Super-hydrophobic surface droplet adhesion characterization method based on analog simulation

Abstract

The invention discloses a super-hydrophobic surface droplet adhesion force characterization method based on analog simulation. The morphology state of the liquid drop in the rolling process of the super-hydrophobic surface is simulated through Fluent software, the morphology characteristic parameters of the liquid drop are obtained, and accurate obtaining of the adhesion force of the liquid drop is achieved in combination with a mathematical equation. According to the method, firstly, the three-dimensional shape of the super-hydrophobic surface microstructure is represented, three-dimensional structure parameters are extracted, and a three-dimensional model is designed based on the structure parameters; grid division and boundary condition setting are carried out on the established three-dimensional model, and the three-dimensional model is imported into Fluent to simulate the morphological change of liquid drops when the liquid drops roll on the super-hydrophobic surface; the spreading radius, the advancing angle, the retreating angle and the rolling angle of the liquid drops in the rolling process are obtained by analyzing the forms of the liquid drops; and representing the adhesion force of the liquid drop in combination with a mathematical equation. The invention provides a low-cost and high-precision method and approach for characterization of the adhesion force when the liquid drops on the super-hydrophobic surface roll, can be widely applied to simulation analysis of morphological change and adhesion force when the liquid drops on the surfaces of different microstructures roll, and plays an important role in directional design of the super-hydrophobic microstructures.

Description

Technical Field

[0001] The present invention belongs to the field of dynamic behavior of droplets on super-hydrophobic surfaces, and in particular relates to a method for simulating the change in the morphological state of a droplet when it rolls on a super-hydrophobic surface and accurately characterizing the adhesion force through a mathematical equation. Background Art

[0002] A superhydrophobic surface refers to a surface on which the contact angle of a droplet is greater than 150° and the rolling angle is less than 10°. These surfaces usually have a micro-nano composite structure and low surface energy, which can make the droplet form a nearly spherical droplet on the surface, and can roll easily, showing low adhesion. Adhesion refers to the interaction between the droplet and the superhydrophobic surface, which determines the slip and adhesion of the droplet on the superhydrophobic surface. It is an important aspect of superhydrophobic research and directly affects the self-cleaning, ice inhibition, antibacterial and other superhydrophobic properties of its surface. The accurate acquisition of adhesion plays an important guiding role in the optimization design of the microstructure of the superhydrophobic surface and the directional design of the superhydrophobic surface. At present, the adhesion acquisition methods are mainly divided into two ways: direct experimental measurement and simulation. Direct experimental measurement is to directly measure the force of the droplet peeling off the surface through a precision force testing instrument. The water droplet needs to be directly connected to the force device, which will cause the water droplet to deform from a nearly spherical shape to other irregular shapes, inevitably leading to inaccuracy. In addition, during the measurement process, the evaporation and deformation of water droplets caused by environmental humidity and gravity, as well as the interference caused by environmental vibration, reduce the accuracy of adhesion characterization and even cause errors. Simulation mainly constructs a microstructure model of the super-hydrophobic surface, combines molecular dynamics or finite element technology to simulate the rolling process of droplets on the super-hydrophobic surface, and calculates the adhesion between the droplets and the super-hydrophobic surface. This simulation method helps to deeply understand and analyze the relationship between the dynamic behavior of droplet rolling and the super-hydrophobic microstructure. Therefore, a simple and accurate method to obtain the adhesion of droplets on super-hydrophobic surfaces has become a key research direction in the current directional design of super-hydrophobic surfaces.

