A magnetic polymer composite film and a preparation method and application thereof

Abstract

The application provides a magnetic polymer composite film and a preparation method and application thereof, and belongs to the technical field of friction materials.The magnetic polymer composite film comprises a P(VDF-TrFE) base film and a plurality of rod-shaped CoFe2O4(RCFO)@PDA magnetic nanoparticles dispersed in the P(VDF-TrFE) base film; the RCFO@PDA magnetic nanoparticles have a core-shell structure, the core layer is rod-shaped nano CoFe2O4, and the shell layer is polydopamine.The RCFO nanoparticles with dielectric properties are embedded in the P(VDF-TrFE) base film, a stripe-shaped surface microstructure is successfully constructed through a magnetic field orientation auxiliary thermal film forming process, the contact area of the friction material is effectively increased, and the dielectric constant is also improved.The magnetic polymer composite film provided by the application is used as a positive electrode friction material of a friction nanogenerator, and the electric output performance of the friction nanogenerator is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of friction materials, in particular to a magnetic polymer composite film and a preparation method and application thereof. BACKGROUND

[0002] As an emerging energy harvesting technology, triboelectric nanogenerator (TENG) based on Maxwell displacement current as driving force is a device that effectively collects low-frequency mechanical energy and converts it into electrical energy using triboelectric and electrostatic induction coupling mechanisms. It has the characteristics of simple structure, low cost, strong environmental adaptability, high output voltage, etc., and can obtain clean and sustainable energy from mechanical vibration, wind, human motion, water and other environments and biological systems to convert it into electrical energy.

[0003] One of the key problems faced by triboelectric nanogenerator in its development is the low surface charge density, which directly affects its current density and power density. Surface charge density is limited by multiple factors, including the triboelectric charge density of the triboelectric layer material, the charge density at air breakdown, the charge density at triboelectric layer breakdown, and the contact efficiency. The surface roughness of the triboelectric layer material is one of the important factors affecting the performance of the triboelectric nanogenerator, as it affects the effective contact area and contact force between surfaces, thereby affecting the degree of charge separation and current output. In addition to the effective contact area, the improvement of the dielectric properties of the triboelectric layer material has a significant impact on the capacitance of the triboelectric layer and its ability to store triboelectric charges. At the same time, the increase in dielectric constant is beneficial to the accumulation of charge density on the copolymer during physical contact, i.e., enhancing the ability of the triboelectric layer to retain surface charges, thereby improving the power output of the triboelectric layer.

[0004] The commonly used triboelectric layer materials currently include FEP, PVC, PTFE, PVDF, etc. These materials are selected due to their different electronegativity differences to improve the triboelectric capacity and surface charge density. However, the dielectric constant of these materials is small, which limits the charge density and performance of TENG. Therefore, there is an urgent need to develop a film material with high surface roughness and excellent dielectric properties as a triboelectric layer material to improve the surface charge density of TENG. SUMMARY

[0005] In view of the technical problems existing in the background art, the present application provides a magnetic polymer composite film and a preparation method and application thereof, aiming to solve the technical problem of low surface charge density of TENG caused by the low surface roughness and small dielectric constant of the existing triboelectric layer material.

[0006] In a first aspect, the present application provides a magnetic polymer composite film, comprising a P(VDF-TrFE) based film and a plurality of RCFO@PDA magnetic nanoparticles dispersed in the P(VDF-TrFE) based film; the RCFO@PDA magnetic nanoparticles have a core-shell structure, the core layer is rod-like nano CoFe2O4, and the shell layer is polydopamine.

[0007] Preferably, the RCFO@PDA magnetic nanoparticles are distributed in the P(VDF-TrFE) based film in a striped manner.

[0008] Preferably, the mass fraction of the RCFO@PDA magnetic nanoparticles in the magnetic polymer composite film is 0.5wt%-7wt%.

[0009] Preferably, the mass fraction of the RCFO@PDA magnetic nanoparticles in the magnetic polymer composite film is 1wt%.

[0010] In a second aspect, the present application provides a preparation method of a magnetic polymer composite film, comprising the following steps:

[0011] S1, preparation of rod-like nano CoFe2O4: a mixed solution containing a soluble iron salt and a soluble cobalt salt is added to an oxalic acid solution, and after mixing, a heating reaction is performed, and after filtration, washing, drying and calcination, rod-like nano CoFe2O4 is obtained;

[0012] S2, preparation of RCFO@PDA magnetic nanoparticles: the rod-like nano CoFe2O4 is added to a Tris-HCl buffer solution and mixed, and after adding dopamine and heating stirring, RCFO@PDA magnetic nanoparticles are obtained after filtration, washing and drying;

[0013] S3, preparation of RCFO@PDA / P(VDF-TrFE) magnetic polymer composite film: the RCFO@PDA magnetic nanoparticles prepared in step S2 are dispersed in a P(VDF-TrFE) organic solution to obtain a suspension, and the suspension is subjected to primary drying and solidification under the action of an external magnetic field, immersed in water for treatment, and then the external magnetic field is removed and subjected to secondary drying and solidification to obtain the magnetic polymer composite film.

