Highly oriented polyvinylidene fluoride-trifluoroethylene film and orientation fixing method thereof

Abstract

The invention provides a highly-oriented polyvinylidene fluoride-trifluoroethylene film and an orientation fixing method thereof, and the orientation fixing method comprises the following steps: placing the highly-oriented polyvinylidene fluoride-trifluoroethylene film in a vacuum coating machine, tightly pressing the tip of one carbon rod in a hole of the other carbon rod, and placing the carbon rod in the coating machine to form a passage; after vacuum pumping, current is turned on for carbon film evaporation, in the evaporation process, carbon at the tip of the carbon rod is evaporated out due to the resistance heat effect, and the carbon uniformly covers the surface of the polyvinylidene fluoride-trifluoroethylene film to form a layer of carbon film. The oriented melting recrystallization of the melt-stretched polyvinylidene fluoride-trifluoroethylene thin film is realized by utilizing the carbon film, and the polyvinylidene fluoride-trifluoroethylene can generate polarization reversal under the action of an externally applied electric field when the crystallinity of the polyvinylidene fluoride-trifluoroethylene is improved, so that the crystallinity of the polyvinylidene fluoride-trifluoroethylene thin film is improved, and the crystallinity of the polyvinylidene fluoride-trifluoroethylene thin film is improved. And the hot working temperature range of the polyvinylidene fluoride-trifluoroethylene sample is widened.

Description

Technical Field

[0001] The present invention relates to the field of ferroelectric polymer materials, and more particularly to a highly oriented polyvinylidene fluoride-trifluoroethylene film and an orientation fixing method thereof. Background Art

[0002] P(VDF-TrFE), a copolymer of vinylidene fluoride and trifluoroethylene, is a highly sought-after ferroelectric polymer material, often fabricated as ultrathin films to reduce operating voltage. In P(VDF-TrFE) ultrathin films, the dipole orientation (from fluorine to hydrogen) is perpendicular to the CC chains. Therefore, when the CC chains are parallel to the film, forming edge-on lamellae, the CC chains can rotate under the influence of an applied electric field, achieving polarization reversal and endowing the P(VDF-TrFE) with excellent ferroelectric properties. However, when the CC chains are perpendicular to the film surface, forming flat lamellae, the dipole orientation is perpendicular to the applied electric field, preventing the CC chains from rotating under the applied field and resulting in a lack of ferroelectricity. Therefore, achieving a ferroelectric edge-on lamellae structure is key to improving the ferroelectric properties of P(VDF-TrFE) ultrathin films.

[0003] Furthermore, the study found that the ferroelectric properties of P(VDF-TrFE) improve with increasing crystallinity. Generally, high-temperature heat treatment can enhance the crystallinity of polymers. However, when the heat treatment temperature exceeds 150°C, the P(VDF-TrFE) ultrathin film melts and recrystallizes to form flat-on crystals due to the influence of the interface on nucleation, resulting in the loss of ferroelectricity. These properties of P(VDF-TrFE) ultrathin films also limit their thermal processing temperature range. Summary of the Invention

[0004] In view of the problems existing in the background technology, the purpose of the present invention is to provide a highly oriented polyvinylidene fluoride-trifluoroethylene film and its orientation fixing method, which fixes the surface molecular chain orientation of the film by vacuum evaporating a layer of carbon film on the surface of the melt-stretched polyvinylidene fluoride-trifluoroethylene film, and uses melt recrystallization to achieve the preparation of a highly crystalline edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene oriented film.

[0005] To achieve the above objectives, the present invention provides a method for fixing the orientation of a highly oriented polyvinylidene fluoride-trifluoroethylene film, wherein the highly oriented polyvinylidene fluoride-trifluoroethylene film is placed in a vacuum coating machine, the tip of a carbon rod is pressed tightly into the hole of another carbon rod, and the film is placed in the coating machine to form a passage; after vacuuming, the current is turned on to evaporate the carbon film. During the evaporation process, the carbon at the tip of the carbon rod evaporates due to the resistive heating effect, and the carbon is evenly covered on the surface of the polyvinylidene fluoride-trifluoroethylene film to form a layer of carbon film.

[0006] Optionally, the current of the vacuum coating machine is 10-20A; the evaporation time is not less than 1 hour; and the thickness of the evaporated carbon film is not less than 30nm.

