WO2023151217A1

WO2023151217A1 - Polymer film polarization method

Info

Publication number: WO2023151217A1
Application number: PCT/CN2022/100860
Authority: WO
Inventors: 胡志军; 何宝胜
Original assignee: 苏州大学
Priority date: 2022-02-14
Filing date: 2022-06-23
Publication date: 2023-08-17
Also published as: CN114613902B; CN114613902A

Abstract

The present invention belongs to the technical field of films, and relates to a polymer film polarization method. The method comprises the following steps: placing a template on a surface of a polymer film to be polarized, the side surface of the template attached to the surface of said polymer film being provided with a micro-nano structure array; heating said polymer film to a viscous state, and under the action of pressure, squeezing part of said polymer film in the viscous state into micro-nano structures on the surface of the template; and performing cooling to cure said polymer film, and peeling off the template, so that a polarization process is completed. According to the polymer film polarization method provided by the present invention, an electric field does not need to be applied during the polarization process, so that the polymer film and a circuit layer will not directly bear a high-voltage electric field. Therefore, the polymer film or an electronic device can be effectively prevented from being broken down, the production qualification rate of polarized films is effectively improved, and large-scale production can be achieved.

Description

A method for polarizing polymer thin films

technical field

The invention belongs to the technical field of thin films, and relates to a method for polarizing a polymer film, in particular to a method for polarizing a polymer film without an electric field.

Background technique

Piezoelectric materials are a class of crystalline materials with special dielectric properties. When they are deformed by an external force, the material will generate surface bound charges due to the displacement of the charge center. This process of converting mechanical energy into electrical energy is often referred to as the direct piezoelectric effect. Conversely, when an electric field is applied to a piezoelectric material, the material deforms due to the displacement of the center of charge. This process of converting electrical energy into mechanical energy is commonly known as the inverse piezoelectric effect. Piezoelectric sensors, transducers, drivers and other devices can be prepared by using the direct piezoelectric effect and inverse piezoelectric effect of piezoelectric materials, which are widely used in the fields of mechanics, acoustics, medicine, aerospace and navigation.

Polarization is an important link in the preparation process of piezoelectric materials and devices. The main purpose is to orient the random dipoles in piezoelectric materials in a specific direction, so that they can exhibit strong piezoelectric properties. In the polarization process, the piezoelectric material or device is usually placed in an electric field. When the strength of the electric field exceeds a certain threshold, the dipoles that were originally oriented in disorder are oriented along the direction of the electric field. According to the different ways of applying the electric field, the current electric field polarization methods are mainly divided into two types. One is the non-contact type, that is, the conductive carriers are injected into the surface of the piezoelectric material by means of corona polarization. When the electric field formed by the accumulated carriers on the surface is higher than a certain threshold, the coupler in the piezoelectric material The poles are oriented in the direction of the electric field. When the electric field is removed, part of the surface charge disappears, and the aligned dipoles form the polarization of the surface. The other is the contact type, that is, the electric field is directly applied to the electrodes on both sides of the piezoelectric material or device. When the applied electric field strength is higher than a certain threshold, the dipole in the piezoelectric material is oriented along the direction of the electric field. When the electric field is removed, the oriented dipoles in the piezoelectric material form the polarization of the surface.

The process of using high-voltage electric fields to polarize piezoelectric materials and devices results in high energy consumption and potential safety hazards. More importantly, high-voltage electric fields may break down piezoelectric materials and devices, especially when piezoelectric devices contain circuit layers such as transistors, resulting in damage to the entire material and electronic devices, so the production pass rate is low, and piezoelectric devices cannot be realized. Mass production of materials and devices.

Contents of the invention

In order to solve the above problems, especially the technical problems of low electric field polarization yield and low production efficiency of polymer piezoelectric material films, the present invention provides a method for polarizing piezoelectric polymer films without electric field.

According to the technical solution of the present invention, the method for polarizing the polymer film comprises the following steps,

S1: The template is placed on the surface of the polymer film to be polarized, and the surface of the template attached to the surface of the polarized polymer film has a micro-nano structure array;

S2: heating the polymer film to be polarized to a viscous fluid state, and extruding a part of the polymer film to be polarized in a viscous fluid state into the micro-nano structure on the surface of the template under pressure;

S3: cooling to solidify the polymer film to be polarized, peeling off the template, and completing the polarization process.

Further, the material of the template is thermosetting resin such as phenolic resin, epoxy resin, furan resin, silicone resin, etc., inorganic oxide such as silicide, nitride, oxide, etc., ceramic material such as silicate, chlorate , borate, etc., metal materials such as aluminum, iron, copper, alloys, etc.

Further, the materials of the piezoelectric polymer film include but are not limited to fluorine-containing resins, such as homopolymers of vinylidene fluoride, copolymers of vinylidene fluoride and trifluoroethylene, copolymers of vinylidene fluoride and chlorotrifluoroethylene Copolymers of vinylidene fluoride and trifluoroethylene, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of vinylidene fluoride and hexafluoropropylene oxide, copolymers of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene materials, other piezoelectric polymers, such as polylactic acid, cellulose, etc. These polymers may be used alone or in mixture.

