Highly oriented polyvinylidene fluoride-trifluoroethylene film as well as preparation method and application thereof

Abstract

The invention provides a highly oriented polyvinylidene fluoride-trifluoroethylene film as well as a preparation method and application thereof. The preparation method 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 to volatilize 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; and (3) stretching the supercooled polyvinylidene fluoride-trifluoroethylene melt on the hot glass platform by using an electric roller, generating an extremely high longitudinal flow gradient in the stretching process, and inducing oriented crystallization of a polyvinylidene fluoride-trifluoroethylene molecular chain to obtain the high-oriented edge-on lamellar crystal structure polyvinylidene fluoride-trifluoroethylene ultrathin film with nanoscale thickness.

Description

Technical Field

[0001] The present invention relates to the field of ferroelectric polymer materials, and more specifically, to a highly oriented poly(vinylidene fluoride-trifluoroethylene) thin film, a preparation method thereof, and an application thereof. Background Art

[0002] Ferroelectric materials are a kind of intelligent materials that can undergo polarization reversal (ferroelectric effect) under the action of an external electric field within a certain temperature range. Ferroelectric materials have a wide range of applications and can be applied to electronic component fields such as memories, transducers, detectors, and frequency converters. In recent years, electronic components have gradually developed towards miniaturization, light weight, and flexibility. Conventional inorganic ferroelectric materials cannot meet the requirements, so ferroelectric polymer materials have attracted more and more attention. Among them, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) is one of the most concerned ferroelectric polymer materials. However, at present, the piezoelectric coefficient (d 33 ≈30 pC / N) of P(VDF-TrFE) is much lower than that of commercial inorganic materials (BaTiO3≈100 pC / N, PZT≈265 pC / N), and its ferroelectric performance needs to be further improved.

[0003] P(VDF-TrFE) is a copolymer of vinylidene fluoride and trifluoroethylene. Trifluoroethylene can increase the steric hindrance of PVDF and is conducive to the formation of the ferroelectric β-phase with an all-trans conformation. The ferroelectric performance of P(VDF-TrFE) is closely related to the crystal orientation behavior. Due to the relatively high coercive field strength (about 50 MV / m), P(VDF-TrFE) is often prepared into ultra-thin films to reduce the operating voltage. In P(VDF-TrFE) ultra-thin films, since the dipole direction of P(VDF-TrFE) (from fluorine to hydrogen) is perpendicular to the C-C molecular chain direction, when the C-C molecular chain direction of P(VDF-TrFE) is parallel to the film surface to form edge-on lamellae, the C-C molecular chains can rotate under the action of an external electric field to achieve polarization reversal and endow P(VDF-TrFE) with good ferroelectricity. When the C-C molecular chains of P(VDF-TrFE) are perpendicular to the film surface to form flat-on lamellae, the dipole is perpendicular to the direction of the external electric field, and the C-C molecular chains cannot rotate under the action of the external electric field, and the material does not have ferroelectricity. Therefore, obtaining the ferroelectric phase edge-on lamellar structure is the key to improving the ferroelectric performance of P(VDF-TrFE) ultra-thin films.

[0004] At present, researchers often prepare P(VDF-TrFE) films with an edge-on lamellar structure by the solution spin-coating method, but the crystals prepared by this method are arranged randomly. Summary of the Invention

[0005] In view of the problems existing in the background art, the purpose of the present invention is to provide a highly oriented poly(vinylidene fluoride-trifluoroethylene) film, a preparation method thereof and an application thereof, which can improve the orientation degree of the poly(vinylidene fluoride-trifluoroethylene) film.

[0006] To achieve the above purpose, the present invention provides a preparation method of a highly oriented poly(vinylidene fluoride-trifluoroethylene) film, which comprises the following steps: (1) preparing a poly(vinylidene fluoride-trifluoroethylene) solution; (2) heating a glass platform, spreading the poly(vinylidene fluoride-trifluoroethylene) solution on the hot glass platform, and volatilizing the solvent on the glass platform to form a poly(vinylidene fluoride-trifluoroethylene) supercooled melt film on the surface of the hot glass platform; (3) using an electric roller to stretch the supercooled poly(vinylidene fluoride-trifluoroethylene) melt on the hot glass platform, generating an extremely high longitudinal flow gradient during the stretching process, inducing the orientation crystallization of poly(vinylidene fluoride-trifluoroethylene) molecular chains, and obtaining a highly oriented edge-on lamellar structure poly(vinylidene fluoride-trifluoroethylene) ultra-thin film with a nanoscale thickness.

[0007] Optionally, the concentration of the poly(vinylidene fluoride-trifluoroethylene) solution is 10-100 mg / mL.

[0008] Optionally, the heating temperature of the glass platform is 135-145 °C.

[0009] Optionally, the solvent of the poly(vinylidene fluoride-trifluoroethylene) solution is a high-boiling solvent.

[0010] Optionally, the high-boiling solvent is at least one of dimethylformamide and xylene.

[0011] Optionally, when poly(vinylidene fluoride-trifluoroethylene) is dissolved in the solvent, the heating temperature is 80-110 °C.

