Device and method for measuring thinning of liquid film between substrate and bubbles

Abstract

The invention relates to the technical field of flotation testing, and particularly discloses a device and a method for measuring thinning of a liquid film between a substrate and bubbles. The device for measuring the thinning of the liquid film between the substrate and the bubbles comprises a cantilever beam stress measurement system, a visualization system and a light path system, the cantilever beam stress measurement system, the bubble and the light path system are sequentially arranged from top to bottom, and the impact area of the cantilever beam stress measurement system and the bubble, the vertex of the bubble and the view field center of the light path system are adjusted to be located on the same axis; the cantilever beam stress measurement system is used for adjusting the spatial position of the bubble; the light path system forms interference fringes based on the spatial position of the bubble; and the visualization system is used for recording the interference fringes and calculating the liquid film thickness of the bubbles according to the interference fringes. The interference image in the contact process of the bubble liquid film and the wall surface is collected, and the wetting behaviors of the liquid film in different chemical environments are researched, so that a data basis can be provided for reagent addition in the flotation process, and the flotation efficiency of target minerals is improved.

Description

Technical Field

[0001] The invention relates to the technical field of flotation testing, and in particular to a device and method for measuring thinning of a liquid film between a substrate and bubbles. Background Art

[0002] Wetting processes can be seen everywhere in our daily lives. In industrial production and medical practice, the study of wetting processes is also indispensable, such as lubrication processes, nanolithography, coating, oil / gas recovery, flotation, air flotation, and surface cleaning. Flotation is an effective means of sorting low-grade fine-grained ores in industry. The flotation process utilizes the difference in hydrophilicity and hydrophobicity of different components, and is enhanced by specific agents. Bubbles are introduced into the raw material slurry so that the hydrophobic components attach to the bubbles and are separated. Generally speaking, the Reynolds number range of the flotation process is usually between 10^4 and 10^6, which is a state with a relatively high Reynolds number. The current devices for studying the interaction between particles and bubbles are generally only carried out in a laminar state (low Reynolds number), which is only suitable for research in a very small Reynolds number range, which is far lower than the actual flotation process fluid parameters.

[0003] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0004] The main purpose of the present invention is to provide a device and method for measuring the thinning of the liquid film between the substrate and the bubbles, aiming to solve the technical problem that it is difficult to measure the thinning process of the liquid film between the substrate and the bubbles during the flotation process in the prior art.

[0005] To achieve the above object, the present invention provides a device for measuring the thinning of a liquid film between a substrate and a bubble, the device comprising: a cantilever beam stress measurement system, a visualization system and an optical path system;

[0006] The cantilever beam stress measurement system, the bubble and the optical path system are arranged in sequence from top to bottom, and the collision area of ​​the cantilever beam stress measurement system and the bubble, the apex of the bubble and the field of view center of the optical path system are adjusted to be located on the same axis;

[0007] The cantilever beam stress measurement system is used to adjust the spatial position of the bubble;

[0008] The optical path system forms interference fringes based on the spatial position of the bubble;

[0009] The visualization system is used to record the interference fringes and calculate the liquid film thickness of the bubble according to the interference fringes.

[0010] Optionally, the cantilever beam stress measurement system comprises: a cantilever beam and a substrate;

[0011] The cantilever beam is connected to the upper side of the substrate, and the lower side of the substrate is close to the apex of the bubble;

[0012] The cantilever beam is used to adjust the displacement of the substrate to adjust the collision area between the substrate and the bubble;

[0013] The cantilever beam is also used to adjust the distance between the lower side of the substrate and the apex of the bubble.

[0014] Optionally, the cantilever beam stress measurement system further includes: a stepping motor and a piezoelectric ceramic positioning table;

[0015] The stepper motor and the piezoelectric ceramic positioning platform are connected in series to control the cantilever beam, and the stepper motor is electrically connected to the piezoelectric ceramic positioning platform;

[0016] The piezoelectric ceramic positioning stage generates a corresponding position voltage signal based on the position coordinates of the bubble, and transmits the position voltage signal to the stepping motor;

[0017] The stepping motor adjusts the position of the substrate to a target position according to the position voltage signal.

[0018] Optionally, the optical path system includes: a dual-band light source, a collimating lens, a dichroic mirror, a half-reflecting half-mirror, and two long-distance working objective lenses;

[0019] The two beams of light of different wavelengths emitted by the dual-band light source pass through the collimating lens and then through the half-reflecting half-mirror to be reflected on the liquid film of the bubble and the surface of the substrate. The reflected light passes through the half-reflecting half-mirror and the dichroic mirror and enters the long-distance working objective lens to be recorded by the visualization system respectively.

[0020] Optionally, the dual-band light source adopts a dual LED light source of a blue light source (430-480nm) and a red light source (620-760nm).

