SUPERHYDROPHOBIC MODIFIED FILM AND MODIFICATION METHOD, AND TRIBOELECTRIC NANOGENERATOR (TENG) COMPOSED THEREOF AND PREPARATION METHOD

Abstract

A superhydrophobic modified film and modification method, and a triboelectric nanogenerator (TENG) composed thereof and a preparation method are disclosed. A polyethylene (PE) film is etched and deposited with an inductively coupled plasma (ICP) etcher in sequence. A nano-textured structure is formed on an upper surface of the PE film and a fluorocarbon layer is further deposited for modification. An upper electrode of the film is constructed by sticking a piece of ultra-thin copper tape on a superhydrophobic surface of the superhydrophobic modified film, and a lower electrode of the film is constructed by spin-coating a conductive polymer on a lower surface of the film after O.sub.2 plasma treatment. Thus, the TENG with high output and a double-electrode working mode based on the superhydrophobic modified greenhouse film is constructed. According to the modification method, the nano-textured structure is constructed on the surface of the film.

Claims

1. A superhydrophobic modification method for a greenhouse film, comprising: 1) placing a polyethylene (PE) film in an inductively coupled plasma (ICP) etcher; 2) etching an upper surface of the PE film for a first predetermined time by the ICP etcher, wherein a nano-textured structure is formed on the upper surface of the PE film; and 3) depositing the upper surface of the PE film for a second predetermined time by the ICP etcher, wherein a fluorocarbon layer is deposited on the nano-textured structure, to complete modification and take out the PE film.

2. The superhydrophobic modification method according to claim 1, wherein in step 2), the upper surface of the PE film is etched at a set ICP power of 100 W and a radio frequency (RF) power of 50 W under the presence of O.sub.2 and CHF.sub.3 at an air pressure of 30 mTorr for 10 min.

3. The superhydrophobic modification method according to claim 1, wherein in step 2), O.sub.2 and CHF.sub.3 have a flow ratio of 1:3.

4. The superhydrophobic modification method according to claim 1, wherein in step 3), the upper surface of the PE film is deposited at a set ICP power of 100 W and an RF power of 50 W under the presence of octafluorocyclobutane (C.sub.4F.sub.8) at an air pressure of 30 mTorr for 30 s.

5. The superhydrophobic modification method according to claim 1, wherein in step 3), a flow rate of the C.sub.4F.sub.8 is set as 50 standard cubic centimeter per minute (sccm).

6. A superhydrophobic modified film, modified by the method according to claims 1.

7. A greenhouse film-based triboelectric nanogenerator (TENG), comprising the superhydrophobic modified film, a lower electrode, and an upper electrode, wherein the lower electrode is arranged on a lower surface of the superhydrophobic modified film, the upper electrode is arranged on an upper surface of the superhydrophobic modified film, and the superhydrophobic modified film is the superhydrophobic modified film according to claim 6.

8. The greenhouse film-based TENG according to claim 7, wherein the greenhouse film-based TENG is for a raindrop energy collection, the greenhouse film-based TENG is constructed on the greenhouse film, and during rainfall, raindrops contact the upper electrode on the upper surface of the superhydrophobic modified film to generate a continuous electrical output through a process of contact electrification and electrostatic induction.

9. A using method of a greenhouse film-based TENG, wherein a superhydrophobic modified film is configured to collect raindrop energy.

10. A preparation method for the greenhouse film-based TENG according to claim 7, comprising: preparing the superhydrophobic modified film with superhydrophobic property on the upper surface of the superhydrophobic modified film, 5 ii) preparing the lower electrode; iii) preparing the upper electrode; and iiii) preparing the greenhouse film-based TENG.

11. The preparation method according to claim 10, wherein step comprises: adding a 15% v/v dimethyl sulfoxide (DMSO) solution to a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) solution, and stirring vigorously at a room temperature for 6 h to obtain a conductive polymer solution; cleaning the lower surface of the superhydrophobic modified film, and conducting an O.sub.2 plasma treatment for 5 min; spin-coating the conductive polymer solution on the lower surface of the superhydrophobic modified film after the O.sub.2 plasma treatment through a square mold; and drying at the room temperature to prepare the lower electrode on the lower surface of the superhydrophobic modified film.