[0012] Optionally, the stretching speed of the electric roller is 4-20 cm / s.

[0013] Optionally, the thickness of the highly oriented poly(vinylidene fluoride-trifluoroethylene) film is 20-100 nm.

[0014] The present invention also provides a highly oriented poly(vinylidene fluoride-trifluoroethylene) film prepared by the preparation method as described above.

[0015] The present invention also provides an application of the highly oriented poly(vinylidene fluoride-trifluoroethylene) film prepared by the preparation method as described above, which is applied to ferroelectric memories.

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

[0017] The present invention realizes the preparation of a nano-scale thickness poly(vinylidene fluoride-trifluoroethylene) ultra-thin film with a highly oriented edge-on lamellar structure by means of melt stretching. It has a higher degree of orientation than the P(VDF-TrFE) film prepared by the conventional solution spin-coating method. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FIG. is a schematic diagram of the melt stretching method according to the present invention.

[0019] Figure 2 FIG. is a view of the film prepared by the preparation method of Example 1 of the present invention attached to a silicon wafer substrate.

[0020] Figure 3 FIG. is a view of the film prepared by the preparation method of Comparative Example 1 of the present invention attached to a silicon wafer substrate.

[0021] Figure 4 FIG. is a bright-field TEM image of poly(vinylidene fluoride-trifluoroethylene) films prepared by the solution spin-coating method (a) and the melt stretching method (b). DETAILED DESCRIPTION OF THE INVENTION

[0022] In order to make the above objects, features, and advantages of the invention more obvious and understandable, the following detailed description of the specific embodiments of the invention is provided.

[0023] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0024] The preparation method of the highly oriented poly(vinylidene fluoride-trifluoroethylene) film according to the present invention comprises the following steps: (1) preparing a poly(vinylidene fluoride-trifluoroethylene) solution; (2) heating a glass platform, spreading the poly(vinylidene fluoride-trifluoroethylene) solution on the hot glass platform, and volatilizing the solvent on the glass platform to form a poly(vinylidene fluoride-trifluoroethylene) supercooled melt film on the surface of the hot glass platform; (3) stretching the supercooled poly(vinylidene fluoride-trifluoroethylene) melt on the hot glass platform using an electric roller, generating an extremely high longitudinal flow gradient during the stretching process, and inducing the crystallization of poly(vinylidene fluoride-trifluoroethylene) molecular chains in an oriented manner to obtain a highly oriented edge-on lamellar structure poly(vinylidene fluoride-trifluoroethylene) ultra-thin film with a nano-scale thickness. Among them, the concentration of the poly(vinylidene 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 poly(vinylidene fluoride-trifluoroethylene) solution can be a high-boiling solvent. The high-boiling solvent can be at least one of dimethylformamide (153 °C) and xylene (138 °C). When poly(vinylidene fluoride-trifluoroethylene) is dissolved in the solvent, the heating temperature can be 80-110 °C. The stretching speed of the electric roller can be 4-20 cm / s. The thickness of the highly oriented poly(vinylidene fluoride-trifluoroethylene) film can be 20-100 nm.

[0025] The highly oriented poly(vinylidene fluoride-trifluoroethylene) film prepared by the preparation method according to the present invention can be applied to ferroelectric memories.

[0026] Hereinafter, a specific preparation method of a highly oriented poly(vinylidene fluoride-trifluoroethylene) film according to the present invention will be described in detail with reference to specific embodiments.

[0027] Example 1

[0028] The preparation method of the highly oriented poly(vinylidene fluoride-trifluoroethylene) film comprises the following steps:

[0029] Preparation of a highly oriented edge-on lamellar structure poly(vinylidene fluoride-trifluoroethylene) film by the melt stretching method: The melt stretching device consists of a hot glass platform and an electric roller, as Figure 1As shown. In the experiment, a poly(vinylidene fluoride-trifluoroethylene) / dimethylformamide solution with a concentration of 20 mg / mL was prepared, and the solution was heated to 90 °C and stirred to ensure that poly(vinylidene fluoride-trifluoroethylene) was uniformly 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, an electric roller was used to stretch the supercooled poly(vinylidene fluoride-trifluoroethylene) melt on the hot glass platform, and the stretching speed was set at 10 cm / s. During the stretching process, the melt was subjected to a great longitudinal tensile force, resulting in a very high longitudinal flow gradient, which made the poly(vinylidene fluoride-trifluoroethylene) molecular chains arrange regularly, induced the orientation crystallization of the poly(vinylidene fluoride-trifluoroethylene) molecular chains, and obtained a poly(vinylidene fluoride-trifluoroethylene) ultra-thin film with a high-orientation edge-on lamellar structure about 50 nm thick. The prepared film is as shown in Figure 2 shown, where, in order to clearly show the film, the prepared film was attached to a silicon wafer substrate.

[0030] Comparative Example 1

[0031] Except that the heating temperature of the glass platform was selected at 150 °C, the others were the same as in Example 1. The prepared film is as shown in Figure 3 shown, where, in order to clearly show the film, the prepared film was attached to a silicon wafer substrate.