[0007] Optionally, the method for preparing the highly oriented polyvinylidene fluoride-trifluoroethylene film comprises the following steps: (1) preparing a polyvinylidene fluoride-trifluoroethylene solution; (2) heating a glass platform, spreading the polyvinylidene fluoride-trifluoroethylene solution on the hot glass platform, volatilizing the solvent on the glass platform, and forming a layer of polyvinylidene fluoride-trifluoroethylene supercooled melt film on the surface of the hot glass platform; (3) using an electric roller to stretch the supercooled polyvinylidene fluoride-trifluoroethylene melt on the hot glass platform, generating an extremely high longitudinal flow gradient during the stretching process, inducing the orientation crystallization of the polyvinylidene fluoride-trifluoroethylene molecular chain, and obtaining a highly oriented edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene ultra-thin film with a nanometer thickness.

[0008] Optionally, the concentration of the polyvinylidene fluoride-trifluoroethylene solution is 10-100 mg / mL.

[0009] Optionally, the heating temperature of the glass platform is 135-145°C.

[0010] Optionally, the solvent of the polyvinylidene fluoride-trifluoroethylene solution is a high boiling point solvent.

[0011] Optionally, the high boiling point solvent is at least one of dimethylformamide and xylene.

[0012] Optionally, when polyvinylidene fluoride-trifluoroethylene is dissolved in a solvent, the heating temperature is 80-110°C.

[0013] Optionally, the stretching speed of the motorized roller is 4-20 cm / s.

[0014] Optionally, the thickness of the highly oriented polyvinylidene fluoride-trifluoroethylene film is 20-100 nm.

[0015] The present invention also provides a highly oriented polyvinylidene fluoride-trifluoroethylene film prepared by the above-mentioned orientation fixing method.

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention utilizes a carbon film to achieve oriented melt recrystallization of a melt-stretched polyvinylidene fluoride-trifluoroethylene film, thereby improving the crystallinity of the polyvinylidene fluoride-trifluoroethylene and ensuring that the polyvinylidene fluoride-trifluoroethylene can undergo polarization reversal under the action of an external electric field, thereby broadening the thermal processing temperature range of the polyvinylidene fluoride-trifluoroethylene sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the melt stretching method according to the present invention.

[0019] Figure 2 Schematic diagram of the carbon film fixing method according to the present invention.

[0020] Figure 3 Schematic diagram of the molecular chain direction and polarization reversal of polyvinylidene fluoride-trifluoroethylene ultra-thin film after melt recrystallization.

[0021] Figure 4 (a), (b), and (c) are TEM bright field images of polyvinylidene fluoride-trifluoroethylene thin films prepared by solution spin coating, TEM bright field images of melt recrystallization of the spin-coated film before carbon film deposition, and TEM bright field images of melt recrystallization of the spin-coated film after carbon film deposition, respectively; (d), (e), and (f) are TEM bright field images of polyvinylidene fluoride-trifluoroethylene thin films prepared by melt stretching, TEM bright field images of melt recrystallization of the melt-stretched film before carbon film deposition, and TEM bright field images of melt recrystallization of the melt-stretched film after carbon film deposition, respectively.

[0022] Figure 5 (a) and (b) are respectively the 1350~750cm of melt-stretched polyvinylidene fluoride-trifluoroethylene film before and after carbon film deposition during heat treatment. -1 FTIR spectra of the band, (c) and (d) correspond to 848cm before and after carbon film deposition, respectively. -1 Curve of the normalized peak intensity of the band changing with temperature. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the invention more obvious and easy to understand, the specific embodiments of the invention are described in detail below.

[0024] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] The method for fixing the orientation of a highly oriented polyvinylidene fluoride-trifluoroethylene film according to the present invention comprises placing the highly oriented polyvinylidene fluoride-trifluoroethylene film in a vacuum coating machine, pressing the tip of a carbon rod tightly against the hole of another carbon rod, and placing the film into the coating machine to form a passage. After evacuation, current is turned on to perform carbon film evaporation. During the evaporation process, carbon at the tip of the carbon rod evaporates due to the resistive heating effect, and the carbon is evenly coated on the surface of the polyvinylidene fluoride-trifluoroethylene film to form a carbon film. The current of the vacuum coating machine can be 10-20A; the evaporation time is no less than 1 hour; and the thickness of the evaporated carbon film is no less than 30nm.