12. The preparation method according to claim 10, wherein step comprises: sticking a piece of thin conductive copper tape on the upper surface of the superhydrophobic modified film at a center line of the lower electrode, to prepare the upper electrode on the upper surface of the superhydrophobic modified film.

13. The preparation method according to claim 10, wherein step comprises: connecting the upper electrode and the lower electrode with two pieces of copper tape, respectively to lead out an output electrical signal.

14. The superhydrophobic modified film according to claim 6, wherein in step 2) of the superhydrophobic modification method, the upper surface of the PE film is etched at a set ICP power of 100 W and a radio frequency (RF) power of 50 W under the presence of O.sub.2 and CHF.sub.3 at an air pressure of 30 mTorr for 10 min.

15. The superhydrophobic modified film according to claim 6, wherein in step 2) of the superhydrophobic modification method, O.sub.2 and CHF.sub.3 have a flow ratio of 1:3.

16. The superhydrophobic modified film according to claim 6, wherein in step 3) of the superhydrophobic modification method, the upper surface of the PE film is deposited at a set ICP power of 100 W and an RF power of 50 W under the presence of C.sub.4F.sub.8 at an air pressure of 30 mTorr for 30 s.

17. The superhydrophobic modified film according to claim 6, wherein in step 3) of the superhydrophobic modification method, a flow rate of the C.sub.4F.sub.8 is set as 50 sccm.

18. The preparation method accordting to claim 10, wherein in the greenhouse film-based TENG, the greenhouse film-based TENG is for a raindrop energy collection, the greenhouse film-based TENG is constructed on the greenhouse film, and during rainfall, raindrops contact the upper electrode on the upper surface of the superhydrophobic modified film to generate a continuous electrical output through a process of contact electrification and electrostatic induction.

19. The preparation method accordting to claim 10, wherein in step 2) of the superhydrophobic modification method, the upper surface of the PE film is etched at a set ICP power of 100 W and a radio frequency (RF) power of 50 W under the presence of O.sub.2 and CHF.sub.3 at an air pressure of 30 mTorr for 10 min.

20. The preparation method accordting to claim 10, wherein in step 2) of the superhydrophobic modification method, O.sub.2 and CHF.sub.3 have a flow ratio of 1:3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIGS. 1A-1F show an SEM characterization of a film after ICP treatment under different RF powers in the present disclosure.

[0062] FIGS. 2A-2F show an EDS characterization of the film after ICP treatment under different RF powers in the present disclosure.

[0063] FIGS. 3A-3F show water static contact angles of the film after ICP treatment under different RF powers in the present disclosure.

[0064] FIG. 4 is a characterization diagram of the self-cleaning performance of a superhydrophobic modified film in the present disclosure.

[0065] FIG. 5 is a schematic diagram of a working mechanism of a TENG in the present disclosure.

[0066] FIGS. 6A-6B show the output performance results of the TENG for water droplets falling at different heights in the present disclosure.

[0067] FIGS. 7A-7B show the output performance results of the TENG for water droplets falling at different frequencies in the present disclosure.

[0068] FIGS. 8A-8B show the output performance results of the TENG for water droplets of different compositions in the present disclosure.

[0069] FIG. 9 is an actual energy supply application diagram of the TENG in the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0070] The present disclosure is described in more detail hereinafter with reference to the accompanying drawings and specific implementations.

[0071] The superhydrophobic modification treatment step of the greenhouse film of the present disclosure involves constructing a nano-textured structure on the surface of the film and covering the surface of the film with a layer of substances with low surface energy through a two-step treatment of ICP etching to endow the film with excellent superhydrophobic and self-cleaning properties.

[0072] Examples of the present disclosure are as follows:

Example 1

[0073] 1) A PE film was placed in an ICP etcher.

[0074] 2) Under conditions of a set ICP power of 100 W and an RF power of 50 W, gas selection of O.sub.2 and CHF.sub.3 (flow rates of O.sub.2 and CHF.sub.3 were set as 15 and 45 sccm respectively), and air pressure of 30 mTorr, an upper surface of the PE film was etched for 10 min by the ICP etcher, such that a nano-textured structure was formed on the upper surface of the PE film to obtain a nanostructured PE film.

