Preparation method of viologen / PVDF-HFP color-changing composite material

Abstract

The invention discloses a preparation method of a viologen / PVDF-HFP (Polyvinylidene Fluoride-Hexafluoropropylene) color-changing composite material, and relates to a preparation method of a color-changing composite material. In a modern electric power system, long-time operation of high-voltage equipment can cause accumulation of charges on the surface of an insulating material. Therefore, development of a visual detection technology suitable for the high-voltage environment is crucial to real-time monitoring of the insulation state. According to the invention, the viologen / PVDF-HFP color-changing composite material (block and film) containing viologen is prepared by using a PVDF-HFP material, so that electrochromic response under high voltage is realized; through FTIR spectral analysis, an obvious absorption peak is observed at 1630 cm <-1 >, and it is proved that viologen is successfully fused into a PVDF-HFP matrix; the viologen / PVDF-HFP color-changing composite material prepared by the invention can bear an electric field as high as 106 V / m, and shows reversible color change along with voltage and duration change.

Description

Technical Field

[0001] The invention relates to a method for preparing a color-changing composite material. Background Art

[0002] In modern power systems, after long-term operation of high-voltage equipment (such as transformers, GIS, high-voltage cables, etc.), space charges will accumulate on the surface of the insulation structure due to the strong electric field, resulting in local electric field distortion and increasing the risk of partial discharge or breakdown. Due to the lack of intuitive warning, maintenance personnel may face the risk of electric shock. Traditional electrochromic materials (such as viologen derivatives) rely on low voltage (<5V) and continuous current (µA~mA level) to drive color change, and cannot adapt to the extremely low leakage current (pA~nA level) and ultra-high electric field (>10 6 V / m) environments. Therefore, developing a high-voltage compatible visual inspection technology that uses electrochromic materials (such as insulator color change) to intuitively reflect the insulation status is crucial for improving grid stability and personnel safety. Therefore, developing visual inspection technology suitable for high-voltage environments is crucial for achieving real-time monitoring of insulation status. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a method for preparing a viologen / PVDF-HFP color-changing composite material.

[0004] A method for preparing a viologen / PVDF-HFP color-changing composite material, wherein the viologen / PVDF-HFP color-changing composite material is in the form of a block, and the preparation method is specifically completed by the following steps:

[0005] 1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system;

[0006] 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a white gel;

[0007] 3. Let the white gel stand at room temperature for a period of time to obtain a milky white transparent block, which is the viologen / PVDF-HFP color-changing composite material.

[0008] A method for preparing a viologen / PVDF-HFP color-changing composite material, wherein the viologen / PVDF-HFP color-changing composite material is in the form of a film, and the preparation method is specifically completed by the following steps:

[0009] 1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system;

[0010] 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a clear and transparent homogeneous solution;

[0011] 3. Allow the clear and transparent homogeneous solution to evaporate naturally at room temperature for a period of time to obtain a gel; then use a stainless steel scraper to evenly coat the gel on a clean glass substrate at room temperature and in a dust-free environment, with the wet film thickness controlled at 300μm~500μm; after coating, transfer the glass substrate to a blast drying oven for drying to obtain a light yellow translucent film, which is the viologen / PVDF-HFP color-changing composite material.

[0012] Principles and advantages of the present invention:

[0013] 1. This invention innovatively utilizes a viologen / PVDF-HFP color-changing composite material, combining high-voltage insulation performance with electrochromic functionality. Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) provides excellent dielectric properties and mechanical strength, while viologen imparts electrochromic properties. Experiments have shown that when the viologen content is 4wt%, the composite material exhibits a significant color change effect visible to the naked eye. This color change is directly triggered by space charge accumulation, rather than traditional current drive, enabling it to operate normally under extremely low current conditions in high-voltage equipment, providing a new approach for insulation status monitoring. However, existing electrochromic technologies are generally based on low-voltage drive (<5V) redox reaction mechanisms, requiring continuous currents in the μA to mA range to maintain the color change reaction, and their charge transfer is typically in the mC / cm 2 The leakage current of the high voltage insulation system is strictly limited to the pA~nA level (charge transfer <1nC / cm 2 ), which is 3-6 orders of magnitude lower than the current required for electrochromism; therefore, there is a fundamental contradiction between the working environment of the insulation system of power equipment and the above characteristics; the present invention prepares a viologen / PVDF-HFP color-changing composite material and explores its electrochromic behavior under high voltage conditions; the material must have both high insulation and electric field response characteristics, and achieve low charge (nC / cm 2 The color change is driven by the level (level), providing a new idea for insulator flashover indication.