[0026] In the method for fixing the orientation of a highly oriented polyvinylidene fluoride-trifluoroethylene film according to the present invention, the method for preparing the highly oriented polyvinylidene fluoride-trifluoroethylene film comprises the following steps: (1) preparing a polyvinylidene fluoride-trifluoroethylene solution; (2) heating a glass platform, spreading the polyvinylidene fluoride-trifluoroethylene solution on the hot glass platform, volatilizing the solvent on the glass platform, and forming a layer of polyvinylidene fluoride-trifluoroethylene supercooled melt film on the surface of the hot glass platform; (3) using an electric roller to stretch the supercooled polyvinylidene fluoride-trifluoroethylene melt on the hot glass platform, generating an extremely high longitudinal flow gradient during the stretching process, inducing the orientation crystallization of the polyvinylidene fluoride-trifluoroethylene molecular chain, and obtaining a highly oriented edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene ultra-thin film with a nanometer thickness. The concentration of the polyvinylidene fluoride-trifluoroethylene solution can be 10-100 mg / mL. The heating temperature of the glass platform can be 135-145° C. The solvent of the polyvinylidene fluoride-trifluoroethylene solution can be a high boiling point solvent. The high-boiling-point solvent can be at least one of dimethylformamide and xylene. When dissolving the polyvinylidene fluoride-trifluoroethylene in the solvent, the heating temperature can be 80-110°C. The stretching speed of the motorized roller can be 4-20 cm / s. The thickness of the highly oriented polyvinylidene fluoride-trifluoroethylene film can be 20-100 nm.

[0027] The orientation fixing method and melt stretching method of the present invention can realize the preparation of a nanometer-thick polyvinylidene fluoride-trifluoroethylene ultra-thin film with a highly oriented edge-on lamellar structure.

[0028] The present invention further fixes the surface molecular chain orientation of the film by vacuum evaporating a layer of carbon film on the surface of the melt-stretched polyvinylidene fluoride-trifluoroethylene film, and uses melt recrystallization to achieve the preparation of a polyvinylidene fluoride-trifluoroethylene oriented film with a high crystallinity edge-on lamellar structure, thereby improving the ferroelectric properties of polyvinylidene fluoride-trifluoroethylene, expanding its processing temperature range, and expanding the application of polyvinylidene fluoride-trifluoroethylene in the field of ferroelectric devices.

[0029] The highly oriented polyvinylidene fluoride-trifluoroethylene film according to the present invention can be applied to ferroelectric memory.

[0030] Hereinafter, a method for fixing the orientation of a highly oriented polyvinylidene fluoride-trifluoroethylene film of the present invention will be described in detail with reference to specific embodiments.

[0031] Example 1

[0032] (1) The preparation of highly oriented edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene film by melt stretching method includes the following steps:

[0033] The melt stretching device consists of a hot glass platform and motorized rollers, such as Figure 1 As shown. In the experiment, a 20 mg / mL polyvinylidene fluoride-trifluoroethylene / dimethylformamide solution was prepared, and the solution was heated to 90°C and stirred to ensure that the polyvinylidene fluoride-trifluoroethylene was evenly dissolved in the dimethylformamide solvent. The above solution was poured onto a glass platform heated to 140°C, and a glass rod was used to evenly spread the solution on the hot glass platform. After the solvent on the hot glass platform evaporated, the supercooled polyvinylidene fluoride-trifluoroethylene melt on the hot glass platform was stretched using an electric roller. The stretching speed was set at 10 cm / s. During the stretching process, an extremely high longitudinal flow gradient was generated, inducing the orientation crystallization of the polyvinylidene fluoride-trifluoroethylene molecular chain, and a highly oriented edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene ultra-thin film with a thickness of about 50 nm was obtained.

[0034] (2) The method for fixing the orientation of a highly oriented polyvinylidene fluoride-trifluoroethylene film comprises the following steps:

[0035] like Figure 2 As shown, the melt-stretched PVDF-TFE film was placed in a vacuum coating machine. The tip of a carbon rod was pressed firmly into the hole of another carbon rod, forming a path. After evacuation, the current was turned on to 13A. Due to the resistive heating effect, carbon evaporated from the tip of the carbon rod, evenly coating the surface of the PVDF-TFE film. After one hour of carbon deposition, a carbon film approximately 30 nm thick formed on the PVDF-TFE film. The carbon-deposited PVDF-TFE film was then heated to 200°C, held at this temperature for 5 minutes, and then cooled to 25°C at a rate of 5°C / min.

[0036] Comparative Example 1

[0037] (1) Preparation of polyvinylidene fluoride-trifluoroethylene film by solution spin coating method includes the following steps:

[0038] Prepare a 10 mg / mL polyvinylidene fluoride-trifluoroethylene / butanone solution and place a substrate, such as a silicon wafer or glass, on a spin coater. Drop an appropriate amount of the solution onto the substrate. Turn on the spin coater and spin coat at 2000 rpm. A film approximately 50 nm thick is obtained.