[0075] 3) Under conditions of a set ICP power of 100 W and an RF power of 50 W, gas selection of only C.sub.4F.sub.8 (a flow rate of the C.sub.4F.sub.8 was set as 50 sccm), and air pressure of 30 mTorr, the upper surface of the PE film was deposited for 30 s by the ICP etcher, such that a fluorocarbon layer was deposited on the the nano-textured structure of the PE film to complete modification and take out the film.

[0076] In the specific implementation, five RF powers of 0, 25, 50, 75, and 100 W were used for testing.

[0077] After the above two-step treatment, the UT films and the films subjected to five ICP (ICP-1/2/3/4/5) treatments were characterized by SEM, and the results are shown in FIGS. 1A-1F. For the UT film, it could be seen that some microcracks were randomly distributed on the surface, and these microcracks were caused by the transportation of the film after purchase and cleaning of the film.

[0078] For the ICP-treated film, it could be seen that the surface was rough, forming nano-bumps, and the distribution was relatively uniform. In addition, with the increase of RF power, the aspect ratio of the nano-bumps increased, and the nano-bumps evolved into nanowires, forming obvious nano-textures. The reason for such a morphological structure lies in different crystalline regions of the selected PE plastic film. The PE was a semi-crystalline material composed of crystalline regions and amorphous regions. However, the etching speed of plasma in different crystalline regions was different. The amorphous region was preferentially dissociated due to the low crystallinity, and the etching was serious, while in the crystalline region, due to the high crystallinity and low etching degree, nano-textures were formed on the surface of PE.

[0079] As the RF power was increased, the surface roughness also increased and the etching became more uniform. When the RF power exceeded 50 W, the nanowires would become entangled and aggregated, maintaining the nanowire array structure perpendicular to the base surface. Therefore, from SEM characterization, it could be seen that the ICP treatment of the film could form a nano-scale rough structure on the surface.

[0080] FIGS. 2A-2F show an EDS characterization of 6 films. The EDS characterization technology is used to measure the elemental composition of the material. It can be seen from the figure that compared with the UT films, all the ICP-treated films contain fluorine (F), while the UT films only contain oxygen (O) and carbon (C), which are the basic constituent elements of the PE material. Moreover, with the increase of RF power, the C element shows a trend of first decreasing and then increasing, while the F element first increases and then decreases. The C/F ratio is the smallest at ICP-3, indicating that when the RF power is at 50 W, the F element content on the surface of the film is the most abundant, that is, the fluorocarbon compound with low surface energy covered on the surface is the most abundant.

[0081] FIGS. 3A-3F show water static contact angles of the films with six different treatment processes. The water static contact angles being greater than 150° indicates that the material has superhydrophobic property. It can be seen from the figure that the contact angle of the original UT film is only about 95°, which means that the hydrophobicity of the original film is poor, while the film treated by ICP has a higher water static contact angle. The contact angles of ICP-3 and ICP-4 both exceed 150°, and the contact angle of ICP-3 is the largest, reaching about 158°, indicating that the film under this treatment process (RF power of 50 W) has the optimal superhydrophobic property, which corresponds to the above SEM and EDS characterizations. When the RF power is 50 W, the surface of the film has an excellent nano-textured structure, and the surface contains the most abundant fluorocarbon compound with low surface energy, so the superhydrophobic property of the film at this treatment is the best.

[0082] FIG. 4 shows a characterization of self-cleaning performance of the film. After the above three steps of verification, it is found that when the ICP power is 100 W and the RF power is 50 W, the film after two-step ICP etching has the optimal superhydrophobic property. The self-cleaning ability of the film is further verified after the film is processed under this process. The surface of the film is covered with dry soil, dead leaves, and hay powder. Because in actual use, soil and grass clippings are the easiest to adhere to the surface of greenhouse film, thereby posing a serious threat to the light transmittance of the film and greatly reducing the light transmittance of the film, which is not conducive to the growth of crops in the greenhouse. Therefore, after these powders are distributed on the surface of the film, the surface is washed with water droplets. It can be seen from the figure that the film after ICP treatment has excellent self-cleaning ability, and these powders are easily washed away. This also proves that in the actual use of the superhydrophobic modified film in the future, even if a lot of dust is adsorbed on the surface, the surface can be easily washed with only a small amount of water, which not only prolongs the service life of the film, but also is helpful for the utilization of solar energy by plants in the greenhouse.

