Carbon quantum dots enhanced polyvinylidene fluoride piezoelectric film and preparation method thereof

Abstract

The application is suitable for the technical field of polyvinylidene fluoride film, and provides a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film and a preparation method thereof.The polyvinylidene fluoride film comprises the following raw materials: hydroxyl functionalized carbon quantum dots, polyvinylidene fluoride, silanized mannitol, ionic liquid, modified betaine and dimethylformamide.The hydroxyl on the hydroxyl functionalized carbon quantum dots interacts with the polyvinylidene fluoride chain, induces the arrangement of dipoles and enhances the formation of beta-phase, improves the piezoelectric performance, and further induces beta-phase crystallization by adding ionic liquid as a molecular wire;by adding modified mannitol, the PVDF molecular chain arrangement is directionally induced, and the siloxane chain enhances the interface compatibility, the short-chain silane plasticizing effect improves the flexibility and mechanical properties of the film;by adding modified betaine, agglomeration can be inhibited;after ultraviolet light irradiation, a three-dimensional crosslinked network is formed in the PVDF film, an ion channel is constructed, and the charge mobility is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyvinylidene fluoride films, and particularly relates to a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film and a preparation method thereof. BACKGROUND

[0002] Polyvinylidene fluoride, abbreviated as PVDF, is a highly non-reactive thermoplastic fluoropolymer, which is soluble in strong polar solvents such as dimethylacetamide, has excellent properties such as anti-aging, chemical resistance, weather resistance, ultraviolet light resistance, and can be used as an engineering plastic for manufacturing sealing rings, corrosion-resistant equipment, capacitors, and also used as coating, insulation material and ion exchange membrane material, etc.

[0003] Polyvinylidene fluoride with beta crystal form has piezoelectricity, and a common method to improve piezoelectricity is mechanical stretching, by stretching the PVDF film, the polymer chain will rearrange, promoting the formation of beta-phase, and the beta-phase is the key to produce piezoelectricity, although this method is effective, but it needs special equipment and precise control of stretching stress; another method is electrode polarization, that is, a high electric field is applied on the PVDF to align its dipole and induce beta-phase crystallization, although this method can improve the piezoelectric performance, but it needs complex equipment and precise control of electric field, which limits its practicality for wide application; solvent casting method is a simple method for preparing film, although this method is easy to implement, but unless combined with additional treatments such as stretching or polarization, the content of beta-phase is low; the complexity of the process makes them difficult to scale in industrial applications.

[0004] Some additives improve the content of beta-phase, but sacrifice other ideal properties of PVDF, such as flexibility, transparency or biocompatibility, for example, certain nanofillers may make the material brittle or opaque, limiting its application in flexible electronics or wearable devices, the use of expensive materials (such as graphene or carbon nanotubes) and complex processes increase the production cost, making these solutions economically poor in large-scale applications. SUMMARY

[0005] The application provides a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film, which aims to solve the above problems.

[0006] The application is implemented as follows: a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film, comprising the following raw materials by weight: hydroxyl functionalized carbon quantum dots 1-3 parts, polyvinylidene fluoride 15-20 parts, silanized mannitol 2-5 parts, ionic liquid 0.5-1 part, modified betaine 1-2 parts, dimethylformamide 100-130 parts.

[0007] Preferably, the following raw materials are included by weight parts: hydroxyl functionalized carbon quantum dots 1.5-2.5 parts, polyvinylidene fluoride 16-19 parts, silanized mannitol 2.5-4.5 parts, ionic liquid 0.6-0.9 parts, modified betaine 1.2-1.8 parts, dimethylformamide 105-125 parts.

[0008] Preferably, the following raw materials are included by weight parts: hydroxyl functionalized carbon quantum dots 2 parts, polyvinylidene fluoride 17.5 parts, silanized mannitol 3.5 parts, ionic liquid 0.75 parts, modified betaine 1.5 parts, dimethylformamide 115 parts.

