CN112745519A - Preparation method of polyvinylidene fluoride film - Google Patents

Preparation method of polyvinylidene fluoride film Download PDF

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CN112745519A
CN112745519A CN201911051720.XA CN201911051720A CN112745519A CN 112745519 A CN112745519 A CN 112745519A CN 201911051720 A CN201911051720 A CN 201911051720A CN 112745519 A CN112745519 A CN 112745519A
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polyvinylidene fluoride
annealing
fluoride film
temperature
film
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CN112745519B (en
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孙晓丽
米策
闫寿科
李慧慧
任忠杰
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Beijing University of Chemical Technology
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    • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C08J2327/16—Homopolymers or copolymers of vinylidene fluoride

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Abstract

The application provides a preparation method of a polyvinylidene fluoride film, which comprises the following steps: the weight average molecular weight is 1.0X 105To 3.0X 105The PVDF of (1) is dispersed in a solvent to form a PVDF solution; forming the PVDF solution on a substrate, and drying and forming to obtain an initial film; melting and recrystallizing the initial film to obtain a recrystallized polyvinylidene fluoride film; and annealing the recrystallized polyvinylidene fluoride film for multiple times to obtain the polyvinylidene fluoride film containing gamma crystals and beta crystals. A method of making a capacitor is also provided.

Description

Preparation method of polyvinylidene fluoride film
Technical Field
The application relates to a preparation method of a polyvinylidene fluoride film.
Background
Polyvinylidene fluoride (PVDF) is a common polymorphic polymer, crystal forms which are discovered to date are alpha, beta, gamma, delta and epsilon, the forming conditions of each crystal form are different, and the mutual conversion among the crystal forms can be realized under the action of heat, electric field, mechanical energy, radiation energy and the like. The PVDF in the gamma crystal form and the beta crystal form externally shows polarity, has good piezoelectric, ferroelectric, dielectric and magnetic properties, can be applied to a piezoelectric sensor for monitoring heartbeat and pulse of a human body, and can also be used for preparing a capacitor and a transistor in a ferroelectric memory. However, the existing preparation method of the PVDF film cannot simultaneously meet the requirements of high total occupation ratio of gamma crystal forms and beta crystal forms in the prepared PVDF, high preparation efficiency, small dependence on substrate materials and the like, and the application of the PVDF is limited.
Disclosure of Invention
In view of this, the application provides a method for preparing a polyvinylidene fluoride film, the dependency of the preparation process on the substrate material is small, the preparation efficiency is high, and the total ratio of the gamma crystal form and the beta crystal form of the obtained polyvinylidene fluoride film is high.
A preparation method of a polyvinylidene fluoride film comprises the following steps: the weight average molecular weight is 1.0X 105To 3.0X 105The PVDF of (1) is dispersed in a solvent to form a PVDF solution; forming the PVDF solution on a substrate, and drying and forming to obtain an initial film; melting and recrystallizing the initial film to obtain a recrystallized polyvinylidene fluoride film; and annealing the recrystallized polyvinylidene fluoride film for multiple times to obtain the polyvinylidene fluoride film containing the gamma crystal form and the beta crystal form.
A method of making a capacitor comprising the steps of: forming a first metal aluminum layer by evaporation; forming a polyvinylidene fluoride film on the surface of the first metal aluminum layer by adopting the preparation method of the polyvinylidene fluoride film; evaporating a second metal aluminum layer on the surface of the polyvinylidene fluoride film to obtain a capacitor; the polyvinylidene fluoride thin film between the first metal aluminum layer and the second metal aluminum layer is an insulating film of the capacitor.
Compared with the prior art, the preparation method of the polyvinylidene fluoride film has the advantages that the dependence of the preparation process on the substrate material is small, the preparation efficiency is high, and the total ratio of the gamma crystal form and the beta crystal form of the obtained polyvinylidene fluoride film is high (more than 50 wt%).
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a melt curve of a recrystallized PVDF film of PVDF according to an embodiment of the present invention, wherein the molecular weight of PVDF is 180000.
FIG. 2 is a melting curve of a recrystallized PVDF film obtained after a first anneal of a PVDF film according to an embodiment of the present application, wherein the molecular weight of the PVDF film is 180000, and the film has both alpha and gamma crystals.
FIG. 3 is a comparison graph of IR spectra of PVDF films obtained after a first and a second anneal, respectively, of one example of the present application; wherein, alpha crystal still exists after the first annealing; after the second annealing, the alpha crystal is almost not generated, and the obtained sample is almost all polar samples containing the gamma crystal and the beta crystal.
FIG. 4 is an infrared spectrum of the polyvinylidene fluoride film of example 1.
FIG. 5 is an X-ray diffraction pattern of the polyvinylidene fluoride film of example 1.
FIG. 6 is an AFM topography of the polyvinylidene fluoride film of example 1.
FIG. 7 is an infrared spectrum of the polyvinylidene fluoride film of comparative example 1.
FIG. 8 is an infrared spectrum of a polyvinylidene fluoride film of comparative example 4
Fig. 9 is a hysteresis chart of a capacitor manufactured according to the third embodiment of the present application.
