between the methods of achieving high conductivity and high elasticity of PEDOT:PSS. To further solve this problem, existing methods choose to add some small molecule dopants to the PEDOT:PSS solution. Such as polar solvents, inorganic acids, ionic liquids, surfactants, etc. The addition of these small molecule dopants can increase the mobility of carriers and thus increase the conductivity of the PEDOT:PSS film. However, small molecules have the risk of leakage, especially when in a body fluid environment (such as the influence of sweat from long-term wear), which is accompanied by a decrease in performance, so it is not suitable for long-term application on the surface of human skin.

[0004] The patent application number is CN202210655816.2, and the invention name is "A dual-network PEDOT flexible conductive polymer and its preparation method". It discloses a flexible conductive polymer prepared by blending a conductive polymer material and a flexible polymer material. This patented method improves the comprehensive performance of the final flexible conductive polymer by adding small molecules and polymers with different functions. For example, ethylene glycol is used to improve conductivity, and PVA and PEGDA are used to improve tensile properties. This material not only has a complex composition, but also still contains small molecule additives, so the problem of small molecule leakage is prone to occur during long-term wear.

[0005] In summary, it is necessary to propose a new strategy and method for flexible conductive polymers. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a flexible conductive polymer film electrode material and a preparation method thereof, and the specific technical solutions are as follows.

[0007] A streamlined flexible conductive polymer film with improved comprehensive performance, the streamlined flexible conductive polymer film consisting of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and a polar small molecule containing both a carbon-carbon double bond and at least one polar functional group; the polar functional group includes a hydroxyl group, a carboxyl group, or an amino group; the weight percentage of the polar small molecule in the streamlined flexible conductive polymer film is 15%-90%.

[0008] PEDOT:PSS has both electronic conductivity and ionic conductivity, and the present invention mainly focuses on improving the electronic conductivity.

[0009] Furthermore, the polar small molecule main chain also includes a butyl group or an ethyl group.

[0010] Furthermore, the polar small molecule is hydrophilic.

[0011] Furthermore, the weight percentage of the polar small molecules in the streamlined flexible conductive polymer film is 30%-75%.

[0012] Furthermore, the polar small molecules include one or more of acrylic acid, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate and β-(acryloyloxy)propionic acid.

[0013] The method for preparing the above-mentioned streamlined flexible conductive polymer film adopts the method of placing the reaction product in a hydrophilic system, mixing it first, and then polymerizing it to obtain the final product. The specific steps are as follows:

[0014] Step 1: Add polar small molecule solution, deionized water, water-soluble initiator and water-soluble crosslinking agent simultaneously, and mix them evenly to obtain a first mixed solution;

[0015] Step 2: Add the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate dispersion to the first mixed solution obtained in step 1 and continue mixing to obtain a second mixed solution, wherein the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate is 1:2.5;

[0016] Step 3: Place the second mixed solution obtained in step 2 under an ultraviolet lamp to allow the water-soluble initiator to initiate a polymerization reaction of the polar small molecules to form a three-dimensional polymerization network of polar small molecules, and the poly (3,4-ethylenedioxythiophene): polystyrene sulfonate is uniformly dispersed in the network to form the streamlined flexible conductive polymer film.

[0017] Furthermore, the water-soluble initiator includes 2,2'-azobisisobutylamidine dihydrochloride, 1-hydroxycyclohexylphenyl ketone or 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, and the molar ratio of the water-soluble initiator to the polar small molecule is 1:50-200 (including 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:110, 1:120, 1:130, 1:140, 1:150, 1:160, 1:170, 1:180, 1:190, 1:200).

[0018] Furthermore, the water-soluble crosslinking agent includes polyethylene glycol diacrylate, N,N'-methylenebisacrylamide or polyethylene glycol dimethacrylate, and the molar ratio of the water-soluble crosslinking agent to the polar small molecule is 1:500-1000 (including 1:500, 1:600, 1:700, 1:800, 1:900, 1:1000).