[0032] Comparative Example 2

[0033] Preparation of poly(vinylidene fluoride-trifluoroethylene) film by solution spin coating method: A poly(vinylidene fluoride-trifluoroethylene) / butanone solution with a concentration of 10 mg / mL was prepared, and substrates such as silicon wafers or glass slides were placed on a spin coater. An appropriate amount of the solution was dropped on the substrate, and the spin coater switch was turned on to spin coat at a speed of 2000 r / min. A film with a thickness of about 50 nm was obtained.

[0034] Performance testing and results

[0035] 1. Referring to Figure 1 、 Figure 2 、 Figure 4 (b), it can be seen that by using the melt stretching method of Example 1, a continuous poly(vinylidene fluoride-trifluoroethylene) ultra-thin film with a high-orientation edge-on lamellar structure at the nanoscale thickness can be prepared.

[0036] In Comparative Example 1, the melt stretching method was also used to prepare the film, but the heating temperature of the glass platform was too high. At this time, the fluidity of poly(vinylidene fluoride-trifluoroethylene) was relatively strong, and a continuous film could not be formed during stretching, as shown in Figure 3As shown. If the temperature of the glass platform is too low, poly(vinylidene fluoride-trifluoroethylene) will rapidly cool down to form a solid film, which does not have fluidity and cannot be stretched at this time. Therefore, the heating temperature is an important factor in the preparation of films by the melt stretching method. If the temperature is too high, a continuous film cannot be formed, and if the temperature is too low, film formation is impossible.

[0037] 2. The microstructure of the poly(vinylidene fluoride-trifluoroethylene) film prepared by the solution spin coating method in Comparative Example 2 is as Figure 4 (a). Poly(vinylidene fluoride-trifluoroethylene) forms edge-on structure lamellae, but the lamellae are isotropic and the crystal arrangement is disordered.

[0038] 3. In Example 1, the melt stretching method is used. During the stretching process, an extremely high longitudinal flow gradient will be generated, inducing the molecular chain orientation crystallization of poly(vinylidene fluoride-trifluoroethylene). The prepared P(VDF-TrFE) film forms edge-on structure lamellae. Compared with Comparative Example 2, Example 1 has a high degree of orientation, as Figure 4 (b).

[0039] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration and not for limiting the scope of the present invention. Those skilled in the art should understand that the above embodiments can be modified 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 preparation method of a highly oriented polyvinylidene fluoride-trifluoroethylene film, characterized in that, It includes the following steps: (1) Prepare a polyvinylidene fluoride-trifluoroethylene solution; (2) Heat the glass platform, spread the polyvinylidene fluoride-trifluoroethylene solution on the hot glass platform, and let the solvent on the glass platform volatilize to form a polyvinylidene fluoride-trifluoroethylene supercooled melt film on the surface of the hot glass platform; (3) Use an electric roller to stretch the supercooled polyvinylidene fluoride-trifluoroethylene melt on the hot glass platform. During the stretching process, an extremely high longitudinal flow gradient is generated to induce the crystallization of polyvinylidene fluoride-trifluoroethylene molecular chains oriented, and a highly oriented edge-on lamellar structure polyvinylidene fluoride-trifluoroethylene ultra-thin film with a nanoscale thickness is obtained.

2. The preparation method of the highly oriented polyvinylidene fluoride-trifluoroethylene film according to claim 1, wherein The concentration of the polyvinylidene fluoride-trifluoroethylene solution is 10 - 100 mg / mL.

3. The preparation method of the highly oriented polyvinylidene fluoride-trifluoroethylene film according to claim 1, characterized in that, The heating temperature of the glass platform is 135 - 145 °C.

4. The preparation method of the highly oriented polyvinylidene fluoride-trifluoroethylene film according to claim 1, characterized in that, The solvent of the polyvinylidene fluoride-trifluoroethylene solution is a high-boiling solvent.

5. The preparation method of the highly oriented polyvinylidene fluoride-trifluoroethylene film according to claim 4, characterized in that, The high-boiling solvent is at least one of dimethylformamide and xylene.

6. The preparation method of the highly oriented polyvinylidene fluoride-trifluoroethylene film according to claim 4, characterized in that, When polyvinylidene fluoride-trifluoroethylene is dissolved in the solvent, the heating temperature is 80 - 110 °C.

7. The preparation method of the highly oriented polyvinylidene fluoride-trifluoroethylene film according to claim 1, characterized in that, The stretching speed of the electric roller is 4 - 20 cm / s.

8. The preparation method of the highly oriented polyvinylidene fluoride-trifluoroethylene film according to claim 1, characterized in that, The thickness of the highly oriented polyvinylidene fluoride-trifluoroethylene film is 20 - 100 nm.

9. A highly oriented polyvinylidene fluoride-trifluoroethylene film prepared by the preparation method according to any one of claims 1 - 8.

10. Use of a highly oriented poly(vinylidene fluoride-trifluoroethylene) film prepared by the preparation method according to any one of claims 1-8, characterized in that, Applied to ferroelectric memories.

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