[0014] 2. The present invention uses PVDF-HFP material to prepare viologen / PVDF-HFP color-changing composite materials (bulk and film) containing viologen to achieve electrochromic response under high voltage; FTIR spectrum analysis shows that at 1630 cm -1 Obvious absorption peaks were observed at the PVDF-HFP matrix, confirming that the viologen has been successfully integrated into the PVDF-HFP matrix. The viologen / PVDF-HFP color-changing composite material prepared by the present invention can withstand up to 10 6V / m electric field and exhibits reversible color change with voltage and duration. Notably, the material maintains dielectric properties comparable to pure PVDF-HFP (dielectric constant ≈ 10 at 50 Hz) while exhibiting only a slight increase in dielectric loss (tanδ < 0.2). This innovative approach successfully combines dual functions: reliable electrical insulation and intuitive visual status indication.

[0015] 3. The viologen / PVDF-HFP color-changing composite material (block) prepared by the present invention has a smooth and flat surface, presents a uniform translucent state under light transmission conditions, and has good elasticity and mechanical strength;

[0016] 4. The viologen / PVDF-HFP color-changing composite material (film) prepared by the present invention exhibits a uniform light yellow translucent state, a smooth surface without cracks, and good mechanical stability and interface bonding strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the structural formula of ethyl viologen dihexafluorophosphate;

[0018] Figure 2 is the structural formula of PVDF-HFP;

[0019] Figure 3 This is a picture of the viologen / PVDF-HFP color-changing composite material block prepared in Example 1;

[0020] Figure 4 This is a picture of the viologen / PVDF-HFP color-changing composite film prepared in Example 3;

[0021] Figure 5 Diagram of the experimental setup for the electrochromic behavior of the sample under high voltage conditions;

[0022] Figure 6 The electrochromic behavior and fading behavior of the viologen / PVDF-HFP color-changing composite material block prepared in Example 1 at 10 min, 20 min, and 30 min;

[0023] Figure 7 The electrochromic, breakdown, and fading behaviors of the viologen / PVDF-HFP color-changing composite material block prepared in Example 2 at 10 min, 20 min, and 30 min;

[0024] Figure 8 IR spectra of the viologen / PVDF-HFP color-changing composite films prepared in Examples 3 to 6;

[0025] Figure 9 is the dielectric constant of the viologen / PVDF-HFP color-changing composite film prepared in Examples 3 and 5;

[0026] Figure 10 The dielectric loss of the viologen / PVDF-HFP color-changing composite film prepared in Examples 3 and 5;

[0027] Figure 11 This is a breakdown probability diagram of the viologen / PVDF-HFP color-changing composite film prepared in Examples 3 and 5. DETAILED DESCRIPTION

[0028] Specific embodiment 1: This embodiment provides a method for preparing a viologen / PVDF-HFP color-changing composite material. The viologen / PVDF-HFP color-changing composite material is in the form of a block. The preparation method is specifically completed by the following steps:

[0029] 1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system;

[0030] 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a white gel;

[0031] 3. Let the white gel stand at room temperature for a period of time to obtain a milky white transparent block, which is the viologen / PVDF-HFP color-changing composite material.

[0032] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the viologen compound in step 1 is ethyl viologen dihexafluorophosphate. The other steps are the same as those in specific embodiment 1.

