Fluid droplet contact angle hysteresis measurement method, device and equipment and storage medium

Abstract

The invention provides a fluid droplet contact angle hysteresis measurement method, device and equipment and a storage medium, and belongs to the technical field of interface flow simulation in seepage physics. According to the method, a contact angle model containing liquid drops and a solid substrate is constructed, the liquid drops are located above the solid substrate, then the energy of the model is minimized to obtain balanced liquid drops, the balanced liquid drops move downwards at a preset speed and are wetted and spread into steady-state liquid drops through liquid-solid interaction, then the liquid drops are acted in the horizontal direction, and the stable-state liquid drops are obtained. And measuring forward and backward contact angles of the liquid drop when the liquid drop is subjected to horizontal force in picoseconds, and finally calculating the difference between the forward and backward contact angles to obtain the contact angle hysteresis of the liquid drop. According to the invention, the forward contact angle and the backward contact angle of the liquid drop in a static state can be accurately measured, and the contact angle hysteresis can be calculated, so that accurate data support is provided for researching liquid-solid interface characteristics.

Description

Technical Field

[0001] This invention relates to the field of interfacial flow simulation technology in seepage physics, specifically to a method for measuring the hysteresis of fluid droplet contact angle, a device for measuring the hysteresis of fluid droplet contact angle, an electronic device, and a computer-readable storage medium. Background Technology

[0002] Contact angle hysteresis refers to the change in contact angle caused by the deformation of a fluid droplet under external force. The difference between the advancing contact angle formed at the droplet's front end and the retreating contact angle formed at the droplet's rear end just before the droplet initiates its displacement is called contact angle hysteresis. Contact angle hysteresis is widely observed in shale oil or tight oil CO2 huff and puff processes. The magnitude of fluid contact angle hysteresis significantly affects the minimum miscibility pressure (MMP) and multiphase flow characteristics of shale oil or tight oil reservoirs. In reservoir simulation, capillary pressure curves are often calculated using fluid saturation as a variable; however, contact angle hysteresis often leads to deviations in capillary pressure calculations. Accurate measurement of contact angle hysteresis is crucial for constructing accurate capillary pressure models and improving the accuracy of reservoir simulations. Therefore, accurate measurement of fluid contact angle hysteresis is necessary.

[0003] Currently, existing technologies measure fluid contact angle hysteresis through the following methods: (1) By discretizing the droplet profile, deriving the system dimensionless free energy function under different wetting states, and optimizing the minimum dimensionless free energy, a variety of factors of liquid and surface are fully considered, effectively breaking through the limitations of traditional calculation methods; (2) Using a laser sensor to scan and analyze the 3D structure of the contact point between the droplet and the solid surface, the hysteresis of the contact angle is calculated through parameter correction and the ASA algorithm.

[0004] However, existing technologies have the following problems: due to the simplification assumptions, calculation bias may occur, especially for nano-sized droplets. The droplet deformation caused by surface roughness and the dense wrinkles in the contact line region make the calculation method based on the spherical cap surface area inaccurate, thus making it impossible to accurately calculate the contact angle hysteresis of micro and nano droplets. Summary of the Invention

[0005] The purpose of this invention is to provide a method, apparatus, device, and storage medium for measuring the contact angle hysteresis of fluid droplets, so as to solve the problem that existing fluid contact angle hysteresis measurement methods cannot accurately measure the contact angle hysteresis of nano-sized droplets.

[0006] To achieve the above objectives, embodiments of the present invention provide a method for measuring the contact angle hysteresis of a fluid droplet, comprising: Construct a contact angle model; wherein the contact angle model includes a droplet and a solid substrate, with the droplet located above the solid substrate; The contact angle model is subjected to energy minimization to obtain the droplet in equilibrium state; A droplet in equilibrium is controlled to move downward at a preset speed at a uniform speed, so that the droplet wets and spreads after contacting the solid substrate, thus obtaining a stable droplet. A horizontal force is applied to a steady-state droplet to measure the forward and backward contact angles of the droplet as it moves horizontally under the horizontal force within a picosecond time. The difference between the forward contact angle and the backward contact angle of the droplet is calculated to obtain the contact hysteresis of the droplet.

[0007] Optionally, the contact angle model is subjected to energy minimization to obtain the droplet in equilibrium, including: The droplet molecules move under a preset interaction potential energy. The position of the droplet within the contact angle model is adjusted so that the potential energy of the contact angle model is at its minimum, so as to obtain the droplet in an equilibrium state.

[0008] Optionally, the position of the droplet within the contact angle model can be adjusted, including: S1, obtain the position coordinates of the droplet's center of mass, the position coordinates of the vertical projection point of the droplet's center of mass on the fixed substrate, the density of the droplet, and the radius of the droplet; S2, calculate the difference between the position coordinates of the droplet's center of mass and the position coordinates of the vertical projection point of the droplet's center of mass on the fixed base, and obtain the height of the droplet's center of mass from the fixed base; S3, based on the droplet's density, radius, and height of its center of mass from the fixed base, yields the droplet's gravitational potential energy. S4. Based on the droplet radius and the preset liquid-gas interface energy coefficient, the liquid-gas interface potential energy is obtained. S5, calculate the sum of the gravitational potential energy of the droplet and the potential energy of the liquid-gas interface to obtain the potential energy of the contact angle model. S6. If the potential energy of the contact angle model is greater than the preset potential energy, adjust the position coordinates of the droplet's center of mass and return to step S2 until the potential energy of the contact angle model is less than or equal to the preset potential energy, and then output the position coordinates of the droplet's center of mass.