Detailed Description
In order to make the technical solutions of the present application better understood, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The preparation method of the polyvinylidene fluoride film with the high total ratio of the gamma crystal form and the beta crystal form in the first embodiment of the application comprises the following steps: (1) preparing a PVDF solution; (2) preparing an initial film; (3) further drying of the initial film; (4) and forming the gamma crystal polyvinylidene fluoride film. As described in detail below.
(1) Preparation of PVDF solution:
the preparation steps of the PVDF solution are as follows: the weight average molecular weight is 1.0X 105To 3.0X 105Is dispersed in a solvent to form a PVDF solution.
Preferably, the PVDF of the present application has a weight average molecular weight of 1.8X 105To 2.7X 105(ii) a More preferably, the PVDF of the present application has a weight average molecular weight of 1.8X 105The PVDF film obtained by adopting the PVDF with the weight average molecular weight has higher content of gamma crystals and beta crystals.
The weight average molecular weight can be measured by a conventional method, for example, a light scattering method, a gel chromatography method, an ultracentrifugation sedimentation rate method, and the like. In the application, the weight average molecular weight of PVDF is controlled in the range, which is beneficial to the spontaneous generation of gamma crystal and beta crystal nucleus, thereby increasing the content of gamma crystal and beta crystal form in the polyvinylidene fluoride film.
Wherein, the PVDF can be a powdery, granular and other commercial PVDF raw material; it should be noted that the PVDF raw material may contain crystal forms of α, β, γ, etc., but the crystal forms of the raw material do not affect the subsequent steps, and since PVDF of various crystal forms does not exist in a crystal form after being dissolved in a solvent, the initial film formed by drying with a common film forming method is basically all of the α crystal form, or is mostly the α crystal form, and is a very small amount of the γ crystal form.
The solvent herein may be selected from one or more of N, N-dimethylformamide DMF, N-dimethylacetamide DMAc, N-methylpyrrolidone NMP, dimethylsulfoxide DMSO, acetone, tetrahydrofuran, and acetonitrile. The solvent is favorable for spontaneous generation of gamma crystals and beta crystal nuclei, so that the content of the gamma crystals and the beta crystal forms in the polyvinylidene fluoride film is increased.
Preferably, the solvent herein is selected from one or more of N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone. More preferably, the solvent herein is N, N-dimethylformamide; wherein, the adoption of N, N-dimethylformamide is more beneficial to the spontaneous generation of gamma crystals and beta crystal nucleuses.
In the present application, the PVDF solution is formed in a concentration of 1 mg/mL (mg/mL) to 100 mg/mL; the concentration of the PVDF solution may preferably be 30mg/mL to 90mg/mL from the viewpoint of promoting spontaneous generation of γ nuclei; still more preferably from 50mg/mL to 80 mg/mL; still more preferably 80 mg/mL.
Among them, PVDF may be mixed with a solvent, and then heated and stirred, thereby promoting dissolution of PVDF. Wherein the temperature for heating to dissolve may be 50 degrees centigrade (° c) to 150 ℃, preferably 80 ℃ to 120 ℃, more preferably 90 ℃ to 110 ℃; the stirring time is 10 hours (h) to 24 hours, preferably 8h to 12 h; the stirring rate is 400 revolutions per minute (rpm) to 700rpm, preferably 500rpm to 600 rpm.
In one embodiment of the present application, the weight average molecular weight is 1.8 × 105Is dispersed in N, N-dimethylformamide and stirred at a stirring speed of 500 to 600rpm for 8 to 12 hours at 110 ℃ to prepare a PVDF solution having a concentration of 30 to 90mg/mL, followed by cooling to room temperature (e.g., 23. + -. 2 ℃).
(2) Preparation of initial film:
the initial film preparation steps of the present application are: and (2) forming the PVDF solution obtained in the step (1) on a substrate, and drying and forming to obtain an initial film.
The substrate includes, but is not limited to, glass, crystalline silicon, potassium bromide, alumina, quartz, and metals; the method has the advantages that the optional substrate range is wide, and the method is not limited by too many special limits, so that the preparation of the polyvinylidene fluoride film is not limited by the substrate material basically, the cost for manufacturing the polyvinylidene fluoride film is reduced, and the application range of the polyvinylidene fluoride film is widened.
The PVDF solution may be formed on the substrate by spin coating or drop coating.
In one embodiment, the initial film is prepared by spin coating the PVDF solution drop-on onto the substrate rotating at high speed at a predetermined spin-on rate while the PVDF is heated, dried and shaped.
In one embodiment, the predetermined spin rate may be 1000rpm to 5000rpm, preferably 2000rpm to 3000 rpm; the spin coating time is determined according to the thickness of the polyvinylidene fluoride thin film to be formed, the spin coating time is longer when a thick film is needed, and the spin coating time is shorter when a thin film is needed, wherein the spin coating time is preferably 1 minute (min) to 2min by integrating the consideration of all factors; the temperature for the heat drying molding, that is, the temperature for the initial film formation may be 40 ℃ to 130 ℃, preferably 70 ℃ to 100 ℃, more preferably 80 ℃ to 90 ℃. In other embodiments, other spin coating conditions may be used as desired.