[0033] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that the mass fraction of the viologen compound in polyvinylidene fluoride-hexafluoropropylene in step 1 is 2 wt% to 4 wt%. The other steps are the same as those in specific embodiments 1 or 2.

[0034] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the constant temperature magnetic stirring temperature in step 2 is 50°C, the magnetic stirring speed is 300-500 rpm, and the magnetic stirring time is 20-40 minutes. The other steps are the same as specific embodiments 1 to 3.

[0035] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the organic solvent in step 2 is acetone; the mass of the mixed system in step 2 is 6.12 g to 6.24 g:(35 mL to 50 mL) by volume; and the standing time in step 3 is 40 to 50 hours. The other steps are the same as specific embodiments 1 to 4.

[0036] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: a method for preparing a viologen / PVDF-HFP color-changing composite material, wherein the viologen / PVDF-HFP color-changing composite material is in the form of a thin film, and the preparation method is specifically completed by the following steps:

[0037] 1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system;

[0038] 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a clear and transparent homogeneous solution;

[0039] Third, the clear, transparent, homogeneous solution was allowed to evaporate naturally at room temperature for a period of time to obtain a gel. The gel was then evenly coated onto a clean glass substrate using a stainless steel scraper at room temperature in a dust-free environment, with the wet film thickness controlled to be between 300 μm and 500 μm. After coating, the glass substrate was transferred to a forced air drying oven for drying, resulting in a pale yellow, translucent film, which is the viologen / PVDF-HFP color-changing composite material. The remaining steps are the same as those in Specific Embodiments 1 to 5.

[0040] Specific Embodiment 7: This embodiment differs from Specific Embodiments 1 to 6 in that the viologen compound in step 1 is ethyl viologen dihexafluorophosphate, and the mass fraction of the viologen compound in polyvinylidene fluoride-hexafluoropropylene is 1 wt% to 4 wt%. The other steps are the same as Specific Embodiments 1 to 6.

[0041] Specific Embodiment 8: This embodiment differs from Specific Embodiments 1 to 7 in that the organic solvent in step 2 is N-N-dimethylformamide; and the mass-to-volume ratio of the mixed system in step 2 to the organic solvent is (6.06 g to 6.24 g):40 mL. The remaining steps are the same as Specific Embodiments 1 to 7.

[0042] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the constant temperature magnetic stirring temperature in step 2 is 60°C, the magnetic stirring speed is 500-600 rpm, and the magnetic stirring time is 120-140 minutes. The other steps are the same as specific embodiments 1 to 8.

[0043] Specific Embodiment 10: This embodiment differs from Specific Embodiments 1 to 9 in that, in step 3, the clear, transparent homogeneous solution is naturally evaporated at room temperature for 1.5 to 2.5 hours to obtain a gel. The gel is then evenly coated on a clean glass substrate at room temperature and in a dust-free environment using a stainless steel scraper with a blade thickness of 200 μm at a 45° angle, with the wet film thickness controlled to be 300 to 500 μm. After coating, the glass substrate is transferred to a forced air drying oven at 60°C and dried for 10 to 12 hours to obtain a light yellow, translucent film, namely, the viologen / PVDF-HFP color-changing composite material. The other steps are the same as Specific Embodiments 1 to 9.

[0044] The following examples are used to verify the beneficial effects of the present invention:

[0045] Example 1: A method for preparing a viologen / PVDF-HFP color-changing composite material, wherein the viologen / PVDF-HFP color-changing composite material is in the form of a block. The preparation method is specifically completed by the following steps:

[0046] 1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system;

[0047] The viologen compound described in step 1 is ethyl viologen dihexafluorophosphate;

[0048] The mass fraction of the viologen compound in the polyvinylidene fluoride-hexafluoropropylene described in step 1 is 4 wt %;

[0049] 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a white gel;

[0050] The temperature of the constant temperature magnetic stirring in step 2 is 50°C, the speed of the magnetic stirring is 300 rpm, and the time of the magnetic stirring is 30 min;

[0051] The organic solvent described in step 2 is acetone;

[0052] The mass ratio of the mixed system described in step 2 to the volume ratio of the organic solvent is 6.24 g:50 mL;

[0053] 3. The white gel was allowed to stand at room temperature for 48 h to obtain a milky white transparent block with a thickness of 2 mm, which was the viologen / PVDF-HFP color-changing composite material block (4 wt %).

