Composite conductive film preparation method and composite conductive film

Abstract

The invention provides a composite conductive film preparation method and a composite conductive film, a PDMS matrix, a multi-walled carbon nanotube, a conductive filler, an anionic dispersant and isopropanol are mixed according to a preset mass ratio to obtain a slurry with a steric hindrance structure; and processing the uniformly mixed slurry by using a mold and a thermocuring process to obtain the composite conductive film with high dispersity, biosafety and machinability.

Description

Technical Field

[0001] This invention relates to the technical field of composite conductive materials, and more specifically, to a method for preparing a composite conductive thin film and the composite conductive thin film. Background Technology

[0002] With the rapid development of cutting-edge technologies such as wearable health monitoring devices, soft robots, and smart electronic skin, flexible electronic devices are facing increasingly stringent requirements for their core functional materials. These materials not only need to possess excellent mechanical flexibility and stretchability, but must also achieve stable and reliable electrical performance output under deformation. Conductive composite materials, as a key foundational material in flexible circuits, directly determine the overall stability and reliability of flexible electronic devices through their comprehensive performance.

[0003] Traditional conductive fillers (such as metal particles and carbon nanotubes) tend to agglomerate and settle in polymer matrices, resulting in uneven spatial distribution of the conductive network. During dynamic deformation, cracks initiate in enriched areas due to stress concentration, while depleted areas form electrical "dead zones," causing drastic fluctuations in material resistance and even momentary signal interruptions. Multi-walled carbon nanotubes (MWCNTs) possess both a high aspect ratio and excellent intrinsic conductivity, making them considered ideal conductive phases. However, their strong van der Waals forces and surface hydrophobicity make them difficult to disperse uniformly in flexible matrices such as polydimethylsiloxane (PDMS), becoming a core bottleneck restricting the performance stability of composite materials.

[0004] In existing technologies, the dispersibility of multi-walled carbon nanotubes in flexible matrices is improved by using highly polar solvents or surfactants. However, the following drawbacks exist: 1) Halogenated solvents have high bioaccumulation, limiting their application in medical and wearable applications. 2) When the conductive filler doping amount is >3 wt%, the viscosity of the prepolymer increases sharply, making stirring and degassing difficult, and pore defects are easily formed after thermosetting. 3) Under dynamic mechanical deformation, the filler re-agglomerates, causing irreversible degradation of conductivity.

[0005] Therefore, there is an urgent need for a composite conductive thin film material that combines high dispersibility, biosafety, and processability. Summary of the Invention

[0006] In view of the above problems, the purpose of this invention is to provide a method for preparing a composite conductive thin film, a composite conductive thin film, a flexible strain sensor, and electronic skin, so as to solve at least one problem existing in the prior art.

[0007] In a first aspect, the present invention provides a method for preparing a composite conductive film, comprising: mixing a PDMS matrix, multi-walled carbon nanotubes, conductive fillers, anionic dispersants, and isopropanol in a preset mass ratio to obtain a homogenized slurry; in the slurry, hydrophobic segments of the anionic dispersant are adsorbed onto the surface of the multi-walled carbon nanotubes, and hydrophilic segments extend to the outside of the multi-walled carbon nanotubes to the PDMS matrix to form a steric hindrance structure; the amount of multi-walled carbon nanotubes is 1-10 parts by mass relative to 100 parts by mass of the PDMS matrix; the amount of isopropanol is 11-19 parts by mass; the homogenized slurry is poured into a mold and cured; wherein the mold is heat-cured at a first set temperature to allow the isopropanol to evaporate; heat-cured at a second set temperature to complete the PDMS crosslinking; and a demolding process is performed to obtain the composite conductive film.

[0008] Alternatively, the anionic dispersant may be sodium dodecyl sulfate.

[0009] In addition, an optional technical solution is that the first set temperature is 60-70℃; and the second set temperature is 80-100℃.