The polyvinylidene fluoride film obtained by the spin-coating method has good uniformity, and the polyvinylidene fluoride film with a very wide thickness range can be obtained; in addition, the spin coating method is more advantageous for obtaining a polyvinylidene fluoride film having a small thickness, for example, a polyvinylidene fluoride film having a thickness of 0.10 micrometers (μm) to 0.80 μm can be obtained.
In one embodiment, the PVDF solution with the concentration of 80mg/mL obtained in the step (1) is subjected to high-speed spin drop coating for 1min at the spin-coating speed of 3000rpm, and is heated, dried and molded at 80 ℃ to obtain an initial film.
In another embodiment, the PVDF solution obtained in step (1) is dropped on a substrate by a dropping film method and dried to form an initial film. Among them, in one embodiment, the initial film forming temperature may be 40 to 130 ℃, preferably 80 to 100 ℃, and more preferably 80 to 90 ℃; the initial film formation time may be 12h to 24h, for example 12h to 18 h; a film layer with more uniform and moderate thickness can be obtained by a film dropping method and the spin coating parameters provided by the application; in other embodiments, other spin coating conditions may be used as desired. The dropping method is suitable for obtaining a polyvinylidene fluoride film having a large thickness, for example, a polyvinylidene fluoride film having a thickness of 0.80 μm or more.
In one embodiment, when the solution obtained in step (1) is uniformly dripped on a substrate by using a dripping film method, the size of the substrate is preferably matched with the volume of the dripped solution so as to obtain a polyvinylidene fluoride film with a predetermined thickness.
(3) Further drying of the initial film:
in this step: the temperature at which the initial film is further dried may be 80 ℃ to 120 ℃, preferably 100 ℃ to 110 ℃; the time for further drying may be 8h to 12h, more preferably 12 h. Further drying of the initial film is effective to remove residual solvent from the initial film. It is understood that the drying temperature and time in this step can be flexibly selected depending on the thickness of the initial film obtained in step (2) and the amount of residual solvent.
The further drying means of this step may be one selected from the group consisting of hot air drying, microwave drying, ultraviolet drying, infrared drying, vacuum drying and freeze drying, and more preferably vacuum drying.
In one embodiment of the present application, the initial film is dried under vacuum at 100 ℃ for 12 h.
In other embodiments, this step may not be performed, i.e., if the resulting initial film is already free of solvent residue, i.e., completely dried, no further drying of this step is required.
(4) Forming the polyvinylidene fluoride film with higher total ratio of the gamma crystal form and the beta crystal form:
in the application, the initial film is subjected to melting recrystallization and then is subjected to multiple annealing, so that the polyvinylidene fluoride film with the total proportion of gamma crystal forms and beta crystal forms exceeding 50 wt% can be obtained.
Specifically, the initial film is first melt-recrystallized to obtain a recrystallized polyvinylidene fluoride film of almost pure α -crystal (see fig. 1), and the melt-recrystallization temperature is higher than the crystalline melting point of the initial film, and generally, the crystalline melting point of polyvinylidene fluoride is about 170 ℃, so that the recommended melt-recrystallization temperature for the initial film is 180 ℃ or higher, preferably, 190 ℃ to 210 ℃, and more preferably, about 200 ℃; the heat preservation time is 1min to 20min, preferably 5min to 10 min; the heating rate of the initial film during the melting recrystallization is 10 ℃/min to 50 ℃/min; the cooling rate when the initial film is subjected to melt recrystallization is from 5 ℃/min to 20 ℃/min.
After the recrystallized polyvinylidene fluoride membrane is cooled to the room temperature, keeping for a preset time; wherein the predetermined time may be 1 to 20min, preferably 10 min; maintaining the predetermined time at room temperature is favorable for the stability of the crystal form of the polyvinylidene fluoride membrane.
Then, carrying out primary annealing on the recrystallized polyvinylidene fluoride film; the annealing heat preservation time of the first annealing is 1min to 10min, preferably 1min to 5 min; the temperature rise rate of the first annealing can be selected in a wide range, preferably 1 ℃/min to 40 ℃/min, more preferably 5 ℃/min to 10 ℃/min; the cooling rate of the first annealing is preferably 1 ℃/min to 25 ℃/min, more preferably 10 ℃/min.
The annealing temperature of the first annealing was determined as follows:
obtaining a melting curve of the recrystallized polyvinylidene fluoride film;
defining the temperature corresponding to the highest point of an alpha crystal melting peak of the melting curve as peak temperature A1, and defining the temperature corresponding to the end point of the melting peak of the melting curve as end temperature A2;
calculating the annealing temperature A of the first annealing, wherein the annealing temperature A ranges from A1-3 ℃ to A2+8 ℃.
More preferably, the annealing temperature a ranges from a1+5 ℃ to a2+5 ℃; experiments prove that the total content of gamma crystals and beta crystals obtained in the annealing temperature A range is higher.