[0009] Preferably, the ionic liquid includes butyl-3-methylimidazolium chloride, the ionic liquid acts as a molecular wire, anchoring carbon quantum dots through cation-π bonding, and the anion interacts with the -CF2- dipole of polyvinylidene fluoride, inducing directional β-phase crystallization.

[0010] Preferably, the method for preparing the hydroxyl functionalized carbon quantum dots (OH-CDs) is as follows:

[0011] Citric acid and glycerol are dissolved in a suitable amount of deionized water at a mass ratio of 1:1;

[0012] Heat in a Teflon-lined autoclave at 150-170°C for 3.5-4.5h;

[0013] Dissolve the product in water, remove large particles by centrifugation at 11000-13000 rpm for 8-12 min;

[0014] Filter the supernatant using a 0.20µm needle filter;

[0015] Dissolve the filtered product in 1000 times weight of deionized water, sonicate until completely dissolved, and characterize using UV-visible and fluorescence spectra.

[0016] Through the interaction of hydroxyl groups on the hydroxyl functionalized carbon quantum dots with PVDF chains, the arrangement of dipoles is induced and the formation of β-phase is enhanced, thereby improving the piezoelectric performance.

[0017] Preferably, the method for preparing the silanized mannitol is as follows:

[0018] Mix mannitol 8-12 parts and deionized water 25-35 parts by weight parts, add citric acid 0.1-0.5 parts;

[0019] Add silane reagent (silane coupling agent KH-560) 6-10 parts dropwise, stir in a 55-65°C water bath for 2-3h;

[0020] Filter the reaction solution through a membrane (0.22μm ceramic membrane) with a molecular weight cutoff >1000 Da;

[0021] The filtrate is spray-dried (inlet temperature 115-125 DEG C, outlet temperature 65-75 DEG C).

[0022] The multiple hydroxyl groups of mannitol provide nucleation sites for CDs, and the mannitol reacts with the ring-opening of the silane to introduce siloxane chains and epoxy groups, the epoxy groups form hydrogen bonds with the fluorine atoms of PVDF to induce the alignment of PVDF molecular chains, and the siloxane chains enhance the interfacial compatibility, and the plasticizing effect of short-chain silane improves the flexibility and mechanical properties of the film.

[0023] Preferably, the preparation method of the modified betaine is as follows:

[0024] Take betaine 3-7 parts, cinnamoyl chloride 1-3 parts, and choline hydroxide aqueous solution with a concentration of 20-30% 3-5 parts by weight;

[0025] Mix the betaine with the choline hydroxide aqueous solution;

[0026] Dropwise add cinnamoyl chloride to the betaine-choline mixture under 0 DEG C ice bath, and react at 25 DEG C for 2-3 h;

[0027] Extract the reaction solution with ethyl acetate for 3 times, and remove the solvent by rotary evaporation to obtain the modified betaine.

[0028] The betaine zwitterion structure wraps the ionic liquid and the hydroxyl functionalized carbon quantum dots, and can inhibit agglomeration; the betaine zwitterion reacts with cinnamoyl chloride under the catalysis of choline hydroxide, the introduced cinnamoyl group contains a photosensitive double bond, the double bond is excited to occur [2+2] cycloaddition reaction under ultraviolet light (254-365 nm), a three-dimensional cross-linked network is formed in the PVDF film, an ion channel is constructed, and the charge mobility is improved.

[0029] The application also provides a preparation method of carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film, comprising the following steps:

[0030] Prepare each raw material according to the proportion;

[0031] Dissolve polyvinylidene fluoride particles in dimethylformamide to obtain a solution;

[0032] Add hydroxyl functionalized carbon quantum dots, silanized mannitol, ionic liquid and modified betaine to the solution, and fully stir and uniformly disperse;

[0033] Deposit the dispersion liquid on a substrate by spin coating method, dry the film at 60 DEG C, and irradiate the film with ultraviolet light for 3-7 min to obtain a composite film; the spin coating technology makes the hydroxyl functionalized carbon quantum dots uniformly distributed and the film uniformly formed, and optimizes the piezoelectric performance.

