A conductive film based on liquid metal fiberization and a method for preparing the same

Abstract

The application relates to a conductive film based on liquid metal fiberization and a preparation method thereof, and relates to the field of polymer conductive film materials.The method comprises the following steps: preparing a composite film by taking 30-45 parts by volume of liquid metal and 55-70 parts by volume of thermoplastic polyurethane as raw materials; and performing mechanical sintering treatment on the composite film, and then performing tensile heat treatment to obtain the conductive film based on liquid metal fiberization. The application mainly uses liquid metal and thermoplastic polyurethane with a suitable proportion as raw materials and performs controllable heat stretching and other processes under suitable parameters, so that the liquid metal particles dispersed in the film are effectively deformed and fiberized in situ, a conductive network containing liquid metal fibers with a high aspect ratio is formed, high-conductivity film materials are prepared under the premise of low liquid metal filling, and a new technical path is provided for the preparation of an LM / TPU composite conductive film.

Description

Technical Field

[0001] This invention relates to the field of polymer conductive film materials, and in particular to a conductive film based on liquid metal fiberization and its preparation method. Background Technology

[0002] Flexible electronics technology, as an important development direction for future electronic devices, shows broad application prospects in wearable health monitoring, implantable medical devices, smart textiles, soft robots, and other fields. The core of flexible electronic devices lies in achieving conductive materials with high conductivity, excellent mechanical flexibility, and environmental stability, especially maintaining stable performance under dynamic deformation conditions. Traditional conductive materials, such as metal films, conductive polymers, and conductive composites, have significant limitations in flexible applications: metal films are prone to fatigue cracking, leading to conductivity failure; conductive polymers (such as poly(3,4-ethylenedioxythiophene), polystyrene sulfonic acid, polypyrrole, and polyaniline) typically have low conductivity; conductive composites often use rigid fillers such as carbon-based, metallic, and two-dimensional transition metal carbonitride compounds, which often leads to a decrease in the flexibility of the composite material. Furthermore, the high filler loading required to achieve high conductivity often causes processing difficulties and a decline in mechanical properties.

[0003] Liquid metal (LM), as a novel functional material, possesses unique physical and chemical properties and is considered an ideal flexible conductive filler. Currently, the most common method for integrating LM into a polymer matrix is ​​to disperse bulk LM into micron- or nano-scale spherical particles through high-speed shearing or ultrasonic treatment, ensuring their uniform distribution within the polymer matrix. However, the point-contact mode of these spherical LM particles makes the construction of the conductive network heavily reliant on high filler concentrations. Furthermore, the fluid properties of LM at high filler concentrations lead to leakage, which can corrode electronic devices. Therefore, achieving high conductivity with low LM filler concentrations has become a critical technical problem urgently needing to be solved in this field. Summary of the Invention

[0004] To address the above problems, this invention provides a conductive film based on liquid metal fiberization and its preparation method.

[0005] In a first aspect, the present invention provides a method for preparing a conductive film based on liquid metal fiberization, comprising the following steps:

[0006] A composite membrane is prepared by mixing 30 to 45 parts by volume of liquid metal and 55 to 70 parts by volume of thermoplastic polyurethane.

[0007] The composite film is subjected to mechanical sintering and then stretching heat treatment to obtain the conductive film based on liquid metal fiberization.

[0008] The working conditions for the tensile heat treatment include: a temperature of 90~110℃ and a tensile strain of 200~800% applied to the composite film.

[0009] Furthermore, the conductive film based on liquid metal fiberization contains fibrous liquid metal, and the aspect ratio of the fibrous liquid metal is 7.1~42.4.

[0010] Furthermore, the liquid metal includes at least one of gallium indium alloy and gallium indium tin alloy.

[0011] Furthermore, in the gallium-indium alloy, the mass ratio of gallium to indium is 75:25, and in the gallium-indium-tin alloy, the mass ratio of gallium, indium, and tin is 66:20.5:13.5.

