A method for predicting wettability of a microstructured surface based on finite element analysis

Abstract

The application discloses a method for predicting the wettability of a microstructure surface based on finite element analysis, and relates to the field of predicting the wettability of a microstructure surface, and comprises the following steps: performing drop simulation calculation, drawing a liquid drop contour line after a water drop is stabilized on the surface, finding out the contact point between the water drop and the surface microstructure, making a tangent line of the contact point, and the angle between the tangent line and the horizontal baseline of the water drop contact surface is the wetting angle beta of the liquid drop on the surface; and comparing the simulated wetting angle beta with the initial wetting angle alpha. The application can physically and realistically simulate the dynamic behavior of a liquid drop on a microstructure surface and the final equilibrium state of the liquid drop by establishing an accurate geometric model containing etched microstructures and coupling a laminar flow physical field and a level set physical field, and can quantitatively judge whether the etched structure enhances hydrophobicity or hydrophilicity by directly comparing the simulated wetting angle beta with the initial planar wetting angle alpha, thereby providing clear and reliable decision-making basis for structure design.

Description

Technical Field

[0001] This invention relates to the field of predicting the wettability of microstructure surfaces, and more specifically to a method for predicting the wettability of microstructure surfaces based on finite element analysis. Background Technology

[0002] Surface wettability, the tendency of a liquid to spread or contract on a solid surface, is a key performance indicator in materials science, microfluidics, biomedicine, and anti-corrosion coatings. Wetting is typically quantified by contact angle; a contact angle greater than 90° is considered hydrophobic, while less than 90° is hydrophilic. Traditional surface wettability research heavily relies on a trial-and-error approach, which involves first fabricating specific micro / nanostructured surfaces in the laboratory (e.g., through photolithography or etching), then conducting tedious physical water-dropping experiments, and finally observing the results using a contact angle meter. This method has the following inherent drawbacks: 1. Long R&D cycle and high cost: Each design iteration requires a complete physical process from design, processing to testing, which is time-consuming and consumes a lot of material and equipment resources.

[0003] 2. Design blindness: Researchers find it difficult to accurately predict how a certain microstructure (such as shape, size, and arrangement) will affect wettability before processing, resulting in a great deal of experience and uncertainty in structural design.

[0004] 3. Experimental limitations: Physical experiments are difficult to conduct or observe wetting behavior at extreme scales (such as very small or complex structures) or in extreme environments (such as high temperature and high pressure).

[0005] In recent years, computer simulation technology has provided a new approach for predicting material properties. Although some computational fluid dynamics (CFD) software can handle multiphase flow problems, these general-purpose software often face challenges when dealing with wettability problems involving microscale, complex geometries, moving contact lines, and solid-liquid-gas three-phase coupling. They usually lack specialized optimization for wetting wall conditions and struggle to accurately capture the dynamic spreading or contraction process of droplets on microstructures, as well as the formation of the final steady-state contact angle. Therefore, there is an urgent need in this field for a method that can efficiently, accurately, and cost-effectively predict the influence of etched surface structures on wettability, in order to overcome the limitations of traditional experimental methods and fill the gaps in existing simulation technologies. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for predicting the wettability of microstructure surfaces based on finite element analysis. By finite element analysis, the wettability of water droplets on the microstructure surface is simulated, thereby providing ideas for the design of etched microstructures in experiments.

[0007] To achieve the above objectives, this invention employs a method for predicting the surface wettability of microstructures based on finite element analysis, comprising: Step 1: Create an initial surface using finite element software. The initial surface has an initial wetting angle α. Step 2: Form an etched surface structure on the initial surface. The etched surface structure includes multiple microstructures, and the shape and size of the microstructures are adjustable. Step 3: Set an air layer and water droplets above the microstructure, and set the material properties of the air layer and water droplets; Step 4: Add a physics field interface and initial conditions. The physics field adopts a laminar phase field or a laminar horizontal set. The water droplet is located in an air layer. Set the temperature, gas velocity, and pressure of the air layer, and the velocity and pressure of the water droplet. The water droplet has a vertical gravitational acceleration. Step 5: Perform mesh generation for the air layer and droplets using a suitable mesh generation method; Step 6: Perform a water droplet simulation calculation. After the water droplet stabilizes on the surface, draw the outline of the droplet, find the contact point between the water droplet and the surface microstructure, draw the tangent at the contact point, and the angle between the tangent and the horizontal baseline of the water droplet contact surface is the wetting angle β of the droplet on the surface; compare the simulated wetting angle β with the initial wetting angle α. If β > α, then it can be determined that the etched surface structure improves hydrophobicity; If β < α, then it can be determined that the etched surface structure improves hydrophilicity.