[0034] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0035] The carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film provided by the application interacts with the hydroxyl group on the hydroxyl functionalized carbon quantum dot and the polyvinylidene fluoride chain, induces the arrangement of dipoles and enhances the formation of a beta phase, improves the piezoelectric performance, and further induces the beta phase crystallization by adding an ionic liquid as a molecular wire; by adding modified mannitol, the multiple hydroxyl groups provide nucleation sites for CDs, the siloxane chain and the epoxy group are introduced, the epoxy group forms a hydrogen bond with the fluorine atom of polyvinylidene fluoride, and the PVDF molecular chain is directionally induced to arrange, and the siloxane chain enhances the interface compatibility, the short-chain silane plasticizing effect improves the flexibility and mechanical properties of the film; by adding modified betaine, the zwitterionic structure of which wraps the ionic liquid and the hydroxyl functionalized carbon quantum dot, can inhibit agglomeration; contains a photosensitive double bond, forms a three-dimensional cross-linked network in the PVDF film after ultraviolet light irradiation, constructs an ion channel, and improves the charge mobility, the hydroxyl functionalized carbon quantum dots are uniformly distributed and the film is uniformly formed by the spin coating technology, the piezoelectric performance is optimized, and complex equipment is not required. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The present application provides a preparation method flow chart of a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film. DETAILED DESCRIPTION

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the description and claims of the application as well as the above abstract are intended to cover all alternatives, modifications, and equivalents included within the scope of the application; the terms "comprising", "having", "including", and "containing" used in the description and in the claims of the application and the above abstract are each intended to encompass the presence of one or more of the stated features, but not preclude the presence or addition of one or more other features.

[0038] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that the embodiments described herein are merely examples from a whole class of comparable embodiments which are claimed as falling within the scope of the present application.

[0039] Embodiment 1

[0040] The embodiment of the present application provides a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film, which comprises the following raw materials in parts by weight: 1 part of hydroxyl functionalized carbon quantum dots, 15 parts of polyvinylidene fluoride, 2 parts of silanized mannitol, 0.5 parts of ionic liquid, 1 part of modified betaine and 100 parts of dimethylformamide, and the preparation method of the carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film is as shown in the following steps. Figure 1 The preparation method of the carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film is as shown in the following steps.

[0041] Prepare the raw materials according to the proportion;

[0042] Dissolve the polyvinylidene fluoride particles in dimethylformamide to obtain a solution;

[0043] Add the hydroxyl functionalized carbon quantum dots, the silanized mannitol, the ionic liquid and the modified betaine into the solution, and fully stir and uniformly disperse them;

[0044] Deposit the dispersion liquid on a substrate by a spin coating method, dry the thin film at 60 DEG C and irradiate it with ultraviolet light for 3 min to obtain a composite thin film.

[0045] The ionic liquid comprises butyl-3-methyl imidazole chloride.

[0046] Preferably, the preparation method of the hydroxyl functionalized carbon quantum dots (OH-CDs) is as follows.

[0047] Dissolve citric acid and glycerol in a proper amount of deionized water at a mass ratio of 1:1;

[0048] Heat in a polytetrafluoroethylene lined autoclave at 150 DEG C for 3.5 h;

[0049] Dissolve the product in water, and remove large particles by centrifugation at 11000 rpm for 8 min;

[0050] Filter the supernatant using a 0.20 mu m needle filter;

[0051] Dissolve the filtered product in 1000 times weight of deionized water, ultrasonic treat until completely dissolved, and use ultraviolet-visible spectroscopy and fluorescence spectroscopy for characterization.

[0052] Further, the preparation method of the silanized mannitol is as follows.