[0010] Alternatively, an optional technical solution involves mixing the PDMS matrix, multi-walled carbon nanotubes, conductive filler, anionic dispersant, and isopropanol according to a preset mass ratio. Vacuum stirring was performed using a non-invasive homogenizer to obtain a well-mixed dispersion with a sterically hindered structure; wherein the stirring rate was 1000 r / min - 1500 r / min and the stirring time was 8-15 minutes. The dispersion was subjected to ultrasonic treatment for 20-45 minutes to obtain a well-mixed slurry.

[0011] In addition, an optional technical solution is that the PDMS matrix is ​​a two-component thermosetting silicone, wherein the mass ratio of prepolymer to curing agent is 15:1.

[0012] In addition, an optional technical solution is to heat-cure the mold at a first set temperature, with the following conditions: vacuum degree ≥ 0.09 MPa and processing time 1-2 hours. During the thermosetting process at the second set temperature, the processing conditions are: normal pressure and processing time is 1.5-3 hours.

[0013] In addition, an optional technical solution is that the mass ratio of the anionic dispersant, multi-walled carbon nanotubes and conductive filler is 1:10:10.

[0014] Secondly, the present invention provides a composite conductive film having a steric hindrance structure; the steric hindrance structure is formed by the adsorption of hydrophobic segments of anionic dispersant on the surface of the multi-walled carbon nanotubes, and the hydrophilic segments extending to the PDMS matrix on the outside of the multi-walled carbon nanotubes.

[0015] Thirdly, the present invention provides a flexible strain sensor, comprising a composite conductive film prepared using the composite conductive film preparation method described above.

[0016] Fourthly, the present invention provides an electronic skin, comprising a composite conductive film prepared using the composite conductive film preparation method described above.

[0017] This invention discloses a method for preparing a composite conductive film, the composite conductive film, a flexible strain sensor, and electronic skin. The method employs thermosetting and template processes, using a non-invasive homogenizer and an ultrasonic machine to prepare a PDMS / MWCNTs / G composite conductive film. Isopropanol is used as a diluent in combination with an anionic dispersant, and stirring is performed using a non-invasive homogenizer to form a steric hindrance structure, thus inhibiting the aggregation of multi-walled carbon nanotubes. Stepped-temperature thermosetting first volatilizes the isopropanol, then completes the PDMS crosslinking, effectively fixing the conductive network structure. This solves the problems of filler addition amount and biosafety issues caused by halogenated solvents in traditional preparation methods. The composite conductive film of this invention, with 5wt% MWCNTs, exhibits a conductivity ≥21.3 S / m (corresponding to a resistivity ≤0.047 Ω·m), ensuring stable signal transmission in flexible electronic devices and providing key material support for high-performance flexible electronic devices.

[0018] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0019] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings. In the drawings: Figure 1 This is a schematic flowchart of a method for preparing a composite conductive thin film according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the spatial steric hindrance structure according to an embodiment of the present invention; Figure 3The graph shows the results of the potential-dispersion stability test of the slurries of Preparation Example 1 and Comparative Example 1 provided according to the present invention. Figure 4 The results of viscosity tests for the slurries of Preparation Example 1 and Comparative Example 2 provided according to the present invention are shown in the figure.

[0020] Figure 5 The graph shows the conductivity test results of the composite conductive films prepared according to Example 2 and Comparative Example 3 provided by the present invention.

[0021] Figure 6 The graph shows the resistance change test results of the composite conductive thin film prepared according to Example 1 of the present invention under strains of 10%, 20%, 30%, and 50%.

[0022] Figure 7 A comparison chart of infrared test results of the composite conductive film prepared in Preparation Example 1 and the composite conductive film prepared in Comparative Example 4 according to the present invention.

[0023] In all the accompanying drawings, the same reference numerals indicate similar or corresponding features or functions. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0025] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0027] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0028] Figure 1 A schematic flowchart of the method for preparing composite conductive thin films is shown.