[0003] Based on the principle of superhydrophobic surface design and preparation, the inventor of this patent application has carried out research on superhydrophobic surface design with the support of projects such as the Hebei Provincial Natural Science Foundation General Project (Research on the superhydrophobic mechanism of the slip zone of Nepenthes and the bionic preparation technology of micro-nano composite structure, E2019208306) and the Central Guidance Local Science and Technology Development Fund Project (Research on femtosecond laser preparation technology of superhydrophobic micro-nano composite structure on titanium alloy surface, 226Z1804G). The micro-morphological structure of the slip zone of Nepenthes that can present superhydrophobic properties was used as the bionic prototype, and a superhydrophobic surface was designed and prepared using 3D printing technology and high-voltage electrostatic adsorption technology. The test results show that the water drop contact angle of the prepared superhydrophobic surface is 152.6°, indicating that it has good superhydrophobic function (authorized invention patent, patent number ZL 202010458218.7; academic paper, Bioinspired, Biomimetic and Nanobiomaterials, 2022, 11(1): 1-7). Therefore, the patent applicant has the basic conditions for designing and preparing super-hydrophobic surfaces and analyzing the morphology of droplets on super-hydrophobic surfaces.

[0004] Invention patent 201910306413.5 discloses a method for numerically simulating the drag reduction effect of a super-hydrophobic surface. The distribution of the flow field on the surface of a super-hydrophobic microstructure is numerically simulated by Fluent, showing the drag reduction effect of the surface. However, this patent only shows the drag reduction effect, does not show the morphology of droplets on the super-hydrophobic surface, and does not accurately obtain the numerical value of the resistance. Invention patent 201110396837.9 discloses a drag-reducing super-hydrophobic coating and a preparation method thereof. The prepared super-hydrophobic surface is slid in a water tank, and the time required for its gliding is calculated to determine the drag reduction effect of the surface as a standard for optimizing the design. This patent can effectively measure the drag reduction effect of super-hydrophobic surfaces on droplets, but does not accurately characterize the size of its value, and it is difficult to accurately regulate and optimize the super-hydrophobic microstructure. Therefore, a method for accurately characterizing the adhesion of droplets on super-hydrophobic surfaces is particularly important. The present invention discloses a method for characterizing the adhesion force of droplets on super-hydrophobic surfaces based on simulation. The method simulates the morphological state of droplets when they roll on the super-hydrophobic surface, and accurately characterizes the adhesion force of droplets on the super-hydrophobic surface in combination with mathematical equations, thereby providing an efficient and simple way to accurately obtain the adhesion force. The method can be widely used in the directional design of super-hydrophobic surface microstructures, and has important application value. Summary of the invention

[0005] The present invention provides a method for characterizing the adhesion of droplets on a super-hydrophobic surface based on simulation. The three-dimensional morphological structural characteristic parameters of the super-hydrophobic surface microstructure are extracted and optimized by three-dimensional white light and scanning electron microscopy, so as to construct a three-dimensional model, perform grid division and boundary condition setting; simulate the morphological state of the droplet during the rolling process on the super-hydrophobic surface in Fluent software; analyze the spreading radius, advancing angle, receding angle, and rolling angle of the droplet during rolling by post-processing software; bring the parameters obtained by the analysis into a mathematical equation to accurately characterize the adhesion of the droplet during rolling. The technical solution adopted by the present invention is: A method for characterizing the adhesion of droplets on a super-hydrophobic surface based on simulation, characterized by comprising the following design steps: Step 1, model construction: extracting the three-dimensional morphological structural characteristic parameters of a given super-hydrophobic surface to construct a three-dimensional structural model; Step 2, simulation: mesh the constructed model and set boundary conditions, and import it into Fluent to simulate the dynamic behavior of droplets when they roll on the super-hydrophobic surface; Step 3, parameter extraction: analyzing the rolling morphology of the droplet frame by frame to obtain the spreading radius, advancing angle, receding angle, and rolling angle parameters during the rolling process of the droplet; Step 4, adhesion characterization: According to the rolling behavior of droplets on the super-hydrophobic surface, the mathematical equation between the adhesion of droplets rolling on the super-hydrophobic surface and the droplet morphology can be expressed as: , Where: and represent the receding angle and advancing angle of the droplet rolling on the super-hydrophobic surface, R represents the spreading radius of the droplet, σ represents the surface tension of the droplet; According to the numerical equation and the parameters obtained in step 3, the adhesion force of the droplet when rolling is characterized; Step 5, accuracy verification: Measure the rolling angle of the droplet on the super-hydrophobic surface through a tilt plate experiment, obtain the morphological changes of the droplet as it rolls through a high-speed camera, and compare them with the simulation results to verify the accuracy of the simulation results.

