Flexible transparent diaphragm, electroacoustic conversion device and preparation method thereof

Abstract

The invention discloses a flexible transparent diaphragm, an electroacoustic conversion device and a preparation method thereof, and relates to the technical field of polymer film materials, the preparation method of the flexible transparent diaphragm comprises the following steps: S1, mixing a metal fluoride solution and a silver nanowire suspension to obtain a mixed solution for later use; s2, preparing a sacrificial film on the substrate; s3, spin-coating the sacrificial film with the mixed solution prepared in the step S1, and heating to decompose the metal fluoride to form a metal oxide to obtain a composite film loaded on a substrate; s4, spin-coating a PVDF solution on the surface of the composite film, and drying; and S5, removing the sacrificial thin film to obtain the flexible transparent diaphragm. The high light transmittance of the flexible transparent membrane based on the silver nanowires can be guaranteed, and meanwhile the oxidation resistance of the flexible transparent membrane is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer thin film materials, and specifically to a flexible transparent film, an electroacoustic conversion device and a preparation method thereof. Background Art

[0002] At present, with the rapid development of fields such as smart devices, wearable devices and smart homes, traditional rigid and relatively large electroacoustic conversion devices such as microphones and speakers can no longer meet the stringent requirements for flexibility, transparency and miniaturization in special application scenarios. For example, in wearable devices such as smart watches and smart glasses, flexible transparent microphones and speakers can not only greatly improve the wearing comfort, but also enhance the aesthetic appearance of the product; in the field of smart homes, flexible transparent speakers integrated on the surfaces of walls, windows, etc. can achieve hidden voice interaction functions, effectively optimizing the user experience. Therefore, developing new flexible transparent materials has become the key to realizing the functions of flexible electroacoustic conversion devices.

[0003] The vibrating diaphragm is an important component for electroacoustic conversion in electroacoustic conversion devices. In a speaker, an audio electrical signal passes through a voice coil to cause it to vibrate reciprocally in a magnetic field, driving the connected vibrating diaphragm to vibrate, and then causing the surrounding air to vibrate to generate sound; in a microphone, sound waves cause the vibrating diaphragm to vibrate with its frequency and amplitude, and convert the diaphragm vibration into an electrical signal carrying sound information by changing the capacitance or other means. In both cases, the vibrating diaphragm is the core component of electroacoustic conversion, and its performance directly affects the conversion quality. Developing a flexible transparent vibrating diaphragm is of great significance to the development of flexible electroacoustic conversion devices.

[0004] The prior art discloses a scheme for preparing a flexible transparent thin film by embedding silver nanowires in a PVDF thin film. However, due to the high activity of the surface atoms of silver nanowires, the quantum size effect and surface effect at the nanoscale, the coordination of surface atoms is unsaturated, there are many dangling bonds and defects, and these active sites are prone to adsorb oxygen molecules, dissociate and activate the oxygen molecules, and then easily trigger an oxidation reaction.

[0005] To avoid the oxidation of silver nanowires, a method can be adopted to prepare a layer of oxide as a protective layer on the surface of the silver nanolayer by physical or chemical vapor deposition. However, the method of directly preparing the protective layer only has a protective layer on the surface of the exposed silver nanowires, and the part where the silver nanowires contact the PVDF film cannot be effectively protected. At the same time, a protective layer will also be formed on the surface of the PVDF film by using the physical or chemical vapor deposition method. At this time, oxides will also exist in the gaps between the silver nanowires. Due to the absorption of photons by the oxides, the light transmittance of the obtained film decreases. In addition, the equipment used for physical or chemical vapor deposition is expensive, resulting in a relatively high production cost of the prepared flexible transparent film. Although the sol-gel method has a relatively low cost for preparing oxides, during the process of preparing the oxide protective layer, high-temperature heat treatment of the film is required, and its temperature is usually above 300°C, exceeding the melting point of the flexible PVDF substrate, thus limiting the application of this method. Summary of the Invention

[0006] The present invention aims to provide a flexible transparent film, an electroacoustic conversion device and a preparation method thereof, so as to improve the antioxidant property while ensuring the high light transmittance of the flexible transparent film based on silver nanowires.

