Glycyrrhetinic acid bio-based anionic surfactant as well as preparation and application thereof

Abstract

The invention relates to a glycyrrhetinic acid bio-based anionic surfactant as well as preparation and application thereof. The glycyrrhetinic acid bio-based anionic surfactant is obtained by taking a natural pentacyclic triterpene compound glycyrrhetinic acid as a raw material through simple chemical modification. The critical micelle concentration of the surfactant at room temperature is 1 * 10 <-4 > mol / L, and the surface tension can be reduced from 71.8 mN / m to 38.8 mN / m. In addition, the surfactant has a good regulation and control effect on the bounce behavior of liquid drops on the hydrophobic solid surface (a hydrophobic PTFE film, green bristlegrass, ixeris denticulata, chenopodium album, corn, wheat and other leaves). When the concentration of the glycyrrhetinic acid bio-based anionic surfactant is higher than 1 * 10 <-4 > mol / L, the bounce behavior of liquid drops on the surface of a hydrophobic solid can be obviously inhibited, splashing, fragmentation and springback of the liquid drops are slowed down, and good spreading is achieved. The glycyrrhetinic acid bio-based anionic surfactant has good biocompatibility, environmental friendliness and excellent interface rheological property, can be used for preparing emulsions, and has a great application prospect in the fields of agriculture, food, cosmetics and the like.

Description

Technical Field

[0001] The invention relates to the technical field of regulating the bouncing behavior of a droplet on a solid surface, and in particular to a glycyrrhetinic acid bio-based anionic surfactant and a preparation method and application thereof. Background Art

[0002] Bio-based surfactants have become the best choice to replace petroleum-based surfactants due to their wide sources, renewable and environmentally friendly advantages, and have attracted the attention of more and more researchers. The structural diversity of these green surfactants derived from nature determines their functional diversity, making them exhibit surface / interface properties and self-assembly behaviors different from traditional small molecule surfactants. They have good dispersing, emulsifying, thickening, flocculating and unique physiological properties, and have great application advantages in many fields such as petroleum industry, agriculture, food, medicine, and daily chemical products.

[0003] In the process of using pesticides, surfactants are often used as important formulation components to improve the stability, efficacy and service life of pesticides, while also reducing the dosage. In the process of spatial delivery of pesticides, the addition of surfactants can effectively inhibit the rolling and loss of droplets on the target surface, increase its spreading and deposition, improve the utilization efficiency of pesticides, and reduce the threat to the ecological environment. However, the surfactants currently used in pesticide formulations are mostly petroleum-based surfactants derived from chemical products and their derivatives. They are not easy to degrade in the environment, are easy to be toxic to non-target organisms and even crops, and remain in the soil, water and atmospheric environment after migration and transformation. The potential risks to the environment, ecology and human life cannot be ignored. Therefore, designing and synthesizing environmentally friendly bio-based surfactants and applying them in the field of pesticides can not only solve the environmental problems caused by existing surfactants, but also conform to the sustainable development concepts of agriculture such as green, ecological and safe.

[0004] Glycyrrhetinic acid (GA) is a pentacyclic triterpene compound widely distributed in nature. It is also one of the main active ingredients of licorice. It has a wide range of pharmacological activities. Its derivatives have good anti-inflammatory, analgesic, anti-tumor, bactericidal and other activities and are widely used in clinical practice. From a structural point of view, glycyrrhetinic acid has an oleanane-type mother core skeleton, which gives it a unique rigid structure and often exhibits distinctive assembly characteristics; at the same time, glycyrrhetinic acid molecules contain hydroxyl and carboxyl functional groups, which are easy to modify through simple chemical reactions. In addition, glycyrrhetinic acid is usually extracted and separated from plants, with abundant content and wide sources, and has been widely reported to have good biocompatibility and easy degradability.