[0014] Preferably, in step S1, the molar ratio of Fe element to Co element in the mixed solution containing a soluble iron salt and a soluble cobalt salt is 2:1.

[0015] Preferably, in step S1, the soluble iron salt includes at least one of iron sulfate, iron nitrate and iron chloride; and the soluble cobalt salt includes at least one of cobalt sulfate, cobalt nitrate and cobalt chloride.

[0016] Preferably, in step S1, the heating reaction temperature is 180-250℃, and the heating reaction time is 12-24h.

[0017] Preferably, in step S1, the calcination temperature is 600-800℃, and the calcination time is 2-4h.

[0018] Preferably, in step S2, the pH of the Tris-HCl buffer solution is 8-9.

[0019] Preferably, in step S2, the mass ratio of the rod-shaped CoFe2O4 nanometer and dopamine is 1:(2-6). The thickness of the outer coating layer can be controlled according to the content of dopamine.

[0020] Preferably, in step S2, the heating and stirring temperature is 40-60℃, and the heating and stirring time is 16-32h.

[0021] Preferably, in step S3, the mass concentration of the P(VDF-TrFE) organic solution is 0.01-1g / mL.

[0022] Preferably, in step S3, the first drying temperature is 80-100℃, and the second drying temperature is 60-80℃.

[0023] Preferably, in step S3, the film thickness of the magnetic polymer composite film is controlled to be 20-45μm.

[0024] In some embodiments, in step S3, the suspension is subjected to first drying and solidification under the action of an external magnetic field, specifically: the obtained suspension is coated on a substrate to which a magnetic field is applied in the horizontal direction of the substrate, the film thickness is controlled to be 20-45μm, and solidification is performed in a vacuum drying oven at 80-100℃ for 4-8h.

[0025] In some embodiments, in step S3, the external magnetic field is then removed and second drying and solidification are performed, specifically: the composite film is peeled off from the substrate, and drying is performed in a vacuum drying oven at 60-80℃ for 1-2h.

[0026] In a third aspect, the present application provides a friction nanogenerator, wherein the positive electrode friction material of the friction nanogenerator comprises the magnetic polymer composite film provided in the first aspect of the present application.

[0027] Preferably, the negative electrode friction material of the friction nanogenerator comprises a PTFE film.

[0028] The application provides a magnetic polymer composite film, and rod-like nano CoFe2O4 is used as a main modification material to increase effective contact area between fillers and a base film P(VDF-TrFE), which helps to promote charge separation effect in a friction process; the rod-like nano CoFe2O4 has high mechanical stimulation response capability. In the friction process, due to large shape size and high mechanical strain, the rod-like nano CoFe2O4 can more effectively sense mechanical energy generated by friction and convert the mechanical energy into electrical energy, thereby improving conversion efficiency.

[0029] The application forms RCFO@PDA magnetic nanoparticles with a core-shell structure by polymerization of dopamine and rod-like nano CoFe2O4, and a uniform polydopamine (PDA) shell layer can be formed on the surface of the rod-like nano CoFe2O4 due to self-polymerization of dopamine; the PDA layer can prevent aggregation of the nano CoFe2O4 and improve uniform dispersion of the particles in a matrix. Meanwhile, the PDA layer can provide a series of functional chemical groups (such as phenolic hydroxyl groups and amino groups), which can form strong interaction with the P(VDF-TrFE) matrix and enhance compatibility of the core-shell structure with the matrix. The P(VDF-TrFE) is a commonly used high-performance polymer matrix, has good polarization characteristics and can exhibit piezoelectric and ferroelectric properties under an electric field. The presence of the PDA shell layer can improve dispersion and distribution of the RCFO nanoparticles in the P(VDF-TrFE) matrix, so that the RCFO can better participate in the polarization process of the P(VDF-TrFE), enhance electrical and magnetoelectric coupling effects of the composite film and improve performance of the composite film in sensing, energy storage and other applications.