[0008] As a further optimization of the above scheme, pressure constraint points are set at the laminar physical field interface. There are one or more pressure constraint points. The main function of pressure point constraint is to fix the pressure value at a certain point in the computational domain and eliminate the non-uniqueness of the pressure term in the Navier-Stokes equations.

[0009] As a further optimization of the above scheme, the governing equations for the velocity field and pressure of the liquid phase in the laminar interface in step 4 are as follows: ; ; in, It is the fluid velocity. It is fluid pressure. It is fluid density. It is dynamic viscosity. This is the viscous force term; It reflects the change in momentum of a fluid due to the different velocity distribution in space; ρg is the gravity term. As the pressure gradient term, it drives the fluid to flow from the high-pressure area to the low-pressure area. In the voids between the microstructures below the water droplet, the air is compressed to form high pressure, and the water droplet is in a Cassie wetted state on the surface. The continuity equation is: ; The transmission at the two-phase fluid interface is achieved by solving the level set equations: ; Where e is a parameter controlling the interface thickness, in the horizontal set interface, the horizontal set interface of the two-phase flow boundary region is represented by the change of the horizontal set variable Φ from 0 to 1, with 0.5 representing the two-phase intersection interface. Represents air. It represents a water droplet.

[0010] As a further optimization of the above scheme, the method for drawing the water droplet contour is to select the fluid volume fraction contour line in the two-dimensional drawing group, and select 0.5 for the contour line to draw the contour.

[0011] As a further optimization of the above scheme, the two sides of the air layer are open boundaries.

[0012] The present invention provides a method for predicting the surface wettability of microstructures based on finite element analysis, which has the following beneficial effects: This invention provides a method for predicting the wettability of microstructure surfaces based on finite element analysis. By establishing an accurate geometric model containing the etched microstructure and coupling laminar flow physics and horizontal ensemble physics, this invention can physically and realistically simulate the dynamic behavior of droplets on the surface of the microstructure and their final equilibrium state. By directly comparing the simulated wetting angle (β) with the initial plane wetting angle (α), it can quantitatively determine whether the etched structure enhances hydrophobicity (β > α) or hydrophilicity (β < α), providing a clear and reliable decision-making basis for structural design. This invention transforms the traditional physical cycle of "design-processing-testing" into a digital cycle of "modeling-simulation-optimization." Researchers can quickly evaluate the wetting effect of various etching structure schemes (such as changing the size, spacing, and shape of rectangular arrays) on a computer before putting them into actual processing. This greatly reduces the number of unnecessary experiments, saves expensive material costs and processing time, and avoids resource waste caused by improper design. Unlike physical experiments, which typically only observe the final contact angle, the simulation method of this invention can visualize the dynamic spreading process of droplets across the entire microstructure surface, the movement behavior of the three-phase contact line, and the distribution of pressure and velocity fields in the micro-region. This provides researchers with a powerful analytical tool to understand the microscopic physical mechanisms of wettability changes, thereby guiding the design of biomimetic surface structures with better performance. The COMSOL software platform used in this invention allows for precise setting and parametric scanning of mesh parameters and physical parameters (such as surface tension and wall wetting angle); this ensures high accuracy and stability of simulation results, and any simulation conditions can be completely reproduced, eliminating random errors introduced by environmental fluctuations, sample differences and other factors in physical experiments.

[0013] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the present invention can be adopted. It should be understood that the embodiments of the present invention are not limited in scope as a result, and that the embodiments of the present invention include many changes, modifications and equivalents within the spirit and scope of the appended claims. Attached Figure Description

[0014] Figure 1 This is a flowchart of the method for predicting the surface wettability of microstructures based on finite element analysis according to the present invention; Figure 2 This is a mesh partition diagram of the water dripping simulation of the present invention; Figure 3 This is a diagram showing the initial state of a water droplet on a microstructure surface according to the present invention. Figure 4 This is a diagram showing the state of water droplets stable on the surface of the microstructure according to the present invention; Figure 5 This is a measurement diagram of the surface wetting angle according to the present invention. Detailed Implementation

[0015] Please refer to the instruction manual appendix. Figures 1-5 This invention provides a technical solution: a method for predicting the wettability of microstructure surfaces based on finite element analysis, comprising: Figure 1 This is a flowchart of a method for predicting the surface wettability of microstructures based on finite element analysis, according to an embodiment of the present invention.