The peak temperatures of the melting curves which can be obtained by adopting different heating rates are slightly different, and for convenience of description, the heating rates adopted when the melting curve of the recrystallized polyvinylidene fluoride film is obtained are all 5 ℃/min; it can be understood that other heating rates can be adopted to obtain the melting curve of the initial film, but the obtained peak temperature needs to be adjusted corresponding to the peak temperature obtained by the heating rate of 5 ℃/min; for example, if the peak temperature of the melting curve obtained at a temperature increase rate of 5 ℃/min is 168 ℃ and the peak temperature of the melting curve obtained at a temperature increase rate of 10 ℃/min is 167.5 ℃, then if the above-mentioned annealing temperature calculation is performed based on the melting curve obtained at a temperature increase rate of 10 ℃/min, a2 becomes 165+ (168-167.5) ° c, i.e., it is necessary to compensate the value of a2 to the peak temperature corresponding to the melting curve obtained at a temperature increase rate of 5 ℃/min; it will be appreciated that the compensation may also be embodied directly at the annealing temperature without adjusting the peak temperature.
In one embodiment, PVDF with the weight average molecular weight of 180000 is selected to be prepared through the steps (1) to (3) to obtain an initial membrane, and then the initial membrane is subjected to melt recrystallization to obtain a recrystallized polyvinylidene fluoride membrane; as shown in fig. 2, the alpha peak temperature a1 corresponding to the melting curve of the recrystallized polyvinylidene fluoride film was 169 ℃, the termination temperature a2 was 175 ℃, and the annealing temperature a of the first annealing of the recrystallized polyvinylidene fluoride film corresponding to the weight average molecular weight was calculated to be 166 ℃ to 183 ℃, preferably 174 ℃ to 180 ℃, more preferably 174 ℃; the first annealing is carried out at the temperature, and the PVDF with the weight-average molecular weight of 180000 can be utilized to form the polyvinylidene fluoride film with higher total content of gamma crystals and beta crystals by combining the annealing parameters and the subsequent steps. The annealing temperature and the preferred annealing temperature can be obtained for PVDF with other molecular weights by the method described above, and are not described herein again.
Referring to fig. 2 and 3, the polyvinylidene fluoride film obtained after the first annealing contains both alpha crystals and gamma crystals; wherein, the formation mechanism of the gamma crystal is mainly the memory effect of the alpha crystal: at the annealing temperature, although the pre-existing alpha crystal lamella in the initial film is melted, the ordered chain segments of the alpha crystal (different from the completely relaxed state of the molecular chain) still remain, and the part of the ordered chain segments of the alpha crystal can be subjected to conformational transition to the gamma crystal during the temperature reduction process, so that the ordered structure of the gamma crystal is generated, and further the gamma crystal lamella is generated; among them, the formation of gamma crystals is accompanied by the formation of a small amount or a trace amount of beta crystals, and the mechanism thereof has yet to be studied.
After the polyvinylidene fluoride membrane after the first annealing is cooled to room temperature, keeping for a preset time; wherein the predetermined time may be 1 to 20min, preferably 10 min.
Then, carrying out secondary annealing on the recrystallized polyvinylidene fluoride film; the annealing parameters of the second annealing, such as annealing temperature, annealing heat preservation time, annealing temperature rise rate, annealing temperature drop rate and the like, can be the same as or different from the annealing parameters of the first annealing.
When the annealing parameters of the second annealing are different from the annealing parameters of the first annealing, the annealing parameters of the second annealing may be: the annealing heat preservation time of the second annealing is 1min to 10min, preferably 1min to 5min, and more preferably 1 min; the temperature rise rate of the second annealing is 1 ℃/min to 20 ℃/min, preferably 5 ℃/min to 10 ℃/min; the cooling rate of the second annealing is 1 ℃/min to 30 ℃/min, preferably 5 ℃/min to 10 ℃/min.
The annealing temperature of the second annealing was determined as follows:
obtaining a melting curve of the polyvinylidene fluoride membrane after the first annealing;
defining the temperature corresponding to the highest point of an alpha crystal melting peak of the melting curve as peak temperature B1, defining the temperature corresponding to the highest point of a gamma crystal melting peak of the melting curve as peak temperature B3, and defining the temperature corresponding to the end point of the melting peak of the melting curve as end temperature B2;
and calculating the annealing temperature B of the second annealing, wherein the annealing temperature B ranges from B1-3 ℃ to B2+5 ℃.
More preferably, the annealing temperature B ranges from B1+5 ℃ to B3+3 ℃; wherein, the total content of the gamma crystal and the beta crystal obtained in the annealing temperature range B is higher.
The peak temperatures of melting curves which can be obtained by adopting different heating rates are slightly different, and for convenience of description, the heating rate adopted when the melting curve of the polyvinylidene fluoride film after the first annealing is obtained is 5 ℃/min; it can be understood that other heating rates can be adopted to obtain the melting curve of the initial film, but the obtained peak temperature needs to be adjusted corresponding to the peak temperature obtained by the heating rate of 5 ℃/min; for example, if the peak temperature of the melting curve obtained at a temperature increase rate of 5 ℃/min is 168 ℃ and the peak temperature of the melting curve obtained at a temperature increase rate of 10 ℃/min is 167.5 ℃, then if the above-mentioned annealing temperature calculation is performed based on the melting curve obtained at a temperature increase rate of 10 ℃/min, B2 becomes 165+ (168-167.5) ° c, i.e., it is necessary to compensate the value of B2 to the peak temperature corresponding to the melting curve obtained at a temperature increase rate of 5 ℃/min; it will be appreciated that the compensation may also be embodied directly at the annealing temperature without adjusting the peak temperature.