[0030] The application embeds the RCFO@PDA magnetic nanoparticles into the P(VDF-TrFE) base film, successfully constructs a stripe-shaped surface microstructure through a magnetic field orientation auxiliary thermal film forming process, effectively increases contact area of the friction material and improves dielectric constant. In addition to the effective contact area, improvement of dielectric performance of the friction layer material has a significant influence on capacitance of the friction layer material and ability of the friction layer material to store friction charges. Meanwhile, the increase of the dielectric constant is beneficial to charge density accumulated on the copolymer in the physical contact process, that is, the ability of the triboelectric layer to retain surface charges is enhanced, so that power output of the triboelectric layer is improved.

[0031] Compared with the prior art, the application has the beneficial effects that:

[0032] The application provides a magnetic polymer composite film, RCFO@PDA magnetic nanoparticles prepared from rod-like nano CoFe2O4 and dopamine are embedded into a P(VDF-TrFE) based film, a striped surface microstructure is successfully constructed through a magnetic field orientation assisted hot film forming process, the contact area of the friction material is effectively increased, and the dielectric constant is also improved. The magnetic polymer composite film provided by the application is used as a positive friction material of a friction nanogenerator, so that the electrical output performance of the friction nanogenerator is obviously improved. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The XRD spectrum of the rod-like nano CoFe2O4 prepared in the embodiment 2 of the application;

[0034] Figure 2 The SEM image of the rod-like nano CoFe2O4 prepared in the embodiment 2 of the application;

[0035] Figure 3 The SEM image of the RCFO@PDA magnetic nanoparticles prepared in the embodiment 2 of the application;

[0036] Figure 4 The surface morphology SEM spectrum of the RCFO@PDA / P(VDF-TrFE) composite film prepared in the embodiment 2 of the application; Figure 4 (a) is the SEM spectrum of the RCFO@PDA / P(VDF-TrFE) composite film under low magnification; Figure 4 (b) is the surface morphology SEM spectrum of the RCFO@PDA / P(VDF-TrFE) composite film under high magnification;

[0037] Figure 5 The optical microscope image of the RCFO@PDA / P(VDF-TrFE) composite film prepared in the embodiment 2 of the application. DETAILED DESCRIPTION

[0038] The embodiments of the technical scheme of the application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical scheme of the application, and therefore only serve as examples, and cannot limit the protection scope of the application.

[0039] The mole ratio of monomers VDF:TrFE in polyvinylidene fluoride-trifluoroethylene P(VDF-TrFE) used in the following embodiments of the application is 70:30.

[0040] I. Preparation method

[0041] Embodiment 1

[0042] The preparation method of the RCFO@PDA / P(VDF-TrFE) magnetic polymer composite film with a RCFO@PDA content of 0.5 wt% includes the following steps:

[0043] S1, preparation of rod-like nano CoFe2O4 (RCFO)

[0044] First, 8 mmol of FeSO4·7H2O and 4 mmol of CoSO4·7H2O were dissolved in a mixed solution of 60 mL of ethylene glycol and 20 mL of deionized water, and ultrasonic treatment was performed at room temperature for 30 min to obtain a mixed solution A. Then, 3 mmol of oxalic acid (C2H2O4·2H2O) was dissolved in a mixed solution of 60 mL of ethylene glycol and 20 mL of deionized water, and magnetic stirring was performed at room temperature for 15 min to obtain a mixed solution B. Then, the mixed solution A was added dropwise to the continuously stirred mixed solution B, and stirring was performed for 10 min to obtain a mixed solution C. The final mixed solution C was poured into a 200 mL PPL-lined autoclave, and heating was performed at 200°C for 12 h. After the reaction was completed, the solution was suction filtered, and washed with ethanol and deionized water for 3 times. Then, the dried sample was calcined in a muffle furnace at 650°C for 2 h to obtain rod-like nano CoFe2O4 (RCFO) material.

[0045] S2, preparation of core-shell structure RCFO@PDA magnetic nanoparticles

[0046] A 0.1 mol / L Tri-HCl buffer solution was prepared, and the pH value of the solution was controlled at about 8.5. 6 g of dopamine (DA) was weighed and added to the Tri-HCl buffer solution for continuous stirring. After the DA was completely dissolved, 1.2 g of RCFO was weighed and added to the prepared solution, and magnetic stirring was performed at 50°C for 24 h. Under the self-polymerization of dopamine (DA), a polydopamine (PDA) layer was formed on the surface of the rod-like nano CoFe2O4. After the reaction was completed, the solution was suction filtered, and washed with ethanol and deionized water for 3 times. After drying, the core-shell structure RCFO@PDA magnetic nanoparticles were obtained.