Further, in the micro-nano structure array, the height of the micro-nano structure is 1nm-1000μm, the width is 1nm-1000μm, and there is no requirement for its period (in the embodiment, for the convenience of preparation, a periodic structure is adopted, and the period is 1nm-1000μm ). There are no specific requirements for the shape of the micro-nano structure, but three-dimensional structures such as pyramids, prisms, cones, and truncated cones and two-dimensional structures such as blazed gratings and trapezoidal gratings are preferred.

Further, in the step S2, the temperature of the polymer film to be polarized is raised above the melting point or the glass transition temperature to form a viscous fluid state, and the specific temperature depends on the material.

Further, in the step S2, the pressure is applied for 1-10 minutes.

Further, in the step S3, the cooling is performed under the condition of maintaining the pressure in the step S2.

Further, the pressure should preferably be capable of extruding the partially viscous polymer film to be polarized into the micro-nano structure on the surface of the template, and its size may be 10-20 MPa.

Under the action of pressure, the polymer film to be polarized undergoes non-uniform deformation, specifically: deformation along the direction of pressure and deformation perpendicular to the direction of pressure will occur. After the polymer film is cured, there will be a strain gradient in the micro-nano structure on the surface of the polymer film, and the polarization process is shown in Figure 1. According to the flexoelectric effect, the existence of the strain gradient will produce polarization intensity, and the magnitude of the polarization intensity is proportional to the magnitude of the strain gradient, as shown in Figure 2.

Compared with the prior art, the technical solution of the present invention has the following advantages: the polymer film polarization method provided by the present invention does not need to apply an electric field during the polarization process, and does not directly withstand the high-voltage electric field on the polymer film and the circuit layer, Therefore, it can effectively prevent the polymer film or electronic device from being broken down, effectively improve the production pass rate of the polarized film, and realize large-scale production.

Description of drawings

Fig. 1 is a schematic diagram of the polarization process of the polymer film of the present invention.

Fig. 2 is a schematic diagram of the relationship between polarization intensity (left) and strain gradient (right) in the polymer polarized film of the present invention.

3 is a schematic diagram (A) of the morphology of the PVDF polarized film in Example 1 and a schematic diagram (B) of the measurement and calculation of the remanent polarization.

4 is a schematic diagram (A) of the morphology of the P(VDF-HFP) polarized film in Example 2 and a schematic diagram (B) of the measurement and calculation of the remanent polarization.

5 is a schematic diagram (A) of the morphology of the P(VDF-TrFE) polarized film in Example 3 and a schematic diagram (B) of the measurement and calculation of the remanent polarization.

Detailed ways

The invention utilizes the flexoelectric effect produced in the non-uniform deformation process to polarize the piezoelectric polymer film. Specifically include: providing a template with a micro-nano structure, which includes an opposite first surface and a second surface, the first surface is a flat surface, and the second surface has a micro-nano structure array; providing a polymer film to be polarized, which includes The opposite third surface and the fourth surface; the template with the micro-nano structure is placed above the polymer film to be polarized, the second surface of the template contacts the third surface of the polymer film to be polarized, and the polymer film is heated to a viscous flow state, and under the action of pressure, the second surface of the template is closely contacted with the third surface of the polymer film, and the micro-nano structure array on the second surface of the template is copied to the third surface of the polymer film. After the polymer film is cooled to a glassy or crystalline state, the template and the polymer film are separated to complete the polarization process.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the examples given are not intended to limit the present invention.

Example 1

Provide a kind of method for preparing polyvinylidene fluoride (PVDF) polarization film in this example, specifically comprise the following steps:

(1) Place the polyvinylidene fluoride (PVDF) film to be polarized on a heating plate, and set the temperature to 180°C;

(2) placing a polydimethylsiloxane (PDMS) template with a blazed grating structure above the PVDF film, the second surface of the template contacts the third surface of the PVDF film;

(3) Apply a pressure of 15 MPa to the PDMS template, continue cooling for 2 minutes, and cool to room temperature (25±5°C) while maintaining the pressure;

(4) The PDMS template is peeled off from the PVDF film to complete the polarization of the PVDF film;

(5) Measured by the atomic force microscope, the height of the blazed grating structure is 2.0 μm, and the period is 13 μm, as shown in Figure 3(A);

(6) The measurement results of the piezoelectric coefficient show that the remnant polarization Pr is 26.7 μC/cm ² , as shown in Fig. 3(B).