[0009] Optionally, the gravitational potential energy of the droplet is obtained based on the droplet's density, radius, and height of its center of mass above the fixed base, including: Using formula (1), the density, radius, and height of the droplet's center of mass from the fixed base are calculated to obtain the droplet's gravitational potential energy. (1); where, This represents the gravitational potential energy of the droplet. This represents the density of the droplet. Indicates the radius of the droplet. Represents pi (π). Represents gravitational acceleration. This indicates the height of the droplet's center of mass from the fixed base.

[0010] Optionally, based on the droplet radius and a preset liquid-gas interfacial energy coefficient, the liquid-gas interfacial potential energy is obtained, including: Using formula (2), the radius of the droplet and the preset liquid-gas interface energy coefficient are calculated to obtain the liquid-gas interface potential energy; (2); where, This represents the potential energy at the liquid-gas interface. This represents the preset liquid-gas interface energy coefficient.

[0011] Optionally, controlling the droplet in equilibrium to move downward at a preset speed at a uniform velocity, so that the droplet wets and spreads upon contact with the solid substrate, resulting in a stable droplet, includes: A downward velocity field perpendicular to the surface of a solid substrate is applied to a droplet in equilibrium, causing the droplet in equilibrium to move downward at a predetermined velocity at a uniform speed. When a droplet in equilibrium comes into contact with a solid substrate, it wets and spreads after contact with the solid substrate. Once the droplet in equilibrium has finished wetting and spreading, a steady-state droplet is obtained.

[0012] Optionally, a horizontal force is applied to the steady-state droplet to measure the forward and backward contact angles of the droplet as it moves horizontally under the horizontal force within a picosecond time, including: By applying a horizontal force field to the right to a steady droplet, the steady droplet is deformed on a fixed substrate. When the droplet deforms to a certain size, it will be displaced under this force. The contact angle within the picosecond time when the droplet's leading edge is displaced is the advancing contact angle, and the contact angle within the picosecond time when the droplet's trailing edge is displaced is the retreating contact angle.

[0013] In a second aspect of the present invention, a fluid droplet contact angle hysteresis measuring device is provided, comprising: The model building module is used to build a contact angle model; the contact angle model includes a droplet and a solid substrate, with the droplet located above the solid substrate; The first processing module is used to perform energy minimization processing on the contact angle model in order to obtain the droplet in equilibrium state; The second processing module is used to control the droplets in equilibrium to move downward at a preset speed at a uniform speed, so that the droplets are wetted and spread after contacting the solid substrate, and thus obtain a stable droplet. The contact angle measurement module is used to apply a horizontal force to a steady-state droplet to measure the forward and backward contact angles of the droplet as it moves horizontally under the horizontal force within a picosecond time. The hysteresis calculation module is used to calculate the difference between the forward contact angle and the backward contact angle of the droplet to obtain the contact angle hysteresis of the droplet.

[0014] In a third aspect of the present invention, an electronic device is provided, comprising: a processor and a memory, the memory storing machine-readable instructions executable by the processor, wherein the machine-readable instructions, when executed by the processor, perform the above-described fluid droplet contact angle hysteresis measurement method.

[0015] In a fourth aspect of the present invention, a computer-readable storage medium is provided, storing computer instructions that, when executed on a computer, cause the computer to perform the above-described fluid droplet contact angle hysteresis measurement method.

[0016] In this embodiment of the invention, through a series of steps such as model building, energy minimization processing, and droplet motion control, the forward contact angle and backward contact angle of a droplet in a static state can be accurately measured, and the contact angle hysteresis can be calculated, providing accurate data for studying the characteristics of the liquid-solid interface.

[0017] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic flowchart of the fluid droplet contact angle hysteresis measurement method provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a droplet in a static state and a droplet at the critical moment of phase transition under the action of external force, provided by an embodiment of the present invention. Figure 3 This is a schematic diagram of the relationship between the horizontal displacement distance and time of a droplet under different horizontal forces, provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of the structure of the fluid droplet contact angle hysteresis measuring device provided in an embodiment of the present invention. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0021] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0022] Example 1 Please refer to Figure 1 , Figure 1 This is a schematic flowchart of a fluid droplet contact angle hysteresis measurement method provided in an embodiment of the present invention. The method includes the following steps: S100, Construct a contact angle model; wherein, the contact angle model includes a droplet and a solid substrate, with the droplet located above the solid substrate; In one specific implementation, the above steps are performed using Lammps software, and the details are described below: Define the dimensions of the simulated box: Determine the spatial range of the simulation, that is, the size of the simulation box. In Lammps, this is done using the "region" command. For example, to create a two-dimensional simulation scene, assuming you want to simulate the contact angle of a droplet on a planar substrate, you can define a two-dimensional rectangular region as the simulation box. You can set its coordinates in the x-direction (horizontal) from 0 to 100 (the units can be determined according to actual needs, such as angstroms), and in the y-direction (vertical) from 0 to 50. The corresponding command would be "region box block 0 100 0 50". For a three-dimensional simulation, such as simulating the contact between a droplet and a substrate in a cubic space, you need to set the coordinate ranges in the x, y, and z directions. The command would be similar to "region box block 0 100 0 50 0 50". The specific range values ​​should be modified according to your pre-determined appropriate dimensions.