[0047] S3, preparation of RCFO@PDA / P(VDF-TrFE) magnetic polymer composite film

[0048] Polyvinylidene fluoride trifluoroethylene P(VDF-TrFE) powder was added to DMF solvent, continuously stirred for 2h, to obtain a uniform mixed solution of 0.05g / mL. The prepared RCFO@PDA magnetic nanoparticles were mixed with the above uniform solution, and the addition amount of RCFO@PDA magnetic nanoparticles was 0.5wt% of the total mass of P(VDF-TrFE) powder and RCFO@PDA magnetic nanoparticles; and after 1h of ultrasonic treatment, a dispersed suspension was formed. The obtained suspension was coated on a glass substrate with a magnetic field applied in the horizontal direction of the substrate, and the film thickness was controlled to be 30μm. In a vacuum drying oven at 80℃, the film was cured for 4h, and then the cured film was immersed in deionized water for 5h. Finally, the composite film was peeled off from the glass substrate and dried in a vacuum drying oven at 60℃ for 1h to obtain an RCFO@PDA / P(VDF-TrFE) composite film with an RCFO@PDA content of 0.5wt%.

[0049] Example 2

[0050] The difference between this embodiment and Example 1 is that in step S3, the preparation of RCFO@PDA / P(VDF-TrFE) composite film, the addition amount of RCFO@PDA magnetic nanoparticles is 1wt% of the total mass of P(VDF-TrFE) powder and RCFO@PDA magnetic nanoparticles; the remaining steps are the same as Example 1; and an RCFO@PDA / P(VDF-TrFE) composite film with an RCFO@PDA content of 1wt% is obtained.

[0051] Example 3

[0052] The difference between this embodiment and Example 1 is that in step S3, the preparation of RCFO@PDA / P(VDF-TrFE) composite film, the addition amount of RCFO@PDA magnetic nanoparticles is 3wt% of the total mass of P(VDF-TrFE) powder and RCFO@PDA magnetic nanoparticles; the remaining steps are the same as Example 1; and an RCFO@PDA / P(VDF-TrFE) composite film with an RCFO@PDA content of 3wt% is obtained.

[0053] Example 4

[0054] The difference between this embodiment and Example 1 is that in step S3, the preparation of RCFO@PDA / P(VDF-TrFE) composite film, the addition amount of RCFO@PDA magnetic nanoparticles is 5wt% of the total mass of P(VDF-TrFE) powder and RCFO@PDA magnetic nanoparticles; the remaining steps are the same as Example 1; and an RCFO@PDA / P(VDF-TrFE) composite film with an RCFO@PDA content of 5wt% is obtained.

[0055] Example 5

[0056] The difference between the present embodiment and Example 1 is that the amount of RCFO@PDA magnetic nanoparticles added in the preparation of the RCFO@PDA / P(VDF-TrFE) composite film in step S3 is 7wt% of the total mass of P(VDF-TrFE) powder and RCFO@PDA magnetic nanoparticles; the remaining steps are the same as those in Example 1; and an RCFO@PDA / P(VDF-TrFE) composite film with an RCFO@PDA content of 7wt% is obtained.

[0057] Comparative Example 1

[0058] The difference between the present comparative example and Example 1 is that the amount of RCFO@PDA magnetic nanoparticles added is 0wt%, and a P(VDF-TrFE) base film is prepared.

[0059] Comparative Example 2

[0060] The difference between the present comparative example and Example 2 is that the rod-shaped CoFe2O4 material is replaced with commercially available CoFe2O4, and the commercially available CoFe2O4 has a spherical morphology.

[0061] The remaining steps are the same as those in Example 2; and a CFO@PDA / P(VDF-TrFE) composite film with a CFO@PDA content of 1wt% is obtained.

[0062] Comparative Example 3

[0063] The difference between the present comparative example and Example 2 is that the preparation of the core-shell structure RCFO@PDA magnetic nanoparticles in step S2 is omitted, and the rod-shaped CoFe2O4 prepared in step S1 is directly compounded with P(VDF-TrFE) while maintaining the same CoFe2O4 content as in Example 2.

[0064] Comparative Example 4

[0065] The difference between the present comparative example and Example 2 is that no magnetic field is applied in step S3.

[0066] Application Example 1

[0067] Preparation of a triboelectric nanogenerator (TENG):

[0068] Two pieces of 5 cm x 5 cm x 0.3 cm acrylic plates were prepared as the substrate of the upper and lower electrodes of the TENG, and copper foil was pasted on the upper and lower substrates with double-sided tape. Then, the RCFO@PDA / P(VDF-TrFE) composite film prepared in Example 1 with a RCFO@PDA content of 0.5wt% and the PTFE finished film were cut into rectangular blocks with a size of 2 cm x 2.5 cm, and were pasted on the conductive copper foil as the positive and negative rubbing materials of the device, respectively, wherein the thickness of the positive rubbing material RCFO@PDA / P(VDF-TrFE) film was 30 μm, and the thickness of the negative rubbing material PTFE film was 0.08 mm.