[0006] Step 1 specifically includes: (1) The three-dimensional morphological structural features of the provided super-hydrophobic surface are extracted using scanning white light interferometry and scanning electron microscopy, and the parameters are appropriately modified to make them more suitable for simulation.

[0007] Step 2 specifically includes: (1) Construct a 3D model based on the 3D morphological and structural characteristic parameters, perform mesh division, refine the mesh at the microstructure, and define the model boundary conditions; (2) Import the VOF and laminar flow models into Fluent, set the simulation conditions according to the super-hydrophobic properties of the provided super-hydrophobic microstructure, and simulate the morphology of the droplet rolling on the super-hydrophobic surface.

[0008] Step 3 specifically includes: (1) The morphological state of the droplet during rolling is analyzed by CFD-post post-processing software, and the droplet spreading radius, advancing angle, receding angle, and rolling angle parameters are obtained during the droplet rolling state for the calculation of adhesion force.

[0009] Step 4 specifically includes: (1) Substitute the droplet spreading radius, advancing angle, and receding angle parameters into the numerical equation to calculate the adhesion force of the droplet as it rolls.

[0010] Step 5 specifically includes: (1) The rolling angle of the droplet on the super-hydrophobic surface was measured by tilt plate experiment and compared with the rolling angle obtained by simulation to verify the accuracy of the simulation; (2) The morphological changes of the droplet during rolling are recorded by a high-speed camera and compared with the morphological changes of the droplet obtained by simulation.

[0011] The invention provides a method for characterizing the adhesion force of a droplet on a super-hydrophobic surface based on simulation. The method comprises the following steps: extracting and optimizing the three-dimensional morphological structural characteristic parameters of a super-hydrophobic surface by three-dimensional white light and a scanning electron microscope, thereby constructing a three-dimensional model, performing mesh division and setting boundary conditions; simulating the morphological state of a droplet in a rolling process on the super-hydrophobic surface in Fluent software; analyzing the morphological state of the droplet during rolling by post-processing software to extract the spreading radius, advancing angle, receding angle and rolling angle of the droplet; and bringing the parameters into a mathematical equation between the adhesion force of a droplet rolling on the super-hydrophobic surface and the morphological state of the droplet, thereby realizing accurate characterization of the adhesion force of the droplet during rolling, and playing an important role in the directional design of a super-hydrophobic surface microstructure. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Flowchart of the simulation of the present invention; Figure 2 Schematic diagram of three-dimensional white light of super-hydrophobic microstructure according to an embodiment of the present invention; Figure 3 A scanning electron microscope schematic diagram of a super-hydrophobic microstructure according to an embodiment of the present invention; Figure 4 A three-dimensional model diagram of a super-hydrophobic microstructure according to an embodiment of the present invention; Figure 5 Schematic diagram of grid division of super-hydrophobic microstructure according to an embodiment of the present invention; Figure 6 A diagram showing the morphology and details of a droplet on a super-hydrophobic surface according to an embodiment of the present invention; Figure 7 A diagram showing the changes in the rolling morphology of a droplet on a super-hydrophobic surface according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The following is a detailed description of a method for characterizing the adhesion of droplets on a super-hydrophobic surface based on simulation in conjunction with the embodiments and drawings.

[0014] The present invention provides a method for characterizing the adhesion of droplets on a super-hydrophobic surface based on simulation. First, the three-dimensional morphology of the super-hydrophobic surface microstructure is characterized, the three-dimensional structural parameters are extracted, and a three-dimensional model is designed based on the structural parameters; the established three-dimensional model is meshed and imported into Fluent to simulate the morphological changes of the droplets as they roll on the super-hydrophobic surface; the spreading radius, advancing angle, receding angle, and rolling angle of the droplets during the rolling process are obtained by analyzing the morphology of the droplets; and the adhesion of the droplets is characterized by combining mathematical equations. The simulation flow chart is shown below: Figure 1 shown.