[0029] The electrostatic repulsion of sodium dodecyl sulfate (SDS) inhibits filler agglomeration, and the viscosity-reducing effect and homogenizing shear force of isopropanol significantly improve the dispersion uniformity of the composite conductive filler. Furthermore, it is less prone to secondary agglomeration during long-term storage, exhibiting superior conductivity stability compared to traditional systems. The raw materials used are low-toxicity isopropanol and non-toxic SDS, which leave no residue after volatilization. The preparation process generates no toxic waste, reducing health risks for operators and minimizing harmful residues in downstream applications, thus complying with environmental regulations and the "green manufacturing" trend. The process requires no complex pretreatment; dispersion is achieved through a simple step of vacuum stirring combined with ultrasonic treatment using a non-invasive homogenizer. Equipment maintenance costs are lower than high-pressure homogenizers, and raw material costs are lower than those of special solvents like NMP, demonstrating significant advantages for industrial scale-up and cost competitiveness. Moreover, the dispersed filler can be directly applied to multiple fields such as conductive coatings, composite materials, and electrode materials without requiring formulation adjustments for different scenarios, offering superior versatility compared to single-function dispersion solutions.

[0030] Preparation Example 1 Experimental materials: MWCNTs and graphene were purchased from Shenzhen Suiheng Technology Co., Ltd.; PDMS and curing agent were purchased from Dow Corning Corporation (USA) and Shanghai Aladdin Biochemical Technology Co., Ltd. Other materials were commercially available.

[0031] S1. According to the preset mass ratio, the PDMS matrix, curing agent, multi-walled carbon nanotubes, conductive material, anionic dispersant, and isopropanol are sequentially added to the sample box of the non-invasive homogenizer; wherein, the anionic dispersant is sodium dodecyl sulfate (SDS); the conductive material (G) is MWCNTs graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, including a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of PDMS matrix, multi-walled carbon nanotubes, MWCNTs graphene, SDS, and isopropanol is 20:1:1:0.1:15.

[0032] S2. Vacuum stirring is performed using a non-invasive homogenizer to obtain a well-mixed dispersion forming a sterically hindered structure; wherein the stirring rate is 1500 r / min and the stirring time is 10 minutes; the dispersion is then ultrasonically treated for 30 minutes at room temperature, power of 200 W, and frequency of 25 kHz to obtain a well-mixed slurry. It should be noted that, compared to existing technologies, the stirring time for chloromethane derivative systems needs to be ≥30 min. This invention significantly shortens the preparation time.

[0033] like Figure 2 As shown, the steric hindrance structure is formed by the adsorption of hydrophobic segments of sodium dodecyl sulfate on the surface of the multi-walled carbon nanotube, and the hydrophilic segments extend to the PDMS matrix on the outside of the multi-walled carbon nanotube.

[0034] S3. Pour the uniformly mixed slurry into the mold and spread it evenly using a scraper. The template in the mold is 120mm long and 0.5mm thick. Optionally, the electrode wire is made of copper wire. Immediately after the slurry is coated, copper wires are embedded at both ends. After step curing, an integrated test electrode is formed for subsequent resistance-strain characterization.

[0035] S4. Place the formed template in an oven for stepped thermosetting; first, thermoset at 60℃ with a vacuum of 0.095 MPa for 1.5 hours to completely evaporate the isopropanol; then, thermoset at 80℃ for 2 hours to form the final product. This yields the PDMS / MWCNTs / G composite conductive film 1.

[0036] After SDS and IPA are added to PDMS, they decompose into anions and form a coating structure around multi-walled carbon nanotubes (MWCNTs), effectively overcoming the aggregation tendency of MWCNTs and achieving highly uniform dispersion in the PDMS matrix. Compared with existing technologies, this invention utilizes the specific coating effect of SDS and the dilution synergistic effect of isopropanol to significantly improve the dispersion uniformity and stability of carbon nanotube materials in flexible polymer substrates. This high dispersion ensures the integrity and uniformity of the conductive network inside the material. When the amount of MWCNTs added is 5 wt% of the PDMS matrix, the conductivity of the resulting flexible conductive material reaches 21.3 S / m, thereby ensuring the accurate and reliable transmission of electrical signals in flexible electronic devices and providing key material support for the development of high-performance flexible electronic devices.

[0037] Preparation Example 2 S1. According to the preset mass ratio, the PDMS matrix, curing agent, multi-walled carbon nanotubes, conductive material, anionic dispersant, and isopropanol are sequentially added to the sample box of the non-invasive homogenizer; wherein, the anionic dispersant is sodium dodecyl sulfate (SDS); the conductive material is MWCNTs graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, including a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of PDMS matrix, multi-walled carbon nanotubes, MWCNTs graphene, SDS, and isopropanol is 100:3:3:0.3:45.