[0012] Furthermore, the glass transition temperature of the soft segment in the thermoplastic polyurethane is -50 to -45°C, and the glass transition temperature of the hard segment in the thermoplastic polyurethane is 58 to 63°C.

[0013] Furthermore, the thermoplastic polyurethane includes polyether-type thermoplastic polyurethane, and the polyether-type thermoplastic polyurethane includes thermoplastic polyurethane with product model Elastollan 2180A10.

[0014] Furthermore, the step of preparing a composite film by mixing 30 to 45 parts by volume of liquid metal and 55 to 70 parts by volume of thermoplastic polyurethane includes the following processes:

[0015] The liquid metal and the thermoplastic polyurethane are added to a solvent in a certain proportion and stirred to obtain a mixture;

[0016] The mixture is injected into a mold and then dried to form the composite film.

[0017] Furthermore, the solvent includes N,N-dimethylformamide, and the concentration of the thermoplastic polyurethane in the mixture is 28~30 g / ml.

[0018] Further, the steps of mechanically sintering the composite film and then performing a stretching heat treatment to obtain the conductive film based on liquid metal fiberization include the following processes:

[0019] The composite membrane is subjected to mechanical sintering at 1-2 MPa pressure for 2-5 minutes, then fixed on the fixture of an electronic universal testing machine and preheated in a preset temperature atmosphere for 8-15 minutes. Then, it is subjected to tensile heat treatment for 55-65 minutes under preset temperature and preset tensile strain conditions. After cooling to room temperature, the conductive membrane based on liquid metal fiberization is obtained.

[0020] Secondly, based on the same inventive concept, the present invention provides a conductive film based on liquid metal fiberization, wherein the conductive film based on liquid metal fiberization is prepared by the preparation method of the conductive film based on liquid metal fiberization described in any one of the first aspects.

[0021] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art:

[0022] This invention provides a conductive film based on liquid metal fiberization and its preparation method. The invention mainly utilizes a suitable ratio of liquid metal and thermoplastic polyurethane as raw materials, and performs controlled thermal stretching under appropriate parameters to effectively deform and fiberize the liquid metal particles dispersed in the film, forming a conductive network containing high aspect ratio liquid metal fibers. Simultaneously, no cracks or LM leakage occur in the material. This achieves the preparation of a high-conductivity film material with low liquid metal filling amount, providing a new technical path for the preparation of LM / TPU composite conductive films. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a cross-sectional morphology diagram of the conductive film obtained in Comparative Example 2 of the present invention; Figure 1 In the middle: (a) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Comparative Example 2 with a size of 50 μm, and (b) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Comparative Example 2 with a size of 10 μm.

[0026] Figure 2 The cross-sectional morphology diagrams are of the conductive films obtained in Examples 1-3; Figure 2 In the image: (a) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Example 1; (b) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Example 2; and (c) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Example 3. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0030] Example 1

[0031] This example provides a conductive film based on liquid metal fiberization, which includes the following raw materials: 30 parts by volume of liquid metal (specifically, a gallium indium tin alloy, wherein the mass ratio of gallium indium tin in the gallium indium tin alloy is 66:20.5:13.5, purchased from Dongguan Qiaotai Metal Technology Co., Ltd.) and 70 parts by volume of thermoplastic polyurethane (specifically, a polyether-type thermoplastic polyurethane, product model Elastollan 2180A10, purchased from BASF AG).

[0032] The above-mentioned method for preparing conductive films based on liquid metal fiberization includes the following steps:

[0033] Step S1: Add TPU (thermoplastic polyurethane) to N,N-dimethylformamide (DMF) and dissolve it by magnetic stirring at room temperature for 4 h to obtain a TPU solution with a concentration of 29.80 g / ml.

[0034] Step S2: Add LM (liquid metal) to the TPU solution obtained in step S1 in the required proportion, and mechanically mix for 13 min to obtain a mixture; after vacuum degassing, pour the mixture into a polytetrafluoroethylene mold and dry it in a 70 ℃ oven for 12 h to remove the solvent, and obtain an LM / TPU composite film.

