Dark field differential dynamic microscopy system and method for bulk phase nanobubble characterization

Abstract

The invention relates to the technical field of bulk-phase nanobubble characterization, and discloses a dark-field differential dynamic microscopic system and method for bulk-phase nanobubble characterization. The system comprises an illumination light path and a measurement light path, wherein the illumination light path comprises a laser, a reflector and a cylindrical lens which are arranged in sequence; the measuring light path comprises a sample pool, a microscope objective lens, a first lens, a second lens, a third lens and a CMOS high-speed camera which are arranged in sequence. The microscope objective lens, the first lens, the second lens, the third lens and the CMOS high-speed camera are located on the same axis. According to the method, the motion information of the volume-phase nanobubbles is obtained through the frequency domain change of the microscopic motion image, so that the particle size of the nanobubbles is calculated. Compared with the existing characterization technology, the method has the advantages that the measurement time and the instrument cost are greatly reduced, the defect that only low-concentration samples are used for characterization in the existing characterization technology is overcome, the applicable sample concentration range is wide, and efficient and accurate characterization of the bulk-phase nanobubbles under the visual condition is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of bulk nanobubble characterization, and in particular relates to a dark field differential dynamic microscopic measurement system and method for bulk nanobubble characterization. Background Art

[0002] Bulk nanobubbles have attracted attention in many fields due to their special physical and chemical properties, and the characterization technology of bulk nanobubbles has always been an important part of bulk nanobubble research. Although the existing bulk nanobubble characterization methods can accurately measure the particle size information of bulk nanobubbles, they all have problems such as high equipment requirements and long measurement time, and can only be applied to the measurement of low-concentration samples, which will bring large errors to the measurement of high-concentration samples.

[0003] At present, dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) are often used in the study of bulk nanobubbles to measure the particle size of bulk nanobubbles. However, both dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) have certain limitations. Nanoparticle tracking analysis (NTA) requires that the particles are optically distinguishable, so it has great limitations in terms of solution concentration and particle size, and the measurement time is long. For high-concentration samples, the correlation function of dynamic light scattering (DLS) is very susceptible to multiple scattering, the experimental setup is more complicated, visual measurement cannot be achieved, and the measurement time is long. Summary of the invention

[0004] The purpose of the present invention is to provide a dark field differential dynamic microscopy measurement system and method for bulk nanobubble characterization, so as to measure bulk nanobubbles with a wide range of samples under visual conditions and obtain the particle size information of bulk nanobubbles. Through dark field differential dynamic microscopy technology, the visualized measurement of bulk nanobubble particle size is realized on the microscope system, and the measurement time is greatly shortened, and high concentration sample measurement can be realized.

[0005] In order to achieve the purpose of the present invention, the present invention provides a dark-field differential dynamic microscopy measurement system for bulk nanobubble characterization, comprising an illumination light path and a measurement light path: the illumination light path comprises a laser, a reflector and a cylindrical lens arranged in sequence, the reflector is used to reflect the incident light emitted by the laser to the cylindrical lens; the measurement light path comprises a sample pool, a microscope objective, a first lens, a second lens, a third lens and a CMOS high-speed camera arranged in sequence, the microscope objective, the first lens, the second lens, the third lens and the CMOS high-speed camera are located on the same axis.

[0006] Furthermore, the laser, the reflector, and the cylindrical lens are located on one side of the sample pool, the incident light passes through the reflector and the cylindrical lens, the reflector and the center of the incident light source are located on the same axis, the reflector and the center of the cylindrical lens are located on another same axis, and the two axes are perpendicular to each other. The microscope objective lens, the first lens, the second lens, the third lens, and the CMOS high-speed camera are located on one side of the sample pool, and the center of the microscope objective lens, the center of the first lens, the center of the second lens, the center of the third lens, and the center of the CMOS high-speed camera are located on the same axis, and are perpendicular to the axis where the cylindrical lens is located.