[0038] S2. Vacuum stirring is performed using a non-invasive homogenizer to obtain a well-mixed dispersion with a steric structure; wherein the stirring rate is 1500 r / min and the stirring time is 8 minutes; the dispersion is ultrasonically treated for 20 minutes at room temperature, power of 200 W and frequency of 25 kHz to obtain a well-mixed slurry.

[0039] S3. Pour the uniformly mixed slurry into the mold and spread it evenly using a scraper. The template in the mold is 120mm long and 0.5mm thick. Optionally, the electrode wire is made of copper wire. Immediately after the slurry is coated, copper wires are embedded at both ends. After step curing, an integrated test electrode is formed for subsequent resistance-strain characterization.

[0040] S4. Place the formed template in an oven for stepped thermosetting; first, thermoset at 70℃ with a vacuum of 0.09 MPa for 1 hour to completely evaporate the isopropanol; then, thermoset at 100℃ for 1.5 hours to form the final product. This yields the PDMS / MWCNTs / G composite conductive film 2.

[0041] Preparation Example 3 S1. According to the preset mass ratio, PDMS matrix, curing agent, multi-walled carbon nanotubes, conductive material, anionic dispersant, and isopropanol are sequentially added to the sample box of the non-invasive homogenizer; wherein, the anionic dispersant is sodium dodecyl sulfate (SDS); the conductive material is MWCNTs graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, including a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of PDMS matrix, multi-walled carbon nanotubes, MWCNTs graphene, SDS, and isopropanol is 100:1:3:0.3:45.

[0042] S2. Vacuum stirring is performed using a non-invasive homogenizer to obtain a well-mixed dispersion with a steric structure; wherein the stirring rate is 1200 r / min and the stirring time is 15 minutes; the dispersion is ultrasonically treated for 45 minutes at room temperature, power of 200 W and frequency of 25 kHz to obtain a well-mixed slurry.

[0043] S3. Pour the well-mixed slurry into the mold and smooth it out by scraping; the template in the mold is 120mm long and 0.5mm thick.

[0044] S4. Place the formed template in an oven for stepped thermosetting; first, thermoset at 65℃ with a vacuum of 0.09 MPa for 2 hours to completely evaporate the isopropanol; then, thermoset at 90℃ for 3 hours to form the final product. The resulting composite conductive film 3 is obtained.

[0045] Preparation Example 4 S1. According to the preset mass ratio, PDMS matrix, curing agent, multi-walled carbon nanotubes, conductive material, anionic dispersant, and isopropanol are sequentially added to the sample box of the non-invasive homogenizer; wherein, the anionic dispersant is sodium dodecyl sulfate (SDS); the conductive material is MWCNTs graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, including a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of PDMS matrix, multi-walled carbon nanotubes, MWCNTs graphene, SDS, and isopropanol is 100:10:3:0.3:45.

[0046] S2. Vacuum stirring is performed using a non-invasive homogenizer to obtain a well-mixed dispersion with a steric structure; wherein the stirring rate is 1000 r / min and the stirring time is 12 minutes; the dispersion is ultrasonically treated for 45 minutes at room temperature, power of 200 W and frequency of 25 kHz to obtain a well-mixed slurry.

[0047] S3. Pour the uniformly mixed slurry into the mold and spread it evenly using a scraper. The template in the mold is 120mm long and 0.5mm thick. S4. Place the formed template in an oven for stepped thermosetting. First, heat-cure at 65℃ and a vacuum of 0.09 MPa for 2 hours to completely evaporate the isopropanol. Then, heat-cure at 90℃ for 3 hours to form the final product. The resulting composite conductive film 4 is obtained.

[0048] The conductivity uniformity of composite conductive films 1, 2, 3 and 4 obtained in Preparation Examples 1-4 was tested. The relative standard deviation (RSD) of the conductivity of the prepared flexible conductive materials was all within 5%, which ensured the accurate and reliable transmission of electrical signals in flexible electronic devices and provided key material support for the development of high-performance flexible electronic devices.