[0007] To solve the above technical problems, the specific solution adopted by the present invention is as follows: A preparation method of a flexible transparent film includes the following steps:

[0008] S1. Mix a metal fluoride solution and a silver nanowire suspension to obtain a mixed solution for standby;

[0009] S2. Prepare a sacrificial film on a substrate;

[0010] S3. Spin-coat the mixed solution prepared in step S1 on the sacrificial film, and heat to decompose the metal fluoride to form a metal oxide, obtaining a composite film loaded on the substrate;

[0011] S4. Spin-coat a PVDF solution on the surface of the composite film and dry it;

[0012] S5. Remove the sacrificial film, and the flexible transparent film is thus prepared.

[0013] As a further optimization of the above technical solution, the metal fluoride is one of chromium fluoride, magnesium fluoride, nickel fluoride, zinc fluoride and aluminum fluoride.

[0014] As a further optimization of the above technical solution, in step S3, the heating temperature is 50 - 150°C, and the heating time is 25 - 35 min.

[0015] As a further optimization of the above technical solution, in step S1, the metal fluoride solution is prepared by dissolving metal fluoride in deionized water and then adding absolute ethanol; after the metal fluoride solution is mixed with the silver nanowire suspension, it is left standing at room temperature for 12 - 24 h to obtain the mixed solution.

[0016] As a further optimization of the above technical solution, the sacrificial film is prepared on the substrate by physical deposition. The sacrificial film is an alumina film with a thickness of 10 - 30 nm, and the substrate is made of glass.

[0017] As a further optimization of the above technical solution, in step S5, the sacrificial film is removed by alkali solution etching.

[0018] The flexible transparent film sheet prepared by the above preparation method.

[0019] An electroacoustic conversion device includes a vibrating diaphragm. The vibrating diaphragm is formed by folding the above flexible transparent film sheet in half. The flexible transparent film sheet includes a PVDF film and metal oxide / silver nanowires embedded on the surface of the PVDF film. The side with the metal oxide / silver nanowires is the conductive surface, and the conductive surface is located on the outside of the folded structure. The vibrating diaphragm is clamped by two sets of relatively arranged flexible transparent substrates. Each set of flexible transparent substrates includes two flexible transparent substrates with ITO surfaces and non - ITO surfaces. The non - ITO surface of the flexible transparent substrate contacts the conductive surface of the vibrating diaphragm.

[0020] Through holes are provided on the flexible transparent substrate, and conductive silver paste in contact with the conductive surface is provided in the through holes.

[0021] A PDMS film is provided on the vibrating diaphragm between the two flexible transparent substrates on the same side.

[0022] A preparation method of an electroacoustic conversion device includes the following steps:

[0023] P1. Fold the flexible transparent film sheet in half so that the conductive surface is on the outside of the folded structure to obtain the vibrating diaphragm.

[0024] P2. Take four flexible transparent substrates and etch through holes on the flexible transparent substrates.

[0025] P3. Clamp the four flexible transparent substrates symmetrically in pairs at both ends of the vibrating diaphragm, leaving a gap between the two flexible transparent substrates on the same side; the non - ITO surface of the flexible transparent substrate is attached to the vibrating diaphragm, and the vibrating diaphragm seals the through holes of the flexible transparent substrate. Conductive silver paste is filled in the through holes of the flexible transparent substrate to form a positive electrode on one side of the vibrating diaphragm and a negative electrode on the other side of the vibrating diaphragm.

[0026] P4. Spin-coat a PDMS solution on the vibrating diaphragm located at the spacing between two flexible transparent substrates, and dry it.

[0027] P5. Apply a voltage through the positive electrode and the negative electrode to polarize the PVDF thin film of the vibrating diaphragm, thereby obtaining the electroacoustic conversion device.

[0028] As a further optimization of the above technical solution, the flexible transparent substrate is a polyethylene terephthalate layer or a polyimide layer with ITO coated on one side.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The present invention directly mixes a silver nanowire suspension with a metal fluoride solution, and then heats it to decompose the metal fluoride to form a metal oxide. The metal oxide prepared by this method coats the silver nanowires, so that the part of the silver nanowires in contact with the PVDF thin film can also be effectively protected, improving the antioxidant property of the silver nanowires.