[0007] Furthermore, the incident light source reaches the cylindrical lens through the reflector, and changes from a point light source to a surface light source and enters the sample pool. The scattered light of the sample passes through the microscope objective lens, the first lens, the second lens, and the third lens, and completes microscopic imaging on the CMOS camera.

[0008] Furthermore, the first lens is a microscope tube lens having a focal length that matches that of a microscope objective lens, and the second lens and the third lens are double convex lenses having the same focal length.

[0009] Furthermore, the microscopic motion image acquisition is completed on a CMOS high-speed camera by capturing the motion state of bulk nanobubbles and extracting each frame of the image.

[0010] The present invention also provides a dark field differential dynamic microscopy measurement method for characterizing bulk nanobubbles, characterized in that the system described in any one of claims 1 to 4 is used, and the method comprises the steps of:

[0011] Injecting bulk nanobubbles into the sample cell;

[0012] The laser emits incident light to the sample pool, and the microscopic motion image is collected on the CMOS high-speed camera;

[0013] Differentiating the collected microscopic motion image to obtain a differential image, performing a two-dimensional fast Fourier transform on the differential image to obtain frequency domain data of the differential image;

[0014] Fit the frequency domain data of the difference image to obtain the amplitude A(q) of the image signal, the noise part B(q) of the camera image, and the intermediate scattering function f(q,Δt);

[0015] The diffusion coefficient of the bulk nanobubbles is obtained by linear fitting of the intermediate scattering function f(q,Δt), and the particle size of the bulk nanobubbles is obtained based on the diffusion coefficient of the bulk nanobubbles.

[0016] Furthermore, the bulk nanobubbles are generated by an electrochemical method.

[0017] Furthermore, the image difference is obtained by subtracting the second to the last photo from the first photo of the microscopic motion image to obtain a difference map D(x, y, t, Δt), which is used to describe the difference in scattered light intensity between the time Δt and the initial time.

[0018] Frequency domain analysis is to perform a two-dimensional fast Fourier transform on the obtained difference image to obtain the spectrum data of the difference image and obtain the image structure function (ISF) by fitting; data fitting is to extract the intermediate scattering function f(q,Δt) from the image structure function (ISF) to obtain the motion information of the bulk nanobubbles, thereby calculating the particle size information of the bulk nanobubbles.

[0019] Furthermore, the frequency domain analysis performs a two-dimensional fast Fourier transform on the obtained difference image to obtain the spectrum data of the difference image, thereby calculating the image structure function (ISF):

[0020] The expression of the difference graph D(x,y,t,Δt) is:

[0021] D(x,y,t,Δt)=I(x,y,t+Δt)-I(x,y,t)

[0022] Where, I(x,y,t) represents the scattered light intensity of the microscopic motion image at time t and the pixel at the coordinate position (x,y), and I(x,y,t+Δt) represents the microscopic motion image information at time Δt after time t;

[0023] The difference graph is transformed into a two-dimensional Fourier transform to obtain the difference graph D(u x ,u y ,Δt):

[0024] |D(u x ,u y ,Δt)| 2 =<|FFT.[ΔI(x,y,Δt)]| 2 >

[0025] Furthermore, different components with the same spatial frequency are radially averaged by data fitting to achieve one-dimensional processing The equation can be decomposed into three independent functions:

[0026] |D(q,Δt) 2 =A(q)[1-f(q,Δt)]+B(q)

[0027] f(q,Δt) is the intermediate scattering function, which can obtain the motion information of bulk nanobubbles. The intermediate scattering function is fitted using the following relationship to obtain the diffusion coefficient of the sample:

[0028]

[0029] The particle size of bulk nanobubbles is calculated based on the diffusion coefficient Dm of bulk nanobubbles and combined with the Einstein-Stokes equation:

[0030]

[0031] Among them, K B is the Boltzmann constant, T is the thermodynamic temperature of the experimental environment (solution), d is the diameter of the bulk nanobubble, and η is the viscosity coefficient of the solution.