[0005] In summary, using natural small molecule glycyrrhetinic acid as the hydrophobic backbone, the hydroxyl group at the 3-position was first hydrophobically modified, and then a hydrophilic sulfonate fragment was introduced at the 28-position to prepare a novel glycyrrhetinic acid-based anionic surfactant. The inhibitory effect of this surfactant on the bouncing behavior of droplets on hydrophobic solid surfaces was systematically studied. The present invention, "A Glycyrrhetinic Acid-Based Anionic Surfactant and Its Preparation and Application", aims to synthesize a novel bio-based surfactant and apply it to the inhibition of the bouncing behavior of droplets on hydrophobic solid surfaces (including PTFE, Setaria viridis, Ixeris denticulata, etc.). The proposal of this invention can better achieve the effective retention of liquid medicine on the leaf surface of crops, and develop new theories and technologies for improving the utilization rate of pesticides. Summary of the Invention

[0006] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide a glycyrrhetinic acid-based anionic surfactant. The synthesis method of this surfactant is simple, and the post-treatment is easy. It can inhibit the bouncing and retraction process of droplets on hydrophobic solid surfaces to varying degrees. Applying this surfactant to the preparation of emulsions has great application prospects in the fields of agriculture, food, cosmetics, etc., and can well solve the environmental problems brought by existing petroleum-based surfactants, contributing to sustainable development.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A glycyrrhetinic acid-based anionic surfactant, characterized in that its structural formula is as follows:

[0009]

[0010] Another object of the present invention is to provide a preparation method of a glycyrrhetinic acid-based anionic surfactant.

[0011] To achieve the above object, the technical solution adopted by the present invention is:

[0012] A preparation method of a glycyrrhetinic acid-based anionic surfactant, characterized by comprising the following steps:

[0013] Step 1, dissolve glycyrrhetinic acid and acetic anhydride in pyridine, add the catalyst 4-dimethylaminopyridine and react to obtain GA-1, that is, 3-acetylglycyrrhetinic acid, and the structural formula of the GA-1 is:

[0014]

[0015] Step 2, GA-1 and 2-aminoethanesulfonic acid are dissolved in a mixed solvent of dichloromethane and N,N-dimethylformamide, and a catalyst 4-dimethylaminopyridine and a condensing agent 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride are added to react to obtain a compound GA-2, wherein the structural formula of the compound GA-2 is:

[0016]

[0017] Step 3, reacting GA-2 with a sodium carbonate solution to obtain a glycyrrhetinic acid bio-based anionic surfactant;

[0018] On the basis of the above scheme,

[0019] In the step 1, the molar ratio of glycyrrhetinic acid to acetic anhydride is 1:1-3, the molar ratio of glycyrrhetinic acid to catalyst 4-dimethylaminopyridine is 50:1-10, the reaction temperature is 50°C, and the reaction time is 6-8h;

[0020] In the step 2, the molar ratio of GA-1 to 2-aminoethanesulfonic acid is 1:1-1.5, the molar ratio of GA-1 to the catalyst 4-dimethylaminopyridine is 1:0.2-1; the molar ratio of GA-1 to the condensing agent 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:1-1.5, the molar ratio of dichloromethane to N,N-dimethylformamide in the mixed solvent is 4:1-3, the reaction temperature is 50°C, and the reaction time is 10-18h;

[0021] In step 3, the molar ratio of compound GA-2 to sodium carbonate is 1:1-1.2, the solvent in the sodium carbonate solution is water, the solvent of GA-2 is methanol, the volume ratio of the above methanol to water is 1:0.2-1, the reaction temperature is room temperature, and the reaction time is 6-10 hours.

[0022] Another object of the present invention is to provide application of glycyrrhetinic acid bio-based anionic surfactant.

[0023] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0024] Application of glycyrrhizic acid bio-based anionic surfactant in regulating the bouncing behavior of droplets on hydrophobic solid surfaces.

[0025] Based on the above scheme, the concentration of anionic surfactant in the droplet is 1×10 -4 mol / L、5×10 -4 mol / L or 1×10 -3 mol / L.

[0026] On the basis of the above scheme, the droplets are generated by a single droplet generator; the falling height of the droplets is 10 to 60 cm.

[0027] Based on the above solution, the hydrophobic solid surface includes: polytetrafluoroethylene and hydrophobic plant leaves.

[0028] On the basis of the above scheme, the hydrophobic plant leaves include: Setaria leaves, Sophora flavescens leaves, Chenopodium album leaves, corn leaves, and wheat leaves.