Example 2

[0083] 1) Preparation of a modified film (superhydrophobic film) with superhydrophobic property on an upper surface

[0084] 1.1) A PE film was placed in an ICP etcher.

[0085] 1.2) Under conditions of a set ICP power of 100 W and an RF power of 50 W, gas selection of O.sub.2 and CHF.sub.3 (flow rates of O.sub.2 and CHF.sub.3 were set as 15 and 45 sccm respectively), and air pressure of 30 mTorr, an upper surface of the PE film was etched for 10 min by the ICP etcher, such that a nano-textured structure was formed on the upper surface of the PE film to obtain a nanostructured PE film.

[0086] 1.3) Under conditions of a set ICP power of 100 W and an RF power of 50 W, gas selection of C.sub.4F.sub.8 (a flow rate of the C.sub.4F.sub.8 was set as 50 sccm), and air pressure of 30 mTorr, the upper surface of the PE film was deposited for 30 s by the ICP etcher, such that a fluorocarbon layer was deposited on the nano-textured structure of the PE film to complete modification and take out the film.

[0087] 2) Preparation of a lower electrode

[0088] 2.1) A 15% v/v DMSO solution was added to a PEDOT:PSS solution, and stirred vigorously at room temperature for 6 h to obtain a conductive polymer solution.

[0089] 2.2) The lower surface of the modified film was cleaned, and O.sub.2 plasma treatment was conducted for 5 min.

[0090] 2.3) 20 .Math.L of the conductive polymer solution was spin coated on the lower surface of the modified film after the O.sub.2 plasma treatment through a square mold with a horizontal section of 3*3 cm.

[0091] 2.4) Drying was conducted at room temperature to prepare the lower electrode on the lower surface of the modified film.

[0092] 3) Preparation of an upper electrode

[0093] A piece of thin conductive copper tape (with a width of about 1 mm) was stuck on the upper surface of the modified film at the center line of the lower electrode to prepare the upper electrode.

[0094] 4) Preparation of a TENG: The upper and lower electrodes were connected with two pieces of copper tape, respectively to lead out an output electrical signal.

[0095] The specific implementation measured an output voltage: The copper tape led out from the upper and lower electrodes was connected to positive and negative electrodes of an oscilloscope to measure the output voltage.

[0096] In the specific implementation, a dripping device and a flow regulator were assembled to simulate the rainfall scene and the raindrop energy collection scene. The device could adjust the falling height (cm) and the frequency (Hz) of the water droplets.

[0097] In order to measure the output performance of water droplets falling at different heights, the heights of the water outlet from the film were set to 5, 25, 50, 75, and 100 cm respectively, the falling frequency of water droplets was controlled to 2 Hz, and the output voltage was displayed by an oscilloscope. It could be seen from FIGS. 6A-6B that at five different falling heights, the output performance of the TENG based on the superhydrophobic film was generally higher than that of the TENG based on the UT film, and the output voltage was about 3 times that of the UT film. With the increase of the falling height of water droplets, the output voltage of the TENGs based on the two films gradually increased, especially when the height was 100 cm, the voltage was the largest. The water droplets falling from a higher altitude fell faster than falling from a lower altitude. When the water droplets hit the upper surface of the film, they were quickly divided into several small droplets. At this time, for the surface of the superhydrophobic film, these droplets could slide off quickly. For the surface of the UT film, its hydrophobicity was poor, and the droplets could not slide off quickly, but a water layer was formed on the surface, which was not conducive to the transfer of charges. Because the primary electrical output was generated due to the process of the previous drop of water flowing away and the next drop being connected. If the hydrophobicity of the film was poor, the water droplets could not flow easily, which inevitably resulted in a lower voltage output. In summary, the film after superhydrophobic treatment was used as a triboelectric layer to construct a TENG, which was more efficient for raindrop energy collection. In addition, the output was still very excellent for water droplets falling from a high altitude, which was very meaningful for raindrop energy collection during actual rainfall.

