High-purity beta-phase PVDF (Polyvinylidene Fluoride) nanofiber membrane as well as preparation method and application thereof

Abstract

The invention belongs to the field of piezoelectric film materials, and particularly relates to a high-purity beta-phase PVDF nanofiber membrane and a preparation method and application thereof. The preparation method comprises the following steps: dissolving PVDF powder with mixed molecular weight in an acetone / N, N-dimethylformamide (DMF) mixed solvent to form a uniform solution, and spinning the obtained solution through an electrostatic spinning machine to prepare the high-purity beta-phase PVDF nanofiber membrane. The PVDF crystal form in the prepared high-purity beta-phase PVDF nanofiber membrane is almost a pure beta crystal form, and the high-purity beta-phase PVDF nanofiber membrane has more excellent electrical properties and application potential.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric thin film materials, specifically relating to a high-purity β-phase PVDF nanofiber membrane, its preparation method, and its application. Background Technology

[0002] Polyvinylidene fluoride (PVDF) is one of the most common piezoelectric polymer materials, possessing not only excellent chemical resistance, heat resistance, and mechanical properties, but also superior ferroelectric and piezoelectric properties. PVDF mainly exists in several crystalline morphologies: α, β, γ, and δ phases, with the β phase exhibiting the best spontaneous polarization and piezoelectric performance. Compared to traditional piezoelectric ceramic materials, PVDF has advantages such as light weight, good flexibility, and strong processability, making it widely applicable in sensors, transducers, self-powered devices, and other fields. However, traditional preparation methods require mechanical stretching or high electric field polarization to induce the transformation of PVDF films from the α phase to the β phase, resulting in complex processes, high energy consumption, and limited β phase content (typically below 90%). Therefore, developing an efficient, controllable, and environmentally friendly method to prepare PVDF materials with high β phase content has become a research hotspot.

[0003] Electrospinning is a simple method for preparing nanofiber structures, involving an electrostatic field and in-situ stretching to induce an enhanced electroactive β phase. While existing techniques exist for preparing PVDF nanofiber membranes via electrospinning, they typically exhibit poor morphology, insufficient β phase content (<90%), or require the addition of nanofillers to induce β phase formation, making the process complex. Therefore, there is a need to develop a simple and convenient process for preparing PVDF nanofiber films with good morphology and a pure β phase solely by adjusting the properties of the PVDF solution and electrospinning parameters. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing high-purity β-phase PVDF nanofiber membranes.

[0005] Another objective of this invention is to provide a high-purity β-phase PVDF nanofiber membrane prepared by the above method. Addressing the problems of poor morphology and lack of high electroactive β-phase content in PVDF piezoelectric fiber materials, which hinders the achievement of high piezoelectric performance, this invention provides a PVDF piezoelectric fiber membrane with an extremely fine diameter (~100 nm). This PVDF nanofiber membrane exhibits good morphology, highly uniform particle size distribution, and excellent piezoelectric properties.

[0006] Another objective of this invention is to provide the application of high-purity β-phase PVDF nanofiber membranes prepared by the above method in piezoelectric materials.

[0007] The objective of this invention is achieved through the following solution:

[0008] A method for preparing a high-purity β-phase PVDF nanofiber membrane is characterized by comprising the following steps: mixing and dissolving two PVDF powders of different molecular weights in a acetone / N,N-dimethylformamide mixed solvent in a certain proportion to form a homogeneous solution, and electrospinning the resulting solution to obtain a high-purity β-phase PVDF nanofiber membrane.

[0009] Preferably, the two PVDF powders with different molecular weights are PVDF 6020 and PVDF 180, with a total mass of 6-8g and a mass ratio of PVDF 6020 to PVDF 180 of 2:(4-6).

[0010] Preferably, the volume ratio of acetone to N,N-dimethylformamide in the mixed solvent is 3:2.

[0011] Preferably, the mass-to-volume ratio of PVDF to the mixed solvent in the solution is 2-10 g: 100 mL.

[0012] Preferably, the voltage for electrospinning is 12–26 kV.

[0013] Preferably, the electrospinning injection speed is 0.6-2.0 mL / h, and the roller rotation speed is 200-3000 rpm.

[0014] Preferably, the receiving distance of the electrospinning is 10-20cm.

[0015] Preferably, the ambient temperature for electrospinning is 25-30℃ and the relative humidity is 40%-60%.

[0016] The high-purity β-phase PVDF nanofiber membrane prepared by the preparation method of the present invention has a β-phase content of greater than 90%.

[0017] The application of the high-purity β-phase PVDF nanofiber membrane described in this invention in piezoelectric materials.

