A method for synergistically improving the dielectric constant and breakdown strength of a polymer film

Abstract

This invention provides a method for synergistically improving the dielectric constant and breakdown strength of polymer films. The method involves completely dissolving 1,4-phenylene diisothiocyanate and 1,4-cyclohexanediamine in polar solvents, then adding the dissolved 1,4-cyclohexanediamine solution to the 1,4-phenylene diisothiocyanate solution and reacting under nitrogen atmosphere and room temperature with stirring to obtain a polythiourea solution. The 1,4-cyclohexanediamine is a mixture of cis-1,4-cyclohexanediamine and trans-1,4-cyclohexanediamine. The polythiourea solution is then filtered to remove impurities. The filtered polythiourea solution is dropped onto a heatable substrate, and subsequently, a casting method is used to evaporate the polar solvent through gradient temperature increases to obtain a polythiourea film. This method can significantly improve the dielectric constant and breakdown strength of polymer films, and its steps are simple and easy to implement, making it widely applicable in the field of high-voltage insulating materials.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage insulating materials, specifically relating to a method for synergistically improving the dielectric constant and breakdown strength of polymer films. Background Technology

[0002] In recent years, with the intensification of the greenhouse effect and the increase in energy demand, the storage and utilization of renewable and clean energy sources such as solar, wind, and tidal energy have become increasingly important. Dielectric energy storage has advantages such as high operating voltage, long service life, high power density, and good cycle stability. Polymer thin-film dielectrics, due to their easy processing, low cost, light weight, and good insulation properties, have become ideal materials for high-energy-density energy storage thin-film capacitors and are widely used in aerospace, new energy vehicles, wind power generation, and photovoltaic power generation.

[0003] Current research on polymer energy storage thin-film dielectrics mainly focuses on ferroelectric materials (such as PVDF-based polymer films), polymer-based composite dielectrics (such as polymers doped with inorganic nanofillers or organic semiconductors), and linear dielectrics (such as polyimide, polyester, polyurea, and polythiourea-based polymer films). Ferroelectric materials possess extremely high dielectric constants, but high dielectric losses under high electric fields are unavoidable, and their relatively low breakdown strength makes it difficult to meet the increasingly higher operating voltages of thin-film capacitors. Polymer-based nanocomposites require consideration of the size, shape, and dispersion of the doped nanoparticles. While improving the dielectric constant, this comes at the cost of reduced breakdown strength, and the problem of electric field distortion caused by the interface between the filler and the polymer matrix has not yet been well resolved. Linear polymer dielectrics exhibit high dielectric constants, breakdown voltages, and low dielectric losses. Furthermore, the dielectric constant and breakdown strength can be simultaneously improved by controlling the molecular structure (such as block copolymerization of high-dielectric and high-temperature materials, blending polymers with strong and weak intermolecular forces, and high-temperature, low-loss main chains with high-dielectric, high-breakdown side branches).

[0004] Existing literature has demonstrated that chain conformation significantly influences intermolecular forces, chain arrangement, and self-assembly in polymers. Studies have also shown that regulating polymer chain conformation can optimize charge transport pathways and alter electrical conductivity and current. This implies that it is feasible to simultaneously improve the dielectric constant and breakdown strength of polymers by controlling chain conformation, but this has been rarely studied. Furthermore, the inherent uncertainty of chain conformation undoubtedly increases the difficulty of enhancing polymer dielectric properties through chain conformation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synergistically improving the dielectric constant and breakdown strength of polymer films to overcome the problems existing in the prior art. The method of this invention can significantly improve the dielectric constant and breakdown strength of polymer films, and the steps are simple and easy, and can be widely used in the field of high voltage insulating materials.

[0006] This invention is achieved through the following technical solution:

[0007] A method for synergistically improving the dielectric constant and breakdown strength of polymer films includes the following steps:

[0008] 1) 1,4-phenyl diisothiocyanate and 1,4-cyclohexanediamine are completely dissolved in polar solvents, and then the dissolved 1,4-cyclohexanediamine solution is added to the 1,4-phenyl diisothiocyanate solution. The reaction is stirred under nitrogen atmosphere and room temperature to obtain polythiourea solution. The 1,4-cyclohexanediamine is a mixture of cis-1,4-cyclohexanediamine and trans-1,4-cyclohexanediamine.