[0015] The present invention provides a method for characterizing the adhesion of droplets on a super-hydrophobic surface based on simulation, which specifically includes the following five steps.

[0016] 1. Model construction: Extract the three-dimensional morphological structural characteristic parameters of the given super-hydrophobic surface to construct a three-dimensional structural model, including: (1) The three-dimensional morphological structural features of the provided titanium alloy super-hydrophobic surface were extracted using scanning white light interferometry and scanning electron microscopy. The super-hydrophobic microstructure consists of periodically arranged truncated cones and blind holes, such as Figure 2 , 3 As shown; (2) Appropriately modify the structural parameters and treat the irregular blind holes on the surface as regular blind holes with equal spacing. The radius of the bottom circle of the truncated cone is R 1 11 μm, top circle radius r 1 5 μm, the height of the truncated cone H 20 μm; blind hole radius r 2 1μm, depth h 2 The thickness of the 3D model is 2 μm. Figure 4 shown.

[0017] 2. Simulation: Divide the constructed model into a grid and import it into Fluent to simulate the dynamic behavior of the droplet when it rolls on the super-hydrophobic surface, including: (1) The three-dimensional model is meshed with a mesh size of 10 μm. The mesh at the microstructure is refined with a mesh size of 1 μm. The model boundary conditions are defined, with the left end of the model as the outlet, the right end of the model and the substrate as the inlet, and the microstructure as the contact surface, as follows: Figure 5 As shown; (2) Import the data into Fluent and select the VOF and laminar flow model. Select titanium alloy and water as the materials, the droplet volume as 5 μL, and place it close to the super-hydrophobic wall to simulate the morphology of the droplet rolling on the super-hydrophobic surface.

[0018] 3. Parameter extraction: Analyze the rolling morphology of the droplet frame by frame to obtain the spreading radius, advancing angle, receding angle, and rolling angle parameters during the rolling process of the droplet, including: (1) Analyze the morphological state of the droplet rolling frame by frame through CFD-post post-processing software to obtain the droplet spreading radius, advancing angle, receding angle, and rolling angle parameters when the droplet is in the rolling state, such as Figure 6 As shown, it is used to calculate the adhesion force; (2) Measure the spreading radius R is 0.685 mm, the advancing angle is 165.01 ± 4.58°, the receding angle is 149.26 ± 4.62°, and the rolling angle is α It is 9.4°.

[0019] 4. Adhesion force characterization: Substitute the droplet spreading radius, advancing angle, and receding angle parameters into the numerical equation to calculate the adhesion force of the droplet when it rolls, including the following: (1) When a droplet slides on an inclined superhydrophobic surface, the morphology of the droplet changes significantly, and its surface tension restricts this change and hinders the sliding behavior. Therefore, a mathematical equation can be established to quantitatively describe the relationship between morphology and adhesion. The mathematical equation is as follows: , Where is the rolling angle, which represents the angle between the sliding direction of the water droplet and the reference direction, R represents the spreading radius of the droplet, σ represents the surface tension of the droplet and can be described by the following equation: , here, b 1 , b 2 , b 3 They represent the shape coefficients of the contact line between the water droplet and the super-hydrophobic surface, which can be expressed as , , , which can be derived by substituting it into equation (2): , in, and They represent the receding angle and advancing angle of the droplet when rolling on the superhydrophobic surface; (2) Based on the above numerical equation and the parameters obtained in step 3, the adhesion force of the droplet rolling on the superhydrophobic surface of titanium alloy is calculated to be 8.22 ± 2.37 μN.