In one embodiment, PVDF with the weight-average molecular weight of 180000 is selected to be prepared through the steps (1) to (3) to obtain an initial membrane, and then the initial membrane is subjected to melt recrystallization and first annealing to obtain a polyvinylidene fluoride membrane containing alpha and gamma crystals; as shown in fig. 3, the melting curve of the polyvinylidene fluoride membrane after the first annealing treatment corresponds to an α peak temperature B1 of 168 ℃, a γ peak temperature B3 of 176 ℃, a termination temperature B2 of 181 ℃, and the annealing temperature B of the polyvinylidene fluoride membrane corresponding to the weight average molecular weight subjected to the second annealing treatment is calculated to be 165 ℃ to 186 ℃, preferably 173 ℃ to 179 ℃, and more preferably 174 ℃; annealing at the temperature, and combining the annealing parameters and the steps, PVDF with the weight average molecular weight of 180000 can be utilized to form the high-content gamma crystal form polyvinylidene fluoride film.
Referring to fig. 3, almost all of the polyvinylidene fluoride film obtained after the second annealing in the present application is in a polar crystal form, wherein mainly gamma crystals and a small amount of beta crystals are contained; wherein, the polar crystal form, no matter gamma or beta crystal, contributes to the electrical property of the polyvinylidene fluoride film, thereby being beneficial to the application of the polyvinylidene fluoride film in the electrical field; in the second annealing, the formation mechanism of the gamma crystal is the synergistic effect of the memory effect of the alpha crystal and the self-nucleation effect of the gamma crystal: at the annealing temperature, although the pre-existing alpha crystal lamella in the initial film is melted, the ordered chain segments of the alpha crystal (different from the completely relaxed state of the molecular chain) still remain, and the part of the ordered chain segments of the alpha crystal can be subjected to conformational transition to the gamma crystal during the temperature reduction process, so that the ordered structure of the gamma crystal is generated, and further the gamma crystal lamella is generated; among them, the formation of gamma crystals is accompanied by the formation of a small amount or a trace amount of beta crystals, and the mechanism thereof has yet to be studied.
Basically, the polyvinylidene fluoride film with the total content of gamma crystals and beta crystals being more than 50 wt% can be obtained by annealing for two times; it is understood that if the content of the gamma crystal form obtained after two annealing processes is not the expected content of the total gamma crystal and beta crystal, the third annealing process, the fourth annealing process, etc. can be performed by adopting the method.
The generation of the alpha crystal form in the polyvinylidene fluoride film can be limited by controlling the temperature rise rate, the annealing temperature, the annealing heat preservation time and the temperature drop rate, so that the polyvinylidene fluoride film with higher total ratio of the gamma crystal form and the beta crystal form is obtained. In the polyvinylidene fluoride film prepared by the preparation method, the gamma crystal form and the beta crystal form a polar phase of the polyvinylidene fluoride film, and in the polar phase, the content of the gamma crystal form is far greater than that of the beta crystal form, generally, the proportion of the content of the gamma crystal form in the polar phase is more than 70%, even more than 99% is possible, that is, in the polyvinylidene fluoride film prepared by the preparation method, the gamma crystal form is dominant, and the preparation method actually aims to form high-content gamma crystal.
According to the preparation method, the polyvinylidene fluoride film with the total content of gamma crystals and beta crystals being more than 50 wt% can be obtained by adopting shorter annealing and heat preservation time, so that the preparation efficiency of the polyvinylidene fluoride film can be improved. Moreover, the total content of the gamma crystal and the beta crystal in the polyvinylidene fluoride film obtained by the method can reach more than 50 wt%.
The thickness range of the gamma crystal polyvinylidene fluoride film obtained by the application is wide, and for example, the thickness range can be 0.1 to 100 mu m.
The second embodiment of the present application provides a method for preparing a polyvinylidene fluoride film having a higher total ratio of the gamma crystal form and the beta crystal form (e.g., more than 90 wt%); in a second embodiment of the present application, a method for preparing a polyvinylidene fluoride film comprises:
(1) the weight average molecular weight is 1.8X 105To 2.7X 105Dispersing the PVDF in N, N-dimethylformamide to obtain a PVDF solution;
(2) the PVDF solution is formed on the substrate by spin coating or dropping film method to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min to 50 ℃/min for melt recrystallization, keeping the temperature for 5min to 10min, and then cooling to room temperature at a cooling rate of 5 ℃/min to 20 ℃/min; keeping for 10min, heating to an annealing temperature A at a heating rate of 5-10 ℃/min for first annealing, keeping the annealing temperature for 1-5 min, and cooling to room temperature at a cooling rate of 5-20 ℃/min; keeping for 10 minutes, heating to an annealing temperature B at a heating rate of 5-10 ℃/min for second annealing, wherein the annealing heat preservation time is 1-5 min, and then cooling to room temperature at a cooling rate of 5-10 ℃/min to obtain the polyvinylidene fluoride film.