[0009] 2) Filter impurities from the polythiourea solution;

[0010] 3) The filtered polythiourea solution is dropped onto a heatable substrate, and then a polythiourea film is obtained by gradient heating to evaporate the polar solvent using a casting method.

[0011] Further, in step 1), the ratio of 1,4-phenyl diisothiocyanate to polar solvent is 1 mmol: 1 mL, and the ratio of 1,4-cyclohexanediamine to polar solvent is 1 mmol: 1 mL.

[0012] Further, in step 1), the molar ratio of 1,4-phenyl diisothiocyanate to 1,4-cyclohexanediamine is 1:1.

[0013] Furthermore, in step 1), the polar solvent used is N,N-dimethylformamide.

[0014] Further, in step 1), the molar ratio between cis-1,4-cyclohexanediamine and trans-1,4-cyclohexanediamine is (6-9):(1-4).

[0015] Furthermore, in step 1), the stirring reaction time is 24 hours.

[0016] Further, in step 2), filtering impurities specifically involves transferring the polythiourea solution into a syringe equipped with a needle filter to filter impurities.

[0017] Furthermore, in step 3), the substrate is a glass plate, which is placed on a horizontal heated platform.

[0018] Furthermore, in step 3), the gradient heating procedure is to hold the temperature at 60°C for 3 hours, at 80°C for 1 hour, and at 100°C for 1 hour, followed by natural cooling to room temperature to obtain a uniform and transparent polythiourea film.

[0019] Further, after naturally cooling to room temperature in step 3), the film is placed in a vacuum oven at 100°C overnight to obtain a dried polythiourea film.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] This invention reacts 1,4-phenyl diisothiocyanate with a mixture of cis- and trans-1,4-cyclohexanediamines. By varying the molar ratio of cis- and trans-1,4-cyclohexanediamines, polythioureas with different chain conformations are obtained, thus exhibiting different dielectric properties. Specifically, the trans conformation promotes the formation of more hydrogen bonds in PTU molecules, leading to a decrease in the interchain spacing, which in turn reduces the hopping distance of charge carriers. Simultaneously, it allows the polythiourea molecular chains to self-assemble into smaller nanodomains, facilitating directional polarization under an electric field and increasing the dielectric constant. Compared to the all-cis conformation C-PTU, the room temperature DC breakdown strength of CT91-PTU containing 10% molar proportion of the trans conformation increased from 498 MV / m to 548 MV / m; the room temperature DC breakdown strength of polythiourea CT73-PTU containing 30% molar proportion of the trans conformation increased from 498 MV / m to 580 MV / m; and the dielectric constant of polythiourea CT64-PTU containing 40% molar proportion of the trans conformation increased from 4.8 to 5.5 (20°C, 10Hz). The method proposed in this invention can significantly improve the dielectric constant and breakdown strength of polymer films, and the steps are simple and the preparation is easy, making it widely applicable in the field of high-voltage insulating materials. Attached Figure Description

[0022] Figure 1 This is a synthetic route diagram for polythiourea containing trans structures in different molar proportions.

[0023] Figure 2 The figures show the infrared spectrum and X-ray diffraction (XRD) curves of polythiourea, where a is the infrared spectrum and b is the XRD curve.

[0024] Figure 3 This is the differential scanning calorimetry (DSC) curve for polythiourea.

[0025] Figure 4 The small-angle scattering (SAXS) curve for polythiourea.

[0026] Figure 5 The images are atomic force microscopy (AFM) images of polythiourea, where a is the morphology of nanodomains of different sizes, and b is the morphology of multiple nanodomains after self-assembly.

[0027] Figure 6 These are transmission electron microscopy (TEM) images of polythiourea. a, b, c, and d represent TEM images of C-PTU, CT91-PTU, CT73-PTU, and CT64-PTU, respectively.

[0028] Figure 7 The graphs show the spectrum of the real part of the dielectric constant and the Weibull distribution of the DC breakdown curve for polythiourea, where a is the spectrum of the real part of the dielectric constant and b is the Weibull distribution of the DC breakdown curve. Detailed Implementation

[0029] The present invention will now be described in further detail.