[0053] Take 8 parts of mannitol and 25 parts of deionized water by weight, and add 0.1 part of citric acid;

[0054] Drop 6 parts of silane reagent (silane coupling agent KH-560), and stir in a 55 DEG C water bath for 2 h;

[0055] Filter the reaction solution by membrane filtration (0.22 mu m ceramic membrane), and the molecular weight cut-off is >1000 Da;

[0056] The filtrate was spray-dried (inlet temperature 115℃, outlet temperature 65℃).

[0057] In this embodiment, the preparation method of the modified betaine is as follows:

[0058] Take 3 parts of betaine, 1 part of cinnamyl chloride, and 3 parts of choline hydroxide aqueous solution with a concentration of 20% by weight;

[0059] Mix the betaine with the choline hydroxide aqueous solution;

[0060] Add cinnamyl chloride dropwise to the betaine-choline mixture under ice bath at 0℃, and react for 2h after warming to 25℃;

[0061] Extract the reaction solution with ethyl acetate for 3 times, and remove the solvent by rotary evaporation to obtain the modified betaine.

[0062] Example 2

[0063] The embodiment of the present application provides a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film, which comprises the following raw materials by weight: 1.5 parts of hydroxyl functionalized carbon quantum dots, 16 parts of polyvinylidene fluoride, 2.5 parts of silanized mannitol, 0.6 parts of ionic liquid, 1.2 parts of modified betaine, and 105 parts of dimethylformamide. Figure 1 The preparation method of the carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film comprises the following steps:

[0064] Prepare each raw material according to the proportion;

[0065] Dissolve the polyvinylidene fluoride particles in dimethylformamide to obtain a solution;

[0066] Add hydroxyl functionalized carbon quantum dots, silanized mannitol, ionic liquid, and modified betaine to the solution, and fully stir and uniformly disperse;

[0067] Deposit the dispersion liquid on a substrate by spin coating method, dry the thin film at 60℃, and irradiate by ultraviolet light for 3min to obtain a composite thin film.

[0068] The ionic liquid comprises butyl-3-methyl imidazole chloride.

[0069] Preferably, the preparation method of the hydroxyl functionalized carbon quantum dots (OH-CDs) is as follows:

[0070] Dissolve citric acid and glycerol in a mass ratio of 1:1 in a proper amount of deionized water;

[0071] Heat in a polytetrafluoroethylene lined autoclave at 150℃ for 3.5h;

[0072] The product was dissolved in water, and large particles were removed by centrifugation at 11000 rpm for 8 min;

[0073] The supernatant was filtered using a 0.20 µm needle filter;

[0074] The filtered product was dissolved in 1000 times by weight of deionized water, ultrasonically treated until completely dissolved, and characterized using UV-visible spectroscopy and fluorescence spectroscopy.

[0075] Further, the preparation method of the silanized mannitol is as follows:

[0076] According to weight parts, 8 parts of mannitol and 25 parts of deionized water were mixed, and 0.1 part of citric acid was added;

[0077] 6 parts of silane reagent (silane coupling agent KH-560) were added dropwise, and stirred in a 55℃ water bath for 2h;

[0078] The reaction solution was filtered through a membrane (0.22μm ceramic membrane), with a molecular weight cutoff of >1000Da;

[0079] The filtrate was spray dried (inlet temperature 115℃, outlet temperature 65℃).

[0080] In this embodiment, the preparation method of the modified betaine is as follows:

[0081] According to weight parts, 3 parts of betaine, 1 part of cinnamoyl chloride, and 3 parts of choline hydroxide aqueous solution with a concentration of 20% were taken;

[0082] The betaine and the choline hydroxide aqueous solution were mixed;

[0083] Cinnamoyl chloride was added dropwise to the betaine-choline mixture under an ice bath at 0℃, and the temperature was raised to 25℃ for reaction for 2h;

[0084] The reaction solution was extracted with ethyl acetate for 3 times, and the solvent was removed by rotary evaporation to obtain the modified betaine.