In the embodiment, the annealing temperature A ranges from A1+5 ℃ to A2+5 ℃; the annealing temperature B ranges from B1+5 ℃ to B3+3 ℃; wherein the definition and obtaining methods of a1, a2, B1, B3, etc. are referred to the first embodiment. In one embodiment, for example, where PVDF having a weight average molecular weight of 180000 is selected, the annealing temperature A ranges from 174 ℃ to 180 ℃ and the annealing temperature B ranges from 173 ℃ to 179 ℃.
In this embodiment, a polyvinylidene fluoride film having a total content of γ crystal and β crystal of more than 90 wt% can be obtained.
It should be noted that the contents not mentioned in the present embodiment can refer to the contents in the first embodiment of the present disclosure, and are not described herein again.
The following description is given with reference to specific examples and comparative examples:
example 1
The preparation method of the gamma crystal form polyvinylidene fluoride film S1 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 deg.C at a heating rate of 10 deg.C/min for annealing for 5min, and cooling to room temperature at a cooling rate of 10 deg.C/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Example 2
The preparation method of the gamma crystal form polyvinylidene fluoride film S2 comprises the following steps:
(1) the weight average molecular weight is 2.3X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 175 ℃ at a heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 3min, and then cooling to room temperature at a cooling rate of 20 ℃/min; after keeping for 10 minutes, raising the temperature to 173 ℃ at the temperature rise rate of 5 ℃/min for secondary annealing, wherein the annealing heat preservation time is 5min, and then lowering the temperature to room temperature at the temperature drop rate of 5 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Example 3
The preparation method of the gamma crystal form polyvinylidene fluoride film S3 comprises the following steps:
(1) the weight average molecular weight is 2.7X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 176 ℃ at a heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; after keeping for 10 minutes, heating to 172 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5min, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Example 4
The preparation method of the gamma crystal form polyvinylidene fluoride film S4 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N-methylpyrrolidone to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by an autodeposition method to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 190 ℃ at a heating rate of 20 ℃/min for melting recrystallization, keeping the temperature for 10min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 deg.C at a heating rate of 10 deg.C/min for annealing for 5min, and cooling to room temperature at a cooling rate of 10 deg.C/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Example 5
The preparation method of the gamma crystal form polyvinylidene fluoride film S5 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 169 deg.C at a heating rate of 10 deg.C/min for annealing for 5min, and cooling to room temperature at a cooling rate of 10 deg.C/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Example 6
The preparation method of the gamma crystal form polyvinylidene fluoride film S6 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 deg.C at a heating rate of 10 deg.C/min for annealing for 5min, and cooling to room temperature at a cooling rate of 10 deg.C/min; keeping for 10 minutes, heating to 169 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5min, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Example 7
The preparation method of the gamma crystal form polyvinylidene fluoride film S7 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 deg.C at a heating rate of 35 deg.C/min for annealing for 5min, and cooling to room temperature at a cooling rate of 10 deg.C/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 1
The preparation method of the polyvinylidene fluoride film D1 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; after keeping for 10min, heating to 150 ℃ at the heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 2
The preparation method of the polyvinylidene fluoride film D2 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; after keeping for 10min, heating to 190 ℃ at the heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 3
The preparation method of the polyvinylidene fluoride film D3 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 ℃ at the heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 150 ℃ at the heating rate of 10 ℃/min for secondary annealing, keeping the annealing temperature for 5min, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 4
The preparation method of the polyvinylidene fluoride film D4 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 ℃ at the heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 190 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5min, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 5
The preparation method of the polyvinylidene fluoride film D5 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105PVDF component ofDispersing in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 ℃ at the heating rate of 45 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 6
The preparation method of the polyvinylidene fluoride film D6 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 ℃ at the heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 30 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 7
The preparation method of the polyvinylidene fluoride film D7 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 ℃ at the heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 10 ℃/min for second annealing, keeping the annealing temperature for 5min, and then cooling to room temperature at the cooling rate of 35 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
Comparative example 8
The preparation method of the polyvinylidene fluoride film D8 comprises the following steps:
(1) the weight average molecular weight is 1.8X 105The PVDF of (a) is dispersed in N, N-dimethylformamide to obtain a PVDF solution.
(2) The PVDF solution was formed on the substrate by spin coating to obtain an initial film.
(3) And (3) drying the initial membrane obtained in the step (2) in vacuum.
(4) Heating the initial film prepared in the step (3) to 200 ℃ at a heating rate of 10 ℃/min for melting recrystallization, keeping the temperature for 5min, and then cooling to room temperature at a cooling rate of 10 ℃/min; keeping for 10min, heating to 174 ℃ at the heating rate of 10 ℃/min for first annealing, keeping the annealing temperature for 10min, and then cooling to room temperature at the cooling rate of 10 ℃/min; keeping for 10 minutes, heating to 174 ℃ at the heating rate of 40 ℃/min for second annealing, keeping the annealing temperature for 5 minutes, and then cooling to room temperature at the cooling rate of 10 ℃/min to obtain the polyvinylidene fluoride film with the thickness of 0.5 mu m. The properties of the resulting polyvinylidene fluoride films are shown in table 1.