[0031] Since the silver nanowires of the present invention are wrapped by oxides, after being embedded in the PVDF thin film, direct contact between oxygen, water molecules, etc. in the air and the silver nanowires is effectively avoided, thereby increasing the antioxidant ability of the silver nanowires and making their electrical properties more stable. When used as an electrode, charge loss on the electrode can be avoided. For a speaker, it can effectively convert an electrical signal into the vibration of a flexible transparent diaphragm, and then emit sound; for a microphone, it can effectively convert the electric charge accumulated on the positive electrode and the negative electrode due to sound into an electrical signal.

[0032] Through the method provided by the present invention, a protective layer can be formed only on the surface of the silver nanowires. When the silver nanowires are spin-coated on the substrate, the gaps between the silver nanowires are not covered by oxides, to a certain extent avoiding interference with the light transmittance of the flexible transparent film. Compared with the scheme of coating a protective layer on the surface of bare silver nanowires, the preparation method of the present invention can significantly improve the optical properties of the obtained flexible transparent diaphragm. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the preparation process of the flexible transparent diaphragm in Example 1;

[0034] Figure 2 It is a schematic diagram of the folding of the flexible transparent diaphragm;

[0035] Figure 3 It is a schematic diagram of the structure after the vibrating diaphragm is assembled on the flexible transparent support frame;

[0036] Figure 4 It is a schematic diagram of the structure of the electroacoustic conversion device;

[0037] Figure 5 The light transmittance of the electroacoustic conversion device prepared in Example 4 within 380 nm - 780 nm;

[0038] Figure 6 The audio signal data output as a speaker by the electroacoustic conversion device prepared in Comparative Example 1. The input signal is the music "Direction of Light", and the selected playing time is about 5 s;

[0039] Figure 7 The audio signal data output as a speaker by the electroacoustic conversion device prepared in Example 4. The input signal is the music "Direction of Light", and the selected playing time is about 5 s;

[0040] Figure 8 The audio signal data recorded as a microphone by the electroacoustic conversion device prepared in Comparative Example 1;

[0041] Figure 9 The audio signal data recorded as a microphone by the electroacoustic conversion device prepared in Example 4;

[0042] Reference numerals: 1, flexible transparent substrate; 101, ITO surface; 102, non-ITO surface; 103, through hole; 2, vibration diaphragm; 3, PDMS film; 4, conductive silver paste. Detailed implementation manners

[0043] The technical solutions of the present invention will be further elaborated in detail below in combination with specific embodiments. For the parts not detailedly recorded and disclosed in the following embodiments of the present invention, they should all be understood as the prior art known or should be known to those skilled in the art. The alumina target, sputtering gas, metal fluoride, deionized water, absolute ethanol, NaOH powder, PDMS solution, and flexible transparent substrate used in the following embodiments are all commercially available products, and the purity of the alumina target is greater than 99.99%.

[0044] The present invention discloses a preparation method of a flexible transparent diaphragm, comprising the following steps:

[0045] S1. Mix a metal fluoride solution and a silver nanowire suspension to obtain a mixed solution for standby.

[0046] Among them, the metal fluoride solution is prepared by dissolving a metal fluoride in deionized water and then adding absolute ethanol; the addition ratio of the metal fluoride, deionized water, and absolute ethanol is 0.01 - 0.1 g: 2 - 25 ml: 5 - 50 ml.

[0047] The concentration of the silver nanowire suspension is 0.5 - 2 mg / ml. The silver nanowire suspension can be a commercially available product or can be prepared by dissolving silver nanowires in absolute ethanol.

[0048] The metal fluoride solution is added to the silver nanowire suspension according to a volume ratio of 0.5 - 2 ml : 8 - 20 ml, and then left standing at room temperature for 12 - 24 h to obtain a mixed solution.

[0049] S2. Prepare a sacrificial film on the substrate. The substrate is a glass substrate, such as a glass slide; the sacrificial film is an alumina film and the thickness of the sacrificial film is 10 - 30 nm. The sacrificial film is prepared on the substrate by physical deposition. Physical deposition includes magnetron sputtering, atomic deposition, and chemical vapor deposition.

[0050] S3. Use a spin coater to spin - coat the mixed solution prepared in step S1 on the sacrificial film on the surface of the substrate, and then place the substrate in an oven at 50 - 150 °C and heat for 25 - 35 min to decompose the metal fluoride to form a metal oxide, obtaining a composite film loaded on the substrate. This composite film is an alumina / silver nanowire / metal oxide composite film, and the metal oxide coats the outside of the silver nanowires.