[0085] Example 3

[0086] The carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film provided by the embodiment of the present application comprises the following raw materials according to weight parts: 2 parts of hydroxyl functionalized carbon quantum dots, 17.5 parts of polyvinylidene fluoride, 3.5 parts of silanized mannitol, 0.75 parts of ionic liquid, 1.5 parts of modified betaine, and 115 parts of dimethylformamide. Figure 1 The preparation method of the carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film comprises the following steps:

[0087] Prepare each raw material according to the ratio;

[0088] Dissolve the polyvinylidene fluoride particles in dimethylformamide to obtain a solution;

[0089] The hydroxyl functionalized carbon quantum dots, the silanized mannitol, the ionic liquid, and the modified betaine are added into the solution and stirred to uniformly disperse;

[0090] The dispersion is deposited on a substrate by a spin coating method, the thin film is dried at 60℃ and irradiated by ultraviolet light for 5 min to obtain a composite thin film.

[0091] The ionic liquid comprises butyl-3-methyl imidazole chloride.

[0092] Preferably, the hydroxyl functionalized carbon quantum dots (OH-CDs) are prepared by the following method:

[0093] Citric acid and glycerol are dissolved in deionized water in a mass ratio of 1:1;

[0094] The mixture is heated in a polytetrafluoroethylene-lined autoclave at 160℃ for 4h;

[0095] The product is dissolved in water, and large particles are removed by centrifugation at 12000rpm for 10min;

[0096] The supernatant is filtered by a 0.20µm needle filter;

[0097] The filtered product is dissolved in 1000 times weight of deionized water, ultrasonically treated until completely dissolved, and characterized by ultraviolet-visible spectroscopy and fluorescence spectroscopy.

[0098] Further, the silanized mannitol is prepared by the following method:

[0099] Mannitol 10 parts and deionized water 30 parts are mixed, and citric acid 0.3 parts is added;

[0100] Silane reagent (silane coupling agent KH-560) 8 parts is added dropwise, and stirred in a 60℃ water bath for 2.5h;

[0101] The reaction solution is filtered by a membrane (0.22μm ceramic membrane) with a molecular weight cutoff of >1000Da;

[0102] The filtrate is spray dried (inlet temperature 120℃, outlet temperature 70℃).

[0103] In this embodiment, the modified betaine is prepared by the following method:

[0104] Betaine 5 parts, cinnamoyl chloride 2 parts, and choline hydroxide aqueous solution with a concentration of 25% 4 parts are taken by weight;

[0105] The betaine and the choline hydroxide aqueous solution are mixed;

[0106] Cinnamoyl chloride was added dropwise into the mixture of betaine-choline under 0℃ ice bath, and the temperature was increased to 25℃ for 2h;

[0107] The reaction solution was extracted with ethyl acetate for 3 times, and the solvent was removed by rotary evaporation to obtain modified betaine.

[0108] Example 4

[0109] The embodiment of the present application provides a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film, which comprises the following raw materials in parts by weight: hydroxyl functionalized carbon quantum dots 2.5 parts, polyvinylidene fluoride 19 parts, silanized mannitol 4.5 parts, ionic liquid 0.9 parts, modified betaine 1.8 parts, dimethylformamide 125 parts, and the preparation method of the carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film comprises the following steps: Figure 1 As shown in the figure, the steps are as follows:

[0110] Prepare each raw material according to the ratio;

[0111] Dissolve the polyvinylidene fluoride particles in dimethylformamide to obtain a solution;

[0112] Add hydroxyl functionalized carbon quantum dots, silanized mannitol, ionic liquid and modified betaine to the solution, and fully stir and uniformly disperse;

[0113] Deposit the dispersion liquid on the substrate by spin coating method, dry the thin film at 60℃ and irradiate it with ultraviolet light for 7min to obtain a composite thin film.