[0029] The synthesized glycyrrhetinic acid bio-based anionic surfactant was dissolved in water and 1×10 -7 mol / L、5×10 -7 mol / L、1×10 -6 mol / L、5×10 -6 mol / L、1×10 -5 mol / L、5×10 -5 mol / L、1×10 -4 mol / L、5×10 - 4 mol / L、1×10 -3 mol / L concentration of the solution. The surface tension of the above series of solutions was first measured by the hanging plate method, and then a high-speed camera was used to capture and track the impact and bounce behavior of the droplets on different hydrophobic solid surfaces.

[0030] The raw material of this surfactant is the natural product glycyrrhetinic acid, which is in line with the concept of green and sustainable development. With the glycyrrhetinic acid skeleton as the hydrophobic segment and the introduction of the hydrophilic sulfonate group, an environmentally friendly bio-based surfactant is constructed. This surfactant has a good effect of reducing the surface tension of the liquid and self-assembles in the solution to form spherical micelles, which can effectively inhibit the bouncing behavior of the liquid on the solid surface and increase the deposition.

[0031] The glycyrrhetinic acid bio-based anionic surfactant and its preparation and application described in the present invention have the following beneficial effects:

[0032] (1) The present invention establishes a method for synthesizing a glycyrrhetinic acid bio-based anionic surfactant by screening reaction conditions. It is found that the hydroxyl group at position 3 is first reacted with acetic anhydride, the carboxyl group at position 28 is then reacted with 2-aminoethanesulfonic acid, and the sulfonic acid is finally neutralized, so that a glycyrrhetinic acid sulfonate compound with high purity and high yield can be easily obtained. The method is short in steps, easy to operate, and simple in post-processing.

[0033] (2) The glycyrrhetinic acid sulfonate surfactant synthesized in the present invention has good surface activity. With the increase of concentration, the surface tension of the solution decreases from 71.8 mN / m to 38.8 mN / m, and the critical micelle concentration is 1×10-4 mol / L, and self-assembled to form spherical micelles.

[0034] (3) The addition of the glycyrrhetinic acid sulfonate surfactant synthesized by the present invention can inhibit the bouncing and retracting process of droplets on hydrophobic solid surfaces to varying degrees. It has a good inhibitory effect on hydrophobic solid surfaces such as PTFE, Setaria viridis, Solanum oleiferum, Quinoa, corn, and wheat, achieving effective regulation of the bouncing and wetting behavior of droplets on solid surfaces.

[0035] (4) The glycyrrhizic acid bio-based anionic surfactant in the present invention has good biocompatibility, environmental friendliness, and excellent interfacial rheological properties, can be used for the preparation of emulsions, and has great application prospects in the fields of agriculture, food, cosmetics, etc. It can well solve the environmental problems caused by existing petroleum-based surfactants and promote sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention has the following accompanying drawings:

[0037] Figure 1 It is the molecular structure of glycyrrhetinic acid bio-based anionic surfactant.

[0038] Figure 2 This is a synthetic route for glycyrrhetinic acid bio-based anionic surfactant.

[0039] Figure 3 This is the H-NMR spectrum of glycyrrhetinic acid bio-based anionic surfactant.

[0040] Figure 4 This is a graph showing the relationship between the surface tension γ of glycyrrhizic acid bio-based anionic surfactant and the concentration C.

[0041] Figure 5 Schematic diagram of the self-assembly of glycyrrhizic acid bio-based anionic surfactant in water to form an assembly.

[0042] Figure 6 Glycyrrhetinic acid bio-based anionic surfactant (concentration 5×10 -4 mol / L) bouncing behavior at different heights on PTFE.

[0043] Figure 7 The bouncing behavior of glycyrrhetinic acid bio-based anionic surfactant with different concentrations on PTFE at a height of 30 cm. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the examples, but the examples do not limit the scope of the present invention. The various materials described in the present invention can be purchased through public commercial channels.

[0045] Example 1: Synthesis of glycyrrhetinic acid bio-based anionic surfactant

[0046] The synthetic route of glycyrrhetinic acid bio-based anionic surfactant is as follows Figure 2 As shown:

[0047] (1) Synthesis of 3-acetyl glycyrrhetinic acid (GA-1): Glycyrrhetinic acid (GA, 10.02 g, 21.29 mmol) was dissolved in 15 mL of pyridine, and 4-dimethylaminopyridine (52 mg, 0.43 mmol) and acetic anhydride (4.02 mL, 42.58 mmol) were added in sequence and stirred, and the mixture was reacted at 50°C for 8 h. Stirring was stopped, and the reaction solution was poured into 500 mL of water, and a large amount of flocculent was precipitated by standing. A white solid was obtained by suction filtration and dried with an infrared lamp. The crude product was separated by column chromatography (eluent: petroleum ether / ethyl acetate = 10:1, v / v) to obtain 10.36 g of white solid GA-1, with a yield of 95%.