[0016] like Figure 1 As shown, the method for predicting the surface wettability of microstructures based on finite element analysis includes the following steps: Step 1: Create an initial surface using finite element software. The initial surface has an initial wetting angle α = 92°. An initial surface was created using COMSOL software, and the initial surface has an initial wetting angle α = ; Step 2: Form an etched surface structure on the initial surface. The etched surface structure includes multiple microstructures, and the shape and size of the microstructures are adjustable. A rectangular microstructure array is created on the initial surface, the array having a height of 0.05 mm and a width of 0.05 mm. Step 3: Set an air layer and water droplets above the microstructure, and set the material properties of the air layer and water droplets.

[0017] An air layer and water droplets are placed above the rectangular array. The boundary of the air layer is an open, non-flowing boundary, and the density of the air layer is set to 1.293 kg / m³. 3 The dynamic viscosity is 1.81 × 10⁻⁶. -5 Pa·s, the density of the water droplets is set to 1.0 × 10⁻⁶ Pa·s. 3 kg / m 3 The dynamic viscosity is 1.01 × 10⁻⁶. -3 Pa·s; the surface tension coefficient of the water droplet is 7.2 × 10⁻⁶ Pa·s. -2 N / m. Step 4: Add a physics field interface and initial conditions. The physics field adopts a laminar phase field or a laminar horizontal set. The water droplet is located in an air layer. Set the temperature, gas velocity, pressure of the air layer and the velocity of the water droplet. The two sides of the air layer are open boundaries. The water droplet has vertical gravitational acceleration. The physical field adopts laminar flow and horizontal set. The temperature of the air layer is 293.15K, the air velocity is 0, and the pressure is 1 atm. The velocity of the water droplets is 1 m / s, the direction of the velocity is the negative y-axis, and the gravitational acceleration is g. Pressure constraint points are set at the interface of the laminar physical field. There are one or more pressure constraint points. The main function of pressure point constraint is to fix the pressure value at a certain point in the computational domain, so as to eliminate the non-uniqueness of the pressure term in the Navier-Stokes equations, thereby ensuring the stability and accuracy of numerical solution.

[0018] The governing equations for the velocity field and pressure of the liquid phase in the laminar flow interface are: ; ; in, It is the fluid velocity. It is fluid pressure. It is fluid density. It is dynamic viscosity. This is the viscous force term; It reflects the change in momentum of a fluid due to the different spatial velocity distribution. ρg is the gravitational term, which is the fundamental reason why water droplets fall vertically. As the pressure gradient term, it drives the fluid to flow from the high-pressure area to the low-pressure area. In the voids between the microstructures below the water droplet, the air is compressed to form high pressure, which can ensure that the water droplet is in a Cassie wetted state on the surface.

[0019] The continuity equation is: ; The transmission at the two-phase fluid interface is achieved by solving the level set equations: ; Where e is a parameter controlling the interface thickness, in the horizontal set interface, the horizontal set interface of the two-phase flow boundary region is represented by the change of the horizontal set variable Φ from 0 to 1, with 0.5 representing the two-phase intersection interface. Represents air. It represents a water droplet.

[0020] Step 5: Perform mesh generation for the air layer and droplets using a suitable mesh generation method; The model was meshed using a free triangular meshing method, with a maximum element size of 0.028 mm and a minimum element size of 4 × 10⁻⁶ mm. -4 mm, maximum unit growth rate is 1.1, curvature factor is 0.25.

[0021] Step 6: Perform a water droplet simulation calculation. After the water droplet stabilizes on the surface, draw the outline of the droplet, find the contact point between the water droplet and the surface microstructure, and draw the tangent at the contact point. The angle between the tangent and the surface is the wetting angle β of the droplet on the surface. Compare the simulated wetting angle β with the initial wetting angle α. If β > α, it can be determined that the etched surface structure improves hydrophobicity; if β < α, it can be determined that the etched surface structure improves hydrophilicity. The method for drawing the water droplet outline is to select the fluid volume fraction contour line in the two-dimensional drawing group, and select 0.5 for the contour line to draw the outline.