[0069] Application Example 2

[0070] The difference between this application example and Application Example 1 is that the RCFO@PDA / P(VDF-TrFE) film prepared in Example 2 with a RCFO@PDA content of 1wt% and the PTFE finished film were cut into rectangular blocks with a size of 2 cm x 2.5 cm, and were pasted on the conductive copper foil as the positive and negative rubbing materials of the device, respectively.

[0071] Application Example 3

[0072] The difference between this application example and Application Example 1 is that the RCFO@PDA / P(VDF-TrFE) film prepared in Example 3 with a RCFO@PDA content of 3wt% and the PTFE finished film were cut into rectangular blocks with a size of 2 cm x 2.5 cm, and were pasted on the conductive copper foil as the positive and negative rubbing materials of the device, respectively.

[0073] Application Example 4

[0074] The difference between this application example and Application Example 1 is that the RCFO@PDA / P(VDF-TrFE) film prepared in Example 4 with a RCFO@PDA content of 5wt% and the PTFE finished film were cut into rectangular blocks with a size of 2 cm x 2.5 cm, and were pasted on the conductive copper foil as the positive and negative rubbing materials of the device, respectively.

[0075] Application Example 5

[0076] The difference between this application example and Application Example 1 is that the RCFO@PDA / P(VDF-TrFE) film prepared in Example 5 with a RCFO@PDA content of 7wt% and the PTFE finished film were cut into rectangular blocks with a size of 2 cm x 2.5 cm, and were pasted on the conductive copper foil as the positive and negative rubbing materials of the device, respectively.

[0077] Comparative Example 5

[0078] The difference between the present comparative example and application example 1 is that the P(VDF-TrFE) based film and the PTFE finished film prepared in Comparative Example 1 are cut into rectangular blocks with a size of 2 cm x 2.5 cm, and are respectively attached to the conductive copper foil as the positive and negative electrode rubbing materials of the device.

[0079] Comparative Example 6

[0080] The difference between the present comparative example and application example 1 is that the CFO@PDA / P(VDF-TrFE) composite film with a CFO@PDA content of 1 wt% prepared in Comparative Example 2 and the PTFE finished film are cut into rectangular blocks with a size of 2 cm x 2.5 cm, and are respectively attached to the conductive copper foil as the positive and negative electrode rubbing materials of the device.

[0081] Comparative Example 7

[0082] The difference between the present comparative example and application example 1 is that the composite film prepared in Comparative Example 3 and the PTFE finished film are cut into rectangular blocks with a size of 2 cm x 2.5 cm, and are respectively attached to the conductive copper foil as the positive and negative electrode rubbing materials of the device.

[0083] Comparative Example 8

[0084] The difference between the present comparative example and application example 1 is that the composite film prepared in Comparative Example 4 and the PTFE finished film are cut into rectangular blocks with a size of 2 cm x 2.5 cm, and are respectively attached to the conductive copper foil as the positive and negative electrode rubbing materials of the device.

[0085] II. Test Methods

[0086] 1. Characterization test of materials

[0087] (1) Structure characterization of rod-shaped cobalt ferrite (RCFO)

[0088] The rod-shaped cobalt ferrite prepared by the hydrothermal method in step S1 of Example 2 was characterized using an X-ray diffractometer; the morphology of the rod-shaped cobalt ferrite was tested using a scanning electron microscope; and the element face distribution of the cobalt ferrite nanorods was tested using EDX (energy dispersive X-ray spectrometer).

[0089] (2) Characterization of core-shell structure RCFO@PDA magnetic nanoparticles

[0090] The morphology of the RCFO@PDA magnetic nanoparticles prepared in step S2 of Example 2 was tested using a scanning electron microscope.

[0091] (3) Magnetic properties of RCFO@PDA / P(VDF-TrFE) composite film

[0092] The hysteresis behavior of the magnetic polymer composite films prepared in Examples 1-5 under an applied magnetic field, and the saturation magnetization (Ms) and coercivity (Hc) thereof were tested using a vibrating sample magnetometer (VSM); the test conditions were: 18000 Oe, room temperature.

[0093] (4) Surface morphology characterization of RCFO@PDA / P(VDF-TrFE) composite films

[0094] The morphology of the different magnetic polymer composite film samples prepared in the examples and comparative examples was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the average roughness (Rq) was calculated according to the AFM results.