[0035] Step S3: The LM / TPU composite film obtained in Step S2 is mechanically sintered at 1.5 MPa for 3.5 min, then clamped on the fixture of an electronic universal testing machine. The temperature of the tensile testing high-temperature chamber is adjusted to 100℃, and after the temperature stabilizes, it is preheated for 10 min. Subsequently, the LM / TPU composite film is subjected to tensile heat treatment with a tensile strain of 200% at a constant temperature of 100℃ for 1 h. The tensile rate of the electronic universal testing machine is 30 mm / min. After cooling to room temperature, the conductive film based on liquid metal fiberization is obtained.

[0036] Example 2

[0037] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 1 only in that:

[0038] (1) The tensile strain applied to the LM / TPU composite film in step S3 is adjusted to 500%.

[0039] Example 3

[0040] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 1 only in that:

[0041] (1) The tensile strain applied to the LM / TPU composite film in step S3 is adjusted to 800%.

[0042] Example 4

[0043] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 1 only in that:

[0044] (1) The volume fraction of liquid metal is adjusted to 35 parts, and the volume fraction of thermoplastic polyurethane is adjusted to 65 parts.

[0045] Example 5

[0046] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 2 only in that:

[0047] (1) The volume fraction of liquid metal is adjusted to 35 parts, and the volume fraction of thermoplastic polyurethane is adjusted to 65 parts.

[0048] Example 6

[0049] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 3 only in that:

[0050] (1) The volume fraction of liquid metal is adjusted to 35 parts, and the volume fraction of thermoplastic polyurethane is adjusted to 65 parts.

[0051] Example 7

[0052] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 1 only in that:

[0053] (1) The volume fraction of liquid metal is adjusted to 40 parts, and the volume fraction of thermoplastic polyurethane is adjusted to 60 parts.

[0054] Example 8

[0055] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 2 only in that:

[0056] (1) The volume fraction of liquid metal is adjusted to 40 parts, and the volume fraction of thermoplastic polyurethane is adjusted to 60 parts.

[0057] Example 9

[0058] This example provides a conductive film based on liquid metal fiberization and its preparation method, which differs from Example 3 only in that:

[0059] (1) The volume fraction of liquid metal is adjusted to 40 parts, and the volume fraction of thermoplastic polyurethane is adjusted to 60 parts.

[0060] Example 10

[0061] This example provides an LM / TPU composite conductive film and its preparation method, which differs from Example 1 in that:

[0062] (1) The liquid metal was adjusted to a gallium-indium alloy, wherein the mass ratio of gallium to indium in the gallium-indium alloy was 75:25, and it was purchased from Dongguan Qiaotai Metal Technology Co., Ltd.

[0063] Comparative Example 1

[0064] This example provides a pure TPU film, the preparation method of which includes the following steps:

[0065] Step S1: Add TPU (same as in Example 1) to N,N-dimethylformamide (DMF) and dissolve it at room temperature by magnetic stirring for 4 hours to obtain a TPU solution with a concentration of 29.80 g / ml.

[0066] Step S2: After vacuum degassing the TPU solution, pour it into a polytetrafluoroethylene mold and dry it in a 70°C oven for 12 hours to remove the solvent, thus obtaining a pure TPU film.

[0067] Comparative Example 2

[0068] This example provides an LM / TPU composite conductive film and its preparation method, which differs from Example 1 in that:

[0069] (1) No stretching heat treatment was performed.

[0070] The above-mentioned LM / TPU composite conductive film includes the following raw materials: 30 parts by volume of liquid metal (same as in Example 1) and 70 parts by volume of thermoplastic polyurethane (same as in Example 1).

[0071] The preparation method of the above-mentioned LM / TPU composite conductive film includes the following steps:

[0072] Step S1: Add TPU to N,N-dimethylformamide (DMF) and dissolve it by magnetic stirring at room temperature for 4 h to obtain a TPU solution with a concentration of 29.80 g / ml.