[0021] Optionally, the visualization system includes: a first high-speed camera and a second high-speed camera;

[0022] The first high-speed camera is arranged in the transmission light path direction of the dichroic mirror, and is used to receive and record the reflected light of the blue light source (430-480nm);

[0023] The second high-speed camera is arranged in the direction of the reflected light path of the dichroic mirror, and is used for receiving and recording the reflected light of the red light source (620-760nm).

[0024] Optionally, the visualization system further comprises: an illumination light source and a third high-speed camera;

[0025] The illumination light source and the third high-speed camera are arranged on a horizontal side between the lower side of the substrate and the apex of the bubble;

[0026] The lighting source is used to provide white light to cooperate with ambient light for lighting;

[0027] The third high-speed camera is used to record the liquid film contact process between the substrate and the bubble.

[0028] In addition, to achieve the above-mentioned purpose, the present invention also proposes a liquid film thinning measurement method, which is applied to the above-mentioned liquid film thinning measurement device between the substrate and the bubble, and the method comprises the following steps:

[0029] The separation distance between the bubble and the substrate is adjusted by adjusting the spatial position of the bubble;

[0030] recording changes in interference fringes based on the separation distance;

[0031] The thickness of the bubble liquid film is calculated according to the change of the interference fringes.

[0032] Optionally, the step of adjusting the separation distance between the bubble and the substrate by adjusting the spatial position of the bubble comprises:

[0033] Acquiring the spatial position of the bubble by a piezoelectric ceramic positioning stage;

[0034] The target position of the bubble is calculated using a visualization system, and a control signal of the target position is generated to drive a stepping motor to adjust the position of the substrate to adjust the separation distance.

[0035] Optionally, after the step of calculating the thickness of the bubble liquid film according to the change of the interference fringes, the method further includes:

[0036] The time during which the thickness of the liquid film is lower than the preset rupture thickness is recorded.

[0037] The technical solution of the present invention proposes a device and method for measuring the thinning of the liquid film between a substrate and a bubble. The device for measuring the thinning of the liquid film between a substrate and a bubble comprises: a cantilever beam stress measurement system, a visualization system and an optical path system; the cantilever beam stress measurement system, the bubble and the optical path system are arranged in sequence from top to bottom, and the collision area of ​​the cantilever beam stress measurement system and the bubble, the vertex of the bubble and the field of view center of the optical path system are adjusted to be located on the same axis; the cantilever beam stress measurement system is used to adjust the spatial position of the bubble; the optical path system forms interference fringes based on the spatial position of the bubble; the visualization system is used to record the interference fringes and calculate the thickness of the liquid film of the bubble according to the interference fringes. By collecting the interference image during the contact between the bubble liquid film and the wall surface, the study of the wetting behavior of the liquid film in different chemical environments can provide data basis for the addition of reagents in the flotation process, thereby improving the flotation efficiency of the target mineral. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of a first embodiment of a device for measuring thinning of a liquid film between a substrate and a bubble proposed by the present invention;

[0039] Figure 2 It is a schematic diagram of the thinning process of the liquid film between the substrate and the bubble according to the first embodiment of the measuring device for thinning the liquid film between the substrate and the bubble proposed by the present invention;

[0040] Figure 3 The figure is a flow chart of an embodiment of a method for measuring thinning of a liquid film proposed by the present invention.

[0041] Explanation of the accompanying drawings: 10, cantilever beam; 20, substrate; 30, bubble; 40, trough body; 50, dual-band light source; 60, collimating lens; 70, dichroic mirror; 80, semi-reflective and semi-transparent mirror; 90, long-distance working objective lens; 101, first high-speed camera; 102, second high-speed camera; 103, third high-speed camera.

[0042] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0043] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0046] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. 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 deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0047] The main solution of the embodiment of the present invention is: the device for measuring the thinning of the liquid film between the substrate and the bubble comprises: a cantilever beam stress measurement system, a visualization system and an optical path system; the cantilever beam stress measurement system, the bubble and the optical path system are arranged in sequence from top to bottom, and the collision area of ​​the cantilever beam stress measurement system and the bubble, the vertex of the bubble and the field of view center of the optical path system are adjusted to be located on the same axis; the cantilever beam stress measurement system is used to adjust the spatial position of the bubble; the optical path system forms interference fringes based on the spatial position of the bubble; the visualization system is used to record the interference fringes and calculate the liquid film thickness of the bubble according to the interference fringes.

[0048] Flotation is an effective means of industrial sorting of low-grade fine-grained ores. The flotation process uses the difference in hydrophilicity and hydrophobicity of different components, and is enhanced by specific reagents. Bubbles are introduced into the raw material slurry so that the hydrophobic components attach to the bubbles and are separated. The Reynolds number range of the flotation process is usually between 10^4 and 10^6, which is a relatively high Reynolds number state. However, the current devices for studying the interaction between particles and bubbles are generally only carried out in a laminar state (low Reynolds number), which is only suitable for research in a very small Reynolds number range, which is far lower than the actual flotation process fluid parameters.

[0049] This scheme collects interference images during the contact process between the bubble liquid film and the wall surface, and studies the wetting behavior of the liquid film in different chemical environments, which can provide data basis for the addition of reagents in the flotation process, thereby improving the flotation efficiency of the target mineral.