[0019] Furthermore, the second mixed solution obtained in step 2 is placed under ultraviolet light for 6-12 hours.

[0020] Furthermore, the mixing method in step 1 and step 2 includes one or more of mechanical stirring, vortex stirring and / or ultrasonic vibration.

[0021] Beneficial technical effects

[0022] 1) This invention first provides a streamlined flexible conductive polymer film composed solely of PEDOT:PSS and a hydrophilic polar small molecule. The addition of this hydrophilic polar small molecule simultaneously enhances both the electrical conductivity and mechanical properties of the conductive polymer film. This represents a significant breakthrough compared to existing methods that often require the simultaneous addition of multiple components to PEDOT:PSS to achieve this material's comprehensive performance improvements.

[0023] 2) The flexible conductive polymer film with streamlined ingredients provided by the present invention can also significantly improve the problem of easy leakage of small molecule additives in traditional flexible conductive polymer films. In order to achieve this technical purpose, the present invention has put a lot of effort into the selection of materials and the improvement of preparation methods. The polar small molecules containing carbon-carbon double bonds selected by the present invention can be polymerized to form a 3D network under the action of a photoinitiator; the functional groups (hydroxyl, carboxyl) contained therein can undergo ion-dipole interactions with PEDOT:PSS, thereby improving the conductivity of PEDOT:PSS. In addition, the method selected by the present invention of mixing all reaction products in a hydrophilic system before polymerization can make the PEDOT:PSS monomer uniformly mixed with the polar small molecules before polymerization. After the polar small molecules are polymerized into a network structure, the PEDOT:PSS is wrapped by this 3D network, further forming the final product, a flexible conductive polymer film. Since the various components in this flexible conductive polymer film are evenly mixed, not only can an effective conductive path be formed, but the polar small molecules have also been polymerized to form a network, thus effectively avoiding the problem of easy leakage of small molecule additives in the flexible conductive polymer film.

[0024] 3) The present invention adopts a method of photo-initiated polymerization reaction. Compared with thermally initiated polymerization reaction, photo-initiation can avoid the problem of deterioration of mechanical properties of flexible conductive polymer films caused by high-temperature heating, thereby ensuring the improvement of the comprehensive performance of the material finally obtained by the present invention.

[0025] 4) Finally, the electrical conductivity of the polymer film material provided by the present invention can reach up to 847S / cm, and the elongation at break can reach 88%. The comprehensive performance is better than most current polymer film materials and fully meets the application requirements of flexible wearable electronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the embodiments or the description of the prior art. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the various elements or parts are not necessarily drawn according to the actual scale. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without inventive work.

[0027] Figure 1 This is a photo of a polymer film prepared in one embodiment of the present invention;

[0028] Figure 2 The electrical conductivity of the polymer films prepared in three embodiments of the present invention;

[0029] Figure 3 The mechanical properties of the polymer films prepared in three embodiments of the present invention are shown in FIG.

[0030] Figure 4 This is the electromyographic signal test result of the polymer film prepared in one embodiment of the present invention;

[0031] Figure 5 Fourier transform infrared spectroscopy results of the polymer film P(4-HBA) / PEDOT:PSS, 4-HBA monomer, and pure polymer P(4-HBA) prepared in one embodiment of the present invention;

[0032] Figure 6 Fourier transform infrared spectroscopy results of the polymer film P(2-HEA) / PEDOT:PSS and 2-HEA monomer and pure polymer P(2-HEA) prepared in one embodiment of the present invention;

[0033] Figure 7 FTIR spectra of the polymer film PAA / PEDOT:PSS and AA monomers, as well as pure polymer PAA, prepared in one embodiment of the present invention. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] As used herein, "and / or" includes any and all combinations of one or more of the associated listed items.

[0036] Herein, "plurality" means two or more than two, ie, it includes two, three, four, five, etc.