[0073] Step S2: Add LM to the TPU solution in the required ratio and mechanically mix for 13 min to obtain a mixture; after vacuum degassing, pour the mixture into a polytetrafluoroethylene mold and dry it in a 70 ℃ oven for 12 h to remove the solvent, thereby obtaining an LM / TPU composite film. Then, mechanically sinter the LM / TPU composite film at a pressure of 1.5 MPa for 3.5 min to obtain an LM / TPU composite conductive film.

[0074] Test Example 1

[0075] This example characterizes the microstructure of Examples 1-3 and Comparative Example 2, which prepared conductive films using the same raw materials and composition. Specific testing methods include: using field emission scanning electron microscopy to characterize the cross-sectional morphology of the conductive film samples. The test results are as follows: Figure 1 and Figure 2 As shown; where, Figure 1 These are cross-sectional scanning electron microscope images of the conductive film sample obtained in Comparative Example 2 at different characterization dimensions. Figure 1 In the middle: (a) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Comparative Example 2 with a size of 50 μm, and (b) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Comparative Example 2 with a size of 10 μm. Figure 2 In the image: (a) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Example 1; (b) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Example 2; and (c) is a cross-sectional scanning electron microscope image of the conductive film sample obtained in Example 3.

[0076] Depend on Figure 1 and Figure 2It can be seen from the cross-sectional scanning electron microscope (SEM) images of the conductive film obtained in Comparative Example 2 that LM particles are uniformly dispersed in the TPU matrix, the LM particles are tightly bonded to the TPU matrix without voids, and the particle size of the LM particles is approximately 10 μm. In contrast, the cross-sectional SEM images of the conductive films obtained in Examples 1-3 show that the LM particles are in-situ fibrous along the stretching direction. At thermal stretching ratios of 200%, 500%, and 800%, the LM lengths are 28 μm, 57 μm, and 89 μm, respectively, and the aspect ratio of the liquid metal remains within the range of 7.1 to 42.4, indicating that the LM particles can undergo good deformation along with the TPU matrix.

[0077] Test Example 2

[0078] In this example, a TH 2515 DC resistance meter was used to test the conductivity of the conductive film samples obtained in the above embodiments and Comparative Example 2. The test method is as follows: silver paste was applied to both ends of the sample to reduce contact resistance. After curing, the volume resistivity of the sample was tested. The conductivity of the sample was calculated using the formula σ = L / (R·S), where σ, L, and S represent the conductivity, length, and cross-sectional area of ​​the sample, respectively.

[0079] The test results are shown in Table 1.

[0080] Table 1

[0081] Test sample Electrical conductivity (S / m) Example 1 4.9 Example 2 <![CDATA[1.4×10 4 ]]> Example 3 <![CDATA[2.7×10 4 ]]> Example 4 <![CDATA[9.0×10 3 ]]> Example 5 <![CDATA[1.3×10 4 ]]> Example 6 <![CDATA[4.3×10 4 ]]> Example 7 <![CDATA[1.5×10 5 ]]> Example 8 <![CDATA[2.9×10 5 ]]> Example 9 <![CDATA[3.1×10 5 ]]> Example 10 4.7 Comparative Example 1 <![CDATA[8.7×10 -12 ]]> Comparative Example 2 <![CDATA[8.0×10 -2 ]]>

[0082] As shown in Table 1:

[0083] Without the addition of LM, the conductivity of pure TPU in Comparative Example 1 was 8.7 × 10⁻⁶. -12 S / m is a typical polymer insulator. When the LM content is 30 vol% (Comparative Example 2), due to the low LM content, the LM particles are separated by the TPU matrix and cannot make effective contact, the conductive network cannot be formed, and the conductivity is only 8.0 × 10⁻⁶. -2 S / m.

[0084] The results from the various examples show that, under the same LM volume fraction, the electrical conductivity of the LM / TPU composite film significantly increases with increasing thermal tensile strain. Specifically, Examples 1 to 3 correspond to LM / TPU composite films prepared under different tensile strains (200%, 500%, and 800%) with an LM content of 30 vol%. Compared to Comparative Example 2 with the same LM content, the electrical conductivity increased by 6.1 × 10⁻⁶. 1 times, 1.8×10 5 times and 3.4×10 5 The result shows that this strategy can achieve electrical conductivity comparable to or even better than high-filler composites with a filling amount far lower than that of traditional preparation methods.