[0095] (5) Dielectric properties of RCFO@PDA / P(VDF-TrFE) composite films

[0096] The dielectric properties of the RCFO@PDA / P(VDF-TrFE) composite films with different RCFO@PDA loadings prepared in the examples and comparative examples were tested by broadband dielectric spectroscopy (Agilent 4284A precision impedance LCR tester); the test conditions were: 10 -2 Hz-10 7 Hz, temperature range: -60°C-130°C. The dielectric constant (ε'), dielectric loss (tan δ) and conductivity (σ) test results of different magnetic polymer composite film samples at 100 Hz were statistically analyzed. ɛ r

[0097] 2. Triboelectric nanogenerator (TENG) electrical output performance test

[0098] The two electrodes of the triboelectric nanogenerator prepared in Application Examples 1-5 and Comparative Examples 5-8 were connected to an electrometer to test the output performance of the TENG. The test frequency of the contact-separation cycle was 5 Hz, the friction layer interval was 0.1 mm, and the open circuit voltage (Voc), short circuit current (Isc) and transferred charge (Q) of different TENGs were measured during the repeated contact and separation motion cycle process under a contact force of 15 N. V oc I sc Q

[0099] III. Analysis of test results of each example and comparative example

[0100] 1. Structural characterization test results of composite film materials

[0101] (1) Structure and morphology characterization of rod-shaped CoFe2O4 (RCFO)

[0102] Figure 1 ​​​​The XRD pattern of the cobalt ferrite nanorods (RCFO) prepared by hydrothermal method has diffraction peaks at 30.0°, 35.4°, 43.0°, 53.4°, 56.9°, 62.5° and 74.0°, respectively, corresponding to the (220), (311), (222), (400), (422), (511), (440) and (533) crystal faces of CoFe2O4 (JCPDS No. 22-1086), indicating that the prepared cobalt ferrite nanoparticles belong to the cubic spinel structure.

[0103] Figure 2 The high-resolution SEM image of the rod-shaped CoFe2O4 nanoparticles shows that the CoFe2O4 nanoparticles form a uniform nanorod structure after being annealed at 650°C for 2h. The high-magnification scanning electron microscopy image clearly shows that the RCFO nanorods are self-assembled from numerous nanoparticles, and have a uniform shape and flat surface.

[0104] (2) Morphology characterization of RCFO@PDA magnetic nanoparticles

[0105] Figure 3 The SEM image of the RCFO@PDA magnetic nanoparticles shows that dopamine forms a uniform polydopamine (PDA) shell layer on the surface of the rod-shaped CoFe2O4 nanoparticles through self-polymerization.

[0106] (3) Magnetic properties of RCFO@PDA / P(VDF-TrFE) composite films

[0107] The saturation magnetization (Ms) and coercivity (Hc) of different magnetic polymer composite film samples under an applied magnetic field are shown in Table 1 below. M H Table 1

[0108] Table 1

[0109]

[0110] The results show that the coercivity of the composite film material remains essentially unchanged with increasing RCFO@PDA content, all around 1133.3 Oe. Under an applied magnetic field of 18000 Oe, the magnetization of the composite film basically reaches saturation; in addition, with increasing RCFO@PDA doping amount, the Ms of the composite material gradually increases from 0.25 emu / g to 3.6 emu / g, which is mainly due to the increase in the number of magnetic particles per unit volume of the composite film caused by the increase in the RCFO@PDA doping amount.

[0111] (4) Surface morphology of RCFO@PDA / P(VDF-TrFE) composite films

[0112] ​The SEM spectrum of the RCFO@PDA / P(VDF-TrFE) composite film prepared in Example 2 is shown in Figure 4 Figure 4 (a) is the SEM spectrum of the RCFO@PDA / P(VDF-TrFE) composite film under low magnification; Figure 4 (b) is the surface morphology SEM spectrum of the RCFO@PDA / P(VDF-TrFE) composite film under high magnification. The results show that after the introduction of magnetic dielectric particles RCFO@PDA and the application of a magnetic field, the RCFO@PDA magnetic nanoparticles are distributed in the form of stripes in the P(VDF-TrFE) base film.

[0113] Figure 5 The optical microscope image of the RCFO@PDA / P(VDF-TrFE) composite film prepared in Example 2 shows that the surface of the composite film introduced RCFO@PDA magnetic nanoparticles has obvious stripes and concave-convex microstructure, which increases the effective contact area.