TABLE 1
Figure BDA0002255492090000161
Figure BDA0002255492090000171
As can be seen from table 1 above, the total content of γ crystal and β crystal in examples 1 to 4 is 95 wt% or more, the total content of γ crystal and β crystal in examples 5 to 7 is 50 wt% or more, the total content of γ crystal and β crystal in comparative examples 1 to 3 and 5 to 7 is 30 wt% or less, and the total content of γ crystal and β crystal in comparative examples 4 and 8 is 5 wt% or less. Among them, as can be seen from examples 4 to 7 and comparative examples 1 to 4, the annealing temperature has a large influence on the formation of γ crystal, and both the first annealing and the second annealing have an influence on the formation of γ crystal and β crystal due to an excessively high or low temperature, and referring to comparative example 4, the second annealing temperature has a large influence on γ crystal and β crystal, and if the temperature is excessively high, almost no γ crystal and β crystal are formed; as can be seen from example 7 and comparative examples 5 to 8, both the temperature increase rate and the temperature decrease rate during annealing have a large influence on the formation of the γ crystal and the β crystal, and both the temperature increase rate and the temperature decrease rate during the first annealing and the second annealing have an influence on the formation of the γ crystal and the β crystal, whereas the temperature increase rate during the second annealing has a larger influence on the formation of the γ crystal and the β crystal, and almost no γ crystal and β crystal are formed directly at an excessively high temperature increase rate, as seen in comparative example 8.
Fig. 4 is an infrared spectrum of the polyvinylidene fluoride film obtained in example 1, fig. 5 is an X-ray diffraction pattern of the polyvinylidene fluoride film obtained in example 1, and it can be seen from fig. 4 and fig. 5 that the total content of γ crystal and β crystal of the polyvinylidene fluoride film obtained in example 1 is extremely high (higher than 95%); fig. 6 is an Atomic Force Microscope (AFM) profile of the polyvinylidene fluoride thin film obtained in example 1 observed by an AFM, and it can be seen from fig. 6 that the gamma crystal and the beta crystal (mainly, gamma crystal) of the polyvinylidene fluoride thin film obtained in example 1 have a curled crystal profile.
Fig. 7 is an infrared spectrum of the polyvinylidene fluoride film obtained in comparative example 1, and it can be seen from fig. 7 that the polyvinylidene fluoride film obtained in comparative example 1 has three crystal forms of α, β and γ crystals at the same time, in which the γ crystal content is low and the β crystal content is not determined.
Fig. 8 is an infrared spectrum of the polyvinylidene fluoride film obtained in comparative example 4, and it can be seen from fig. 8 that the polyvinylidene fluoride film obtained in comparative example 4 is almost pure α crystal, and the contents of γ crystal and β crystal are extremely low (not measured).
The following describes the method for testing the above data:
testing the characteristic spectral band (infrared spectrogram) of the crystal form of the polyvinylidene fluoride film by using an infrared spectrometer:
an FTIR-650 Fourier transform infrared spectrometer is adopted to test the internal crystal form of the polyvinylidene fluoride film, the substrate used for the test is a silicon wafer substrate or a potassium bromide substrate, the test mode is a transmission mode, and the test wave band is 400 to 4000 per centimeter (cm)-1) Resolution of the instrument is 4cm-1。
Testing the crystal form (X-ray diffraction pattern) of the polyvinylidene fluoride film by using an X-ray diffractometer:
an X-ray diffractometer is adopted to test the internal crystal form of the polyvinylidene fluoride film, and the manufacturer of the X-ray diffractometer is a Beijing synchrotron radiation center 1W1A diffuse reflection line station. The test mode was a grazing incidence wide angle mode with an incidence angle of 0.2 °, an X-ray wavelength of 0.154 nanometers (nm), and a camera length of 420 millimeters (mm).
Testing the morphology of the polyvinylidene fluoride film AFM:
the morphology of the polyvinylidene fluoride film is tested by adopting AFM, the test mode is a non-contact mode (Tapping mode), and the scanning size of the height map is 5um x 5 um.
A third embodiment of the present application provides a method of manufacturing a capacitor, comprising the steps of:
(1) evaporating a first metal aluminum layer on the surface of the glass by using a vacuum evaporation method; in one embodiment, the thickness of the first metallic aluminum layer is in the range of 40-80nm, preferably 60 nm.
(2) Forming a polyvinylidene fluoride film on the surface of the first metal aluminum layer by the method described in the first embodiment, wherein the total content of gamma crystals and beta crystals in the polyvinylidene fluoride film is 50 wt% or more; in one embodiment, the polyvinylidene fluoride film has a thickness of 0.1 μm to 5 μm, preferably 0.55 μm;
(3) evaporating a second metal aluminum layer on the surface of the polyvinylidene fluoride film by using a vacuum evaporation method to obtain a capacitor; in one embodiment, the thickness of the second metallic aluminum layer is the same as the thickness of the first metallic aluminum layer, i.e. the thickness is in the range of 40-80nm, preferably the thickness of the second metallic aluminum layer is 60 nm.
The first metal aluminum layer and the second metal aluminum layer are two electrodes in the capacitor respectively, and the polyvinylidene fluoride film between the first metal aluminum layer and the second metal aluminum layer is an insulating film of the capacitor.