[0049] Comparative Example 1 S1. According to the preset mass ratio, add the PDMS matrix, curing agent, multi-walled carbon nanotubes, conductive material, and isopropanol sequentially into the sample box of the non-invasive homogenizer; wherein, the conductive material is MWCNTs graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, including a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of PDMS matrix, multi-walled carbon nanotubes, MWCNTs graphene, and isopropanol is 20:1:1:15.

[0050] S2. Vacuum stirring is performed using a non-invasive homogenizer to obtain a well-mixed dispersion; wherein the stirring rate is 1500 r / min and the stirring time is 10 minutes; the dispersion is ultrasonically treated for 30 minutes at room temperature, power of 200 W and frequency of 25 kHz to obtain a well-mixed slurry.

[0051] The slurries from Preparation Example 1 and Comparative Example 1 were subjected to Zeta potential-dispersion stability tests using a laser Doppler electrophoresis apparatus. The test temperature was 25°C, the equilibration time was 120 seconds, and the electric field strength was 10 kV / m. -1 Phase diagram linearity > 0.95, single measurement coefficient of variation < 5%, otherwise repeat the test. The results of the potential-dispersion stability test are as follows: Figure 3 As shown.

[0052] Through observation Figure 3 As can be seen, by adding sodium dodecyl sulfate (SDS) to form a sterically hindered structure, and by monitoring the zeta potential, the potential of the dispersion system is ≥ Stable at 30 mV. The Zate potential of the slurry in Preparation Example 1 was reduced to -41 mV, achieving highly uniform dispersion of MWCNTs in PDMS.

[0053] It should be noted that the dispersibility of MWCNTs (multi-walled carbon nanotubes) can be reflected by Zeta potential testing. The core principle is that the Zeta potential directly characterizes the charged state of the MWCNT surface, and its absolute value determines the strength of the electrostatic repulsion between particles. This repulsion is a key factor in preventing MWCNT aggregation and maintaining stable dispersion. The specific reasons are as follows: 1. The aggregation nature of MWCNTs: MWCNTs have hydrophobic surfaces, large specific surface areas, and high surface energy, making them highly susceptible to aggregation due to van der Waals forces, resulting in poor dispersibility. To achieve stable dispersion, external forces or interfacial regulation are needed to enhance the repulsion between particles. 2. The relationship between Zeta potential and surface charge: When MWCNTs (especially after surface modification or the addition of dispersants such as SDS) are dispersed in a liquid medium, their surfaces adsorb charges (such as anions or cations from the dispersant) and form a "diffuse electric double layer" around them. The zeta potential is the potential value of the "sliding surface" (the interface between MWCNTs and the medium in the electric double layer), directly reflecting its surface charge density. 3. Direct correspondence with dispersibility: If the absolute value of the zeta potential is small (usually <20mV): it indicates that the MWCNTs have low surface charge, weak electrostatic repulsion between particles, insufficient to resist van der Waals forces, and are prone to aggregation, resulting in poor dispersibility. If the absolute value of the zeta potential is large (usually >30mV): it indicates high surface charge density, strong electrostatic repulsion between particles, effectively preventing aggregation, resulting in a more stable dispersion system and good dispersibility. Therefore, by testing the change in zeta potential, the dispersion stability of MWCNTs in the medium can be directly determined.

[0054] Comparative Example 2 S1. According to the preset mass ratio, the PDMS matrix, curing agent, multi-walled carbon nanotubes, conductive material, and anionic dispersant are sequentially added to the sample box of the non-invasive homogenizer; wherein, the anionic dispersant is sodium dodecyl sulfate (SDS); the conductive material is MWCNTs graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, including a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of PDMS matrix, multi-walled carbon nanotubes, MWCNTs graphene, and SDS is 20:1:1:0.1.

[0055] S2. Vacuum stirring is performed using a non-invasive homogenizer to obtain a well-mixed dispersion; wherein the stirring rate is 1500 r / min and the stirring time is 10 minutes; the dispersion is ultrasonically treated for 30 minutes at room temperature, power of 200 W and frequency of 25 kHz to obtain a well-mixed slurry.