[0023] Set boundary conditions Setting boundary conditions for the simulation box determines the behavior of atoms at the boundaries and the interaction between the simulation region and the outside world. In Lammps, the "boundary" command is used to specify these conditions. Common boundary conditions include "s" for fixed boundaries, where atoms cannot cross and physical quantities at the boundary remain constant; "p" for periodic boundaries, where atoms can pass through one side and enter from the opposite side, often used to simulate infinitely large systems or eliminate boundary effects; and "f" for free boundaries, where atoms can freely cross, similar to open boundaries. For example, in a two-dimensional droplet contact angle simulation, if you want the x-direction (horizontal direction) to simulate an infinitely long substrate, you would set it to a periodic boundary. The bottom of the y-direction, being the edge of the solid substrate, would be set to a fixed boundary to prevent solid atoms from moving, and the top would be set to a free boundary to simulate communication with the outside world. The command would be "boundary psf". For three-dimensional simulations, these boundary conditions must be flexibly combined according to the specific physical scenario. For example, "boundary ppsf" can indicate that the x and y directions are periodic boundaries, and the bottom of the z-direction is fixed while the top is free.

[0024] Define the properties of solid substrate materials: (1) Atom type and mass definition: First, the atom type to be used to simulate the solid substrate must be determined. Use the "atom_style" command to select the appropriate atom style. For example, the "atomic" style only considers simple cases such as basic atomic properties. After selecting the style, use the "mass" command to define the mass of the corresponding atom type. For example, to simulate a solid substrate composed of platinum atoms, the mass of a platinum atom is approximately 195.08 amu. The corresponding command is "atom_style atomic", and then "mass 1 195.08" (here it is assumed that the platinum atom type number is 1).

[0025] (2) Potential energy function and related parameter settings: A suitable potential energy function needs to be selected to describe the interaction between atoms. Different materials are suitable for different potential energy functions. For a metallic solid substrate such as platinum, the Embedded Atom Method (EAM) is commonly used. First, the potential energy parameter file for the corresponding material must be downloaded (generally, a suitable EAM parameter file for platinum can be obtained from relevant material databases or literature). Then, the "pair_style" and "pair_coeff" commands are used to load the potential energy function and set specific parameters. For example, "pair_style eam" indicates the use of the EAM potential energy function, and "pair_coeff * * Pt.eam" loads the corresponding EAM parameter file for the previously defined atom type 1 (platinum atom) (here, it is assumed that the file name is Pt.eam).

[0026] (3) Surface Energy and Roughness Related Settings (Indirect Reflection): In Lammps, surface energy-related characteristics are indirectly reflected through the selected potential energy function and atomic arrangement. To simulate a rough solid substrate surface, for example, first create a flat solid substrate atomic layer (use commands such as "create_box" and "create_atoms" to generate an atomic layout at the bottom of the simulation box), and then create a roughness effect by randomly moving the positions of some atoms. For example, first use "create_box" to create a simulation box that can hold a certain number of atoms (e.g., 1000, the number can be adjusted according to the simulation precision), and then use "create_atoms" to generate atoms of type 1 in this box area. This creates a simple flat atomic layer. Afterwards, roughness can be created by randomly changing the y-coordinate of some bottom atoms (assuming the z-coordinate is 0 to represent the substrate plane) using methods such as loops. However, the actual code implementation of this part is slightly more complicated; this is just a general idea.

[0027] Define the properties of liquid materials: (1) Atom type and mass definition: Similarly, the atom type corresponding to the simulated liquid must be determined first. Taking argon as an example (here, it is assumed that spherical atoms are simply used to simulate the oxygen atom part in the argon molecule for simplification), first set the atom style, for example, still using the "atomic" style. The oxygen atom mass of argon is about 39.95 amu, so use the two commands "atom_styleatomic" and "mass 2 39.95" (here, it is assumed that the atom type number related to argon is 2).

[0028] (2) Potential energy function and parameter settings: For liquids, potential energy functions such as Lennard-Jones potential are commonly used to describe interatomic interactions. Use the "pair_style" command to set the potential energy function to be used. For example, "pair_stylelj / Ptt 2.5" sets the Lennard-Jones potential energy function and specifies parameters such as the cutoff distance (here the cutoff distance is set to 2.5, the specific value can be adjusted according to the actual situation). Then use the "pair_coeff" command to set the potential energy parameters for the interaction between atom types. For example, "pair_coeff 2 2 0.1 1.0" sets the potential energy parameters for the interaction of atom type 2 (representing argon-related atoms) itself (the parameter values ​​here are just examples, and the actual values ​​need to be adjusted according to the precise situation).

[0029] Specifically, Table 1 below provides an example of the interaction parameters between atoms:

[0030] (3) Properties such as density, surface tension, and viscosity are reflected (indirectly): Density can be indirectly achieved by controlling the number of liquid atoms generated and the volume of the simulation box. For example, referring to the idea of ​​the ideal gas law, the number of atoms required at a given density is calculated first, and then the corresponding atomic layout is generated. As for macroscopic properties such as surface tension and viscosity, they are reflected by the selected potential energy function and the comprehensive situation of atomic motion and interaction during the simulation process. It is not possible to directly set a parameter to correspond to them. In the subsequent simulation of droplet behavior, the relevant performance is observed and analyzed to compare and verify with these properties in reality.

[0031] Creating an atomic layout for a solid substrate: In the predefined bottom region of the simulation box (based on the previously defined region "box" and boundary conditions), the atomic arrangement of the solid substrate is generated using the "create_box" and "create_atoms" commands. Similar to the previous example of generating a solid substrate composed of platinum atoms, first, the simulation box is created using "create_box," specifying that it can accommodate atoms of type 1. Then, "create_atoms" is used to generate the corresponding atoms within this "box" region. This forms a simple substrate with a single atom thickness (for more complex solid structures, such as multi-layered atoms or special structures, further code must be written to implement appropriate atomic stacking, etc.), and these atoms are uniformly distributed in the bottom region of the simulation box.