Example 2

Provide a kind of method for preparing poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) polarized film in this example, specifically comprise the following steps:

(1) Place the P(VDF-HFP) film to be polarized on a heating plate, and set the temperature to 170°C;

(2) Place a polydimethylsiloxane (PDMS) template with a blazed grating structure on top of the P(VDF-HFP) film, and the second surface of the template contacts the third surface of the P(VDF-HFP) film ;

(3) Apply a pressure of 15 MPa to the PDMS template, cool after 2 minutes, and cool to room temperature while maintaining the pressure;

(4) Peel off the PDMS template from the P(VDF-HFP) film to complete the polarization of the P(VDF-HFP) film;

(5) Measured by the atomic force microscope, the height of the blazed grating structure is 2.0 μm, and the period is 13 μm, as shown in Figure 4(A);

(6) The measurement result of the piezoelectric coefficient shows that the remnant polarization Pr is 33.5 μC/cm ² , as shown in Fig. 4(B).

Example 3

Provide a kind of method for preparing poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) polarized film in this example, specifically comprise the following steps:

(1) Place the P(VDF-TrFE) film to be polarized on a heating plate, and set the temperature to 160°C;

(2) Place a polydimethylsiloxane (PDMS) template with a blazed grating structure on top of the P(VDF-TrFE) film, and the second surface of the template contacts the third surface of the P(VDF-TrFE) film to be prepared. surface;

(3) Apply a pressure of 15 MPa to the PDMS template, cool the heating plate after 2 minutes, and cool to room temperature while maintaining the pressure;

(4) Peel off the PDMS template from the P(VDF-TrFE) film to complete the polarization of the P(VDF-TrFE) film;

(5) Measured by the atomic force microscope, the height of the blazed grating structure is 2.0 μm, and the period is 13 μm, as shown in Figure 5(A);

(6) The measurement result of the piezoelectric coefficient shows that the remnant polarization Pr is 28.3 μC/cm ² , as shown in Fig. 5(B).

Example 4

(1) Place the polyvinylidene fluoride (PVDF) film to be polarized on a heating plate, and set the temperature to 190°C;

(3) Apply a pressure of 13 MPa to the PDMS template, cool after 2 minutes, and cool to room temperature while maintaining the pressure;

(5) Measured by the atomic force microscope, the height of the blazed grating structure is 200.0 μm, and the period is 100 μm.

Example 5

(2) placing the polydimethylsiloxane (PDMS) template with the truncated cone structure above the PVDF film, the second surface of the template contacts the third surface of the PVDF film;

(5) As measured by the atomic force microscope, the upper surface width of the frustoconical structure is 1.3 μm, the lower surface width is 2.9 μm, the thickness is 2.5 μm, and the period is 50 μm.

Apparently, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation. For those of ordinary skill in the art, on the basis of the above description, other changes or changes in various forms can also be made. It is not necessary and impossible to exhaustively list all the implementation manners here. However, the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims

A method for polarizing a polymer film, characterized in that it comprises the following steps,

S1: The template is placed on the surface of the polymer film to be polarized, and the surface of the template attached to the surface of the polarized polymer film has a micro-nano structure array;

S2: heating the polymer film to be polarized to a viscous fluid state, and extruding a part of the polymer film to be polarized in a viscous fluid state into the micro-nano structure on the surface of the template under pressure;

S3: cooling to solidify the polymer film to be polarized, peeling off the template, and completing the polarization process.
The method for polarizing a polymer film according to claim 1, wherein the template is made of thermosetting resin, inorganic oxide, ceramic or metal.
The method for polarizing a polymer film according to claim 1, wherein the material of the template is selected from phenolic resin, epoxy resin, furan resin, silicone resin, silicide, nitride or oxide, silicic acid Salt, chlorate, borate, aluminum, iron, copper or alloys.
The method for polarizing a polymer film according to claim 1, wherein the material of the polymer film to be polarized is selected from one or more of fluorine-containing resin, polylactic acid and cellulose.
The method for polarizing a polymer film according to claim 4, wherein the fluorine-containing resin is selected from the group consisting of homopolymers of vinylidene fluoride, copolymers of vinylidene fluoride and trifluoroethylene, vinylidene fluoride and trifluoroethylene Copolymers of chlorofluoroethylene, copolymers of vinylidene fluoride and trifluoroethylene, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of vinylidene fluoride and hexafluoropropylene oxide, copolymers of vinylidene fluoride and hexafluoropropylene One or more of tetrafluoroethylene copolymers.
The method for polarizing a polymer film according to claim 1, wherein, in the array of micro-nanostructures, the micro-nanostructures are shaped as pyramids, frustums, cones, frustums, blazed gratings or trapezoidal gratings.
The method for polarizing a polymer film according to claim 1 or 6, characterized in that the height of the micro-nano structure is 1 nm-1000 μm, and the width is 1 nm-1000 μm.
The method for polarizing a polymer film according to claim 1, wherein in the step S2, the temperature of the polymer film to be polarized is raised above the melting point or glass transition temperature to form a viscous fluid state.
The method for polarizing a polymer film according to claim 1, characterized in that, in the step S3, the cooling is carried out under the condition of maintaining the pressure in the step S2.
The method for polarizing a polymer film according to claim 1 or 9, wherein the pressure is 10-20 MPa.