[0056] The slurries of Preparation Example 1 and Comparative Example 2 were subjected to viscosity tests using a rotational rheometer; the shear rates ranged from 0.1 to 100 s⁻¹.-1 Logarithmic scan, taking equilibrium viscosity at each point ( < 5%). Record 1 second. -1 and 10 s -1 The apparent viscosity was used as the primary comparison value. At least three tests were performed for each group, and the average value ± SD was taken. The viscosity test results are as follows: Figure 4 As shown.

[0057] Through observation Figure 4 It is evident that diluting multi-walled carbon nanotubes (MWCNTs) with isopropanol reduced the processing viscosity of the 5 wt% MWCNTs system from >100,000 mPa·s to ≤5,000 mPa·s, overcoming the process bottleneck of high-doping concentrations being unable to form the nanotubes. Furthermore, the biotoxicity (LD50) of isopropanol (IPA) is significantly reduced. 50 =5,000 mg / kg) is only a chloromethane derivative (chloroform LD50). 50 =908 mg / kg) is 1 / 5 of that, ensuring the safety of medical wearable applications.

[0058] Comparative Example 3 S1. The PDMS matrix, curing agent, multi-walled carbon nanotubes (MWCNTs), and conductive material are mixed according to a preset mass ratio to obtain a homogenized slurry. The conductive material is MWCNTs graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, comprising a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of the PDMS matrix, multi-walled carbon nanotubes, and MWCNTs graphene is 100:3:5. This is prepared using a traditional dry mixing method. The mass ratio of the PDMS matrix to the multi-walled carbon nanotubes is 100:3, forming a 3 wt% dry mixing doping system.

[0059] S2. Pour the well-mixed slurry into the mold and spread it evenly using a scraper. Connect the electrode wires to both ends. The template in the mold is 120mm long and 0.5mm thick, and the electrode wires are copper wires. S3. Place the formed template into an oven for heat curing; to obtain the composite conductive film D3.

[0060] The conductivity of the composite conductive film 2 from Preparation Example 2 and the composite conductive film D3 from Comparative Example 3 was tested. This was to quantitatively compare the effects of different formulations on the conductivity of the PDMS / MWCNTs / G composite film and verify the effectiveness of the conductive network construction. The four-probe resistivity test was performed using a four-probe method, and the results are shown below. Figure 5 .

[0061] Through observation Figure 5As can be seen, after IPA dilution, the conductivity reached 21.3 S / m with 3wt% MWCNTs doping, which is more than 70% higher than that of the traditional dispersion process (dry mixing method) of Comparative Example 3, indicating that the conductive network of the composite conductive film obtained by the preparation method of the present invention is more compact.

[0062] The composite conductive film 1 obtained in Preparation Example 1 was subjected to resistance change tests at strains of 10%, 20%, 30%, and 50%. Wires were led from both ends of the material and connected to a resistance meter to test the resistance, which was then placed in a tensile testing machine for stretching. Under uniaxial tensile conditions, the resistance change was caused by the geometric deformation of the conductive network and the change in tunneling spacing. The resistance-strain curves were recorded in real time using a four-wire or two-wire method, and the normalized resistance change rate was calculated. The tensile testing machine was a universal testing machine with a load accuracy of ±0.5%. A digital multimeter (Keysight 34470A or equivalent) in four-wire mode with a sampling frequency ≥10 Hz was used to acquire resistance data. Synchronous recording between the tensile testing machine and the multimeter was achieved via LAN / Trigger. The resistance change test results of the composite conductive film material at strains of 10%, 20%, 30%, and 50% were obtained.

[0063] Through observation Figure 6 As can be seen, when the composite conductive film 1 obtained in Example 1 was stretched by 10%, 20%, 30%, and 50% respectively, the resistance change rate was less than 10%, and the resistance change rate deviation at 50% tensile strain was ≤5%. This indicates that the prepared flexible conductive film material possesses certain tensile stability. This demonstrates that the composite conductive film prepared by this invention solves the signal distortion problem caused by dynamic deformation.