[0051] S4. Use a spin coater to spin - coat a PVDF (Chinese name: polyvinylidene fluoride) solution on the surface of the composite film, and then place the substrate in an oven at 90 °C for 30 min for drying treatment, and then naturally cool. After drying and cooling, the PVDF solution forms a PVDF film, and the silver nanowires coated with a metal oxide layer are embedded in the PVDF film.

[0052] S5. Remove the sacrificial film by alkali etching to obtain the flexible transparent film. Specifically, place the glass substrate in a NaOH solution with a mass percentage of 1 - 10% and a temperature of 45 - 70 °C. The alkali solution etches the alumina film until the film on the surface of the glass substrate falls off and floats on the water surface. Then, use the glass substrate to pick up this layer of film and wash it with deionized water to remove the residual NaOH solution and other impurities. After natural drying, the flexible transparent film can be obtained. This flexible transparent film is a metal oxide / silver nanowire / PVDF composite film.

[0053] It should be noted that when spin - coating the mixed solution on the sacrificial film on the surface of the substrate in step S3, the number of spin - coating times and the rotation speed of the spin coater can be adjusted according to the requirements for the light transmittance and sheet resistance of the flexible transparent film. The more spin - coating times and the lower the rotation speed of the spin coater, the lower the light transmittance of the flexible transparent film. The thickness of the prepared flexible transparent film is preferably 5 - 20 μm.

[0054] The present invention also discloses an electro - acoustic conversion device and a preparation method thereof. As Figure 3 、 4As shown in the figure, the electroacoustic conversion device includes a vibrating diaphragm 2 formed by folding the above-mentioned flexible transparent diaphragm in half. The flexible transparent diaphragm includes a PVDF film and metal oxide / silver nanowires embedded on one surface of the PVDF film. The surface with the metal oxide / silver nanowires is the conductive surface, and the conductive surface is located on the outside of the folded structure.

[0055] The vibrating diaphragm 2 is clamped by two sets of relatively arranged flexible transparent substrates 1. Each set of flexible transparent substrates 1 includes two flexible transparent substrates 1 with an ITO surface 101 and a non-ITO surface 102. One surface of the flexible transparent substrate 1 is coated with an ITO (Chinese name: indium tin oxide) transparent conductive film, which is its ITO surface, and the opposite surface is its non-ITO surface. The non-ITO surface 102 of the flexible transparent substrate 1 is in contact with the conductive surface of the vibrating diaphragm 2.

[0056] Through holes 103 are provided on the flexible transparent substrate 1. The through holes 103 of the same set of flexible transparent substrates 1 are concentrically distributed. The axial distance between the through holes 103 of the two flexible transparent substrates 1 on the same side of the vibrating diaphragm 2 is L, and L = 4 - 9 mm. Conductive silver paste 4 in contact with the conductive surface of the vibrating diaphragm 2 is provided in the through holes 103 to connect the conductive surface with the ITO surface 101, forming the positive and negative electrodes of the electroacoustic conversion device. The positive and negative electrodes are respectively located on both sides of the vibrating diaphragm 2.

[0057] A PDMS film 3 is provided on the vibrating diaphragm 2 between the two flexible transparent substrates 1 on the same side of the vibrating diaphragm 2 to prevent the vibrating diaphragm 2 from being damaged by the outside.

[0058] The preparation method of the electroacoustic conversion device is as follows:

[0059] P1. Fold the flexible transparent diaphragm in half so that the conductive surface is located on the outside of the folded structure to obtain the vibrating diaphragm 2.

[0060] P2. Take four flexible transparent substrates 1 and etch through holes 103 on the flexible transparent substrates 1. The diameter of the through holes 103 is 0.5 - 1 mm.

[0061] P3. Clamp the four flexible transparent substrates 1 symmetrically in pairs at both ends of the vibrating diaphragm 2, leaving a gap between the two flexible transparent substrates 1 on the same side; the non-ITO surface 102 of the flexible transparent substrate 1 is attached to the vibrating diaphragm 2, and the vibrating diaphragm 2 blocks the through holes 103 of the flexible transparent substrate 1. Print conductive silver paste 4 at the through holes 103 of the flexible transparent substrate 1 to form a positive electrode on one side of the vibrating diaphragm 2 and a negative electrode on the other side of the vibrating diaphragm 2.