[0039] (2) The method for fixing the orientation of the polyvinylidene fluoride-trifluoroethylene film comprises the following steps:

[0040] A PVDF-TFE film, prepared by solution spin coating, was placed in a vacuum coating machine. After evacuation, the current was turned on and set to 13A. The carbon tip of the carbon rod evaporated due to resistive heating, evenly coating the surface of the PVDF-TFE film. After one hour of evaporation, a carbon film approximately 30nm thick formed on the PVDF-TFE film. The carbon-deposited PVDF-TFE film was then heated to 200°C, held at this temperature for 5 minutes, and then cooled to 25°C at a rate of 5°C / min.

[0041] Performance testing and results

[0042] 1. Comparative Example 1 The microstructure of the polyvinylidene fluoride-trifluoroethylene film prepared by solution spin coating is as follows Figure 4 (a) PVDF-TRIF forms edge-on structure lamellae, but the lamellae are isotropic and their crystal arrangement is disordered. The PVDF-TRIF film of Comparative Example 1 is heated to 200°C, kept at this temperature for 10 minutes, and then cooled to 25°C at 5°C / min. PVDF-TRIF forms flat-on structure lamellae by melt recrystallization, as shown in FIG. Figure 4 (b) After vacuum evaporation of a carbon film on the surface of the PVDF-TRIF film of Comparative Example 1, the film was heated to 200°C, kept at this temperature for 10 minutes, and then cooled to 25°C at a rate of 5°C / min. The PVDF-TRIF film still formed edge-on structure lamellae during melt recrystallization, as shown in FIG. Figure 4 (c) This is because the carbon film fixes the molecular chain orientation on the surface of the PVDF-TFE film and uses it as a nucleation point to induce the melt recrystallization of PVDF-TFE to form edge-on structured lamellae.

[0043] 2. The polyvinylidene fluoride-trifluoroethylene film prepared by melt stretching method in Example 1 also forms edge-on structure lamellae. Compared with Comparative Example 1, Example 1 has a high degree of orientation, such as Figure 4 (d) The melt-stretched polyvinylidene fluoride-trifluoroethylene film of Example 1 was heated to 200°C, kept at this temperature for 10 minutes, and then cooled to 25°C at a rate of 5°C / min. The polyvinylidene fluoride-trifluoroethylene melt recrystallized to form flat-on structure lamellae, such as Figure 4(e) However, after vacuum evaporation of a carbon film on the surface of the polyvinylidene fluoride-trifluoroethylene film prepared in Example 1, it was heated to 200°C, kept at this temperature for 10 minutes, and then cooled to 25°C at a rate of 5°C / min. The polyvinylidene fluoride-trifluoroethylene melt recrystallization still produced edge-on structure lamellae, such as Figure 4 (f) This is because the carbon film fixes the molecular chain orientation on the surface of the PVDF-TFE film and uses it as a nucleation point to induce the melt recrystallization of PVDF-TFE to form edge-on structured lamellae.

[0044] Depend on Figure 4 (a) (d) It can be seen that the solution spin coating method can prepare edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene film, but the crystal arrangement is disordered and the crystals are isotropic. The polyvinylidene fluoride-trifluoroethylene film prepared by the melt stretching method still maintains the edge-on lamellar structure, but the crystals are anisotropic and the crystal arrangement has high orientation. Figure 4 (a) (d) It can be seen that the orientation degree of the polyvinylidene fluoride-trifluoroethylene film prepared in Example 1 is higher than that in Comparative Example 1. Figure 4 (b)(c)(e)(f) show that vacuum evaporation of carbon film on the surface of edge-on lamellar structure film can fix the orientation of polyvinylidene fluoride-trifluoroethylene molecular chain and induce polyvinylidene fluoride-trifluoroethylene melt recrystallization to still form edge-on lamellar structure. Carbon film has a good fixation effect on polyvinylidene fluoride-trifluoroethylene molecular chain. Figure 4 (c) and Figure 4 (f) It can be seen that after the edge-on lamellar structure film is vacuum-deposited with a carbon film to fix its orientation, the orientation degree of the polyvinylidene fluoride-trifluoroethylene film of Example 1 is still higher than that of Comparative Example 1.

[0045] Depend on Figure 4 (e) and Figure 4 (f) It can be seen that vacuum evaporation of a carbon film on the surface of the PVDF-TRIF film can fix the molecular chain orientation of the film and achieve oriented melt recrystallization of the PVDF-TRIF film. The effect is shown in the schematic diagram. Figure 3 As shown in the figure, when a conventional edge-on lamellar PVDF-TFE film is heated to 200°C to melt and then cooled to crystallize, the molecular chains change from lying flat to standing sideways, forming flat-on lamellae. However, when a carbon film is vacuum-evaporated on the surface of an edge-on lamellae PVDF-TFE film, the PVDF-TFE melts and recrystallizes at 200°C, and the molecular chains continue to grow flat, forming edge-on lamellae.