[0064] Comparative Example 4 S1. According to the preset mass ratio, the PDMS matrix, curing agent, multi-walled carbon nanotubes, conductive material, anionic dispersant, and isopropanol are sequentially added to the sample box of the non-invasive homogenizer; wherein, the anionic dispersant is sodium dodecyl sulfate (SDS); the conductive material is graphene. The PDMS matrix is ​​a two-component thermosetting organosilicon, including a prepolymer and curing agent in a mass ratio of 15:1. The mass ratio of PDMS matrix, multi-walled carbon nanotubes, graphene, SDS, and isopropanol is 20:1:1:0.1:15.

[0065] S2. Vacuum stirring is performed using a non-invasive homogenizer to obtain a well-mixed dispersion with a steric structure; wherein the stirring rate is 1500 r / min and the stirring time is 10 minutes. The dispersion was ultrasonically treated for 30 minutes at room temperature, with a power of 200 W and a frequency of 25 kHz to obtain a well-mixed slurry.

[0066] S3. Pour the well-mixed slurry into the mold and spread it evenly using a scraper. Connect the electrode wires to both ends. The template in the mold is 120mm long and 0.5mm thick, and the electrode wires are copper wires. S4. Place the formed template in an oven for heat curing; heat cure at 80℃ for 3.5 hours to obtain the composite conductive film D4.

[0067] The infrared spectra of "Example 1: Sample Preparation with Added Isopropanol and Step-Cured Method" and "Comparative Example 4: Sample Preparation with Added Isopropanol and No Step-Cured Method" were tested and compared. The results are as follows: Figure 7 As shown. By observation Figure 7 As can be seen, in the spectrum of the sample from Example 1 of the step-type thermosetting preparation, the 3200-3600 cm⁻¹... -1 The broad OH peak completely disappeared, and at 1370 cm⁻¹... -1 The characteristic doublet of isopropanol also showed no absorption signal; meanwhile, the spectrum only retained the characteristic peaks of PDMS and SDS (such as 1260 cm⁻¹). -1 1020-1090cm -1 2850-2920 cm -1 Furthermore, the peak shape and intensity are completely consistent with the spectrum of the "pure PDMS / SDS / MWCNTs / G system without isopropanol", proving that there is no isopropanol residue.

[0068] It should be noted that the comparison principle of the above infrared spectra is based on the key characteristic peak of isopropanol: hydroxyl (-OH) stretching vibration: 3200-3600 cm⁻¹ -1 (Strong and broad absorption peak, due to intermolecular hydrogen bonding of isopropanol); Methyl (-CH3) bending vibration: 1370 cm⁻¹ -1 (Isopropanol's signature "double peak," due to the vibrational coupling of two equivalent methyl groups, is the core peak that distinguishes it from other alcohols); CO stretching vibration: 1050-1100 cm⁻¹ -1 (Weak peak, can be omitted, but can be used as an auxiliary judgment peak). Peaks of other components in the system (interference needs to be excluded): PDMS: main peak at 1260 cm⁻¹ -1 (Si-CH3 bending), 1020-1090 cm -1 (Si-O-Si stretching), no -OH and 1370 cm⁻¹ -1 Bimodal; SDS: Main peak at 2850-2920 cm⁻¹ -1 (-CH2- stretching), 1050 cm -1 (-SO4) - (Extendable), also without 3200-3600 cm -1 -OH peak and 1370 cm⁻¹-1 Bimodal absorption peaks; MWCNTs: No obvious characteristic absorption peaks, do not interfere with the judgment.

[0069] Example 1 A flexible strain sensor was fabricated using the composite conductive film 1 obtained in Example 1. In one example, the composite conductive film 1 was subjected to electrode integration, in-situ encapsulation, or transfer bonding processes to obtain the flexible strain sensor. The flexible strain sensor exhibited a linear fit R0 to the resistance-strain curve within the 0–50% strain range. 2 >0.99; after 500 cycles of 0–50% loading, the rate of change of resistance decreases by <5%.