[0032] Creating a liquid atom layout: For the liquid component, such as simulating a droplet-shaped liquid placed on a solid substrate, we first need to estimate the approximate number of atoms required for the droplet (this can be determined using methods like density calculations mentioned earlier). Then, we generate these atoms in a suitable area above the solid substrate to simulate the initial shape of the droplet. A simple approach is to first determine the coordinates of the droplet's center (assuming it's a certain distance above the center of the simulation box), and then generate atoms around this center within a certain radius to approximate the droplet's shape. For example, assuming the droplet's center coordinates in two dimensions are "x = 50", "y = 25", the radius is set to 10, and the atom type is 2 (liquid atoms), we can generate atoms one by one using loops or similar methods. First, we calculate the coordinates of each atom (using a simplified formula based on a circular distribution, but in practice, more comprehensive considerations are needed, such as atom size, to avoid atom overlap), and then use the "create_atoms" command to generate the atoms. However, this is just a simplified example; in practical applications, the code for generating the liquid atom layout needs to be optimized and improved based on specific simulation accuracy requirements and the actual shape of the droplet. After generating the atomic layout of the solid substrate and the liquid, it is necessary to further set up the interaction between them, and then run simulations and other subsequent operations to observe the contact angle formed by the droplets on the solid substrate and the related dynamic behavior changes.

[0033] S200, the contact angle model is subjected to energy minimization to obtain the droplet in equilibrium state; In one specific implementation, the above steps are performed using Lammps software, and the details are described below: Choosing a potential function: First, select a suitable potential function for the interactions between the droplet and the solid substrate, as well as within the liquid. Common liquids (such as argon) may use potential functions corresponding to the argon molecular model, such as the Lennard-Jones potential or TIP4P; if the solid substrate is metallic, embedded atom potentials (EAM) may be used. Specify the potential function type using the `pair_style` command (e.g., `pair_style lj / Ptt 2.5` indicates selecting the Lennard-Jones potential with a cutoff distance of 2.5), and then use the `pair_coeff` command to set the specific potential function parameters between different atom types.

[0034] Energy minimization operation: The `minimize` command is used to perform energy minimization calculations. The syntax is generally like `minimize 1.0e-4 1.0e-6 1000 10000`. The first two parameters are the energy convergence tolerance (convergence is considered achieved if the sum of forces and the change in energy are less than the corresponding values), and the last two parameters are the maximum number of iterations and the maximum number of steps, which can be adjusted according to the complexity of the actual system and the required computational accuracy. After running this command, Lammps will automatically adjust the atomic positions to minimize the energy of the entire system (especially the droplet portion), promoting the spread of the liquid on the solid substrate.

[0035] Specifically, the droplet molecules move under a preset interaction potential energy, and the position of the droplet within the contact angle model is adjusted so that the potential energy of the contact angle model is at its minimum, so as to obtain the droplet in an equilibrium state.

[0036] In one embodiment, adjusting the position of the droplet within the contact angle model specifically includes the following steps: S1, obtain the position coordinates of the droplet's center of mass, the position coordinates of the vertical projection point of the droplet's center of mass on the fixed substrate, the density of the droplet, and the radius of the droplet; S2, calculate the difference between the position coordinates of the droplet's center of mass and the position coordinates of the vertical projection point of the droplet's center of mass on the fixed base, and obtain the height of the droplet's center of mass from the fixed base; S3, based on the droplet's density, radius, and height of its center of mass from the fixed base, yields the droplet's gravitational potential energy. Specifically, using formula (1), the density of the droplet, the radius of the droplet, and the height of the droplet's center of mass from the fixed base are calculated to obtain the gravitational potential energy of the droplet; (1); where, This represents the gravitational potential energy of the droplet. This represents the density of the droplet. Indicates the radius of the droplet. Represents pi (π). Represents gravitational acceleration. This indicates the height of the droplet's center of mass from the fixed base.

[0037] S4. Based on the droplet radius and the preset liquid-gas interface energy coefficient, the liquid-gas interface potential energy is obtained. Using formula (2), the radius of the droplet and the preset liquid-gas interface energy coefficient are calculated to obtain the liquid-gas interface potential energy; (2); where, This represents the potential energy at the liquid-gas interface. This represents the preset liquid-gas interface energy coefficient.

[0038] S5, calculate the sum of the gravitational potential energy of the droplet and the potential energy of the liquid-gas interface to obtain the potential energy of the contact angle model. S6. If the potential energy of the contact angle model is greater than the preset potential energy, adjust the position coordinates of the droplet's center of mass and return to step S2 until the potential energy of the contact angle model is less than or equal to the preset potential energy, and then output the position coordinates of the droplet's center of mass.

[0039] S300 controls the droplet in equilibrium to move downward at a preset speed at a uniform speed, so that the droplet wets and spreads after contacting the solid substrate, thus obtaining a stable droplet; In one embodiment, step S300 specifically includes: S310, apply a downward velocity field perpendicular to the surface of the solid substrate to the droplet in equilibrium, so that the droplet in equilibrium moves downward at a predetermined speed at a uniform speed. S320, when a droplet in equilibrium comes into contact with a solid substrate, the droplet is wetted and spread after contact with the solid substrate; S330, after the droplet in equilibrium state has finished wetting and spreading, a steady-state droplet is obtained.