[0018] This invention employs different PVDF mass ratios to alter the overall molecular weight and molecular weight distribution of the spinning solution. Furthermore, the molecular weight and its distribution affect the diameter of the spun PVDF nanofibers. The nanofiber diameter influences the formation and content of the PVDF β phase. During electrospinning, this result is due to a combination of factors. Specifically, during electrospinning, the local electric field strength experienced by the fiber is inversely proportional to its diameter. A finer diameter is more conducive to the strong electric field driving the CF2 dipole moment alignment in the PVDF molecular chain, promoting the formation of the all-trans (TTTT) conformation β phase. Simultaneously, finer fibers have a larger specific surface area, resulting in faster solvent evaporation and cooling rates. Rapid solidification inhibits the crystallization of the thermodynamically stable α phase, forcing the metastable β phase to nucleate.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] (1) The PVDF crystal form in the high-purity β-phase PVDF nanofiber membrane prepared by this invention is almost pure β crystal form, which has better electrical properties and application potential.

[0021] (2) The high-purity β-phase PVDF nanofibers prepared by this invention have a diameter of about 100 nm, which are true nanofibers, giving the fiber membrane good flexibility, mechanical properties and a nearly pure β electroactive phase.

[0022] (3) The high-purity β-phase PVDF nanofiber membrane prepared by the present invention has excellent piezoelectric properties. Under a loading force of 14.7N, the voltage output can reach 7.453V and the voltage sensitivity is 294.8±15.3mV / N. Attached Figure Description

[0023] Figure 1 This describes the electrospinning process for preparing the high-purity β-phase PVDF nanofiber membrane obtained in Example 1 of this invention.

[0024] Figure 2 The image shows the SEM morphology and particle size distribution of the high-purity β-phase PVDF nanofiber membrane obtained in Example 1 of this invention.

[0025] Figure 3 The image shows the FT-IR spectrum of the high-purity β-phase PVDF nanofiber membrane obtained in Example 1 of this invention.

[0026] Figure 4 This is a schematic diagram of the structure of the high-purity β-phase PVDF nanofiber membrane device obtained in Example 1 of the present invention.

[0027] Figure 5 The graph shows the output voltage of the high-purity β-phase PVDF nanofiber membrane obtained in Example 1 of this invention as a function of the applied force. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0029] Unless otherwise specified, all reagents used in the examples are commercially available.

[0030] PVDF 6020: Purchased from Solvay, molecular weight ~670,000.

[0031] PVDF 180: Purchased from Sigma-Aldrich, molecular weight ~180,000.

[0032] Acetone and N,N-dimethylformamide (DMF) solvent: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., analytical grade.

[0033] Example 1

[0034] (1) Preparation of mixed molecular weight PVDF solution

[0035] 1) Measure N,N-dimethylformamide and acetone in a volume ratio of 2:3 and prepare 100 mL of mixed solvent.

[0036] 2) Weigh 2g of PVDF 6020 and 5g of PVDF 180 at a mass ratio of 2:5 as solutes, add them to the mixed solvent, and heat in a water bath at 60℃ for 2 hours until completely dissolved to prepare a spinning solution.

[0037] (2) Preparation of pure β-phase PVDF nanofiber membrane

[0038] The homogeneous PVDF mixture obtained in step (1) was transferred into a 10 mL syringe and installed on the injection pump of the electrospinning machine. The electrospinning parameters were adjusted as follows: voltage 20 kV, receiving distance 15 cm, injection speed 0.8 mL / h, size 25 metal needle, ambient temperature maintained at approximately 25 °C, relative humidity maintained at 50-60%, and roller receiver rotation speed set to 200 rpm, resulting in a pure β-phase PVDF nanofiber membrane. Figure 2 (a) It can be observed that the PVDF nanofiber film has a good morphology and uniform particle size. Statistical analysis yielded its particle size distribution histogram, as shown below. Figure 2 (b) The average diameter is 108±22 nm. The results of the pure β-phase PVDF nanofiber membrane obtained by FT-IR attenuated total reflectance (ATR) mode are as follows: Figure 3The unique absorption bands of the nonpolar α phase are located at 764 and 975 cm⁻¹. -1 The unique absorption bands of the polar β phase are located at 840 and 1276 cm⁻¹. -1 The specific content of its β-phase crystals can be obtained through formula (1):

[0039]

[0040] Where F(β) represents the content of β-phase crystals, and 1-F(β) is the content of α-phase crystals, A α and A β The samples were at 764 cm. -1 (characteristic peaks of α-phase crystals) and 840 cm⁻¹ -1 The absorbance intensity at the characteristic peak of the β-phase crystal was calculated. The β-phase content of the PVDF nanofiber film obtained in Example 1 reached 95.0%.

