A method and system for measuring surface tension based on magnetic beads

Abstract

The present invention discloses a method and system for measuring surface tension based on magnetic beads. The method includes: placing the magnetic beads into a liquid droplet and controlling the central points of the magnetic beads, the liquid droplet and the magnet to be on the same vertical line; collecting an image of the liquid droplet and intercepting the upper part of the liquid droplet and the magnetic beads as a whole for force analysis, and constructing a surface tension calculation formula; based on the surface tension calculation formula, obtaining the liquid droplet contour information and performing calculations to obtain the surface tension. The system includes: a control module, an analysis module, and a calculation module. By using the present invention, it is possible to deduce and calculate the magnitude of the surface tension only by analyzing the shape of the liquid droplet and magnetic force calculation. As a method and system for measuring surface tension based on magnetic beads, the present invention can be widely applied to the field of liquid droplet tension measurement.

Description

Technical Field

[0001] The present invention relates to the field of droplet tension measurement, and particularly to a surface tension measurement method and system based on magnetic microspheres. Background Art

[0002] Currently, the common methods for measuring surface tension include the Du Noüy ring method, the Wilhelmy plate method, the pendant drop method, and contact angle measurement. The Du Noüy ring method and the Wilhelmy plate method both use precise force sensors to obtain tensile force information and then calculate the surface tension of the liquid, which requires a high precision of the instrument. At the same time, due to the size of the ring and the plate, a relatively large volume of liquid is still required for measurement. Compared with the traditional weighing principle measurement method, the pendant drop method has certain advantages in accuracy and reliability. However, the pendant drop method is based on two major assumptions - the liquid droplet is in static equilibrium and axisymmetric about the center. Based on these two characteristics, droplets with a volume of several microliters or even larger are required to ensure the balance between the interfacial tension and gravity of the droplet. Therefore, it is not suitable for measuring smaller volume droplets. Contact angle measurement is calculated using the Young-Laplace equation. However, since the equation involves the surface tensions of the gas-solid interface, the liquid-solid interface, and the gas-liquid interface, more known conditions are required for solution. Summary of the Invention

[0003] In order to solve the above technical problems, the object of the present invention is to provide a surface tension measurement method and system based on magnetic microspheres, which can deduce and calculate the magnitude of the surface tension only by analyzing the droplet shape and magnetic force.

[0004] The first technical solution adopted by the present invention is: a surface tension measurement method based on magnetic microspheres, comprising the following steps:

[0005] Put the magnetic microsphere into the liquid droplet and control the centers of the magnetic microsphere, the liquid droplet, and the magnet to be on the same vertical line;

[0006] Collect the liquid droplet image and intercept the upper part of the liquid droplet and the magnetic microsphere as a whole for force analysis, and construct a surface tension calculation formula;

[0007] Based on the surface tension calculation formula, obtain the liquid droplet contour information and perform calculations to obtain the surface tension.

[0008] Further, the step of putting the magnetic microsphere into the liquid droplet and controlling the centers of the magnetic microsphere, the liquid droplet, and the magnet to be on the same vertical line specifically includes:

[0009] Suck the solution and drop it on the substrate to form a liquid droplet;

[0010] Measure the mass of the magnetic microsphere and put it into the liquid droplet;

[0011] Fix a magnet above the droplet;

[0012] Move the substrate to control the centers of the magnetic bead, the droplet, and the magnet to be on the same vertical line.

[0013] Furthermore, the step of collecting the droplet image, intercepting the region above the droplet and the magnetic bead as a whole for force analysis, and constructing the surface tension calculation formula specifically includes:

[0014] Collect a side view of the droplet and the magnetic bead based on the camera;

[0015] Taking the plane at the bottom of the droplet as the reference plane, intercept the region above the droplet according to the preset interval height to obtain an intercepted image;

[0016] Taking the plane at the bottom of the intercepted image as the intercepting plane, perform force analysis on the region above the droplet and the magnetic bead as a whole, and construct the surface tension calculation formula.