[0046] The temperature at which the polar ferroelectric phase transitions to the non-polar paraelectric phase is called the Curie temperature. When the temperature is higher than the Curie temperature, the ferroelectric material exhibits paraelectricity and no longer has ferroelectricity. When the temperature is lower than the Curie temperature, ferroelectricity appears. The Curie temperature is the key to determining the operating temperature range. Figure 5 In the infrared spectrum of polyvinylidene fluoride-trifluoroethylene in (a), 848 cm -1 The peak represents the symmetrical stretching vibration of the C-C bond. The change in the intensity of this peak can characterize the change in the ferroelectric phase of polyvinylidene fluoride-trifluoroethylene. -1 The peak intensity decreases as the temperature increases and disappears when it is above the Curie temperature. When the temperature decreases, the peak reappears and increases as the temperature decreases. This change is because the ferroelectric phase transitions to the paraelectric phase during the heating process and the paraelectric phase transitions to the ferroelectric phase during the cooling process. Figure 5 As can be seen from (b), when a carbon film is vacuum-deposited on the surface of PVDF-TRIF, the 848 cm -1 The peak change trend is consistent with that of the film without carbon film. -1 The temperature at which the infrared peak intensity changes fastest is the Curie transition temperature. Figure 5 It can be seen from (c) and (d) that when a layer of carbon film is vacuum evaporated on the surface of PVDF-TRIF, the Curie temperature of PVDF-TRIF is very small when it is heated up and cooled down. The Curie temperature is basically unaffected by the carbon film and does not affect the operating temperature range of PVDF-TRIF.

[0047] Although some specific embodiments of the present invention have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It should be understood by those skilled in the art that modifications may be made to the above embodiments without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A method for fixing the orientation of a highly oriented polyvinylidene fluoride-trifluoroethylene film, characterized in that: A highly oriented polyvinylidene fluoride-trifluoroethylene film is placed in a vacuum coating machine, and the tip of a carbon rod is pressed tightly into the hole of another carbon rod, which is then placed in the coating machine to form a passage. After vacuuming, the current is turned on to evaporate the carbon film. During the evaporation process, the carbon at the tip of the carbon rod evaporates due to the resistive heating effect, and the carbon is evenly covered on the surface of the polyvinylidene fluoride-trifluoroethylene film to form a layer of carbon film.

2. The orientation fixing method according to claim 1, characterized in that: The current of the vacuum coating machine is 10-20A; the evaporation time is not less than 1 hour; and the thickness of the evaporated carbon film is not less than 30nm.

3. The orientation fixing method according to claim 1, characterized in that: The method for preparing the highly oriented polyvinylidene fluoride-trifluoroethylene film comprises the following steps: (1) preparing a polyvinylidene fluoride-trifluoroethylene solution; (2) heating a glass platform, spreading the polyvinylidene fluoride-trifluoroethylene solution on the hot glass platform, volatilizing the solvent on the glass platform, and forming a layer of polyvinylidene fluoride-trifluoroethylene supercooled melt film on the surface of the hot glass platform; (3) The supercooled polyvinylidene fluoride-trifluoroethylene melt on the hot glass platform is stretched using an electric roller. During the stretching process, an extremely high longitudinal flow gradient is generated, which induces the oriented crystallization of the polyvinylidene fluoride-trifluoroethylene molecular chains, and obtains a highly oriented edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene ultra-thin film with a nanometer thickness.

4. The orientation fixing method according to claim 3, characterized in that: The concentration of the polyvinylidene fluoride-trifluoroethylene solution is 10-100 mg / mL.

5. The orientation fixing method according to claim 3, characterized in that: The heating temperature of the glass platform is 135-145℃.

6. The orientation fixing method according to claim 3, characterized in that: The solvent of the polyvinylidene fluoride-trifluoroethylene solution is a high boiling point solvent.

7. The orientation fixing method according to claim 6, characterized in that: The high boiling point solvent is at least one of dimethylformamide and xylene.

8. The orientation fixing method according to claim 3, characterized in that: The stretching speed of the motorized roller is 4-20 cm / s.

9. The orientation fixing method according to claim 3, characterized in that: The thickness of the highly oriented polyvinylidene fluoride-trifluoroethylene film is 20-100 nm.

10. A highly oriented polyvinylidene fluoride-trifluoroethylene film prepared according to the orientation fixing method according to any one of claims 1 to 9.

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