[0054] Example 2: This example differs from Example 1 in that the mass fraction of the viologen compound in the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) in Step 1 is 2 wt %, and the mass fraction of the viologen / PVDF-HFP color-changing composite material obtained in Step 3 is 2 wt %. All other steps and parameters are the same as in Example 1.

[0055] In order to study the electrochromic behavior of the viologen / PVDF-HFP color-changing composite material block, a dedicated test system was built. Power equipment usually operates at a voltage of kilovolts, and the electric field strength often exceeds 10 6 V / m. In order to explore the potential application of electrochromic materials in high-voltage systems, the present invention uses a block of viologen / PVDF-HFP color-changing composite material; Figure 5 A diagram of the experimental setup demonstrating the electrochromic behavior of a sample under high-voltage conditions; this test system is capable of detecting the material's color change characteristics upon charge injection. The experimental sample was placed between two parallel copper electrodes and secured using a custom fixture to meet testing requirements. A DC voltage of 6 kV (equivalent to an electric field strength of 3 kV / mm) was applied to the bulk viologen / PVDF-HFP color-changing composite material, and tests were performed at various time intervals to systematically investigate its electrochromic response.

[0056] Composite materials containing 2wt% and 4wt% viologen were experimentally studied; for the 4wt% sample, the voltage was applied for 10 minutes, 20 minutes and 30 minutes, respectively, and the experimental results showed significant time-dependent electrochromic behavior. Figure 6 The color change of a 4 wt% viologen / PVDF-HFP color-changing composite bulk after 10, 20, and 30 minutes is shown. After 10 minutes of voltage application, purple spots appeared in the contact area between the sample and the electrode, concentrated in areas of high electric field intensity. This is due to the large fluctuations in electric field intensity at the edges of the cylindrical electrode. When the voltage duration was extended to 20 minutes, the purple area expanded significantly, and the color saturation increased. This indicates that more viologen molecules underwent redox reactions during this period. After 30 minutes of voltage application, the electrochromic region expanded further, with a more intense purple color and a wider spatial coverage. Notably, the color change exhibited a radial propagation pattern from the electrode edge toward the center, which is directly related to the spatial inhomogeneity of the electric field distribution. The observed electrochromic behavior is primarily attributed to two key factors: first, as the electric field continues to be applied, charge is gradually injected into the material, triggering a significant electrochromic effect within the material; second, the concentration of reduced viologen continues to increase, and the accumulation of these reduced species in the material further enhances the color change. The purple color gradually fades within 4 hours, leaving behind a yellowish trace. This phenomenon can be attributed to the charge behavior and properties of viologen. On the one hand, the injected charge in the material decreases over time, causing the color to gradually fade. On the other hand, due to incomplete charge dissipation or the influence of the internal chemical environment of the material, some viologen molecules fail to fully reoxidize, resulting in residual yellow traces.

[0057] Figure 7The color change of a 2wt% viologen / PVDF-HFP color-changing composite block is demonstrated. One hour after applying voltage, the sample underwent electrical breakdown, with the breakdown point showing obvious signs of carbonization. The sample then gradually faded within 2 hours. Compared with the 4wt% sample, the color change area of ​​the 2wt% sample was lighter purple and faded faster. The electrochromic phenomenon in these areas is mainly due to recoverable charge accumulation. In contrast, the color change at the breakdown point and its surrounding area is permanent, which may be due to the irreversible chemical changes in the material caused by local high temperature.