[0114] The average roughness (Rq) results calculated from the Rq histogram obtained by AFM measurement are shown in Table 2

[0115] Table 2

[0116]

[0117] ​The results of Table 2 show that the average roughness (Rq) of the pure P(VDF-TrFE) film prepared in Comparative Example 1 is 6 nm. Due to the introduction of RCFO@PDA nanoparticles, the roughness of the RCFO@PDA / P(VDF-TrFE) film shows a trend of first increasing and then decreasing. In particular, the Rq of the RCFO@PDA / P(VDF-TrFE) composite film with 1 wt% RCFO@PDA increases to 45.8 nm, but when the content of RCFO@PDA exceeds 1 wt%, the roughness decreases, indicating that there may be a critical value for the degree of loose arrangement of particles. When the particle content exceeds the critical value, the particles agglomerate, making the roughness of the film lower than that of the film with loose particle arrangement, but the roughness is still much higher than that of the pure P(VDF-TrFE) film. The results of Comparative Example 2 and Example 2 show that rod-shaped iron cobaltate nanoparticles are more likely to form irregular structures on the surface of the base film due to their high aspect ratio, thereby increasing the surface roughness. Compared with the rod-shaped iron cobaltate particles in Example 2, spherical iron cobaltate particles may exhibit lower structural complexity. The high aspect ratio (i.e., length-diameter ratio) of the rod-shaped particles makes them more likely to self-assemble into structures with obvious concave-convex structures on the film surface, increasing the roughness of the film. In contrast, the particles in Comparative Example 2 may result in a smoother film surface due to their more symmetrical shape, resulting in lower roughness. The results of Comparative Example 3 and Example 2 show that the addition of dopamine-coated nanoparticles CoFe2O4 without dopamine modification leads to the aggregation of nanoparticles, resulting in a decrease in the surface roughness of the composite film. In Comparative Example 3, dopamine is not used for modification, which means that the surface of the nanoparticles lacks surface modification, and the interaction force between the particles may cause the aggregation of the particles. This aggregation causes the particles to form more uniform and less surface undulations on the surface of the base film, thereby reducing the roughness of the film. In contrast, the PDA coating in Example 2 can effectively reduce the aggregation of particles, maintain the dispersibility of particles, and possibly result in more surface irregularities, thereby increasing the roughness. The results of Comparative Example 4 and Example 2 show that the composite film without magnetic field treatment may lack ordered striated microstructures on the surface, resulting in lower roughness. Magnetic field treatment can guide the alignment of magnetic particles in a specific direction, thereby forming ordered surface microstructures and increasing the surface roughness. The composite film in Comparative Example 4 is not subjected to magnetic field treatment, resulting in the failure of magnetic particles to self-assemble into striated structures on the surface of the base film. The distribution of particles may be random or more uniform, resulting in a smoother surface of the film and thus lower roughness.

[0118] (5) Dielectric properties of RCFO@PDA / P(VDF-TrFE) composite films

[0119] The dielectric constant (ε') and dielectric loss (tan δ) of different magnetic polymer composite film samples at 100 Hz are shown in Table 3. ɛ r

[0120] Table 3​

[0121]

[0122] From the results of Table 3, it can be seen that the dielectric constant of the RCFO@PDA / P(VDF-TrFE) composite film is higher than that of the pure P(VDF-TrFE) film, and the dielectric constant increases with the increase of the loading amount of RCFO@PDA. Since improving the dielectric constant of the triboelectric material is an effective way to improve the charge density, the increase of the dielectric constant helps to improve the output performance of the TENG. The results of Comparative Example 2 and Example 2 show that the aspect ratio of the rod-like magnetic nanoparticles is high, which enhances the interfacial polarization effect, thereby increasing the dielectric constant and dielectric loss; the results of Comparative Example 3 and Example 2 show that the nanoparticles without dopamine coating are prone to agglomeration, which increases the leakage channel, resulting in a significant increase in dielectric loss; the results of Comparative Example 4 and Example 2 show that the application of a magnetic field treatment can induce the particles to form an ordered structure, which reduces the local electric field distortion, thereby reducing the dielectric loss, and at the same time has a certain optimization effect on the dielectric constant.

[0123] 2. RCFO@PDA / P(VDF-TrFE) / / PTFE TENG electrical output performance

[0124] Under the conditions of a test frequency of 5 Hz, a friction layer spacing of 0.1 mm, and a contact force of 15 N, the open-circuit voltage (V V oc ), short-circuit current (I I sc ), and transferred charge (Q Q ) of different TENGs are shown in Table 4 below.