[0037] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0038] As used in this specification, the term "about" typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0039] In this specification, certain embodiments may be disclosed in a format that is within a certain range. It should be understood that such descriptions of "being within a certain range" are merely for convenience and brevity and should not be interpreted as a rigid limitation on the disclosed range. Therefore, the description of a range should be considered to have specifically disclosed all possible sub-ranges and independent numerical values ​​within this range. For example, the description of a range of 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within this range, such as 1, 2, 3, 4, 5, and 6. Regardless of the breadth of the range, the above rules apply.

[0040] The “comprehensive performance improvement” mentioned in the present invention refers to the simultaneous improvement of the electrical conductivity and mechanical properties of the material, wherein the mechanical properties include tensile fracture stress and / or Young's modulus.

[0041] Example 1

[0042] Pipette 222 μL of 4-hydroxybutyl acrylate into a glass vial, add 98 μL of deionized water, 0.23 mg of 2,2'-azobisisobutylamidine dihydrochloride, and 2 μL of a 1 M polyethylene glycol diacrylate aqueous solution (575 Da, same below), and vortex stir for 2 minutes to prepare a 4-hydroxybutyl acrylate (4-HBA) solution. The molar ratio of initiator to 4-HBA is 1:50-200. The molar ratio of crosslinker to 4-HBA is 1:500-1000. Pipette 0.4 mL of PH1000 dispersion (i.e., a PEDOT:PSS aqueous solution with a solids content of 1.3 wt%, same below) into a glass vial, stir at room temperature with a magnetic stir bar at 1000 rpm, and pipette 22 μL of the 4-HBA solution into the vial. Stir for 20 minutes to prepare a polymer blend solution. 200 μL of the prepared polymer blend solution was pipetted and dropped onto a glass substrate, and then polymerized under an ultraviolet lamp at room temperature for 6-12 h to obtain a polymer film.

[0043] It is understood that the initiator of this embodiment can also be replaced by 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone. The cross-linking agent can also be replaced by N,N'-methylenebisacrylamide or polyethylene glycol dimethacrylate.

[0044] The conductivity of the polymer film prepared in this example is 847 S / cm, and the elongation at break is 88%.

[0045] The electrical conductivity of polymer film materials with different 4-hydroxybutyl acrylate contents is as follows Figure 2 As shown in the figure, the conductivity increases with the increase of 4-hydroxybutyl acrylate content, reaching the highest at 75wt% 4-hydroxybutyl acrylate content. When the weight percentage of 4-hydroxybutyl acrylate is 90wt%, the conductivity decreases due to the lack of conductive component PEDOT:PSS.

[0046] Mechanical properties of polymer film materials with different 4-hydroxybutyl acrylate contents are as follows Figure 3 As shown in the figure, the elongation at break increases with the increase of 4-hydroxybutyl acrylate content, while the tensile stress at break and Young's modulus decrease with the increase of 4-hydroxybutyl acrylate content.

[0047] Figure 5Fourier transform infrared spectra of the polymer film P(4-HBA) / PEDOT:PSS prepared in this example, along with 4-HBA monomer and pure P(4-HBA) polymer, are shown. The disappearance of the characteristic absorption peak of —C═CH2 in the P(4-HBA) / PEDOT:PSS polymer film demonstrates complete covalent crosslinking of the 4-HBA monomers within the film, eliminating the risk of small-molecule monomer leakage.

[0048] Example 2

[0049] Pipette 210 μL of 2-hydroxyethyl acrylate into a glass vial, add 98 μL of deionized water, 0.23 mg of 2,2'-azobisisobutylamidine dihydrochloride, and 2 μL of polyethylene glycol diacrylate aqueous solution, and vortex stir for 2 minutes to prepare a 2-hydroxyethyl acrylate (2-HEA) solution. The molar ratio of initiator to 2-HEA is 1:50-200. The molar ratio of crosslinker to 2-HEA is 1:500-1000. Pipette 0.4 mL of PH1000 dispersion into a glass vial, stir at 1000 rpm with a magnetic stir bar at room temperature, pipette 22 μL of the 2-HEA solution, and stir for 20 minutes to prepare a polymer blend solution. Pipette 200 μL of the prepared polymer blend solution dropwise onto a glass substrate and polymerize under UV light at room temperature for 6-12 hours to produce a polymer film.