[0040] In one specific implementation, the above steps are performed using Lammps software, and the details are described below: (1) Time step selection: First, the simulation time step must be determined. The selection of the time step is crucial; it needs to be small enough to ensure the stability and accuracy of the simulation, but not so small as to lead to excessive computation and low simulation efficiency. For molecular dynamics simulations involving droplet motion, the time step is typically in the range of femtoseconds (10⁻¹). 5 The time step is on the order of seconds. For example, depending on the system being simulated and the properties of the liquid or solid, a time step of 1 femtosecond (i.e., 1e-15 seconds) can be selected. In Lammps, this can be set using the following command: timestep 1e-15.

[0041] (2) Ensemble selection: An ensemble determines the macroscopic constraints of the system during the simulation process. Common types include microcanonical ensembles (NVE), canonical ensembles (NVT), and isothermal-isobaric ensembles (NPT).

[0042] Microcanonical ensemble (NVE): The number of particles (N), volume (V), and energy (E) of the system remain constant. It is suitable for simulating the dynamic behavior of isolated systems. However, it is used relatively less in actual cases where droplets interact with the substrate and are in motion, because it is difficult to ensure that the situation of complete isolation and strict energy conservation is consistent with the actual physical scenario.

[0043] Canonical ensemble (NVT): Keeping the number of particles (N), volume (V), and temperature (T) constant, the system temperature is adjusted by coupling with a virtual heat bath to maintain it at the set value. It is well-suited for simulating processes such as droplet motion in a constant temperature environment, which is consistent with the situation in many actual experiments conducted under constant temperature conditions.

[0044] Isothermal-isobaric ensemble (NPT): The number of particles (N), pressure (P), and temperature (T) of the system remain constant. It is often used to simulate the changes of the system under isothermal and isobaric conditions, such as the behavior of droplets on a substrate under external pressure and constant temperature.

[0045] Depending on the specific simulation requirements, if the simulation is conducted in a constant temperature environment, a canonical ensemble (NVT) can usually be selected. This can be set using the following command (assuming a temperature of 300 K, which can be adjusted as needed): `fix 1 all nvttemp 300 300 100`. Here, "fix" indicates applying a constraint or operation, "1" is the constraint number (different numbers can be defined to distinguish different operations), "all" indicates applying the operation to all atoms, "nvt" indicates that the NVT ensemble is used, and "temp 300 300 100" represents the target temperature (300 K), the temperature fluctuation range (within 300 K, generally set to the same value as the target temperature to ensure relative temperature stability), and the coupling strength (100, the coupling speed can be adjusted according to the simulation situation).

[0046] (3) Determine the method of applying external force To make a droplet move downwards, a downward force needs to be applied to the droplet atoms. This can be achieved by applying a constant external force along the direction of gravity (usually the negative y-direction, depending on your coordinate system) to the droplet atom group (assuming it has been previously defined as `droplet_group`). In Lammps, the "fix" command combined with the "addforce" keyword is used to apply the external force. For example, to apply a force of 0.01 (the unit must match the unit of force in the simulation, such as the atomic unit of force; this is just an example and needs to be adjusted according to the actual situation) along the negative y-direction to each atom of the droplet atom group, the command is as follows: The command `fix 2 droplet_group addforce 0 -0.01 0` applies a second constraint (numbered 2) to the droplet_group. The `addforce 0-0.01 0` specifies the force components applied in the x, y, and z directions. The x and z components are 0, and the y component is -0.01, meaning that a force is applied only in the y direction (downward).

[0047] (4) Run a simulation to make the droplets move: After setting the time step, ensemble, and applied external force, the simulation can be started, allowing the droplet to move downwards under the applied force. Use the "run" command to specify the number of simulation steps, for example, 10,000 steps (the exact number of steps depends on factors such as the initial state of the droplet, the desired motion effect, and the system response time; it can be adjusted through multiple trials). The command is as follows: During the run 10000, Lammps calculates the changes in the position and velocity of the droplet atoms at each step based on the set physical model and parameters. The droplet gradually moves downward under the applied external force and the interaction with the solid substrate and the surrounding environment (conditions determined by the ensemble).

[0048] (5) Determine whether the droplet is stationary and obtain a sample of the droplet in a stationary state: Determine the criteria for judging stillness To determine whether a droplet is stationary on a solid substrate, a reasonable criterion needs to be established. This can typically be considered from the following aspects: Atomic velocity: Observe the magnitude of the velocity of the droplet atoms. If the average velocity of the droplet atoms in all directions is close to zero (for example, less than a very small velocity threshold, such as 1e-6 (the unit is set according to the velocity unit, such as meters / second, etc.)), it can be preliminarily considered that the droplet is close to a stationary state.

[0049] Energy Change: Monitor the total energy of the system and the potential energy of the droplets. When the energy change is less than a very small energy threshold (similar to the energy tolerance in the previous energy minimization, such as 1e-6 (the unit is set according to the energy unit)) in a continuous series of steps (e.g., 100 consecutive steps, which can be adjusted according to the simulation), it can also help to determine that the droplet motion tends to be stable and stationary.

[0050] Continuous monitoring and acquisition of static state During the simulation, the above-mentioned criteria for determining stillness are continuously checked. This can be done by reviewing the simulation results output by Lammps (including atomic velocities, energy, etc.) or by automatically analyzing this data using scripts. Once the droplet meets the stillness criteria, its current state is the desired still state. The atomic coordinates and other relevant data can be saved (using Lammps commands like "write_data," such as "write_data static_droplet.data" to save the data to a file named "static_droplet.data" for later analysis and visualization). This successfully obtains the still state of the droplet. Figure 2 As shown on the left side of the image.