[0032] Compared with the prior art, the present invention can at least achieve the following beneficial effects:

[0033] (1) The dark-field differential dynamic microscopy measurement system and method for bulk nanobubble characterization of the present invention can accurately measure the particle size of bulk nanobubbles, and greatly reduce the measurement time and instrument cost compared to existing characterization technologies, while achieving efficient and accurate characterization of bulk nanobubbles.

[0034] (2) The present invention applies dark field differential dynamic microscopy to the characterization of bulk nanobubbles, and obtains the motion information of bulk nanobubbles by image processing to achieve particle size characterization. Compared with existing characterization methods, this method reduces the equipment requirements and improves the measurement speed, which has obvious technical advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The figure is a schematic flow chart of a dark-field differential dynamic microscopy measurement method for characterizing bulk nanobubbles in an embodiment of the present invention.

[0036] Figure 2 Schematic diagram of the overall structure of the dark-field differential dynamic microscopy system in an example of the present invention.

[0037] Figure 3 This is a fitting result diagram of bulk nanobubbles in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art. If the manufacturer of the reagents or instruments used is not indicated, they are deemed to be conventional products that can be purchased commercially.

[0039] In the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes, and do not specifically refer to the order or sequence, nor are they used to limit the present invention. They are only used to distinguish components or operations described with the same technical terms, and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0040] See also Figure 2 The present invention provides a dark field differential dynamic microscopy measurement system for bulk nanobubble characterization, comprising an illumination optical path and a measurement optical path, wherein the illumination optical path comprises a laser 1, a reflector 2, and a cylindrical lens 3, and the measurement optical path comprises a sample pool 4, a microscope objective 5, a first lens 6, a second lens 7, a third lens 8, and a CMOS high-speed camera 9. The dark field differential dynamic microscopy system is used to complete the acquisition of microscopic motion images.

[0041] The laser 1, the reflector 2, and the cylindrical lens 3 are arranged in sequence and located on one side of the sample pool 4. The incident light of the laser 1 passes through the cylindrical lens 3 through the reflector 2. The reflector 2 and the center of the incident light source are located on the same axis. The centers of the reflector 2 and the cylindrical lens 3 are located on another same axis, and the two axes are in a perpendicular relationship. The laser 1 is used to generate an incident light beam. The reflector 2 provides a dark field lateral illumination mode so that the light source is incident from the side of the sample pool 4. The cylindrical lens 3 changes the point light source of the laser 1 into a line light source and is incident on the sample pool 4. The microscope objective 5, the first lens 6, the second lens 7, the third lens 8, and the CMOS high-speed camera 9 are arranged in sequence and located on the other side of the sample pool 4. The center of the microscope objective 5, the center of the first lens 6, the center of the second lens 7, the center of the third lens 8, and the center of the CMOS high-speed camera 9 are located on the same axis and are in a perpendicular relationship with the axis of the cylindrical lens 3 to ensure that the image finally observed by the CMOS high-speed camera 9 has no distortion. The first lens 6 is a microscope tube lens that matches the focal length of the microscope objective lens 5, and is responsible for receiving the light transmitted from the objective lens and focusing the light into the second lens 7. The second lens 7 magnifies the image passing through the first lens 6 again to ensure that only sample information is in the field of view of the CMOS high-speed camera 9. The third lens 8 is the imaging lens of the CMOS high-speed camera 9. The light beam passes through the first lens 6, the second lens 7, and the third lens 8, and completes the microscopic imaging together with the CMOS high-speed camera 9.

[0042] The second lens 7 and the third lens 8 together with the CMOS high-speed camera 9 complete microscopic imaging. After the system collects the motion image of the sample, the motion information of the sample is obtained through the dark field differential dynamic microscopy technology.

[0043] In some embodiments of the present invention, the laser 1 uses a laser with a power of 12mW and a wavelength of 635nm; the sample pool 4 uses a four-sided light-transmitting glass sample pool, and the sample is added after ultrasonic cleaning, and the sample is fixed in the sample pool 4 through a sample pool holder; the microscope objective 5 is an infinite long working distance objective with a magnification of 20 times; the first lens 6 is a microscope tube lens that matches the focal length of the microscope objective 5; the second lens 7 and the third lens 8 are both double convex lenses.