[0114] The ionic liquid comprises butyl-3-methyl imidazole chloride.

[0115] Preferably, the preparation method of the hydroxyl functionalized carbon quantum dots (OH-CDs) is as follows:

[0116] Dissolve citric acid and glycerol in a proper amount of deionized water in a mass ratio of 1:1;

[0117] Heat in a high-pressure kettle with a polytetrafluoroethylene liner at 170℃ for 4.5h;

[0118] Dissolve the product in water, remove large particles by centrifugation at 13000rpm for 12min;

[0119] Filter the supernatant using a 0.20µm needle filter;

[0120] Dissolve the filtered product in 1000 times weight of deionized water, ultrasonic treat until completely dissolved, and use ultraviolet-visible spectrum and fluorescence spectrum for characterization.

[0121] Further, the preparation method of the silanized mannitol is as follows:

[0122] Take mannitol 12 parts, deionized water 35 parts by weight, add citric acid 0.5 parts;

[0123] Drop 10 parts of silane reagent (silane coupling agent KH-560), 65℃ water bath stirring for 3h;

[0124] The reaction solution is filtered by membrane (0.22μm ceramic membrane), the molecular weight cut-off is >1000Da;

[0125] The filtrate is spray dried (the inlet temperature is 125℃, and the outlet temperature is 75℃).

[0126] In this embodiment, the preparation method of the modified betaine is as follows:

[0127] Take betaine 7 parts, cinnamyl chloride 3 parts, and choline hydroxide aqueous solution with a concentration of 30% 5 parts by weight;

[0128] Mix betaine with choline hydroxide aqueous solution;

[0129] Drop cinnamyl chloride into the betaine-choline mixture at 0℃ ice bath, and react for 3h after warming to 25℃;

[0130] The reaction solution is extracted with ethyl acetate for 3 times, and the solvent is removed by rotary evaporation to obtain modified betaine.

[0131] Example 5

[0132] The embodiment of the present application provides a carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film, which comprises the following raw materials by weight: hydroxyl functionalized carbon quantum dots 3 parts, polyvinylidene fluoride 20 parts, silanized mannitol 5 parts, ionic liquid 0.1 parts, modified betaine 2 parts, and dimethylformamide 130 parts. Figure 1 The preparation method of the carbon quantum dot enhanced polyvinylidene fluoride piezoelectric film is as shown in the figure, which comprises the following steps:

[0133] Prepare each raw material according to the ratio;

[0134] Dissolve polyvinylidene fluoride particles in dimethylformamide to obtain a solution;

[0135] Add hydroxyl functionalized carbon quantum dots, silanized mannitol, ionic liquid and modified betaine to the solution, and fully stir and uniformly disperse;

[0136] Deposit the dispersion liquid on the substrate by spin coating method, dry the thin film at 60℃, and irradiate by ultraviolet light for 7min to obtain a composite thin film.

[0137] The ionic liquid comprises butyl-3-methyl imidazole chloride.

[0138] Preferably, the preparation method of the hydroxyl functionalized carbon quantum dots (OH-CDs) is as follows:

[0139] Citric acid and glycerol were dissolved in a proper amount of deionized water at a mass ratio of 1:1;

[0140] Heating at 170℃ in a polytetrafluoroethylene lined autoclave for 4.5h;

[0141] The product was dissolved in water, and large particles were removed by centrifugation at 13000rpm for 12min;

[0142] The supernatant was filtered using a 0.20µm needle filter;

[0143] The filtered product was dissolved in 1000 times weight of deionized water, ultrasonically treated until completely dissolved, and characterized using ultraviolet-visible spectrum and fluorescence spectrum.