[0017] Furthermore, the surface tension calculation formula is as follows:

[0018]

[0019] In the above formula, F mag represents the magnetic force, m represents the total mass of the magnetic bead and the intercepted liquid, ρ represents the liquid density, S represents the area of the measurement cross-section, l represents the perimeter of the measurement cross-section, θ represents the angle between the liquid surface and the horizontal plane, r b represents the radius of the reference plane, θ b represents the angle between the reference liquid surface and the horizontal plane, and Δh represents the height difference between the cross-section and the reference plane.

[0020] Furthermore, the step of obtaining the droplet contour information based on the surface tension calculation formula, performing calculations, and obtaining the surface tension specifically includes:

[0021] Collect the image to be measured and perform binarization on the image to be measured to obtain a binarized image;

[0022] Perform edge detection on the binarized image for the droplet and the magnetic bead to obtain a clear image;

[0023] Obtain the droplet contour information according to the clear image, and calculate the surface tension in combination with the surface tension calculation formula.

[0024] Furthermore, the droplet contour information includes the area of the measurement cross-section, the perimeter of the measurement cross-section, the angle between the liquid surface and the horizontal plane, the radius of the reference plane, the angle between the reference liquid surface and the horizontal plane, and the height difference between the cross-section and the reference plane.

[0025] The second technical solution adopted by the present invention is: a surface tension measurement system based on a magnetic bead, including:

[0026] A control module for placing magnetic beads into a droplet and controlling the central points of the magnetic beads, the droplet, and the magnet to be on the same vertical line;

[0027] An analysis module for collecting droplet images, intercepting the upper part of the droplet and the magnetic beads as a whole for force analysis, and constructing a surface tension calculation formula;

[0028] A calculation module for obtaining droplet contour information and performing calculations based on the surface tension calculation formula to obtain the surface tension.

[0029] The beneficial effects of the method and system of the present invention are as follows: The present invention uses magnetocapillary action for surface tension measurement. Since the size of the magnetic beads is controllable, measurement can be carried out with a relatively small droplet volume. And because the magnetic beads can be manipulated and moved by a magnet and a magnetic field, the surface tension of a certain local area of the liquid surface can be measured. At the same time, the basic principle of this method is to calculate the surface tension through force balance. The magnitudes of various forces can be obtained only by analyzing the droplet shape and magnetic force calculation, and then the surface tension magnitude can be calculated by formula derivation, without the need for precise force sensors and other equipment, having a certain degree of simplicity and convenience. Description of the Drawings

[0030] Figure 1 is a flowchart of the steps of a method for measuring surface tension based on magnetic beads according to the present invention;

[0031] Figure 2 is a schematic diagram of the force analysis of magnetic beads and droplets in a specific embodiment of the present invention;

[0032] Figure 3 is a schematic diagram of a simple experimental device for measuring the surface tension of a liquid in a specific embodiment of the present invention;

[0033] Figure 4 is a flowchart of the image analysis and processing steps for analyzing the shape of the captured droplet in a specific embodiment of the present invention;

[0034] Figure 5 is a block diagram of the structure of a system for measuring surface tension based on magnetic beads according to the present invention. Detailed Embodiments

[0035] The following further describes the present invention in detail with reference to the drawings and specific embodiments. For the step numbers in the following embodiments, they are only set for the convenience of explanation and illustration, and no limitation is placed on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0036] As Figure 1 shown, the present invention provides a method for measuring surface tension based on magnetic beads, and the method includes the following steps:

[0037] Place the magnetic microsphere into the droplet and control the central points of the magnetic microsphere, the droplet, and the magnet to be on the same vertical line;

[0038] Collect the droplet image and intercept the upper part of the droplet and the magnetic microsphere as a whole for force analysis, and construct the calculation formula for surface tension;

[0039] Specifically, intercept the upper part of the droplet and the magnetic microsphere as a whole for force analysis. The magnetic microsphere is subject to an attractive force F mag from the magnet, with the direction vertically upward; the liquid is subject to the surface tension acting downward along the tangent direction of the liquid surface. The angle between the liquid surface and the horizontal direction is θ, and the vertical component of the surface tension is lγsinθ, where l is the perimeter of the lower surface (l = πr 2 , r is the radius of the lower surface), γ is the surface tension coefficient (referred to as surface tension); the magnetic microsphere and the liquid are also subject to the gravity mg acting vertically downward, m is the total mass of the magnetic microsphere and the liquid, and g is the acceleration due to gravity; in addition, the lower surface is subject to the pressure P from the liquid at the bottom acting vertically upward.