[0044] Among them, the basic principles of dark field differential dynamic microscopy are as follows:

[0045] The Brownian motion of bulk nanobubbles over a period of time is captured by a dark-field differential dynamic microscopy measurement system, and all frames of the video are extracted to obtain a set of images I(x, y, t), which represents the scattered light intensity and the pixel at the coordinate position (x, y) of the microscopic motion image at time t. Starting from the second image, the first image is subtracted until the last image, and a difference image D(x, y, t, Δt) is obtained to describe the difference in scattered light intensity between time Δt and the initial time:

[0046] D(x,y,t,Δt)=I(x,y,t+Δt)-I(x,y,t)

[0047] I(x,y,t+Δt) is the microscopic motion image information at time Δt after time t;

[0048] The difference image only retains the motion information of the particles and eliminates the influence of static noise. Then the difference image is transformed into a two-dimensional Fourier transform to calculate the image structure function (ISF):

[0049] |D(u x ,u y ,Δt)| 2 =<|FFT.[ΔI(x,y,Δt)]| 2 >

[0050] D(u x ,u y ,Δt) represents the difference image after two-dimensional Fourier transform, FFT.[.....] represents fast Fourier transform. For each difference image with a fixed time interval, multiple difference images with the same time interval Δt can be averaged in time to reduce system errors and improve calculation accuracy. ΔI(x,y,Δt) is the image information after time averaging. ux ,u y Represents the coordinate system in the Fourier transform frequency domain, which can radially average different components with the same spatial frequency to achieve one-dimensional processing u is the spatial frequency. For ease of processing, the spatial frequency u is replaced by the wave vector q = 2πu, and the equation can be decomposed into three independent functions:

[0051] |D(q,Δt)| 2 =A(q)[1-f(q,Δt)]+B(q)

[0052] Among them, D(q,Δt) is the frequency domain data of the difference image after the two-dimensional Fourier transform after the wave vector q replaces the spatial frequency, A(q) is the amplitude of the image signal, which depends on the characteristics of the sample and the imaging system, B(q) is regarded as the noise part of the microscopic motion image; f(q,Δt) is the intermediate scattering function, which can obtain the motion information of the particles. The wave vector value q is determined by the pixel size of the CMOS high-speed camera and the resolution of the microscopic motion image. According to the imaging principle of the dark field image, the initial fitting values ​​of A(q), B(q) and f(q,Δt) are selected, and the frequency domain data D(q,Δt) of the difference image is fitted to obtain the amplitude A(q) of the image signal, the noise part B(q) of the camera image and the intermediate scattering function f(q,Δt). Then use:

[0053]

[0054] and:

[0055]

[0056] By fitting the above relationship between f(q,Δt) and τ(q), we can get the diffusion coefficient Dm of the bulk nanobubble. Finally, the Einstein-Stokes equation is used to determine the particle size of the bulk nanobubble:

[0057]

[0058] Among them, K B is the Boltzmann constant, T is the thermodynamic temperature of the experimental environment, d is the diameter of the bulk nanobubble, and η is the viscosity coefficient of the solution.

[0059] See also Figure 1 The present invention provides a dark field differential dynamic microscopy measurement method for characterizing bulk nanobubbles, comprising the following steps:

[0060] Step 1: Produce bulk nanobubbles.

[0061] In some embodiments of the present invention, nanobubbles are generated by electrochemical method, and a salt solution is electrolyzed by an electrochemical device at 20 V for 20 minutes to obtain stable bulk nanobubbles. The bulk nanobubbles generated in this embodiment have a diameter of 323.2 nm.

[0062] Step 2: Inject the prepared bulk nanobubbles into the sample pool 4 in the dark field differential dynamic microscopy system.