[0048] (2) Synthesis of GA-2: GA-1 (1.89 g, 3.69 mmol), DMAP (450 mg, 3.69 mmol), EDCI (709 mg, 3.69 mmol) were dissolved in anhydrous dichloromethane (20 mL) and DMF (5 mL), stirred for 30 min, then 2-aminoethanesulfonic acid (463 mg, 3.69 mmol) was added, and the temperature was raised to 50°C and reacted for 12 h. Stirring was stopped, and the solvent was removed by rotary evaporation. The solid residue was washed with dilute hydrochloric acid (1 mol / L) 3 times and then washed with water 3 times. After each washing, centrifugation was performed to remove the supernatant, and finally a yellow-brown solid was separated. The crude product was separated by column chromatography (eluent: dichloromethane / methanol = 10:1 to 5:1, v / v) to obtain 1.80 g of white solid GA-2 with a yield of 81%.

[0049] (3) Synthesis of glycyrrhetinic acid sulfonate: GA-2 (1.00 g, 1.65 mmol) was dissolved in methanol (15 mL), and then an aqueous solution (5 mL) of sodium carbonate (175 mg, 1.65 mmol) was added, and the mixture was reacted at room temperature for 8 h. Stirring was stopped, the solvent was dried, and the crude product was separated by column chromatography (eluent: dichloromethane / methanol = 10:1 to 1:1, v / v) to obtain 1.03 g of white solid glycyrrhetinic acid sulfonate GASS (i.e., glycyrrhetinic acid bio-based anionic surfactant), with a yield of 89%.

[0050] The structure of the synthesized glycyrrhetinic acid sulfonate compound was characterized. An appropriate amount of the final product was weighed into a nuclear magnetic resonance tube, dissolved with deuterated DMSO, and tested using a nuclear magnetic resonance spectrometer at 25°C. Figure 3It can be seen from the nuclear magnetic resonance spectrum of glycyrrhetinic acid sulfonate that the chemical shift, integration and coupling splitting of each hydrogen are consistent with the target molecule, indicating that the target product is obtained, and the spectrum has no impurity peaks, proving that the product has reached a high purity.

[0051] 1 H NMR (300 MHz, DMSO-d 6 , δppm): 7.71(s,1H,-N H -C=O), 5.56 (s, 1H, -C H -C=O), 4.41 (m, 1H, O=COC H ), 2.55(dd, 2H, C H 2 -NH-), 2.43 (dd, 2H, C H 2 -SO 3 Na), 2.00, 1.63, 1.36, 1.34, 1.26, 1.07, 1.04, 1.00, 0.90, 0.83, 0.73.

[0052] Example 2: Determination of surface tension of glycyrrhetinic acid bio-based anionic surfactant

[0053] Prepare a series of surfactant aqueous solutions with different concentrations (1×10 -7 mol / L、5×10 -7 mol / L、1×10 - 6 mol / L、5×10 -6 mol / L、1×10 -5 mol / L、5×10 -5 mol / L、1×10 -4 mol / L、5×10 -4 mol / L、1×10 - 3 mol / L), and the surface tension was measured at 25°C using the hanging plate method. Each sample was measured five times, and a curve of the change of the surface tension of the solution with the concentration was drawn.

[0054] from Figure 4 The relationship between the surface tension γ of the glycyrrhetinic acid bio-based anionic surfactant and the concentration C shows that the compound has good surface activity. With the increase of concentration, the surface tension of the solution decreases from 71.8mN / m to 38.8mN / m, and the critical micelle concentration is 1×10 -4 mol / L.

[0055] Example 3: Study on the self-assembly properties of glycyrrhetinic acid bio-based anionic surfactant in aqueous solution

[0056] In the aqueous solution of glycyrrhetinic acid-based anionic surfactant, as the concentration increases, it gradually migrates from the gas-liquid interface to the bulk phase. Therefore, after reaching the critical micelle concentration, it will orderly aggregate in the aqueous solution to form assemblies. In the experiment, a transmission electron microscope was used to observe the assemblies.