[0051] It should be noted that after the droplets spontaneously spread and stopped spreading, the droplet distribution became stable and axially symmetric. The system temperature then slowly increased by 5 K, before returning to the initial temperature within 6 ns. The contact angle along the contact line stopped changing and remained constant; this is recorded as the static contact angle.

[0052] S400 applies a horizontal force to a steady-state droplet to measure the forward and backward contact angles of the droplet as it moves horizontally under the horizontal force within a picosecond time. In one embodiment, step S400 specifically includes: By applying a horizontal force field to the right to a steady droplet, the steady droplet is deformed on a fixed substrate. When the droplet deforms to a certain size, it will be displaced under this force. The contact angle within the picosecond time when the droplet's leading edge is displaced is the advancing contact angle, and the contact angle within the picosecond time when the droplet's trailing edge is displaced is the retreating contact angle.

[0053] In one specific implementation, the above steps are performed using Lammps software, and the details are described below: Applying a horizontal force to the right causes the droplet to spread forward: (1) Determine the force application method: To make a droplet in a static state spread forward (horizontally to the right) on a solid substrate, a horizontal force to the right needs to be applied to the droplet atoms. Assuming that the group of droplet atoms has been defined as droplet_group, in the simulation software (taking Lammps as an example), the "fix" command combined with the "addforce" keyword is used to apply the external force. For example, if you want to apply a force of appropriate size (this size needs to be determined comprehensively based on the simulation system, droplet properties, and the desired spreading effect, etc., assuming it is set to 0.005 here, with the unit consistent with the unit of force in the simulation, such as the force unit under the atomic unit system, etc.) along the positive x direction (horizontally to the right, depending on the set coordinate system) to each atom of the droplet atom group, the corresponding command is as follows: The command `fix 3 droplet_group addforce 0.005 0 0` applies the following constraint: "fix 3" indicates that this is the third constraint applied (constraint numbers can be defined as needed), and the target is the droplet_group. "addforce 0.005 0 0" indicates the force components applied in the x, y, and z directions. The x-direction force is 0.005 (i.e., a horizontal force to the right), and the y and z-directions are 0, meaning that a force is applied only in the horizontal right direction.

[0054] (2) Running the simulation to promote droplet spreading: After setting the applied external force, use the "run" command to run the simulation according to the previously set simulation parameters (such as time step, ensemble, etc., which have been determined and maintained appropriately during the previous model building and droplet movement). This will allow the droplet to begin spreading forward on the solid substrate under the action of the horizontal rightward external force. For example, run 5000 steps (the specific number of steps needs to be adjusted comprehensively based on factors such as the initial state of the droplet, the properties of the solid substrate, and the desired degree of spreading; a suitable number of steps can be determined through multiple trials). The command is as follows: During the simulation run 5000, the droplet atoms gradually change position under the influence of various factors such as the external force, interaction with the solid substrate, and their own surface tension, thus spreading to the right on the substrate.

[0055] (3) Measuring the forward contact angle: During the forward spread of the droplet, it is necessary to measure its forward contact angle. The following methods can typically be used to achieve this measurement (the following example uses visualization; different simulation software may have built-in measurement tools or analysis modules, but the principles are similar): Use the visualization tool配套with the simulation software (such as Lammps can be combined with visualization software such as VMD) to visually display the states of the droplet spreading at different moments during the simulation. After the droplet reaches a relatively stable spreading state (which can be judged by observing that the droplet shape does not change significantly within a certain number of steps and related physical quantities such as energy also tend to be stable), through the angle measurement function in the visualization software (usually, elements such as the three-phase line where the droplet contacts the solid substrate and the tangent of the droplet surface can be manually selected to measure the angle), directly measure the advancing contact angle value at this time, such as Figure 2 shown.

[0056] Apply a horizontal leftward force to make the droplet spread backward: (1) Determine the force application method: Similar to applying the rightward force in the previous step S410, this time it is necessary to make the droplet spread horizontally to the left (negative x direction), so a horizontal leftward force needs to be applied to the droplet atom group. Similarly, assume the droplet atom group name is droplet_group. If you want to apply a force of a suitable magnitude (such as set to 0.005, which also needs to be determined by comprehensively considering relevant factors, and the unit is the same as before) along the negative x direction to each atom in the group, the corresponding command in Lammps is as follows: fix 4 droplet_group addforce -0.005 0 0, where "fix 4" is the fourth applied constraint number, acting on the droplet atom group droplet_group, and "addforce -0.005 0 0" means the force applied in the x direction is -0.005 (i.e., horizontal leftward), and the y and z directions are 0, only applying force in the horizontal leftward direction.

[0057] (2) Run the simulation to promote droplet spreading: After setting the external force to the left, according to the existing simulation parameter settings, use the "run" command again to run the simulation, so that the droplet spreads backward on the solid substrate under the action of this horizontal leftward external force. For example, run 5000 steps (the specific number of steps also needs to be adjusted comprehensively according to the actual situation), and the command is as follows: run 5000. During the running process, the droplet will gradually change its shape towards the left under the combined action of this external force, the solid substrate, and its own surface tension, realizing the dynamic process of backward spreading.

[0058] (3) Measure the receding contact angle: After the droplet spreads backward and reaches a relatively stable state (the method of judging the stable state is similar to that when measuring the advancing contact angle before, observing changes in shape, energy, etc.), measure the receding contact angle. The measurement method is basically the same as the method of measuring the advancing contact angle before: Visualization tools (such as VMD) are used to visualize the droplet spreading state. Then, using their angle measurement function, the receding contact angle is manually measured by selecting relevant geometric elements (three-phase line, droplet surface tangent, etc.) at the contact point between the droplet and the solid substrate. Figure 2 As shown.