[0062] P4. Spin-coat a PDMS (Chinese name: polydimethylsiloxane) solution on the surface of the vibrating diaphragm 2 at the gap between the two flexible transparent substrates 1, and dry it to form the PDMS film 3.

[0063] P5. Apply voltage across the positive and negative electrodes to polarize the PVDF film of the diaphragm 2, thereby obtaining the electroacoustic conversion device.

[0064] The present invention utilizes the principle that metal fluoride hydrolyzes into metal hydroxide in deionized water and then decomposes into metal oxide at a heating temperature below 150 °C to prepare an oxide protective layer. Since the metal fluoride solution and the silver nanowire suspension are mixed during the preparation process, the metal hydroxide will coat the surface of the silver nanowires. Therefore, the prepared oxide only exists on the surface of the silver nanowires. The flexible transparent film prepared by this method not only has low cost, but also greatly improves its optical properties and stability, and has broad application prospects in the field of electroacoustic conversion devices.

[0065] Since the thickness of the flexible transparent diaphragm prepared by the present invention is 5 - 20 μm and is sensitive to vibration, the thickness of the folded diaphragm 2 is only 10 - 40 μm. When a sound signal acts on the diaphragm 2, the vibration amplitude of the diaphragm 2 will change with the strength of the sound signal. Since the PVDF film has a piezoelectric effect, when the diaphragm 2 vibrates, the amount of charge accumulated on the positive and negative electrodes will also change, thereby changing the output current. The sound can be recorded by recording the output current. At the same time, when a current with an audio signal passes through the PVDF film, due to the change in the current signal, the amount of charge on the positive and negative electrodes of the PVDF film will change. At this time, the inverse piezoelectric effect of the PVDF film will cause the PVDF film to undergo mechanical deformation and generate vibration, thereby generating sound.

[0066] Example 1

[0067] A method for preparing a flexible transparent diaphragm, as Figure 1 shown, includes the following steps:

[0068] S1. Dissolve 0.04 g of chromium fluoride in 10 ml of deionized water, and then add 20 ml of absolute ethanol to obtain a chromium fluoride solution;

[0069] Add 0.5 ml of the chromium fluoride solution to 10 ml of a silver nanowire suspension with a concentration of 1 mg / ml, and let it stand at room temperature for 24 h to form a mixed solution of chromium fluoride and silver nanowires;

[0070] S2. Load the alumina target into a magnetron sputtering instrument, take a glass slide as the glass substrate, and prepare a 20 nm thick alumina film on the glass substrate through a radio frequency power supply;

[0071] S3. On the glass substrate deposited with an alumina thin film, spin-coat the mixed solution prepared in step S1 using a spin coater. The spin coater runs at a low speed (rotation speed of 500 r / min) for 5 s, then at a high speed (rotation speed of 1500 r / min) for 20 s, and repeat the spin-coating 4 times. After that, place the glass substrate in an oven at 90 °C for 30 min. By heating, chromium fluoride decomposes to form chromium oxide, and the chromium oxide coats the outer surface of the silver nanowires, obtaining an alumina / silver nanowire / chromium oxide composite film loaded on the glass substrate;

[0072] S4. Dissolve a certain amount of PVDF powder in N,N-dimethylacetamide solution, and make a ratio according to the mass ratio of 1:20. Stir well for 5 h at 60 °C using a stirrer until completely dissolved to prepare a PVDF solution;

[0073] On the surface of the composite film prepared in step S3, spin-coat a layer of PVDF solution using a spin coater. The spin coater runs at a low speed (rotation speed of 500 r / min) for 10 s, then at a high speed (rotation speed of 1500 r / min) for 30 s. After that, place the glass substrate in an oven at 90 °C for 30 min of drying treatment, and then naturally cool to room temperature, so as to embed the silver nanowires wrapped with chromium oxide into the PVDF film. The formed PVDF film has a thickness of 15 μm.

[0074] S5. Weigh 3 g of NaOH powder and dissolve it in 100 ml of deionized water. Place the glass substrate obtained in step S4 into the prepared NaOH solution, and heat the NaOH solution using a water bath to make its temperature 50 °C, so as to corrode the alumina thin film until the film naturally falls off and floats on the water surface. Then use the glass substrate to pick up this layer of film and wash it with deionized water to remove the residual NaOH solution and other impurities. After natural drying, an chromium oxide / silver nanowire / PVDF composite film, that is, a flexible transparent film sheet, can be obtained.