[0058] Example 3: A method for preparing a viologen / PVDF-HFP color-changing composite material, wherein the viologen / PVDF-HFP color-changing composite material is in the form of a thin film. The preparation method is specifically completed by the following steps:

[0059] 1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system;

[0060] The viologen compound described in step 1 is ethyl viologen dihexafluorophosphate;

[0061] The mass fraction of the viologen compound in the polyvinylidene fluoride-hexafluoropropylene described in step 1 is 4 wt %;

[0062] 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a clear and transparent homogeneous solution;

[0063] The organic solvent described in step 2 is N-N dimethylformamide;

[0064] The mass ratio of the mixed system described in step 2 to the volume ratio of the organic solvent is 6.24 g:40 mL;

[0065] The constant temperature magnetic stirring temperature in step 2 is 60°C, the magnetic stirring speed is 500 rpm, and the magnetic stirring time is 120 min;

[0066] 3. The clear and transparent homogeneous solution was naturally evaporated at room temperature for 2 hours to obtain a gel; then, at room temperature and in a dust-free environment, a stainless steel scraper with a blade thickness of 200 μm was used to evenly coat the gel at a 45° tilt angle on a clean glass substrate, and the wet film thickness was controlled at 300 μm; after coating, the glass substrate was transferred to a forced air drying oven at a temperature of 60°C and dried for 12 hours to obtain a light yellow translucent film, which is the viologen / PVDF-HFP color-changing composite material film (4wt%).

[0067] Example 4: This example differs from Example 3 in that the mass fraction of the viologen compound in the polyvinylidene fluoride-hexafluoropropylene film in Step 1 is 3 wt %, and the mass fraction of the viologen / PVDF-HFP color-changing composite film obtained in Step 3 is 3 wt %. All other steps and parameters are the same as in Example 3.

[0068] Example 5: This example differs from Example 3 in that the mass fraction of the viologen compound in the polyvinylidene fluoride-hexafluoropropylene film in Step 1 is 2 wt %, and the mass fraction of the viologen / PVDF-HFP color-changing composite film obtained in Step 3 is 2 wt %. All other steps and parameters are the same as in Example 3.

[0069] Example 6: This example differs from Example 3 in that the viologen compound in step 1 is reduced to 1 wt % of the polyvinylidene fluoride-hexafluoropropylene mass fraction, and the viologen / PVDF-HFP color-changing composite film obtained in step 3 is reduced to 1 wt %. All other steps and parameters are the same as in Example 3.

[0070] Figure 8 IR spectra of the viologen / PVDF-HFP color-changing composite films prepared in Examples 3 to 6;

[0071] First, several characteristic absorption peaks of viologen were observed in the spectra of the doped samples, which were completely absent in the spectrum of pure PVDF-HFP. The most notable one was at 1630 cm -1 The strong absorption peak at 2+ ) is the most characteristic peak of viologen compounds. Another key evidence is the peak at 560 cm -1 The absorption peak appears at , which corresponds to the hexafluorophosphate anion (PF6 - ) deformation vibration mode. The appearance of these two characteristic peaks provides direct molecular level evidence for the successful doping of viologen. Secondly, at 3100 cm -1 The weak absorption peak observed near further supports the conclusion that the doping is successful. This peak originates from V 2+ The CH stretching vibration of the aromatic ring and ethyl group in the structure. It is worth noting that as the doping concentration increases from 1wt% to 4wt%, the intensity of this peak shows a significant enhancement trend, which is consistent with the 1630cm -1 and 560cm -1 The change pattern of the characteristic peaks at the same concentration is consistent, and this concentration-dependent change pattern provides a quantitative basis for the doping process.