[0057] From Figure 5 it can be seen that the glycyrrhetinic acid-based anionic surfactant will self-assemble in water to form spherical micelles with a diameter of 8 - 15 nm. It is speculated that the formation mechanism is that the hydrophobic glycyrrhetinic acid skeleton accumulates inside, and the hydrophilic sulfonate groups are arranged outside, finally forming spherical micelles.

[0058] Example 4: Study on the regulation of the bouncing behavior of droplets on a PTFE hydrophobic membrane by glycyrrhetinic acid-based anionic surfactant

[0059] The materials used in the experiment were PTFE, the camera was a Nikon camera, and the droplets were extruded by a Flow EZ precision pressure controller to ensure that the size of each droplet was the same. After the droplets were extruded by the syringe, a high-speed camera was used to record the spreading, retraction, and bouncing of the droplets on the surface of the PTFE hydrophobic membrane.

[0060] Figure 6 The impact and deposition states of the glycyrrhetinic acid-based anionic surfactant with a concentration of 5×10 -4 mol / L dripping on the PTFE membrane at different heights were recorded. After the droplets dropped from a high place onto the solid surface, they began to spread under the action of inertial force. After reaching the maximum spread, they began to retract under the action of surface tension and finally deposited on the solid surface. By analyzing the video data, the contact, spreading, retraction, bouncing, and final state moments of the droplets at different heights were obtained. It can be seen from the figure that as the dripping height of the droplets continuously increases, the maximum spreading area of the droplets on the PTFE membrane gradually increases, and a small amount of fragmentation of the droplets begins to occur. When the dripping height is in the range of 10 - 20 cm, the droplets will not break, but the final spreading area is small; when the falling height is 30 cm, after the droplets reach the maximum spread, a small amount of fragmented droplets splash out from the edge, and after a slight rebound, they deposit on the surface; when the dripping height of the droplets rises to more than 40 cm, after the droplets reach the maximum spread, they basically do not rebound and finally deposit with a large area.

[0061] In Figure 7 the bouncing of different concentrations of glycyrrhetinic acid-based anionic surfactant on the PTFE membrane at a height of 30 cm, as the concentration of the liquid medicine increases, the rebound height of the droplets decreases significantly, and the final spreading area becomes larger, especially for 1×10 -3mol / L solution, with basically no splashing and fragmentation, indicating that high concentrations of glycyrrhetinic acid bio-based anionic surfactant can have a good inhibitory effect on the bouncing of droplets, making it easier for droplets to adhere to the PTFE hydrophobic membrane.

[0062] Example 5: Study on the regulation of droplet bouncing behavior on the leaf surface of weed Chenopodium album by glycyrrhizic acid bio-based anionic surfactant

[0063] Freshly picked weed quinoa leaves were used in the experiment, and the camera and droplet generating device were the same as in Example 4. The research concentration was 1×10 - 3 The contact, spreading, retraction, bounce and final state moments obtained when mol / L glycyrrhetinic acid bio-based anionic surfactant was dropped on the surface of the weed Chenopodium album leaf at different heights. It can be seen that as the drop height increases, the spread area of ​​the drop is constantly increasing. And its bounce height, within the drop height range of 0-60cm, will decrease as the drop height increases.

[0064] The bouncing of different concentrations of glycyrrhizic acid bio-based anionic surfactant on the surface of the weedy Chenopodium album leaf at a height of 30 cm shows that with the increase of surfactant concentration, the droplet spreading area at the same height does not change significantly, but the rebound height after impact is significantly reduced. At the same time, the droplet fragmentation and splashing are also significantly reduced. In other words, high concentrations of surfactant (concentration greater than 1×10 -4 mol / L) can inhibit the bouncing of droplets on the surface of weedy Chenopodium album.