[0075] Example 2

[0076] A preparation method of a flexible transparent film sheet, comprising the following steps:

[0077] S1. Take 0.01 g of aluminum fluoride and dissolve it in 10 ml of deionized water, then add 20 ml of absolute ethanol to obtain an aluminum fluoride solution;

[0078] Add 0.5 ml of the aluminum fluoride solution to 10 ml of a silver nanowire suspension with a concentration of 2 mg / ml, and let it stand at room temperature for 24 h to form a mixed solution of aluminum fluoride and silver nanowires;

[0079] S2. Load the alumina target into a magnetron sputtering instrument, and deposit a 20-nm alumina thin film on a glass substrate through a radio frequency power supply.

[0080] S3. On the glass substrate deposited with the alumina thin film, spin-coat the mixed solution prepared in step S1 using a spin coater. The spin coater runs at a low speed (rotation speed of 500 r / min) for 5 s, then at a high speed (rotation speed of 1500 r / min) for 20 s, and repeat the spin coating 3 times. Then, place the glass substrate in an oven at 90 °C for 30 min. By heating, aluminum fluoride decomposes to form alumina, thereby obtaining an alumina / silver nanowire / alumina composite film loaded on the glass substrate.

[0081] S4. Dissolve a certain amount of PVDF powder in an N,N-dimethylacetamide solution, and mix them in a mass ratio of 1:20. Stir well at 60 °C for 5 h using a stirrer until completely dissolved to prepare a PVDF solution.

[0082] On the surface of the composite film prepared in step S3, spin-coat a layer of PVDF solution using a spin coater. The spin coater runs at a low speed (rotation speed of 1000 r / min) for 10 s, then at a high speed (rotation speed of 2000 r / min) for 30 s. Then, place the glass substrate in an oven at 90 °C for 30 min for drying treatment, and then naturally cool to room temperature, thereby embedding the silver nanowires into the PVDF film. The formed PVDF film has a thickness of 5 μm.

[0083] Step S5 is generally the same as S5 in Example 1 and will not be elaborated here.

[0084] Example 3

[0085] This example has the same overall steps as Example 1, except that in this example, chromium fluoride in Example 1 is replaced with nickel fluoride.

[0086] Example 4

[0087] A method for preparing an electroacoustic conversion device includes the following steps.

[0088] P1. As shown in Figure 2 , fold the flexible transparent diaphragm prepared in Example 1 so that the conductive surface is on the outside of the folded structure to obtain a vibrating diaphragm.

[0089] P2. Take four polyethylene terephthalate layers (i.e., PET layers) as flexible transparent substrates. One side of each flexible transparent substrate is an ITO surface coated with an ITO transparent conductive thin film, and the opposite side is its non-ITO surface. Etch through holes with a diameter of 0.5 mm on the flexible transparent substrates.

[0090] P3. Clamp two pairs of flexible transparent substrates symmetrically at both ends of the vibrating diaphragm. There is a spacing between the two flexible transparent substrates on the same side, and the axis spacing of the through-holes of the two flexible transparent substrates on the same side is 5 mm. The non-ITO surface of the flexible transparent substrate is attached to the conductive surface of the vibrating diaphragm. The vibrating diaphragm seals the through-holes of the flexible transparent substrate, and a layer of conductive silver paste is printed at the through-holes of the flexible transparent substrate to form a positive electrode on one side of the vibrating diaphragm and a negative electrode on the other side of the vibrating diaphragm;

[0091] P4. Spin-coat a PDMS solution on the conductive surface of the vibrating diaphragm at the spacing between the two flexible transparent substrates and dry it; the PDMS solution is a commercially available product.

[0092] P5. Apply a voltage through the positive electrode and the negative electrode to polarize the PVDF film of the vibrating diaphragm, and then the electroacoustic conversion device is obtained.

[0093] Figure 5 The figure shows the transmittance of the electroacoustic conversion device prepared in Example 4 within the visible light range of 380 nm - 780 nm. It can be seen that the average transmittance of the flexible transparent diaphragm within 380 nm - 780 nm is 80.8%.

[0094] Example 5

[0095] The overall steps of this example are the same as those of Example 4, except that:

[0096] In this example, the flexible transparent diaphragm prepared in Example 2 is folded in half so that the conductive surface is located on the outside of the folded structure to obtain a vibrating diaphragm. The flexible transparent substrate is a polyimide layer (i.e., PI layer) with an ITO transparent conductive film plated on one side.