[0070] Example 2 The composite conductive film 1 obtained in Preparation Example 1 was used to prepare electronic skin. In one example, the composite conductive film 1 underwent microstructure transfer, heating / sensing electrodes were integrated, and a 20 µm ultrathin PDMS encapsulation layer was spin-coated onto the entire film. After curing, a flexible heating electronic skin was formed. The obtained flexible heating electronic skin can achieve a steady-state temperature difference of ≤ ±0.4 ℃ within an effective area of ​​4 cm × 4 cm, and its performance degradation is <5% after 500 cycles of 0-50% stretching.

[0071] The composite conductive film obtained using this invention can also be used in wearable electrodes and conductive paths in elastic circuits. Based on the material's excellent fatigue resistance and strain stability, it can meet the range of motion angles of body joints in wearable flexible electronic products, ensuring accurate signal sensing. Compared to traditional rigid sensing circuits, it also has stretchability.

[0072] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within the present invention. No reference numerals in the appended diagrams should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other elements or steps, and the singular does not exclude the plural.

[0073] However, those skilled in the art should understand that various modifications can be made to the composite conductive film preparation method and the composite conductive film proposed in this invention without departing from the scope of this invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for preparing a composite conductive thin film, characterized in that, include, PDMS matrix, multi-walled carbon nanotubes, conductive filler, anionic dispersant and isopropanol are mixed in a preset mass ratio to obtain a well-mixed slurry. In the slurry, the hydrophobic segments of the anionic dispersant are adsorbed onto the surface of the multi-walled carbon nanotubes, and the hydrophilic segments extend to the outside of the multi-walled carbon nanotubes to form a steric hindrance structure in the PDMS matrix; the amount of the multi-walled carbon nanotubes is 1-10 parts by mass relative to 100 parts by mass of the PDMS matrix; the amount of the isopropanol is 11-19 parts by mass. The mixed slurry is poured into a mold and cured; wherein the mold is heat-cured at a first set temperature to allow isopropanol to evaporate; and heat-cured at a second set temperature to complete PDMS crosslinking. A composite conductive film is obtained through a demolding process.

2. The method for preparing a composite conductive thin film according to claim 1, characterized in that, The anionic dispersant is sodium dodecyl sulfate.

3. The method for preparing a composite conductive thin film according to claim 1, characterized in that, The first set temperature is 60-70℃; the second set temperature is 80-100℃.

4. The method for preparing a composite conductive thin film according to claim 1, characterized in that, The process of mixing PDMS matrix, multi-walled carbon nanotubes, conductive filler, anionic dispersant, and isopropanol according to a preset mass ratio includes the following steps: Vacuum stirring was performed using a non-invasive homogenizer to obtain a well-mixed dispersion with a sterically hindered structure; wherein the stirring rate was 1000 r / min - 1500 r / min and the stirring time was 8-15 minutes. The dispersion was subjected to ultrasonic treatment for 20-45 minutes to obtain a well-mixed slurry.

5. The method for preparing a composite conductive thin film according to claim 1, characterized in that, The PDMS matrix is ​​a two-component thermosetting silicone, wherein the mass ratio of prepolymer to curing agent is 15:

1.

6. The method for preparing a composite conductive thin film according to claim 1, characterized in that, During the heat curing process of the mold at the first set temperature, the processing conditions are: vacuum degree ≥ 0.09 MPa, processing time 1-2 hours; During the thermosetting process at the second set temperature, the processing conditions are: normal pressure and processing time is 1.5-3 hours.

7. The method for preparing a composite conductive thin film according to claim 2, characterized in that, The mass ratio of the anionic dispersant, multi-walled carbon nanotubes, and conductive filler is 1:10:

10.

8. A composite conductive thin film, characterized in that, The composite conductive film has a steric hindrance structure; the steric hindrance structure is formed by the adsorption of hydrophobic segments of anionic dispersant on the surface of multi-walled carbon nanotubes, and the hydrophilic segments extending to the PDMS matrix on the outside of the multi-walled carbon nanotubes.

9. A flexible strain sensor, characterized in that, This includes composite conductive films prepared using the composite conductive film preparation method described in claim 1.

10. An electronic skin, characterized in that, This includes composite conductive films prepared using the composite conductive film preparation method described in claim 1.

Images