[0144] Further, the preparation method of the silanized mannitol is as follows:

[0145] Take mannitol 12 parts and deionized water 35 parts by weight, add citric acid 0.5 parts;

[0146] Add 10 parts of silane reagent (silane coupling agent KH-560) dropwise, and stir in a 65℃ water bath for 3h;

[0147] The reaction solution was filtered through a membrane (0.22μm ceramic membrane) with a molecular weight cutoff of >1000Da;

[0148] The filtrate was spray dried (inlet temperature 125℃, outlet temperature 75℃).

[0149] In this embodiment, the preparation method of the modified betaine is as follows:

[0150] Take betaine 7 parts, cinnamoyl chloride 3 parts, and 30% choline hydroxide aqueous solution 5 parts by weight;

[0151] Mix the betaine with the choline hydroxide aqueous solution;

[0152] Add cinnamoyl chloride dropwise to the betaine-choline mixture under ice bath at 0℃, and warm up to 25℃ for 3h;

[0153] Extract the reaction solution with ethyl acetate 3 times, and remove the solvent by rotary evaporation to obtain the modified betaine.

[0154] Comparative Example 1: Compared with Example 3, no hydroxyl functionalized carbon quantum dots are contained.

[0155] Comparative Example 2: Compared with Example 3, no silanized mannitol is contained.

[0156] Comparative Example 3: Compared with Example 3, without modified betaine.

[0157] Comparative Example 4: Compared with Example 3, without ionic liquid.

[0158] Comparative Example 5: Compared with Example 3, without hydroxyl functionalized carbon quantum dots and silanized mannitol.

[0159] Comparative Example 6: Compared with Example 3, the modified betaine is replaced by ordinary betaine.

[0160] Comparative Example 7: Compared with Example 3, the silanized mannitol is replaced by ordinary mannitol.

[0161] Comparative Example 8: Compared with Example 3, without ultraviolet light.

[0162] Control group: pure PVDF film (without additives).

[0163] Performance test

[0164] Piezoelectric coefficient

[0165] Tester: Quasi-static d 33 Tester (IEEE 176-1987).

[0166] Beta phase content

[0167] Method: FTIR analysis, calculate the peak area ratio of 1275 cm -1 (beta phase) and 763 cm -1 (alpha phase).

[0168] Conductivity (σ)

[0169] Method: Four-probe method (ASTM F390)

[0170] Mechanical properties

[0171] Tensile strength / elongation at break: universal material testing machine (ASTM D638).

[0172] The test results are as follows Table 1:

[0173] Table 1 Performance test results

[0174]

[0175] From the above results, it can be seen that the PVDF film prepared by the present application has high beta phase content, good piezoelectric properties and mechanical properties.

[0176] It should be noted that, for the foregoing embodiments, for the sake of simple description, they are all expressed as a series of action combinations, but those skilled in the art should know that the present application is not limited by the order of the described actions, because according to the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily necessary for the present application.

[0177] In the embodiments provided in the present application, it should be understood that the disclosed device can be implemented in other ways. For example, the device embodiments described above are only schematic. The division of the above units is only a logical function division. There can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed coupling or communication connection between each other can be indirect coupling or communication connection through some interface, device or unit, and can be electrical or other forms.

[0178] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, that is, they can be located in one place, or can be distributed on a plurality of network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the present embodiment.

[0179] The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the protection scope of the application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art can still make some modifications to the features of the embodiments of the present application according to the circumstances without creative labor, such as mutual combination, addition or deletion or other adjustment, so as to obtain different other technical solutions which do not deviate from the concept of the present application in essence. These technical solutions also belong to the scope of the present application.