[0097] After testing, the average transmittance of the electroacoustic conversion device prepared in this example within 380 nm - 780 nm is 81.5%.

[0098] Example 6

[0099] The overall steps of this example are the same as those of Example 4, except that:

[0100] In this example, the flexible transparent diaphragm prepared in Example 3 is folded in half so that the conductive surface is located on the outside of the folded structure to obtain a vibrating diaphragm;

[0101] The diameter of the through-holes etched on the flexible transparent substrate made of PET material is 1 mm, and the axis spacing of the through-holes of the flexible transparent substrates on the same side of the vibrating diaphragm is 10 mm.

[0102] After testing, the average transmittance of the electroacoustic conversion device prepared in this example within 380 nm - 780 nm is 76.2%.

[0103] Comparative Example 1

[0104] A layer of chromium oxide was prepared on the surface of silver nanowires by magnetron sputtering as a protective layer, and then a flexible transparent film was prepared. The electroacoustic conversion device was prepared in the same manner as in Example 4, so that the light transmittance of the electroacoustic conversion device prepared in Comparative Example 1 within 380 nm - 780 nm was close to that of the electroacoustic conversion device prepared in Example 4. Among them, the process of preparing the flexible transparent film in this Comparative Example 1 is as follows:

[0105] S1. Load the alumina target into the magnetron sputtering instrument, and prepare a 20 nm alumina thin film on the glass substrate through a radio frequency power supply;

[0106] S2. On the glass substrate deposited with the alumina thin film, spin-coat a silver nanowire suspension with a concentration of 1 mg / ml using a spin coater. The spin coater runs at a low speed (rotation speed of 500 r / min) for 5 s, and then at a high speed (rotation speed of 1500 r / min) for 20 s. Spin coating is repeated 4 times. Then, place the glass substrate in an oven at 90°C for 30 min to obtain an alumina / silver nanowire composite film loaded on the glass substrate;

[0107] S3. Dissolve a certain amount of PVDF powder in N,N-dimethylacetamide solution, and mix it in a mass ratio of 1:20. Stir well at 60°C for 5 h using a stirrer until completely dissolved to prepare a PVDF solution;

[0108] On the surface of the composite film prepared in step S2, spin-coat a layer of PVDF solution using a spin coater. The spin coater runs at a low speed (rotation speed of 500 r / min) for 10 s, and then at a high speed (rotation speed of 1500 r / min) for 30 s. Then, place the glass substrate in an oven at 90°C for 30 min for drying treatment, and then naturally cool it to room temperature, so as to embed the silver nanowires wrapped with chromium oxide into the PVDF film. The formed PVDF film has a thickness of 15 μm.

[0109] S5. Weigh 3 g of NaOH powder and dissolve it in 100 ml of deionized water. Place the glass substrate obtained in step S4 into the prepared NaOH solution, and heat the NaOH solution using a water bath to make its temperature 50°C, so as to corrode the alumina thin film until the film naturally falls off and floats on the water surface. Then, pick up this layer of film with the glass substrate and wash it with deionized water to remove the residual NaOH solution and other impurities. After natural drying, a silver nanowire / PVDF composite film can be obtained.

[0110] S6. Load the chromium oxide target into a magnetron sputtering instrument, and deposit a layer of chromium oxide on the surface of the silver nanowire / PVDF composite film by radio frequency sputtering. By adjusting the sputtering time, the light transmittance of the prepared chromium oxide / silver nanowire / PVDF flexible transparent film is made close to that of the flexible transparent film used in Example 4.

[0111] Result test:

[0112] 1) When the electroacoustic conversion device is used as a speaker, Figure 6 、 7 For the data of the output signals of Comparative Example 1 and Example 4, the input signal is the music "Direction of Light", and the selected playing time is about 5 s. Under the condition of the same light transmittance, the sheet resistance of the flexible transparent film in Example 4 is 14.7 Ω / sq., and the sheet resistance of the flexible transparent film in Comparative Example 1 is 16.3 Ω / sq. At this time, part of the charge will be consumed, so its amplitude is lower than that of the speaker prepared in Example 4.