[0050] It is understood that the initiator of this embodiment can also be replaced by 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone. The cross-linking agent can also be replaced by N,N'-methylenebisacrylamide or polyethylene glycol dimethacrylate.

[0051] The electrical conductivity of polymer film materials with different 2-hydroxyethyl acrylate contents is as follows Figure 2 As shown in Figure 2, the conductivity increases with the increase of 2-hydroxyethyl acrylate content, reaching the highest at 75wt% 2-hydroxyethyl acrylate content. When the weight percentage of 2-hydroxyethyl acrylate is 90wt%, the conductivity decreases due to the lack of conductive component PEDOT:PSS.

[0052] Mechanical properties of polymer film materials with different 2-hydroxyethyl acrylate contents are as follows Figure 3 As shown in the figure, the elongation at break increases with the increase of 2-hydroxyethyl acrylate content, while the tensile stress at break and Young's modulus decrease with the increase of 2-hydroxyethyl acrylate content.

[0053] Figure 6Fourier transform infrared spectra of the polymer film P(2-HEA) / PEDOT:PSS prepared in this example, along with 2-HEA monomer and pure P(2-HEA) polymer, are shown. The disappearance of the characteristic absorption peak of —C═CH2 in the P(2-HEA / PEDOT:PSS polymer film demonstrates complete covalent crosslinking of the 2-HEA monomers within the polymer film, eliminating the risk of small-molecule monomer leakage.

[0054] Example 3

[0055] Pipette 224 μL of acrylic acid into a glass vial, add 98 μL of deionized water, 0.23 mg of 2,2'-azobisisobutylamidine dihydrochloride, and 2 μL of polyethylene glycol diacrylate aqueous solution, and vortex stir for 2 minutes to prepare an acrylic acid (AA) solution. The molar ratio of initiator to acrylic acid is 1:50-200. The molar ratio of crosslinker to acrylic acid is 1:500-1000. Pipette 0.4 mL of PH1000 dispersion into a glass vial, add a magnetic stir bar, and stir at 1000 rpm at room temperature. Pipette 22 μL of the acrylic acid solution and stir for 20 minutes to prepare a polymer blend solution. Pipette 200 μL of the prepared polymer blend solution dropwise onto a glass substrate, and then polymerize under UV light at room temperature for 6-12 hours to produce a polymer film.

[0056] It is understood that the initiator of this embodiment can also be replaced by 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone. The cross-linking agent can also be replaced by N,N'-methylenebisacrylamide or polyethylene glycol dimethacrylate.

[0057] The electrical conductivity of polymer film materials with different acrylic acid contents is as follows Figure 2 As shown in FIG, the conductivity increases with the increase of acrylic acid content, reaching the highest at 75 wt% acrylic acid content. When the weight percentage of acrylic acid is 90 wt%, the conductivity decreases due to the lack of conductive component PEDOT:PSS.

[0058] Mechanical properties of polymer film materials with different acrylic acid contents Figure 3 As shown in the figure, the elongation at break increases with the increase of acrylic acid content, while the tensile stress at break and Young's modulus decrease with the increase of acrylic acid content.

[0059] Figure 7Fourier transform infrared spectra of the polymer film PAA / PEDOT:PSS prepared in this example, along with AA monomer and pure PAA. The disappearance of the characteristic absorption peak of —C═CH2 in the PAA / PEDOT:PSS film demonstrates complete covalent crosslinking of the AA monomers within the film, eliminating the risk of small-molecule monomer leakage.