[0063] Step 3: Turn on the laser 1 to emit incident light into the sample pool 4 , and complete the acquisition of the microscopic motion image on the CMOS high-speed camera 9 .

[0064] Step 4: Differentiate the acquired microscopic motion image to obtain a differential image; perform a two-dimensional fast Fourier transform on the differential image to obtain a differential image D(u x u y ,Δt), and use the wave vector q instead of the spatial frequency u to obtain the frequency domain data D(q,Δt) of the difference image.

[0065] Step 5: Select the initial fitting value according to the imaging principle of the dark field image, fit the frequency domain data D(q,Δt) of the difference image, and obtain the amplitude A(q) of the image signal, the noise part B(q) of the camera image, and the intermediate scattering function f(q,Δt).

[0066] Step 6: Perform linear fitting on the intermediate scattering function f(q,Δt) to obtain the diffusion coefficient of the bulk nanobubbles, and use the Einstein-Stokes equation to calculate the particle size of the bulk nanobubbles.

[0067] In some embodiments of the present invention, the fitting results of bulk nanobubbles measured by dark field differential dynamic microscopy are as follows: Figure 3 As shown, according to the principle of dark field differential dynamic microscopy, the intercept obtained after linear fitting is the diffusion coefficient of bulk nanobubbles. The fitting result obtained in this embodiment is 326.7nm, with a relative error of less than 5%.

[0068] In the field of bulk nanobubble characterization technology, there is currently no characterization technology with low equipment requirements, fast measurement, and visualization, which greatly increases the cost and time cost of measuring instruments; and it is difficult to accurately measure high-concentration samples, and the concentration range of samples that can be analyzed is relatively narrow. The aforementioned embodiment of the present invention provides a dark-field differential dynamic microscopy measurement system for bulk nanobubble characterization. Dark-field differential microscopy is an image analysis method that combines scattering sensitivity with microscopic imaging visualization, which can obtain the movement information of bubbles and combine theoretical simulation with actual experiments. It also greatly reduces the threshold of equipment requirements, improves the measurement speed, and can measure samples in a wider concentration range. The present invention is of great significance to the characterization technology research and stability research of bulk nanobubbles.

[0069] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A dark-field differential dynamic microscopy measurement system for bulk nanobubble characterization, characterized in that: The method comprises an illumination optical path and a measurement optical path: the illumination optical path comprises a laser, a reflector and a cylindrical lens which are arranged in sequence, and the reflector is used to reflect the incident light emitted by the laser to the cylindrical lens; the measurement optical path is used to collect the microscopic motion image of the bulk nanobubble, and the measurement optical path comprises a sample pool, a microscope objective lens, a first lens, a second lens, a third lens and a CMOS high-speed camera which are arranged in sequence, and the microscope objective lens, the first lens, the second lens, the third lens and the CMOS high-speed camera are located on the same axis.

2. The dark field differential dynamic microscopy measurement system for bulk nanobubble characterization according to claim 1, characterized in that: The laser, the reflector, and the cylindrical lens are located on one side of the sample pool, and the incident light passes through the reflector and the cylindrical lens. The reflector and the center of the incident light source are located on the same axis, and the reflector and the center of the cylindrical lens are located on another same axis, and the two axes are perpendicular to each other; the microscope objective, the first lens, the second lens, the third lens, and the CMOS high-speed camera are located on one side of the sample pool, and the axes on which the microscope objective, the first lens, the second lens, the third lens, and the CMOS high-speed camera are located are perpendicular to the axis on which the cylindrical lens is located.

3. The dark field differential dynamic microscopy measurement system for bulk nanobubble characterization according to claim 1, characterized in that: The microscopic motion image of bulk nanobubbles is acquired by a CMOS high-speed camera, and the momentary motion state of bulk nanobubbles is photographed by a CMOS high-speed camera, and each frame of the image is extracted.