[0022] In practice: A water droplet simulation was performed with a calculation time of 0.04s. It was necessary to ensure that the water droplet could stabilize on the surface after this time. Each time step was 0.001s. The smaller the time step, the clearer the water droplet's falling process and its dynamic behavior on the microstructure surface could be.

[0023] refer to Figure 4 The image shown is of a water droplet stable on a surface. The outline of the water droplet was drawn using COMSOL's 2D drawing tools, and then the horizontal baseline and tangent of the water droplet in contact with the surface were drawn. refer to Figure 5 The angle enclosed by the outline of the water droplet shown is 127°, that is, the surface wetting angle of this rectangular array structure is β=127°. Therefore, β > α, which means that this rectangular array structure can improve the hydrophobicity of the surface.

[0024] In summary, this invention establishes an accurate geometric model containing etched microstructures and couples laminar flow physical fields and horizontal slab physical fields, enabling a physically realistic simulation of the dynamic behavior of droplets on the surface of microstructures and their final equilibrium state. By directly comparing the simulated wetting angle (β) with the initial planar wetting angle (α), it is possible to quantitatively determine whether the etched structure enhances hydrophobicity (β > α) or hydrophilicity (β < α), providing a clear and reliable decision-making basis for structural design.

Claims

1. A method for predicting the surface wettability of microstructures based on finite element analysis, characterized in that, include: Step 1: Create an initial surface using finite element software. The initial surface has an initial wetting angle α. Step 2: Form an etched surface structure on the initial surface. The etched surface structure includes multiple microstructures, and the shape and size of the microstructures are adjustable. Step 3: Set an air layer and water droplets above the microstructure, and set the material properties of the air layer and water droplets; Step 4: Add a physics field interface and initial conditions. The physics field adopts a laminar phase field or a laminar horizontal set. The water droplet is located in an air layer. Set the temperature, gas velocity, and pressure of the air layer, and the velocity and pressure of the water droplet. The water droplet has a vertical gravitational acceleration. Step 5: Perform mesh generation for the air layer and droplets using a suitable mesh generation method; Step 6: Perform a water droplet simulation calculation. After the water droplet stabilizes on the surface, draw the outline of the droplet, find the contact point between the water droplet and the surface microstructure, draw the tangent at the contact point, and the angle between the tangent and the horizontal baseline of the water droplet contact surface is the wetting angle β of the droplet on the surface; compare the simulated wetting angle β with the initial wetting angle α. If β > α, then it can be determined that the etched surface structure improves hydrophobicity; If β < α, then it can be determined that the etched surface structure improves hydrophilicity.

2. The method for predicting the surface wettability of microstructures based on finite element analysis according to claim 1, characterized in that: Pressure constraint points are set at the interface of the laminar physical field. There are one or more pressure constraint points. The main function of pressure point constraint is to fix the pressure value at a certain point in the computational domain and eliminate the non-uniqueness of the pressure term in the Navier-Stokes equations.

3. The method for predicting the surface wettability of microstructures based on finite element analysis according to claim 1, characterized in that: The governing equations for the velocity field and pressure of the liquid phase in the laminar flow interface in step 4 are as follows: ； ； in, It is the fluid velocity. It is fluid pressure. It is fluid density. It is dynamic viscosity. This is the viscous force term; It reflects the change in momentum of a fluid due to the different velocity distribution in space; ρg is the gravity term. As the pressure gradient term, it drives the fluid to flow from the high-pressure area to the low-pressure area. In the voids between the microstructures below the water droplet, the air is compressed to form high pressure, and the water droplet is in a Cassie wetted state on the surface. The continuity equation is: ； The transmission at the two-phase fluid interface is achieved by solving the level set equations: ； Where e is a parameter controlling the interface thickness, in the horizontal set interface, the horizontal set interface of the two-phase flow boundary region is represented by the change of the horizontal set variable Φ from 0 to 1, with 0.5 representing the two-phase intersection interface. Represents air. It represents a water droplet.

4. The method for predicting the surface wettability of microstructures based on finite element analysis according to claim 1, characterized in that: The method for drawing the water droplet outline is to select the fluid volume fraction contour line in the two-dimensional drawing group, and select 0.5 for the contour line to draw the outline.

5. The method for predicting the surface wettability of microstructures based on finite element analysis according to claim 1, characterized in that: The air layer has open boundaries on both sides.

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