[0020] 5. Accuracy verification: The rolling angle of the droplet on the super-hydrophobic surface is measured by tilting plate experiment, and the morphological changes of the droplet during rolling are obtained by high-speed camera. The results are compared with the simulation results to verify the accuracy of the simulation results, including the following: (1) The rolling angle of the droplet on the super-hydrophobic surface of titanium alloy measured by the tilt plate experiment is 7.87 ± 0.28°, which is 1.53° different from the rolling angle of 9.4° obtained by simulation. Due to the simplification of the model structure and the inability to maintain accurate consistency of the droplet volume, the deviation of 1.53° is within a reasonable range. (2) The morphological changes of the droplet during rolling are recorded by a high-speed camera and compared with the morphological changes of the droplet obtained by simulation, such as Figure 7 As shown in the figure, the morphological changes of the simulated droplets during the rolling process are highly consistent with the actual rolling process, which verifies the accuracy of the simulation results.

Claims

1. A method for characterizing the adhesion of droplets on super-hydrophobic surfaces based on simulation, characterized in that The design steps include: Step 1, model construction: extracting the three-dimensional morphological structural characteristic parameters of a given super-hydrophobic surface to construct a three-dimensional structural model; Step 2, simulation: mesh the constructed model and set boundary conditions, and import it into Fluent to simulate the dynamic behavior of droplets when they roll on the super-hydrophobic surface; Step 3, parameter extraction: Analyze the morphological state of the droplet rolling frame by frame to obtain the spreading radius, advancing angle, receding angle, and rolling angle parameters during the droplet rolling process; Step 4, adhesion characterization: According to the rolling behavior of the droplet on the super-hydrophobic surface, the mathematical equation between the adhesion of the droplet rolling on the super-hydrophobic surface and the droplet morphology can be expressed as:

2. Where: and represent the receding angle and advancing angle of the droplet rolling on the super-hydrophobic surface, R represents the spreading radius of the droplet, σ represents the surface tension of the droplet; According to the numerical equation and the parameters obtained in step 3, the adhesion force of the droplet when rolling is characterized; Step 5, accuracy verification: Measure the rolling angle of the droplet on the super-hydrophobic surface through a tilt plate experiment, obtain the morphological changes of the droplet as it rolls through a high-speed camera, and compare them with the simulation results to verify the accuracy of the simulation results.

3. The method for characterizing the adhesion of droplets on super-hydrophobic surfaces based on simulation according to claim 1 is characterized in that: Step 1 specifically includes: (1) The three-dimensional morphological structural characteristic parameters of the super-hydrophobic surface are extracted using scanning white light interferometry and scanning electron microscopy, and the parameters are appropriately modified to make them suitable for simulation.

4. The method for characterizing the adhesion of droplets on super-hydrophobic surfaces based on simulation according to claim 1 is characterized in that: Step 2 specifically includes: (1) Construct a 3D model based on the 3D morphological and structural characteristic parameters, perform mesh division, refine the mesh at the microstructure, and define the model boundary conditions; (2) Import the VOF and laminar flow models into Fluent, set the simulation conditions according to the super-hydrophobic properties of the provided super-hydrophobic microstructure, and simulate the morphology of the droplet rolling on the super-hydrophobic surface.

5. The method for characterizing the adhesion of droplets on super-hydrophobic surfaces based on simulation according to claim 1 is characterized in that: Step 3 specifically includes: (1) The morphological state of the droplet during rolling is analyzed by CFD-post post-processing software, and the droplet spreading radius, advancing angle, receding angle, and rolling angle parameters are obtained for the calculation of adhesion force.

6. The method for characterizing the adhesion of droplets on super-hydrophobic surfaces based on simulation according to claim 1 is characterized in that: Step 4 specifically includes: (1) Substitute the droplet spreading radius, advancing angle, and receding angle parameters into the numerical equation to calculate the adhesion force of the droplet as it rolls.

7. The method for characterizing the adhesion of droplets on super-hydrophobic surfaces based on simulation according to claim 1 is characterized in that: Step 5 specifically includes: (1) The rolling angle of the droplet on the super-hydrophobic surface was measured by tilting plate experiment and compared with the rolling angle obtained by simulation to verify the accuracy of the simulation; (2) The morphological changes of the droplet during rolling are recorded by a high-speed camera and compared with the droplet morphological changes obtained by simulation.

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