[0030] A method for synergistically improving the dielectric constant and breakdown strength of polymer films includes the following steps:

[0031] 1) Dissolve 1,4-phenyl diisothiocyanate and 1,4-cyclohexanediamine completely in a polar solvent. The ratio of 1,4-phenyl diisothiocyanate to polar solvent is 1 mmol:1 mL, and the ratio of 1,4-cyclohexanediamine to polar solvent is 1 mmol:1 mL. The polar solvent is N,N-dimethylformamide (DMF), and the molar ratio of 1,4-phenyl diisothiocyanate to 1,4-cyclohexanediamine is 1:1. The molar ratio of 1,4-cyclohexanediamine used is (6-9):( A mixture of cis-1,4-cyclohexanediamine and trans-1,4-cyclohexanediamine (1-4), for example, when cis-1,4-cyclohexanediamine is 0.7 mmol and trans-1,4-cyclohexanediamine is 0.3 mmol, the amount of 1,4-phenyl diisothiocyanate should be 1 mmol. Then, the dissolved 1,4-cyclohexanediamine solution is added to the 1,4-phenyl diisothiocyanate solution, and the reaction is stirred for 24 hours under nitrogen atmosphere and room temperature to obtain a polythiourea solution.

[0032] 2) Transfer the above polythiourea solution into a syringe equipped with a needle filter to filter out impurities;

[0033] 3) Using the casting method, the filtered polythiourea solution is dropped onto a clean glass plate that has been placed on a horizontal hot plate. The polar solvent is evaporated by gradient heating (60℃, 3 hours; 80℃, 1 hour; 100℃, 1 hour). After being placed in a vacuum oven at 100℃ overnight, a dry polythiourea film is obtained.

[0034] The embodiments of the present invention will be described in detail below with reference to the examples. These embodiments represent preferred solutions of the present invention and should not be construed as limiting the scope of the invention. Unless otherwise specified, the methods and experimental equipment used in the following embodiments are conventional methods and instruments.

[0035] Example 1

[0036] See Figure 1 A method for preparing a polymer film that synergistically enhances the dielectric constant and breakdown strength includes the following steps;

[0037] 1) Dissolve 1 mmol of 1,4-phenyl diisothiocyanate completely in 1 ml of polar solvent DMF. After complete dissolution, dissolve 0.9 mmol of cis-1,4-cyclohexanediamine and 0.1 mmol of trans-1,4-cyclohexanediamine separately in polar solvent DMF and add them to the DMF solution of the dissolved 1,4-phenyl diisothiocyanate. Then mix the 0.9 mmol cis-1,4-cyclohexanediamine solution and the 0.1 mmol trans-1,4-cyclohexanediamine solution thoroughly and add them to the 1 mmol 1,4-phenyl diisothiocyanate solution. Stir and react for 24 hours under nitrogen atmosphere and room temperature to obtain polythiourea solution.

[0038] 2) Transfer the above polythiourea solution into a syringe equipped with a needle filter to filter out impurities;

[0039] 3) Using the casting method, the filtered polythiourea solution is dropped onto a clean glass plate that has been placed on a horizontal hot plate. The polar solvent is evaporated by gradient heating (60℃, 3 hours; 80℃, 1 hour; 100℃, 1 hour). After being placed in a vacuum oven at 100℃ overnight, a dry polythiourea film is obtained.

[0040] Example 2

[0041] See Figure 1 A method for preparing a polymer film that synergistically enhances the dielectric constant and breakdown strength includes the following steps;

[0042] 1) Dissolve 1 mmol of 1,4-phenyl diisothiocyanate completely in 1 ml of polar solvent DMF. After complete dissolution, add 0.7 mmol of cis-1,4-cyclohexanediamine and 0.3 mmol of trans-1,4-cyclohexanediamine to the DMF solution of the dissolved 1,4-phenyl diisothiocyanate. Stir the reaction under nitrogen atmosphere and room temperature for 24 hours to obtain a polythiourea solution.