[0072] Figure 9 is the dielectric constant of the viologen / PVDF-HFP color-changing composite film prepared in Examples 3 and 5;

[0073] Figure 9 The dielectric constants of viologen / PVDF-HFP color-changing composite materials are shown. As shown in the figure, PVDF-HFP and its samples doped with 2wt% and 4wt% viologen exhibit non-monotonic, frequency-dependent dielectric behavior. In the low-frequency range (1-100 Hz), the dielectric constant εr gradually decreases with increasing frequency, while viologen doping significantly increases the relative dielectric constant εr (4wt% sample reaches 27, pure PVDF-HFP is 16 at 0.1 Hz). This enhancement is mainly due to two mechanisms: 1) interfacial polarization at the heterogeneous interface; 2) cooperative dipole coupling between the N group of viologen and the CF bond in PVDF-HFP. In the medium-frequency range (10 2 -10 4 Hz), εr decreases sharply due to dipole relaxation (50% reduction for 4wt% sample). 4 -10 6 Hz), εr tends to be stable and the doping effect becomes negligible.

[0074] Figure 10 The dielectric loss of the viologen / PVDF-HFP color-changing composite film prepared in Examples 3 and 5;

[0075] Figure 10 The dielectric loss (tan δ) factors of 2wt% and 4wt% viologen / PVDF-HFP color-changing composite films at room temperature (25°C) are shown. The tan δ values ​​of pure PVDF-HFP and viologen-doped samples gradually decrease with increasing frequency and then stabilize. Notably, viologen doping significantly increases tan δ, with the 4wt% sample seeing a more pronounced increase than the 2wt% sample. This enhancement is primarily attributed to the migration loss of viologen anions. At an operating frequency of 50 Hz, the tan δ value of the doped sample only modestly increases compared to pure PVDF-HFP, while its dielectric constant remains comparable to that of PVDF (εr ≈ 10). These properties make viologen / PVDF-HFP color-changing composite films ideal for insulation monitoring in power equipment.

[0076] Figure 11 The breakdown probability diagram of the viologen / PVDF-HFP color-changing composite film prepared in Examples 3 and 5;

[0077] Viologen / P(VDF-HFP) composite films with varying viologen contents were sequentially placed in a constant-temperature dimethyl silicone oil bath. Electrical breakdown strength tests were conducted in a constant-temperature, dry environment using a spherical-plate electrode system. The samples were placed in a pressure-resistant, constant-temperature dimethyl silicone oil bath to suppress surface discharge. A high-voltage DC power supply was used to apply voltage at a constant ramp rate of 1.0 kV / s, with 10 repeats per group. Weibull distribution analysis (with a 63.2% confidence level) revealed that viologen doping significantly degraded the breakdown performance of the PVDF-HFP composite. The characteristic breakdown field strength of the pure sample was 798.0 kV / mm. The scale parameter decreased to 321.9 kV / mm (a 59.7% decrease) with the addition of 2 wt% viologen. When the doping level was increased to 4 wt%, the scale parameter further decreased to 197.0 kV / mm (a 75.3% cumulative decrease compared to the pure sample). Viologen-doped PVDF-HFP, due to its high breakdown field strength, shows potential as a color-indicating insulating coating on silicone rubber and cross-linked polyethylene insulators. For silicone rubber insulators, the DC breakdown field strength is typically between 25 kV / mm and 35 kV / mm. PVDF-HFP doped with 4wt% viologen exhibits an even higher breakdown field strength and a more pronounced color change, making it suitable for use as a color-indicating insulating coating. For cross-linked polyethylene insulators, the DC breakdown field strength is typically above 200 kV / mm, even reaching 400 kV / mm. PVDF-HFP doped with 2wt% viologen achieves a breakdown field strength of 321.9 kV / mm. While the color change effect is not as pronounced as with 4wt%, it can still be used as a color-indicating insulating coating on these surfaces.