Claims

1. A carbon quantum dot-reinforced polyvinylidene fluoride piezoelectric film, characterized in that, The raw materials include the following by weight: 1-3 parts of hydroxyl-functionalized carbon quantum dots, 15-20 parts of polyvinylidene fluoride, 2-5 parts of silanized mannitol, 0.5-1 part of ionic liquid, 1-2 parts of modified betaine, and 100-130 parts of dimethylformamide. The preparation method of the silanized mannitol is as follows: By weight, mix 8-12 parts mannitol and 25-35 parts deionized water, and add 0.1-0.5 parts citric acid. Add 6-10 parts of silane reagent and stir in a water bath at 55-65℃ for 2-3 hours; The reaction solution is filtered through a membrane. Filtrate spray drying; The modified betaine is prepared as follows: Take 3-7 parts by weight of betaine, 1-3 parts of cinnamoyl chloride, and 3-5 parts of a 20-30% aqueous solution of choline hydroxide. Mix betaine with an aqueous solution of choline hydroxide; Cinnamyl chloride was added dropwise to a betaine-choline mixture under an ice bath at 0°C, and the mixture was heated to 25°C and reacted for 2-3 hours. The reaction solution was extracted three times with ethyl acetate, and the solvent was removed by rotary evaporation to obtain modified betaine. The method for preparing the carbon quantum dot-reinforced polyvinylidene fluoride piezoelectric film includes the following steps: Prepare all raw materials according to the specified proportions; PVDF particles were dissolved in dimethylformamide to obtain a solution; Add hydroxyl-functionalized carbon quantum dots, silanized mannitol, ionic liquid, and modified betaine to the solution, and stir thoroughly to disperse them evenly. The dispersion was deposited on the substrate by spin coating, and the film was dried at 60°C and irradiated with ultraviolet light for 3-7 minutes to obtain the composite film.

2. The carbon quantum dot-reinforced polyvinylidene fluoride piezoelectric film as described in claim 1, characterized in that, The raw materials include the following by weight: 1.5-2.5 parts of hydroxyl-functionalized carbon quantum dots, 16-19 parts of polyvinylidene fluoride, 2.5-4.5 parts of silanized mannitol, 0.6-0.9 parts of ionic liquid, 1.2-1.8 parts of modified betaine, and 105-125 parts of dimethylformamide.

3. The carbon quantum dot-reinforced polyvinylidene fluoride piezoelectric film as described in claim 2, characterized in that, The raw materials include the following by weight: 2 parts hydroxyl-functionalized carbon quantum dots, 17.5 parts polyvinylidene fluoride, 3.5 parts silanized mannitol, 0.75 parts ionic liquid, 1.5 parts modified betaine, and 115 parts dimethylformamide.

4. The carbon quantum dot-reinforced polyvinylidene fluoride piezoelectric film as described in claim 1, characterized in that, The ionic liquid includes butyl-3-methylimidazolium chloride.

5. The carbon quantum dot-reinforced polyvinylidene fluoride piezoelectric film as described in claim 1, characterized in that, The preparation method of the hydroxyl-functionalized carbon quantum dots is as follows: Dissolve citric acid and glycerol in an appropriate amount of deionized water at a mass ratio of 1:

1. Heating in a polytetrafluoroethylene-lined autoclave at 150-170℃ for 3.5-4.5 hours; The product was dissolved in water, and large particles were removed by centrifugation at 11,000-13,000 rpm for 8-12 minutes. The supernatant was filtered using a 0.20µm syringe filter; The filtered product was dissolved in 1000 times its weight of deionized water, sonicated until completely dissolved, and characterized using UV-Vis and fluorescence spectroscopy.

6. The method for preparing a carbon quantum dot-reinforced polyvinylidene fluoride piezoelectric film as described in any one of claims 1-5, characterized in that, Includes the following steps: Prepare all raw materials according to the specified proportions; PVDF particles were dissolved in dimethylformamide to obtain a solution; Add hydroxyl-functionalized carbon quantum dots, silanized mannitol, ionic liquid, and modified betaine to the solution, and stir thoroughly to disperse them evenly. The dispersion was deposited on the substrate by spin coating, and the film was dried at 60°C and irradiated with ultraviolet light for 3-7 minutes to obtain the composite film.

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