[0043] 2) Transfer the above polythiourea solution into a syringe equipped with a needle filter to filter out impurities;

[0044] 3) Using the casting method, the filtered polythiourea solution is dropped onto a clean glass plate that has been placed on a horizontal hot plate. The polar solvent is evaporated by gradient heating (60℃, 3 hours; 80℃, 1 hour; 100℃, 1 hour). After being placed in a vacuum oven at 100℃ overnight, a dry polythiourea film is obtained.

[0045] Example 3

[0046] See Figure 1 A method for preparing a polymer film that synergistically enhances the dielectric constant and breakdown strength includes the following steps;

[0047] 1) Dissolve 1 mmol of 1,4-phenyl diisothiocyanate completely in 1 ml of polar solvent DMF. After complete dissolution, dissolve 0.6 mmol of cis-1,4-cyclohexanediamine and 0.4 mmol of trans-1,4-cyclohexanediamine separately in polar solvent DMF and add them to the DMF solution of the dissolved 1,4-phenyl diisothiocyanate. Then mix the 0.6 mmol cis-1,4-cyclohexanediamine solution and the 0.4 mmol trans-1,4-cyclohexanediamine solution thoroughly and add them to the 1 mmol 1,4-phenyl diisothiocyanate solution. Stir and react for 24 hours under nitrogen atmosphere and room temperature to obtain polythiourea solution.

[0048] 2) Transfer the above polythiourea solution into a syringe equipped with a needle filter to filter out impurities;

[0049] 3) Using the casting method, the filtered polythiourea solution is dropped onto a clean glass plate that has been placed on a horizontal hot plate. The polar solvent is evaporated by gradient heating (60℃, 3 hours; 80℃, 1 hour; 100℃, 1 hour). After being placed in a vacuum oven at 100℃ overnight, a dry polythiourea film is obtained.

[0050] Comparative Example

[0051] The preparation method of fully cis conformation polythiourea C-PTU includes the following steps:

[0052] 1) Dissolve 1 mmol of 1,4-phenyl diisothiocyanate and 1 mmol of cis-1,4-cyclohexanediamine completely in 1 ml of polar solvent DMF. Then add the DMF solution of the dissolved cis-1,4-cyclohexanediamine to the DMF solution of 1,4-phenyl diisothiocyanate. Stir and react for 24 hours under nitrogen atmosphere and room temperature to obtain polythiourea solution.

[0053] 2) Transfer the above polythiourea solution into a syringe equipped with a needle filter to filter out impurities;

[0054] 3) Using the casting method, the filtered polythiourea solution is dropped onto a clean glass plate that has been placed on a horizontal hot plate. The polar solvent is evaporated by gradient heating (60℃, 3 hours; 80℃, 1 hour; 100℃, 1 hour). After being placed in a vacuum oven at 100℃ overnight, a dry C-PTU film is obtained.

[0055] like Figure 2 As shown in the infrared spectrum, at 3240 cm⁻¹ -1 The broad peak at the position represents the deformation vibration of bonded NH that participates in hydrogen bond formation. It can be seen that as the molar proportion of trans conformation increases, the deformation vibration of bonded NH reaches its maximum value in CT73-PTU, indicating that it has the highest hydrogen bond content. Figure 2 b is the XRD curve of PTU. The broad diffraction peaks indicate that PTU is an amorphous polymer. The 2θ angle corresponding to the peak position corresponds to the interchain spacing of PTU; the larger the 2θ, the smaller the interchain spacing. Figure 2 As can be seen from b, the broad diffraction peak of CT73-PTU corresponds to the largest 2θ angle, indicating that it has the smallest interchain spacing. Combined with the fact that CT73-PTU has the smallest charge jump distance in Table 1, this suggests that the increased breakdown strength of CT73-PTU is attributed to the reduced jump distance caused by the decreased interchain spacing. This hinders carrier migration under the electric field, reduces the probability of carrier collisional ionization, and thus increases the breakdown strength. Figure 7 b).

[0056] Table 1. Chain spacing, jump spacing, and breakdown strength of PTU specimens.