[0059] It should be noted that since the response time of a droplet can be accurate to 1 picosecond and the spatial resolution can be accurate to 0.1 nanometers, high spatiotemporal resolution hysteresis data can be obtained.

[0060] In one specific embodiment, a bulk force ranging from 0.49 pN to 6.95 pN is applied to a droplet in equilibrium. This bulk force propels the droplet and alters its shape. The relationship between the horizontal distance the droplet travels and time is shown in the curve below. Figure 3 As shown. In this embodiment, the forward and backward contact angles of droplets under different external forces can be measured, which is more accurate than the traditional tilting plate method and suction method.

[0061] S500 calculates the difference between the forward contact angle and the backward contact angle of the droplet to obtain the contact angle hysteresis of the droplet.

[0062] In one specific implementation, the above steps are performed using Lammps software, and the details are described below: (1) Data acquisition: The coordinates of atoms at the contact edge between the droplet and the solid substrate are obtained by simulating the atomic coordinate file (such as the previously mentioned dump.atom file). This step can be accomplished by writing external data processing scripts (such as Python scripts combined with scientific computing libraries like NumPy and SciPy) to read the corresponding coordinate data.

[0063] (2) Contact angle calculation: Two-dimensional case: Based on the obtained atomic coordinates of the droplet edge, its relative position to the substrate in the horizontal direction (usually set as the x-axis direction) and the vertical direction (set as the y-axis direction) is determined.

[0064] Assuming the coordinates of a point on the droplet edge are (x_i, y_i), the contact angle can be calculated using simple trigonometric functions. For example, we can define the contact angle θ based on the angle between the tangent to the droplet profile and the substrate plane. If the horizontal distance Δx and vertical distance Δy of the droplet edge point relative to the substrate at a certain position are known, then tanθ = Δy / Δx, and thus the contact angle θ = arctan(Δy / Δx) can be calculated. For the entire droplet edge, multiple representative points can be selected, and the contact angles calculated using this method can be averaged to obtain an approximate value of the contact angle in a stationary state (the forward and backward contact angles are the same value when stationary, and are not distinguished for now).

[0065] Three-dimensional situation: The situation is relatively complex, involving spatial geometric calculations. Vector operations are needed to determine the angle between the droplet surface normal and the substrate plane.

[0066] For example, first select the coordinates of several adjacent atoms on the surface of the droplet (generally at least three points to determine a plane), construct vectors through these points, and use operations such as vector cross product to find the normal vector n of the droplet surface at the contact edge, while determining the normal vector of the base plane (usually (0, 0, 1), assuming the base plane is a horizontal xy plane).

[0067] Then, the included angle θ is calculated using the vector dot product formula cosθ = n · m / (|n| × |m|) (where m is the normal vector of the base plane, · represents the dot product operation, and |n| and |m| are the moduli of the corresponding vectors). This included angle is the contact angle. Similarly, multiple points can be selected at different positions on the edge of the droplet, and the average value can be taken as the contact angle in the static state.

[0068] (3) Calculate the contact angle hysteresis Contact hysteresis = advancing contact angle - retreating contact angle.

[0069] In this embodiment of the invention, through a series of steps such as model building, energy minimization processing, and droplet motion control, the forward contact angle and backward contact angle of a droplet in a static state can be accurately measured, and the contact angle hysteresis can be calculated, providing accurate data for studying the characteristics of the liquid-solid interface.

[0070] Example 2 Based on the same inventive concept, such as Figure 4 As shown, this embodiment of the invention also provides a fluid droplet contact angle hysteresis measuring device 200, comprising: The model building module 210 is used to build a contact angle model; wherein the contact angle model includes a droplet and a solid substrate, with the droplet located above the solid substrate; The first processing module 220 is used to perform energy minimization processing on the contact angle model to obtain the droplet in equilibrium state; The second processing module 230 is used to control the droplet in equilibrium to move downward at a preset speed so that the droplet is wetted and spread after contacting the solid substrate to obtain a stable droplet. The contact angle measurement module 240 is used to apply a horizontal force to a steady-state droplet to measure the forward and backward contact angles of the steady-state droplet when it moves horizontally under the horizontal force within a picosecond time. The hysteresis calculation module 250 is used to calculate the difference between the forward contact angle and the backward contact angle of the droplet to obtain the contact angle hysteresis of the droplet.

[0071] It should be understood that this device corresponds to the above-described embodiment of the fluid droplet contact angle hysteresis measurement method and is capable of performing the various steps involved in the above-described method embodiment. The specific functions of this device can be found in the description above, and detailed descriptions are omitted here to avoid repetition. The device includes at least one software functional module that can be stored in memory or embedded in the device's operating system (OS) in the form of software or firmware.

[0072] Example 3 Based on the same inventive concept, embodiments of the present invention also provide an electronic device, including: a processor and a memory, wherein the memory stores machine-readable instructions executable by the processor, and when the machine-readable instructions are executed by the processor, the above-described fluid droplet contact angle hysteresis measurement method is performed.

[0073] In a typical configuration, an electronic device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0074] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0075] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0076] Example 4 Based on the same inventive concept, embodiments of the present invention also provide a computer-readable storage medium storing computer instructions, which, when executed on a computer, cause the computer to perform the above-described fluid droplet contact angle hysteresis measurement method.