[0041] (3) Fabrication of pure β-phase PVDF nanofiber piezoelectric sensor device

[0042] The prepared PVDF nanofiber film was then... Figure 4 The PVDF nanofibers were cut to 1.0cm × 1.0cm size and sandwiched on both sides with PET films coated with an ITO conductive layer. The outermost layer was sealed with polyimide tape to avoid gaps between different materials. The resulting PVDF piezoelectric sensor was periodically compressed along the thickness direction by a linear motor. The open-circuit voltage output under different loading forces was collected by a force sensor and an electrometer. The test results are as follows: Figure 5 (a).

[0043] Comparative Example 1

[0044] The preparation process of this comparative example is basically the same as that of Example 1, except that when preparing the electrospinning solution, 1g of PVDF 6020 and 3g of PVDF 180 were weighed and mixed at a mass ratio of 1:3 as solutes, and added to the mixed solvent. The mixture was heated for 2 hours to prepare a clear solution. Other spinning conditions remained unchanged, and it was found that the fiber morphology was poor, with even a large number of breaks and non-fiber formation, failing to reach the spinning window.

[0045] Comparative Example 2

[0046] The preparation process of this comparative example is basically the same as that of Example 1, except that when preparing the electrospinning solution, 1g of PVDF 6020 and 5g of PVDF 180 were weighed and mixed at a mass ratio of 1:5 as solutes, and added to the mixed solvent. The mixture was heated for 2 hours to prepare a clear solution. With other spinning conditions unchanged, it was found that the fibers still had defects such as beading, and the breakage phenomenon was still serious, indicating that the degree of molecular chain entanglement was still insufficient and the spinning window had not been reached.

[0047] Comparative Example 3

[0048] The preparation process of this comparative example is basically the same as that of Example 1, except that when preparing the electrospinning solution, 2g and 3g of PVDF 6020 and PVDF 180 were weighed and mixed at a mass ratio of 2:3 as solutes, and added to the mixed solvent. The solution was heated for 2 hours to prepare a clear solution. Other spinning conditions remained unchanged. It was found that there were no defects such as beading in the fiber morphology, but some fibers were broken, which will have an adverse effect on the mechanical properties of the fibers.

[0049] Comparative Example 4

[0050] The preparation process of this comparative example is basically the same as that of Example 1, except that in the preparation of the electrospinning solution, 2g and 7g of PVDF 6020 and PVDF 180 were weighed and mixed at a mass ratio of 2:7 as solutes, added to the mixed solvent, and heated for 2 hours to prepare a clear solution. Other spinning conditions remained unchanged, and it was found that the fiber morphology remained good, but the average diameter increased to 205nm. This indicates that the solution concentration had exceeded the minimum entanglement concentration. As the viscosity increased, the stability of the solution improved, but the fiber stretching and polarization effect in the electric field weakened, resulting in a thicker fiber diameter and a decrease in the β-phase content of PVDF to 84.5%.

[0051] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-purity β-phase PVDF nanofiber membrane, characterized in that, Includes the following steps: Two PVDF powders with different molecular weights were mixed and dissolved in a mixture of acetone and N,N-dimethylformamide to form a homogeneous solution. The resulting solution was then electrospun to obtain a high-purity β-phase PVDF nanofiber membrane.

2. The method for preparing high-purity β-phase PVDF nanofiber membrane according to claim 1, characterized in that: The two PVDF powders with different molecular weights are PVDF 6020 and PVDF 180, with a total mass of 6-8g and a mass ratio of PVDF 6020 to PVDF 180 of 2:(4-6).

3. The method for preparing the high-purity β-phase PVDF nanofiber membrane according to claim 1, characterized in that: The volume ratio of acetone to N,N-dimethylformamide in the mixed solvent is 3:

2.

4. The method for preparing high-purity β-phase PVDF nanofiber membrane according to claim 1, characterized in that: The mass-to-volume ratio of PVDF to the mixed solvent in the solution is 2-10 g: 100 mL.

5. The method for preparing the high-purity β-phase PVDF nanofiber membrane according to claim 1, characterized in that: The voltage for electrospinning is 12–26 kV.

6. The method for preparing the high-purity β-phase PVDF nanofiber membrane according to claim 1, characterized in that: The electrospinning injection speed is 0.6-2.0 mL / h, and the roller rotation speed is 200-3000 rpm.

7. The method for preparing high-purity β-phase PVDF nanofiber membrane according to claim 1, characterized in that: The receiving distance for electrospinning is 10-20cm.

8. The method for preparing high-purity β-phase PVDF nanofiber membrane according to claim 1, characterized in that: The electrospinning environment is 25-30℃ and the relative humidity is 40%-60%.

9. The high-purity β-phase PVDF nanofiber membrane prepared by any one of claims 1-8, characterized in that, The high-purity β-phase PVDF nanofiber membrane has a β-phase content of greater than 90%.

10. The application of the high-purity β-phase PVDF nanofiber membrane according to claim 9 in piezoelectric materials.

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