[0113] 2) When the electroacoustic conversion device is used as a microphone, Figure 8 、 9 For the signal data recorded by Comparative Example 1 and Example 4, obviously, the signal amplitude recorded by the microphone prepared in Example 4 is higher than that recorded by the microphone prepared in Comparative Example 1.

[0114] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a flexible transparent film, characterized in that: The following steps are involved: S1, mixing the metal fluoride solution and the silver nanowire suspension to obtain a mixed solution for standby use; S2, preparing a sacrificial film on a substrate; S3, spin coating the mixed solution obtained in step S1 on the sacrificial film, heating to decompose the metal fluoride to form metal oxide, and obtaining a composite film supported on the substrate; S4, spin coating PVDF solution on the surface of the composite film and drying; S5, removing the sacrificial film to obtain the flexible transparent film.

2. The method for preparing a flexible transparent film according to claim 1, characterized in that: The metal fluoride is one of chromium fluoride, magnesium fluoride, nickel fluoride, zinc fluoride and aluminum fluoride.

3. The method for preparing a flexible transparent film according to claim 1, characterized in that: In step S3, the heating temperature is 50-150° C. and the heating time is 25-35 min.

4. The method for preparing a flexible transparent film according to claim 1, characterized in that: In step S1, the metal fluoride solution is prepared by dissolving the metal fluoride in deionized water and then adding anhydrous ethanol; the metal fluoride solution is added to the silver nanowire suspension and mixed, and then allowed to stand at room temperature for 12-24 hours to obtain a mixed solution.

5. The method for preparing a flexible transparent film according to claim 1, characterized in that: The sacrificial film is prepared on the substrate by physical deposition. The sacrificial film is an aluminum oxide film with a thickness of 10-30 nm. The substrate is made of glass.

6. The method for preparing a flexible transparent film according to claim 1, characterized in that: In step S5, the sacrificial film is removed by etching with alkaline solution.

7. A flexible transparent film obtained by the preparation method according to any one of claims 1 to 6.

8. An electroacoustic conversion device, comprising a vibrating diaphragm (2), characterized in that: The vibrating diaphragm (2) is formed by folding the flexible transparent diaphragm according to claim 7, the flexible transparent diaphragm comprising a PVDF film and metal oxide / silver nanowires embedded on the surface of the PVDF film, the side with the metal oxide / silver nanowires being a conductive surface, and the conductive surface being located on the outer side of the folded structure; The vibrating diaphragm (2) is clamped by two sets of flexible transparent substrates (1) arranged opposite to each other, each set of flexible transparent substrates (1) comprising two flexible transparent substrates having an ITO surface (101) and a non-ITO surface (102), and the non-ITO surface (102) of the flexible transparent substrate (1) is in contact with the conductive surface of the vibrating diaphragm (2); A through hole (103) is provided on the flexible transparent substrate (1), and a conductive silver paste (4) in contact with the conductive surface is provided in the through hole (103); A PDMS film (3) is provided on the vibration membrane (2) between two flexible transparent substrates (1) located on the same side.

9. A method for preparing the electroacoustic conversion device as claimed in claim 8, characterized in that: The following steps are involved: P1. Fold the flexible transparent film in half so that the conductive surface is located on the outside of the folded structure to obtain a vibrating film (2); P2, taking four flexible transparent substrates (1), and etching through holes (103) on the flexible transparent substrates (1); P3. Four flexible transparent substrates (1) are symmetrically clamped at two ends of the vibration diaphragm (2), with a spacing between two flexible transparent substrates (1) located on the same side; the non-ITO surface (102) of the flexible transparent substrate (1) is bonded to the vibration diaphragm (2), the vibration diaphragm (2) blocks the through hole (103) of the flexible transparent substrate (1), and the through hole (103) of the flexible transparent substrate (1) is filled with conductive silver paste (4) to form a positive electrode located on one side of the vibration diaphragm (2) and a negative electrode located on the other side of the vibration diaphragm (2); P4, spin coating a PDMS solution on the vibration membrane (2) located at the interval between the two flexible transparent substrates (1), and drying; P5. Voltage is applied via the positive and negative electrodes to polarize the PVDF film of the vibration diaphragm (2), thereby obtaining the electroacoustic conversion device.

10. The method for preparing the electroacoustic conversion device according to claim 9, characterized in that: The flexible transparent substrate (1) is a polyethylene terephthalate layer or a polyimide layer with ITO coated on one side.

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