[0125] Table 4

[0126]

[0127] The results of Table 4 show that after the introduction of RCFO@PDA particles, the transferred charge increases. Compared with the pure P(VDF-TrFE), when the RCFO@PDA / P(VDF-TrFE) composite film with a RCFO@PDA content of 1wt% is used as the positive friction layer, the electrical output is the highest, with a V oc , scThe maximum values of Vop, Iop and Qop were 5.94 V, 0.102 µA and 1.92 nC, respectively. This could be attributed to the gradual increase of surface roughness of the composite film with the increase of RCFO@PDA content, which increased the effective rubbing area during the contact separation process. When the content of magnetic particles was too high, the particles were arranged closely, although the dielectric constant increased slightly, which reduced the roughness of the composite film as the rubbing layer. Therefore, the corresponding decrease of TENG output performance could be attributed to the combined effect of the decrease of roughness and the increase of dielectric constant. When the content of magnetic particles was too high, the magnetic particles were exposed outside the matrix, which reduced the effective rubbing area. The results of Comparative Example 2 and Example 2 showed that rod-like magnetic particles could more effectively enhance the interfacial polarization effect than spherical particles, which significantly improved the open-circuit voltage, short-circuit current and transferred charge. The results of Comparative Example 3 and Example 2 showed that the core-shell structure formed by dopamine coating improved the particle dispersibility and enhanced the interfacial polarization effect, which improved the electrical performance of the composite film. The results of Comparative Example 4 and Example 2 showed that the magnetic field treatment induced the ordered arrangement of particles, which optimized the interfacial polarization effect and further improved the open-circuit voltage, short-circuit current and transferred charge performance.

[0128] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and exerting the same effects as the technical idea within the scope of the technical solution of the present application are included in the technical scope of the present application. Furthermore, within the scope of the gist of the present application, other modes obtained by applying various modifications that can be thought of by those skilled in the art to the embodiments or by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A magnetic polymer composite film, characterized by, The magnetic polymer composite film comprises a P(VDF-TrFE) base film and a plurality of RCFO@PDA magnetic nanoparticles dispersed in the P(VDF-TrFE) base film; the RCFO@PDA magnetic nanoparticles have a core-shell structure, the core layer is rod-shaped nano CoFe2O4, and the shell layer is polydopamine; and the RCFO@PDA magnetic nanoparticles are distributed in the P(VDF-TrFE) base film in a striped manner. The preparation method of the magnetic polymer composite film comprises the following steps: S1, preparation of rod-shaped nano CoFe2O4: a mixed solution containing soluble iron salt and soluble cobalt salt is added to an oxalic acid solution, and after being uniformly mixed, a heating reaction is performed, and after filtration, washing, drying and calcination, rod-shaped nano CoFe2O4 is obtained; S2, preparation of RCFO@PDA magnetic nanoparticles: the rod-shaped nano CoFe2O4 is added to a Tris-HCl buffer solution and uniformly mixed, and after adding dopamine, heating and stirring are performed, and after filtration, washing and drying, RCFO@PDA magnetic nanoparticles are obtained; S3, preparation of RCFO@PDA / P(VDF-TrFE) magnetic polymer composite film: the RCFO@PDA magnetic nanoparticles prepared in step S2 are dispersed in a P(VDF-TrFE) organic solution to obtain a suspension, the suspension is subjected to primary drying and solidification under the action of an external magnetic field, is subjected to immersion treatment in water, and then the external magnetic field is removed and secondary drying and solidification are performed, to obtain the magnetic polymer composite film.

2. The magnetic polymer composite film according to claim 1, characterized in that, The mass fraction of the RCFO@PDA magnetic nanoparticles in the magnetic polymer composite film is 0.5wt%-7wt%.

3. The magnetic polymer composite film according to claim 1, wherein In the step S1, the heating reaction is performed at a temperature of 180-250℃ for 12-24h.

4. The magnetic polymer composite film according to claim 1, wherein In the step S1, the calcination is performed at a temperature of 600-800℃ for 2-4h.

5. The magnetic polymer composite film according to claim 1, wherein In the step S2, the Tris-HCl buffer solution has a pH of 8-9; the heating and stirring are performed at a temperature of 40-60℃ for 16-32h.

6. The magnetic polymer composite film according to claim 1, wherein The mass ratio of the rod-shaped nano CoFe2O4 to dopamine is 1:(2-6).

7. The magnetic polymer composite film according to claim 1, wherein In the step S3, the mass concentration of the P(VDF-TrFE) organic solution is 0.01-1g / mL; the primary drying temperature is 80-100℃, and the secondary drying temperature is 60-80℃.

8. A friction nanogenerator, characterized in that, The positive friction material of the triboelectric nanogenerator comprises the magnetic polymer composite film according to any one of claims 1-7.

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