[0040] Select a certain horizontal plane far from the magnetic microsphere as the reference plane, and calculate the additional pressure inside the droplet through the Laplace pressure difference formula , where r1 and r2 are the principal radii of curvature of the curved liquid surface. For the liquid surface far from the magnetic microsphere, assume it is a spherical surface, θ b is the angle between the liquid surface below the reference plane and the horizontal plane, and r b is the radius of the reference plane. The internal pressure of the liquid at a height of Δh above the reference plane can be determined by the hydrostatic pressure difference formula:

[0041]

[0042] where ρ is the liquid density. This pressure acts on the lower surface of the intercepted surface with an area of S, generating a vertical upward pressure

[0043]

[0044] In the static state, Figure 2 all the acting forces in the right figure need to be balanced in the vertical direction, that is

[0045]

[0046] From this, the calculation formula for surface tension can be obtained:

[0047]

[0048] Therefore, when the magnetic force F mag, on the basis of the liquid density ρ, through image analysis, measure the cross-sectional area S, perimeter l, the angle θ between the liquid surface and the horizontal plane, and the reference plane radius r b and the angle θ between the reference liquid surface and the horizontal plane b , the height difference Δh between the cross-section and the reference plane, and the total mass m of the magnetic small ball and the intercepted liquid, then the surface tension of the liquid can be measured.

[0049] The total mass m can be obtained by measuring the mass of the magnetic small ball using an analytical balance and calculating the liquid mass through image analysis, and then adding the two. Accurately measuring the mass of the magnetic small ball is the key to ensuring the measurement accuracy.

[0050] The attraction force F of the magnet on the magnetic small ball mag increases as the distance between the magnet and the magnetic small ball decreases. Based on the magnetization curve of the magnetic small ball and the magnetic field distribution around the magnet, through the formula calculate the attraction force.

[0051] Based on the surface tension calculation formula, obtain the droplet contour information and perform calculations to obtain the surface tension.

[0052] Specifically, referring to Figure 4 , collect the image to be measured and perform binarization on the image to be measured to obtain a binarized image; perform edge detection on the binarized image for the droplet and the magnetic small ball to obtain a clear image; obtain the droplet contour information according to the clear image, and calculate the surface tension in combination with the surface tension calculation formula. Specific Example 1:

[0054] S1. Prepare a clean silicon wafer as the substrate for the measurement experiment, place the silicon substrate on the placement table of the device, and use a pipette to aspirate 5 μL of water droplets onto the silicon substrate;

[0055] S2. Weigh the mass of the magnetic small ball using an analytical balance, and then place it into the water droplet dropped on the substrate in the first step;

[0056] S3. Place a magnet on the lower surface of the displacement platform, and adjust the position of the silicon substrate so that the centers of the magnetic small ball, the water droplet, and the magnet are on the same vertical line;

[0057] S4. Refer to the schematic diagram of the measurement device Figure 3 , start the measurement experiment, adjust the distance between the magnet and the magnetic small ball. As the distance shortens, the magnetic force on the magnetic small ball increases, and the water droplet deforms due to capillary action. At the same time, use a camera to record the deformation process of the water droplet;

[0058] S5. Analyze the shape of the collected water droplet, use the compiled software to obtain the droplet contour information and perform calculations to obtain the necessary data for calculating the surface tension, and then calculate the surface tension at different cross-sectional heights through the formula. Specific Embodiment 2:

[0060] S1. Prepare a silicon surface modified with a PFPE (perfluoropolyether) coating as the substrate for the measurement experiment, and use the dip-coating method to prepare a firm PFPE coating on the silicon surface;

[0061] S2. Use a pipette to take 200 μL of PFPE solution and place it in a petri dish. Then immerse a clean silicon wafer in the solution and pull it out at a certain inclined angle after a few seconds. Heat it in an oven at 130 °C for 30 minutes. Wash it with n-hexane and dry it to obtain the final sample. Place the PFPE-modified silicon substrate on the placement platform of the device, and use a pipette to aspirate 5 μL of water droplet and place it on the silicon substrate;

[0062] S3. Weigh the mass of the magnetic beads with an analytical balance, and then put them into the liquid droplet dropped on the substrate in Step 2;

[0063] S4. Place a magnet on the lower surface of the displacement platform, and adjust the position of the substrate so that the centers of the magnetic beads, the liquid droplet, and the magnet are on the same vertical line;

[0064] S5. After preparing the above steps, the measurement experiment can be started. Adjust the distance between the magnet and the magnetic beads. As the distance shortens, the magnetic force on the magnetic beads increases, and the liquid droplet deforms due to capillary action. At the same time, use a camera to record the deformation process of the liquid droplet;

[0065] S6. Analyze the shape of the collected liquid droplet, use the compiled software to obtain the liquid droplet contour information and calculate the necessary data for calculating the surface tension, and then calculate the surface tension at different cross-sectional heights through the formula. Specific Embodiment 3:

[0067] S1. Prepare a silicon surface modified with a PFPE (perfluoropolyether) coating as the substrate for the measurement experiment, and use the dip-coating method to prepare a firm PFPE coating on the silicon surface;

[0068] S2. Use a pipette to take 200 μL of PFPE solution and place it in a petri dish. Then immerse a clean silicon wafer in the solution and pull it out at a certain inclined angle after a few seconds. Heat it in an oven at 130 °C for 30 minutes. Wash it with n-hexane and dry it to obtain the final sample;

[0069] S3. Place the PFPE-modified silicon substrate on the placement platform of the device, and use a pipette to aspirate 5 μL of n-hexane and place it on the silicon substrate;

[0070] S4. Weigh the mass of the magnetic beads with an analytical balance, and then put them into the liquid droplet dropped on the substrate in Step 3;

[0071] S5. Place a magnet on the lower surface of the displacement platform, and adjust the position of the substrate so that the centers of the magnetic bead, the droplet, and the magnet are on the same vertical line;

[0072] S6. After preparing the above steps, the measurement experiment can be started. Adjust the distance between the magnet and the magnetic bead. As the distance shortens, the magnetic force on the magnetic bead increases, and the droplet deforms due to capillary action. At the same time, use a camera to record the deformation process of the droplet;

[0073] S7. Analyze the shape of the collected droplet, use the compiled software to obtain the droplet contour information and calculate it to obtain the necessary data for calculating the surface tension, and then calculate the surface tension at different cross-sectional heights through the formula.

[0074] As Figure 5 shown, a surface tension measurement system based on a magnetic bead includes:

[0075] A control module for placing the magnetic bead into the droplet and controlling the centers of the magnetic bead, the droplet, and the magnet to be on the same vertical line;

[0076] An analysis module for collecting droplet images and intercepting the upper part of the droplet and the magnetic bead as a whole for force analysis, and constructing a surface tension calculation formula;

[0077] A calculation module, based on the surface tension calculation formula, obtains the droplet contour information and calculates to obtain the surface tension.

[0078] The content in the above method embodiments is applicable to the present system embodiment. The functions specifically implemented by the present system embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0079] A surface tension measurement device based on a magnetic bead:

[0080] At least one processor;

[0081] At least one memory for storing at least one program;

[0082] When the at least one program is executed by the at least one processor, the at least one processor implements the above-mentioned surface tension measurement method based on a magnetic bead.