In one embodiment, a first metal aluminum layer is evaporated on the glass surface by a vacuum evaporation method, and the thickness of the first metal aluminum layer is 60 nm; forming a polyvinylidene fluoride film on the surface of the first metal aluminum layer by the method described in the first embodiment or the second embodiment, wherein the total content of gamma crystals and beta crystals in the polyvinylidene fluoride film is more than 50 wt%, and the thickness of the polyvinylidene fluoride film is 0.55 μm; and evaporating a second metal aluminum layer on the surface of the polyvinylidene fluoride film by using a vacuum evaporation method to obtain a capacitor, wherein the thickness of the second metal aluminum layer is also 60 nm. As shown in fig. 9, it is found that the capacitor of this embodiment has superior electrical properties as shown by the hysteresis loop diagram of the capacitor of this embodiment.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present application and not for limiting, and although the present application is described in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application.

Claims (10)

1. A preparation method of a polyvinylidene fluoride film comprises the following steps:
the weight average molecular weight is 1.0X 105To 3.0X 105The PVDF of (1) is dispersed in a solvent to form a PVDF solution;
forming the PVDF solution on a substrate, and drying and forming to obtain an initial film;
melting and recrystallizing the initial film to obtain a recrystallized polyvinylidene fluoride film;
and annealing the recrystallized polyvinylidene fluoride film for multiple times to obtain the polyvinylidene fluoride film containing gamma crystals and beta crystals.
2. The method of preparing a polyvinylidene fluoride film according to claim 1, wherein a temperature corresponding to a highest point of an alpha-crystal melting peak defining a melting curve of the recrystallized polyvinylidene fluoride film is a peak temperature a1, a temperature corresponding to a termination point of the melting peak defining the melting curve is a termination temperature a2, and an annealing temperature at which the recrystallized polyvinylidene fluoride film is subjected to a first annealing is in a range of a1 "3 ℃ to a2+8 ℃.
3. The method of preparing a polyvinylidene fluoride film of claim 2, wherein the annealing temperature for the first annealing of the recrystallized polyvinylidene fluoride film is in the range of a1+5 ℃ to a2+5 ℃.
4. The method of preparing a polyvinylidene fluoride film according to any one of claims 1 to 3, wherein the temperature increase rate of the first annealing of the recrystallized polyvinylidene fluoride film is 1 to 40 ℃/min; and the cooling rate of the recrystallized polyvinylidene fluoride film for the first annealing is 1-25 ℃/min.
5. The method of preparing a polyvinylidene fluoride film according to any one of claims 1 to 4, wherein the recrystallized polyvinylidene fluoride film is annealed twice; defining the temperature corresponding to the highest point of an alpha crystal melting peak of a melting curve of the polyvinylidene fluoride membrane after the first annealing as a peak temperature B1, defining the temperature corresponding to the highest point of a gamma crystal melting peak of the melting curve as a peak temperature B3, defining the temperature corresponding to a melting peak termination point of the melting curve as a termination temperature B2, and carrying out the second annealing on the recrystallized polyvinylidene fluoride membrane at an annealing temperature of B1-3 ℃ to B2+5 ℃.
6. The method of making a polyvinylidene fluoride film of claim 5, wherein the second annealing of the recrystallized polyvinylidene fluoride film is performed at an annealing temperature ranging from B1+5 ℃ to B3+3 ℃.
7. The method of preparing a polyvinylidene fluoride film according to claim 5 or 6, wherein the temperature increase rate of the second annealing of the recrystallized polyvinylidene fluoride film is 1 ℃/min to 20 ℃/min; and the temperature reduction rate of carrying out secondary annealing on the recrystallized polyvinylidene fluoride film is 1-30 ℃/min.
8. The method of preparing polyvinylidene fluoride film of any one of claims 1 to 7, wherein the PVDF has a weight average molecular weight of 1.8 x 105PVDF of (1); the annealing temperature range of the first annealing treatment of the recrystallized polyvinylidene fluoride film is 166 ℃ to 183 ℃, and the annealing temperature range of the second annealing treatment of the recrystallized polyvinylidene fluoride film is 165 ℃ to 186 ℃.
9. The method of preparing a polyvinylidene fluoride film according to claim 8, wherein the annealing temperature for the first annealing of the recrystallized polyvinylidene fluoride film is in the range of 174 ℃ to 180 ℃ and the annealing temperature for the second annealing of the recrystallized polyvinylidene fluoride film is in the range of 173 ℃ to 179 ℃.
10. A method of making a capacitor comprising the steps of:
forming a first metal aluminum layer by evaporation;
forming a polyvinylidene fluoride film on the surface of the first metal aluminum layer by the method for preparing a polyvinylidene fluoride film according to any one of claims 1 to 9; and
evaporating a second metal aluminum layer on the surface of the polyvinylidene fluoride film to obtain a capacitor; the polyvinylidene fluoride thin film between the first metal aluminum layer and the second metal aluminum layer is an insulating film of the capacitor.
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CN114614193A (en) * 2022-03-25 2022-06-10 中南大学 Polarized composite diaphragm and preparation and application thereof
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CN115212727B (en) * 2022-06-21 2024-01-02 清华大学 Porous vibration filter membrane and preparation method thereof

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