[0077] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0078] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0079] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0080] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0081] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0082] In addition, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0083] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0084] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for measuring the hysteresis of fluid droplet contact angle, characterized in that, include: Construct a contact angle model; wherein the contact angle model includes a droplet and a solid substrate, with the droplet located above the solid substrate; The contact angle model is subjected to energy minimization to obtain the droplet in equilibrium state; A droplet in equilibrium is controlled to move downward at a preset speed at a uniform speed, so that the droplet wets and spreads after contacting the solid substrate, thus obtaining a stable droplet. A horizontal force is applied to a steady-state droplet to measure the forward and backward contact angles of the droplet as it moves horizontally under the horizontal force within a picosecond time. The difference between the forward contact angle and the backward contact angle of the droplet is calculated to obtain the contact hysteresis of the droplet.

2. The method for measuring the hysteresis of fluid droplet contact angle according to claim 1, characterized in that, The contact angle model is subjected to energy minimization to obtain the droplet in equilibrium, including: The droplet molecules move under a preset interaction potential energy. The position of the droplet within the contact angle model is adjusted so that the potential energy of the contact angle model is at its minimum, so as to obtain the droplet in an equilibrium state.

3. The method for measuring the hysteresis of fluid droplet contact angle according to claim 2, characterized in that, Adjusting the position of the droplet within the contact angle model includes: S1, obtain the position coordinates of the droplet's center of mass, the position coordinates of the vertical projection point of the droplet's center of mass on the fixed substrate, the density of the droplet, and the radius of the droplet; S2, calculate the difference between the position coordinates of the droplet's center of mass and the position coordinates of the vertical projection point of the droplet's center of mass on the fixed base, and obtain the height of the droplet's center of mass from the fixed base; S3, based on the droplet's density, radius, and height of its center of mass from the fixed base, yields the droplet's gravitational potential energy. S4. Based on the droplet radius and the preset liquid-gas interface energy coefficient, the liquid-gas interface potential energy is obtained. S5, calculate the sum of the gravitational potential energy of the droplet and the potential energy of the liquid-gas interface to obtain the potential energy of the contact angle model. S6. If the potential energy of the contact angle model is greater than the preset potential energy, adjust the position coordinates of the droplet's center of mass and return to step S2 until the potential energy of the contact angle model is less than or equal to the preset potential energy, and then output the position coordinates of the droplet's center of mass.

4. The method for measuring the hysteresis of fluid droplet contact angle according to claim 3, characterized in that, Based on the droplet's density, radius, and height of its center of mass above the fixed base, the droplet's gravitational potential energy is obtained, including: Using formula (1), the density, radius, and height of the droplet's center of mass from the fixed base are calculated to obtain the droplet's gravitational potential energy. (1); where, This represents the gravitational potential energy of the droplet. This represents the density of the droplet. Indicates the radius of the droplet. Represents pi (π). Represents gravitational acceleration. This indicates the height of the droplet's center of mass from the fixed base.

5. The method for measuring the hysteresis of fluid droplet contact angle according to claim 3, characterized in that, Based on the droplet radius and a preset liquid-gas interfacial energy coefficient, the liquid-gas interfacial potential energy is obtained, including: Using formula (2), the radius of the droplet and the preset liquid-gas interface energy coefficient are calculated to obtain the liquid-gas interface potential energy; (2); where, This represents the potential energy at the liquid-gas interface. This represents the preset liquid-gas interface energy coefficient.

6. The method for measuring the hysteresis of fluid droplet contact angle according to claim 1, characterized in that, Controlling a droplet in equilibrium to move downwards at a predetermined velocity at a uniform speed, allowing the droplet to wet and spread upon contact with a solid substrate, resulting in a stable droplet, includes: A downward velocity field perpendicular to the surface of a solid substrate is applied to a droplet in equilibrium, causing the droplet in equilibrium to move downward at a predetermined velocity at a uniform speed. When a droplet in equilibrium comes into contact with a solid substrate, it wets and spreads after contact with the solid substrate. Once the droplet in equilibrium has finished wetting and spreading, a steady-state droplet is obtained.

7. The method for measuring the hysteresis of fluid droplet contact angle according to claim 1, characterized in that, A horizontal force is applied to a steady-state droplet to measure the forward and backward contact angles of the droplet as it moves horizontally under this force within a picosecond time interval, including: By applying a horizontal force field to the right to a steady droplet, the steady droplet is deformed on a fixed substrate. When the droplet deforms to a certain size, it will be displaced under this force. The contact angle within the picosecond time when the droplet's leading edge is displaced is the advancing contact angle, and the contact angle within the picosecond time when the droplet's trailing edge is displaced is the retreating contact angle.

8. A fluid droplet contact angle hysteresis measuring device, characterized in that, include: The model building module is used to build a contact angle model; the contact angle model includes a droplet and a solid substrate, with the droplet located above the solid substrate; The first processing module is used to perform energy minimization processing on the contact angle model in order to obtain the droplet in equilibrium state; The second processing module is used to control the droplets in equilibrium to move downward at a preset speed at a uniform speed, so that the droplets are wetted and spread after contacting the solid substrate, and thus obtain a stable droplet. The contact angle measurement module is used to apply a horizontal force to a steady-state droplet to measure the forward and backward contact angles of the droplet as it moves horizontally under the horizontal force within a picosecond time. The hysteresis calculation module is used to calculate the difference between the forward contact angle and the backward contact angle of the droplet to obtain the contact angle hysteresis of the droplet.

9. An electronic device, characterized in that, include: A processor and a memory, the memory storing machine-readable instructions executable by the processor, which, when executed by the processor, perform the fluid droplet contact angle hysteresis measurement method according to any one of claims 1-7.

10. A computer-readable storage medium storing computer instructions, characterized in that, When the computer instructions are executed on the computer, the computer performs the fluid droplet contact angle hysteresis measurement method according to any one of claims 1-7.

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