[0083] The content in the above method embodiments is applicable to the present device embodiment. The functions specifically implemented by the present device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0084] A storage medium stores instructions executable by a processor, characterized in that: the instructions executable by the processor, when executed by the processor, are used to implement the above-mentioned method for measuring surface tension based on magnetic beads.

[0085] The content in the above method embodiments is applicable to the present storage medium embodiment. The functions specifically implemented by the present storage medium embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0086] The above has specifically described the preferred embodiments of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included within the scope defined by the claims of the present application.

Claims

1. A method for measuring surface tension based on magnetic beads, characterized in that Including the following steps: Put the magnetic microspheres into the droplet and control the central points of the magnetic microspheres, the droplet and the magnet to be on the same vertical line; Collect the droplet image, intercept the upper part of the droplet and the magnetic microspheres as a whole for force analysis, and construct a surface tension calculation formula; Based on the surface tension calculation formula, obtain the droplet contour information and perform calculations to obtain the surface tension; Manipulate and move the magnetic microspheres through the magnet and the magnetic field to measure the surface tension of a certain part of the liquid surface; The step of collecting the droplet image, intercepting the upper part of the droplet and the magnetic microspheres as a whole for force analysis, and constructing a surface tension calculation formula specifically includes: Collect the side view of the droplet and the magnetic microspheres based on the camera; Taking the plane at the bottom of the droplet as the reference plane, intercept the upper region of the droplet according to the preset interval height to obtain an intercepted image; Taking the plane at the bottom of the intercepted image as the intercepting plane, perform force analysis on the upper region of the droplet and the magnetic microspheres as a whole, and construct a surface tension calculation formula; The surface tension calculation formula is as follows: In the above formula, F mag represents the magnetic force, m represents the total mass of the magnetic ball and the intercepted liquid, g represents the acceleration due to gravity, ρ represents the liquid density, S represents the area of the measurement cross-section, l represents the perimeter of the measurement cross-section, θ represents the angle between the liquid surface and the horizontal plane, r b represents the reference plane radius, θ b represents the angle between the reference liquid surface and the horizontal plane, and Δh represents the height difference between the cross-section and the reference plane.

2. According to the method for measuring surface tension based on magnetic microspheres described in claim 1, the step of putting the magnetic microspheres into the droplet and controlling the central points of the magnetic microspheres, the droplet and the magnet to be on the same vertical line specifically includes: Absorb the solution and drop it on the substrate to form a droplet; Measure the mass of the magnetic microspheres and put them into the droplet; Fix the magnet above the droplet; Move the substrate to control the central points of the magnetic microspheres, the droplet and the magnet to be on the same vertical line.

3. The surface tension measurement method based on magnetic beads according to claim 1, wherein The step of obtaining the droplet contour information and performing calculations based on the surface tension calculation formula to obtain the surface tension specifically includes: Collect the image to be measured and perform binarization on the image to be measured to obtain a binarized image; Perform edge detection on the binarized image for the droplet and the magnetic microspheres to obtain a clear image; Obtain the droplet contour information according to the clear image, and calculate the surface tension in combination with the surface tension calculation formula.

4. The surface tension measurement method based on magnetic beads according to claim 3, wherein The droplet contour information includes the area of the measurement cross-section, the perimeter of the measurement cross-section, the angle between the liquid surface and the horizontal plane, the radius of the reference plane, the angle between the reference liquid surface and the horizontal plane, and the height difference between the cross-section and the reference plane.

5. A surface tension measurement system based on magnetic beads, characterized in that, Used to execute a method for measuring surface tension based on magnetic microspheres as described in claim 1, including: A control module for putting the magnetic microspheres into the droplet and controlling the central points of the magnetic microspheres, the droplet and the magnet to be on the same vertical line; An analysis module for collecting the droplet image, intercepting the upper part of the droplet and the magnetic microspheres as a whole for force analysis, and constructing a surface tension calculation formula; A calculation module, based on the surface tension calculation formula, obtaining the droplet contour information and performing calculations to obtain the surface tension.

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