4. The dark field differential dynamic microscopy measurement system for bulk nanobubble characterization according to any one of claims 1 to 3, characterized in that: The first lens is a microscope tube lens with a focal length that matches that of the microscope objective lens, and the second lens and the third lens are both double convex lenses with the same focal length.

5. A dark-field differential dynamic microscopy measurement method for bulk nanobubble characterization, characterized in that: Using the system according to any one of claims 1 to 4, the method comprises the steps of: Injecting bulk nanobubbles into the sample cell; The laser emits incident light to the sample pool, and the microscopic motion image is collected on the CMOS high-speed camera; Differentiating the collected microscopic motion image to obtain a differential image, performing a two-dimensional fast Fourier transform on the differential image to obtain frequency domain data of the differential image; Fit the frequency domain data of the difference image to obtain the amplitude A(q) of the image signal, the noise part B(q) of the camera image, and the intermediate scattering function f(q,Δt); The diffusion coefficient of the bulk nanobubbles is obtained by linear fitting of the intermediate scattering function f(q,Δt), and the particle size of the bulk nanobubbles is obtained based on the diffusion coefficient of the bulk nanobubbles.

6. The dark field differential dynamic microscopy measurement method for bulk nanobubble characterization according to claim 5, characterized in that: The bulk nanobubbles are generated by an electrochemical method.

7. The dark field differential dynamic microscopy measurement method for bulk nanobubble characterization according to claim 5, characterized in that: Image difference is obtained by subtracting the second to last pictures from the first picture in the microscopic motion image to obtain a difference image.

8. The dark field differential dynamic microscopy measurement method for bulk nanobubble characterization according to claim 5, characterized in that: The method comprises: performing a difference on the collected microscopic motion image to obtain a difference image, and performing a two-dimensional fast Fourier transform on the difference image to obtain frequency domain data of the difference image, including: The expression of the difference graph D(x,y,t,Δt) is: D(x,y,t,Δt)=I(x,y,t+Δt)-I(x,y,t) Where, I(x,y,t) represents the scattered light intensity of the microscopic motion image at time t and the pixel at the coordinate position (x,y), and I(x,y,t+Δt) represents the microscopic motion image information at time Δt after time t; The difference graph is transformed into a two-dimensional Fourier transform to obtain the difference graph D(u x ,u y ,Δt): |D(u x ,u y ,Δt)| 2 =<|FFT.[ΔI(x,y,Δt)]| 2 > In the formula, D(u x ,u y ,Δt) represents the difference image after two-dimensional Fourier transform, FFT.[.....] represents fast Fourier transform, ΔI(x,y,Δt) represents the image information after time averaging, u x ,u y Represents the coordinate system in the Fourier transform frequency domain, spatial frequency Substituting the wave vector q = 2πu for the spatial frequency u, we obtain: |D(q,Δt) 2 =A(q)[1-f(q,Δt)]+B(q) Where D(q,Δt) is the frequency domain data of the difference image after two-dimensional Fourier transformation after the wave vector q replaces the spatial frequency, A(q) is the amplitude of the image signal, B(q) represents the noise part of the microscopic motion image; f(q,Δt) is the intermediate scattering function.

9. The dark field differential dynamic microscopy measurement method for bulk nanobubble characterization according to claim 8, characterized in that: The frequency domain data D(q,Δt) of the difference image is fitted to obtain the amplitude A(q) of the image signal, the noise part B(q) of the microscopic motion image, and the intermediate scattering function f(q,Δt).

10. The dark field differential dynamic microscopy measurement method for bulk nanobubble characterization according to claim 9, characterized in that: The diffusion coefficient Dm of the bulk nanobubble is obtained by fitting the intermediate scattering function f(q,Δt) through the following relationship; The particle size of bulk nanobubbles is calculated based on the diffusion coefficient Dm of bulk nanobubbles and combined with the Einstein-Stokes equation: Among them, K B is the Boltzmann constant, T is the thermodynamic temperature of the experimental environment, d is the diameter of the bulk nanobubble, and η is the viscosity coefficient of the solution.

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