[0078] This paper demonstrates the innovative application of viologen / PVDF-HFP color-changing composite materials in online insulation monitoring of power equipment. By manufacturing two different forms of the material - bulk and thin film, the present invention explores the synergistic effect between electrochromic behavior and dielectric properties. In the bulk form, when the applied electric field strength exceeds 10 6 At 100 V / m, the charge injected into the electrode causes a significant color change. This electrochromic effect has two notable characteristics: ① Doping concentration dependence: By adjusting the viologen content (2wt%, 4wt%), an adjustable color change from colorless to deep purple can be achieved; ② Time accumulation characteristics: A sustained electric field gradually deepens the color. Dielectric testing confirms that these composite films have excellent insulation properties that match high-voltage requirements. However, the addition of viologen reduces the breakdown field strength, which is attributed to the charge accumulation caused by the introduction of charge traps in the viologen bipyridine structure and the formation of micropores at the organic / polymer interface (especially at 4wt%, where viologen aggregates to form a percolation network), which induces local electric field distortion. The material developed in this invention can dynamically convert invisible charge into real-time optical signals, providing a new method for visually monitoring the insulation state.

Claims

1. A method for preparing a viologen / PVDF-HFP color-changing composite material, characterized in that The viologen / PVDF-HFP color-changing composite material is in the form of a block, and the preparation method is specifically completed by the following steps:

1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system; 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a white gel; 3. Let the white gel stand at room temperature for a period of time to obtain a milky white transparent block, which is the viologen / PVDF-HFP color-changing composite material.

2. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 1, characterized in that The viologen compound described in step 1 is ethyl viologen dihexafluorophosphate.

3. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 1, characterized in that The mass fraction of the viologen compound in step 1 to polyvinylidene fluoride-hexafluoropropylene is 2wt%~4wt%.

4. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 1, characterized in that The temperature of the constant temperature magnetic stirring in step 2 is 50° C., the speed of the magnetic stirring is 300 rpm to 500 rpm, and the time of the magnetic stirring is 20 min to 40 min.

5. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 1, characterized in that The organic solvent in step 2 is acetone; the mass of the mixed system in step 2 and the volume ratio of the organic solvent is (6.12g~6.24g): (35mL~50mL); the standing time in step 3 is 40h~50h.

6. A method for preparing a viologen / PVDF-HFP color-changing composite material, characterized in that The viologen / PVDF-HFP color-changing composite material is in the form of a thin film, and the preparation method is specifically completed by the following steps:

1. Weigh dry polyvinylidene fluoride-hexafluoropropylene and viologen compound, mix them evenly to obtain a mixed system; 2. Add the mixed system to the organic solvent and stir magnetically at constant temperature for a period of time to obtain a clear and transparent homogeneous solution; 3. Allow the clear and transparent homogeneous solution to evaporate naturally at room temperature for a period of time to obtain a gel; then, use a stainless steel scraper to evenly coat the gel on a clean glass substrate at room temperature and in a dust-free environment, with the wet film thickness controlled at 300μm~500μm; After coating, the glass substrate was transferred to a blast drying oven for drying to obtain a light yellow translucent film, which was the viologen / PVDF-HFP color-changing composite material.

7. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 6, characterized in that The viologen compound described in step 1 is ethyl viologen dihexafluorophosphate; the mass fraction of the viologen compound described in step 1 in polyvinylidene fluoride-hexafluoropropylene is 1wt%~4wt%.

8. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 6, characterized in that The organic solvent in step 2 is N-N dimethylformamide; the mass ratio of the mixed system in step 2 to the volume ratio of the organic solvent is (6.06 g ~ 6.24 g): 40 mL.

9. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 6, characterized in that The temperature of the constant temperature magnetic stirring in step 2 is 60° C., the speed of the magnetic stirring is 500 rpm to 600 rpm, and the time of the magnetic stirring is 120 min to 140 min.

10. The method for preparing a viologen / PVDF-HFP color-changing composite material according to claim 6, characterized in that In step 3, the clear, transparent homogeneous solution is naturally evaporated at room temperature for 1.5 to 2.5 hours to obtain a gel. The gel is then evenly coated on a clean glass substrate at a 45° angle using a stainless steel scraper with a blade thickness of 200 μm at room temperature in a dust-free environment, with the wet film thickness controlled to be 300 to 500 μm. After coating, the glass substrate was transferred to a forced air drying oven at 60°C and dried for 10 to 12 hours to obtain a light yellow translucent film, which was the viologen / PVDF-HFP color-changing composite material.

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