[0085] This phenomenon can be attributed to the random distribution of conductive particles in traditional conductive composite materials (such as Comparative Example 2), resulting in a polymer interface layer in the formed conductive network that hinders current transmission, thus limiting the improvement of conductivity. The method proposed in this patent, through controlled stretching at low LM content, causes the dispersed LM particles to fiberize in situ, forming a conductive fiber network with a high aspect ratio. This significantly reduces the percolation threshold for forming conductive pathways and enhances conductivity. Based on this mechanism, the composite films prepared in Examples 4 to 9, at the same LM volume fraction, exhibit increased conductivity with tensile strain, ultimately achieving a conductivity as high as 3.1 × 10⁻⁶. 5 A conductive composite film with a conductivity of S / m; simultaneously, due to the high conductivity of gallium indium tin alloy (3.46 × 10⁻⁶ m / s); 6 S / m is higher than that of gallium-indium alloy (3×10). 6 When the LM was replaced with a gallium-indium alloy (Example 10), the conductivity decreased compared to Example 1. Furthermore, the present invention can only effectively control the material strain when the tensile heat treatment temperature is controlled at 90~110℃ and the applied tensile strain is 200~800%. At other temperatures (such as 70℃ or 125℃) or at a tensile strain of 1000%, the high strain of the material cannot be controlled, leading to cracks and LM leakage, thus failing to meet basic usage requirements.

[0086] In summary, this invention has successfully constructed a high-performance conductive composite material with low LM content through a simple and efficient stretching and fiberization strategy, and can prevent leakage problems, which is an innovative breakthrough in the field of LM-based conductive thin film research.

[0087] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0088] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a conductive film based on liquid metal fiberization, characterized in that, Includes the following steps: 30 to 45 parts by volume of liquid metal and 55 to 70 parts by volume of thermoplastic polyurethane are added to a solvent in a certain proportion and stirred to obtain a mixture; the mixture is injected into a mold and then dried to form a composite film. The composite film is subjected to mechanical sintering and then stretching heat treatment to obtain the conductive film based on liquid metal fiberization. The working conditions for the tensile heat treatment include: a temperature of 90~110℃ and a tensile strain of 800% applied to the composite film. The conductive film based on liquid metal fiberization contains fibrous liquid metal, and the aspect ratio of the fibrous liquid metal is 7.1~42.

4.

2. The method for preparing a conductive film based on liquid metal fiberization according to claim 1, characterized in that, The liquid metal includes at least one of gallium indium alloy and gallium indium tin alloy.

3. The method for preparing a conductive film based on liquid metal fiberization according to claim 2, characterized in that, In the gallium-indium alloy, the mass ratio of gallium to indium is 75:25, and in the gallium-indium-tin alloy, the mass ratio of gallium, indium, and tin is 66:20.5:13.

5.

4. The method for preparing a conductive film based on liquid metal fiberization according to claim 1, characterized in that, The glass transition temperature of the soft segment in the thermoplastic polyurethane is -50 to -45°C, and the glass transition temperature of the hard segment in the thermoplastic polyurethane is 58 to 63°C.

5. The method for preparing a conductive film based on liquid metal fiberization according to claim 1, characterized in that, The thermoplastic polyurethane includes polyether-type thermoplastic polyurethane, and the polyether-type thermoplastic polyurethane includes thermoplastic polyurethane with product model Elastollan 2180A10.

6. The method for preparing a conductive film based on liquid metal fiberization according to claim 1, characterized in that, The solvent includes N,N-dimethylformamide, and the concentration of the thermoplastic polyurethane in the mixture is 28~30 g / ml.

7. A conductive film based on liquid metal fiberization, characterized in that, The conductive film based on liquid metal fiberization is prepared by the method for preparing a conductive film based on liquid metal fiberization according to any one of claims 1 to 6.

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