[0060] Example 4

[0061] Verification of the effects of molecules with different polarity

[0062] Table 1 Conductivity of polymer films prepared with different polar molecules

[0063]

[0064] Table 2 Elongation at break of polymer films prepared with different polar molecules

[0065]

[0066] Tables 1 and 2 compare the effects of 4-hydroxybutyl acrylate, 2-hydroxyethyl acrylate, and acrylic acid on the mechanical properties of PEDOT:PSS. The larger the molecular weight of the small molecule, the longer the polymer side chain after polymerization (after polymerization, the portion of the small molecule minus the carbon-carbon double bond becomes the side chain of the polymer), making it more difficult to form intermolecular or intramolecular interactions. Therefore, poly(4-hydroxybutyl acrylate) with longer side chains has the lowest glass transition temperature and is therefore more effective in improving mechanical properties. However, when the material ratio reaches 90%, excess 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate will precipitate on the film surface and the surrounding substrate, affecting the tensile test results. Therefore, the subsequent data is not of reference value.

[0067] Other performance verification.

[0068] The following table provides different small molecule materials and PEDOT:PSS to prepare polymer films and test the electrical conductivity of different materials.

[0069] Table 3 Electrical conductivity of different materials (S / cm)

[0070]

[0071] It can be seen from Table 3 that when the small molecule material does not contain a C=C double bond or is hydrophobic, the conductivity of the synthesized polymer film is low or it cannot be synthesized.

[0072] Table 4 Solubility of different film materials in DI solution

[0073] Materials / Time 1 hour 1 day 1 week Present invention 1 - - - Present invention 2 - - - Control 1 ++ +++ +++ Control 2 + ++ +++

[0074] Note: “+” represents the observed degree of solubility; the more “+”, the more dissolved; “-” represents no dissolution.

[0075] Invention 1: PEDOT:PSS+4-hydroxybutyl acrylate

[0076] Invention 2: PEDOT:PSS+2-hydroxyethyl acrylate

[0077] Control 1: PEDOT:PSS

[0078] Control 2: PEDOT:PSS + 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

[0079] The results in Table 4 show that the less easily a small molecule dissolves in DI solution, the less likely it is to leak from the polymer film, and the more stable the polymer film is during long-term wear.

[0080] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for preparing a flexible conductive polymer film, characterized in that: The specific steps are as follows: Step 1: Add polar small molecules, deionized water, a water-soluble initiator, and a water-soluble crosslinking agent simultaneously, and mix them evenly to obtain a first mixed solution; The polar small molecule is 4-hydroxybutyl acrylate; The water-soluble initiator is a photoinitiator; The water-soluble cross-linking agent is polyethylene glycol diacrylate, N,N'-methylenebisacrylamide or polyethylene glycol dimethacrylate; Step 2: Add the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate dispersion to the first mixed solution obtained in step 1 and continue mixing to obtain a second mixed solution, wherein the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate is 1:2.5; Step 3: placing the second mixed solution obtained in step 2 under an ultraviolet lamp to allow the water-soluble photoinitiator to initiate a polymerization reaction of the polar small molecules to form a polar small molecule three-dimensional polymer network, wherein the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate is uniformly dispersed in the network to form the flexible conductive polymer film; the weight percentage of the polar small molecules in the flexible conductive polymer film is 30%-75%.

2. The preparation method according to claim 1, wherein The water-soluble initiator includes 2,2'-azobisisobutylamidine dihydrochloride or 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, and the molar ratio of the water-soluble initiator to the polar small molecule is 1:50-200.

3. The preparation method according to claim 1, wherein The molar ratio of the water-soluble cross-linking agent to the polar small molecule is 1:500-1000.

4. The preparation method according to claim 1, wherein Place the second mixed solution obtained in step 2 under ultraviolet light for 6-12 hours.

5. The preparation method according to claim 1, wherein The mixing method in step 1 and step 2 includes mechanical stirring or ultrasonic vibration.

6. A flexible conductive polymer film prepared by the preparation method according to any one of claims 1 to 5.

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