[0098] In order to measure the output performance of water droplets falling at different frequencies and facilitate experimental operation, the heights of the water outlet from the film were set to 15 cm, the falling frequency was controlled to 0.5, 1, 2, 4, and 6 Hz, and the output voltage was displayed by an oscilloscope. It can be seen from FIGS. 7A-7B that the output performance of the TENG based on the superhydrophobic film was also higher than that of the TENG based on the UT film under five different falling frequencies, and the output voltage was also about 3 times that of the UT film, which was consistent with the results of the above-mentioned investigation. In addition, with the increase of the falling frequency of water droplets, the output voltage of the TENGs based on the two films gradually increased. The reason for this difference was closely related to the hydrophobicity of the film. For the UT film, the hydrophobicity was poor, the water droplets would stay on the surface, and when the falling frequency of water droplets further increased, a water flow was formed directly on the surface. Therefore, a higher falling frequency was less favorable for the charge transfer. For the superhydrophobic film, no matter how much the falling frequency was increased, the water droplets could slide off quickly, and the liquid-solid contact interface could be refreshed stably without forming a water layer. Therefore, the increase in the falling frequency of droplets meant that the surface charges were rapidly injected to the saturation state, resulting in greater charge transfer and higher output. Therefore, the above studies showed that the TENG with superhydrophobic surface had good output performance for raindrops from the sky regardless of the amount of rainfall.

[0099] Considering the complex composition of actual rainwater, the practical application performance of the constructed TENG is further explored in different solutions. Five different solutions were selected, including deionized water, tap water, collected rainwater, 0.01 M sodium chloride solution, 0.01 M sulfuric acid solution, and 0.01 M ammonium sulfate solution. The falling height of the water droplets was set to 15 cm, and the falling frequency was set to 2 Hz. The reason for selecting these solutions was that the main component of rainwater is water, and the rainwater also contained a small amount of sulfur dioxide, nitrogen dioxide, impurities and floating dust, while acid rain with a pH less than 5.6 contained more sulfate ions, ammonium ions, chloride ions, and sodium ions. Considering these conditions, these solutions were selected for exploration. It can be seen from FIGS. 8A-8B that the output voltage of deionized water was the highest, followed by rainwater and tap water; sodium chloride, sulfuric acid, and ammonium sulfate solutions had lower output. In addition, the output of the TENG constructed with the film subjected to superhydrophobic treatment was also about 3 times that of the TENG constructed with the UT film. There might be two reasons for the difference in output voltage in different solutions, one was that the initial conductivity of different liquids was different, and the other was that the induced charges generated by the liquid-solid interaction were different. Compared to other liquids, deionized water had the highest output performance because it did not contain any impurities and ions, so there was less interference. The impurities and ions in the solution would interfere with the contact electrification between the liquid and the surface of the film, resulting in charge screening, which in turn reduces the output performance. Therefore, these liquids had limited charge retention capacity, which would undoubtedly reduce the charge density of the surface of the film. The output voltage of the collected rainwater was also higher than that of other liquids, possibly due to the fact that it had previously carried positive charges as fell from the air. The raindrops were charged in contact with air or floating particles, creating a triboelectric charge. In summary, the TENG constructed with the superhydrophobic film had excellent output for water droplets in different solutions, so it is very promising in practical applications.

[0100] Finally, the TENG based on the film subjected to superhydrophobic treatment was placed on an acrylic plate and tilted about 45° to simulate the top of the greenhouse. The dripping height was controlled to 15 cm, the frequency was 2 Hz, and the dripping liquid was collected rainwater. As shown in FIG. 9, the TENG could charge the capacitor by collecting raindrop energy, and when charged for a period of time, the capacitor could supply power to a timer without a battery. If the timer could successfully display the value, it meant that the TENG has practical use value. After raindrop energy was collected for about 10 min, the timer could be successfully powered by a 10 .Math.F capacitor to work normally for about 15 s. Therefore, this proved that the TENG has good practical application value and could also successfully supply power to small electronic devices like timers or common temperature and humidity sensors in greenhouses.