[0065] Example 6: Study on the regulation of droplet bouncing behavior on the leaf surface of Sophora flavescens by glycyrrhizic acid bio-based anionic surfactant

[0066] Freshly picked oleander leaves were used, and the camera and droplet generation device were the same as in Example 4. The research concentration was 1×10 - 3 The contact, spreading, retraction, bounce and final state diagrams obtained by dropping mol / L glycyrrhizic acid bio-based anionic surfactant on the surface of Sophora flavescens leaves at different heights show that the maximum spreading area of ​​the droplet continues to increase as the drop height increases. When the drop height is in the range of 0-60cm, the droplets will break and splash to varying degrees as the drop height increases. When the drop height is 0-25cm, the droplets will not significantly retract, rebound or splash after they hit the leaf surface and spread inertially; when the drop height is 30-40cm, there is a small amount of rebound and splash, and the drop height continues to increase, and the droplets are almost completely splashed with little deposition.

[0067] Example 7: Study on the regulation of droplet bouncing behavior on corn leaf surface by glycyrrhetinic acid bio-based anionic surfactant

[0068] Freshly picked corn leaves were used, and the camera and droplet generating device were the same as in Example 4. The contact, spreading, retraction, bounce and final state diagrams were obtained by dropping a bio-based anionic surfactant of glycyrrhizic acid with a concentration of 1×10 mol / L on the surface of corn leaves at different heights. As the droplet height increases, the spreading area of ​​the droplet continues to increase. When the drop height is in the range of 0-60 cm, the droplets will break and splash significantly as the drop height increases. Only when the drop height is lower than 20 cm, the droplets will not retract, rebound or splash significantly after spreading on the leaf surface; when the drop height is greater than 40 cm, it will almost completely splash, with little deposition.

[0069] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A glycyrrhetinic acid bio-based anionic surfactant, It is characterized in that Its structural formula is as follows:

2. The method for preparing a glycyrrhetinic acid bio-based anionic surfactant according to claim 1, It is characterized in that The following steps are involved: Step 1, dissolving glycyrrhetinic acid and acetic anhydride in pyridine, adding a catalyst 4-dimethylaminopyridine to react to obtain GA-1, i.e. 3-acetyl glycyrrhetinic acid, wherein the structural formula of GA-1 is: Step 2, GA-1 and 2-aminoethanesulfonic acid are dissolved in a mixed solvent of dichloromethane and N,N-dimethylformamide, and a catalyst 4-dimethylaminopyridine and a condensing agent 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride are added to react to obtain a compound GA-2, wherein the structural formula of the compound GA-2 is: Step 3, reacting GA-2 with a sodium carbonate solution to obtain a glycyrrhetinic acid bio-based anionic surfactant.

3. The method for preparing a glycyrrhetinic acid bio-based anionic surfactant according to claim 2, Features: In the step 1, the molar ratio of glycyrrhetinic acid to acetic anhydride is 1:1-3, the molar ratio of glycyrrhetinic acid to catalyst 4-dimethylaminopyridine is 50:1-10, the reaction temperature is 50°C, and the reaction time is 6-8h. In the step 2, the molar ratio of GA-1 to 2-aminoethanesulfonic acid is 1:1-1.5, the molar ratio of GA-1 to the catalyst 4-dimethylaminopyridine is 1:0.2-1; the molar ratio of GA-1 to the condensing agent 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:1-1.5, the molar ratio of dichloromethane to N,N-dimethylformamide in the mixed solvent is 4:1-3, the reaction temperature is 50°C, and the reaction time is 10-18h; In step 3, the molar ratio of compound GA-2 to sodium carbonate is 1:1-1.2, the solvent in the sodium carbonate solution is water, the solvent of GA-2 is methanol, the volume ratio of the above methanol to water is 1:0.2-1, the reaction temperature is room temperature, and the reaction time is 6-10 hours.

4. Application of the glycyrrhizic acid bio-based anionic surfactant as described in claim 1 in regulating the bouncing behavior of droplets on a hydrophobic solid surface.

5. The use according to claim 4, Features: The concentration of anionic surfactant in the droplet is 1×10 -4 mol / L、5×10 -4 mol / L or 1×10 -3 mol / L.

6. The use according to claim 4, Features: The droplets are generated by a single droplet generator; the drop height of the droplets is 10 to 60 cm.

7. The use according to claim 4, Features: The hydrophobic solid surface includes: polytetrafluoroethylene and hydrophobic plant leaves.

8. The use according to claim 7, Features: The hydrophobic plant leaves include: Setaria viridis leaves, Sophora flavescens leaves, Chenopodium album leaves, corn leaves and wheat leaves.

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