[0057]

[0058] Figure 3 This is the DSC curve of PTU. As can be seen from the figure, after introducing the trans conformation, PTU changes from an initial glass transition temperature (T0). g The glass transition temperature (PTU) becomes two different glass transition temperatures, which is a sign of phase separation in cis and trans PTUs. At the same time, phase separation also means the formation of a two-phase interface. Figure 4 This is the SAXS curve of PTU. It can be seen that the introduction of the trans conformation makes PTU more efficient at q = 0.069 nm. -1 and q = 0.099nm -1 Two additional scattering peaks appeared at the initial q = 0.064 nm. -1 The peak at q = 0.06 nm shifted to the left. -1 This indicates that the trans conformation, in addition to promoting the self-assembly of PTU molecular chains to form smaller nanodomains, also creates a completely new type of nanodomain. Figure 5 The image shows the AFM morphology of PTU, clearly demonstrating a change in nanodomain size after the introduction of the trans conformation. This further confirms the existence of phase separation. Subsequently, TEM images were used to observe the two-phase interface formed after phase separation, such as... Figure 6 As shown, the arrows represent the locations of phase separation interfaces. It can be seen that with the increase of the in-conformation, phase separation becomes increasingly pronounced, and the number of two-phase interfaces increases. This greatly enhances interfacial polarization and increases the dielectric constant. Figure 7 a).

[0059] In summary, this invention improves the dielectric constant and DC breakdown strength of PTU by changing the content of the in-conformation. The method proposed in this invention can be widely applied in fields such as energy storage film capacitors, high-voltage insulation devices, and power electronic equipment.

[0060] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for synergistically improving the dielectric constant and breakdown strength of polymer films, characterized in that, Includes the following steps: 1) 1,4-phenyl diisothiocyanate and 1,4-cyclohexanediamine are completely dissolved in polar solvents, and then the dissolved 1,4-cyclohexanediamine solution is added to the 1,4-phenyl diisothiocyanate solution. The reaction is carried out under nitrogen atmosphere and room temperature with stirring to obtain a polythiourea solution. The 1,4-cyclohexanediamine is a mixture of cis-1,4-cyclohexanediamine and trans-1,4-cyclohexanediamine, and the molar ratio between cis-1,4-cyclohexanediamine and trans-1,4-cyclohexanediamine is (6-9):(1-4). 2) Filter impurities from the polythiourea solution; 3) The filtered polythiourea solution is dropped onto a heatable substrate, and then a polythiourea film is obtained by gradient heating to evaporate the polar solvent using a casting method.

2. The method for synergistically improving the dielectric constant and breakdown strength of a polymer film according to claim 1, characterized in that, In step 1), the ratio of 1,4-phenyl diisothiocyanate to polar solvent is 1 mmol: 1 mL, and the ratio of 1,4-cyclohexanediamine to polar solvent is 1 mmol: 1 mL.

3. The method for synergistically improving the dielectric constant and breakdown strength of polymer films according to claim 1, characterized in that, In step 1), the molar ratio of 1,4-phenyl diisothiocyanate to 1,4-cyclohexanediamine is 1:

1.

4. The method for synergistically improving the dielectric constant and breakdown strength of polymer films according to claim 1, characterized in that, In step 1), the polar solvent used is N,N-dimethylformamide.

5. The method for synergistically improving the dielectric constant and breakdown strength of polymer films according to claim 1, characterized in that, In step 1), the stirring reaction time is 24 hours.

6. The method for synergistically improving the dielectric constant and breakdown strength of a polymer film according to claim 1, characterized in that, In step 2), the impurities are filtered out by transferring the polythiourea solution into a syringe equipped with a needle filter.

7. The method for synergistically improving the dielectric constant and breakdown strength of polymer films according to claim 1, characterized in that, In step 3), the substrate is a glass plate, which is placed on a horizontal heated platform.

8. The method for synergistically improving the dielectric constant and breakdown strength of polymer films according to claim 1, characterized in that, In step 3), the gradient temperature program is to hold the temperature at 60℃ for 3 hours, at 80℃ for 1 hour, and at 100℃ for 1 hour, and then let it cool naturally to room temperature to obtain a uniform and transparent polythiourea film.

9. The method for synergistically improving the dielectric constant and breakdown strength of a polymer film according to claim 8, characterized in that, After naturally cooling to room temperature in step 3), the film is placed in a vacuum oven at 100°C overnight to obtain a dry polythiourea film.

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