[0050] Reference Figure 1 , Figure 1 This is a schematic diagram of the structure of the first embodiment of the device for measuring the thinning of the liquid film between the substrate and the bubble proposed by the present invention. Figure 1 A first embodiment of a device for measuring thinning of a liquid film between a substrate and a bubble of the present invention is provided.

[0051] In this embodiment, the device for measuring the thinning of the liquid film between the substrate and the bubble includes: a cantilever beam stress measurement system, a visualization system and an optical path system; the cantilever beam stress measurement system, the bubble and the optical path system are arranged in sequence from top to bottom, and the collision area of ​​the cantilever beam stress measurement system and the bubble, the apex of the bubble and the field of view center of the optical path system are adjusted to be located on the same axis.

[0052] It should be noted that the cantilever beam stress measurement system can be used to adjust the spatial position of the bubble; the optical path system can form interference fringes based on the spatial position of the bubble; and the visualization system can be used to record the interference fringes and calculate the liquid film thickness of the bubble based on the interference fringes.

[0053] It should be understood that the flotation process utilizes the difference in hydrophilicity and hydrophobicity of different components, and is enhanced by specific reagents. Bubbles are introduced into the raw material slurry so that the hydrophobic components adhere to the bubbles and are separated. The liquid film wetting process can be roughly divided into three stages, taking the contact between bubbles and hydrophobic solid particles as an example: first, the bubbles and particles gradually approach each other, and the liquid film between the particles and bubbles gradually becomes thinner; when the thickness of the liquid film between the bubbles and the particles reaches the critical thickness, the liquid film becomes unstable and ruptures, forming a three-phase contact; finally, the three-phase contact line expands outward until it reaches a steady state. On the contrary, if the bubbles collide with the hydrophilic particles, three-phase contact may not occur in the end, and the liquid film will reach an equilibrium thickness, that is, the bubbles and the hydrophilic particles will not effectively adhere to each other.

[0054] Among them, the Reynolds number is a dimensionless number used in fluid mechanics to characterize flow conditions, which can reflect the relative proportion of inertial force to viscous force. The Reynolds number range of the flotation process is usually between 10^4 and 10^6, which belongs to the medium Reynolds number state. The traditional measurement of the interaction force between bubbles and minerals of different hydrophobicity can only study the wetting behavior at a low Reynolds number due to the limitation of the movement rate of the displacement adjustment mechanism, which is far lower than the actual flotation process fluid parameters. Low Reynolds number refers to the flow state of a fluid with a low Reynolds number, usually manifested as a laminar state. At this time, the viscous force has a greater impact on the flow field than the inertial force, while the medium Reynolds number refers to the flow state of a fluid with a Reynolds number between low and high Reynolds numbers.

[0055] In this embodiment, the cantilever beam stress measurement system may include: a cantilever beam 10 and a substrate 20; the cantilever beam 10 is connected to the upper side of the substrate 20, and the lower side of the substrate 20 is close to the apex of the bubble 30; the cantilever beam 10 can be used to adjust the displacement of the substrate 20 to adjust the collision area between the substrate 20 and the bubble 30; the cantilever beam 10 can also be used to adjust the distance between the lower side of the substrate 20 and the apex of the bubble 30. The bubble surface is a flat hemispherical shape, and the bubble is fixedly set at the bottom of the tank body 40 (a quartz container with surface treatment).

[0056] It should be noted that ore mineral particles, including hydrophobic particles and hydrophilic particles, may be arranged on the substrate, and the corresponding substrates are hydrophilic substrates and hydrophobic substrates. Mineral flotation can generally be achieved because the target mineral is hydrophobic and the gangue mineral is hydrophilic. The greater the difference in hydrophilicity and hydrophobicity between the two, the easier it is to separate them. The liquid film between the hydrophobic particles and the bubbles is unstable and prone to rupture, resulting in adhesion of the particles and bubbles. The liquid film between the hydrophilic particles and the bubbles is in a thermodynamically stable state, and the liquid film between the two is difficult to rupture.

[0057] Furthermore, the cantilever beam stress measurement system may also include: a stepper motor and a piezoelectric ceramic positioning table; the stepper motor and the piezoelectric ceramic positioning table control the cantilever beam in series, and the stepper motor is electrically connected to the piezoelectric ceramic positioning table; the piezoelectric ceramic positioning table generates a corresponding position voltage signal based on the position coordinates of the bubble, and transmits the position voltage signal to the stepper motor; the stepper motor adjusts the position of the substrate to the target position according to the position voltage signal.

[0058] It should be noted that, since the critical thickness of the liquid film during the wetting process is generally between 20-300nm, the positioning accuracy requirement in displacement control needs to reach the nanometer level. At the low Reynolds number scale, the influence of hydrodynamic pressure on the thinning process is relatively low. At this time, the liquid film thinning process is mainly dominated by the separation pressure, and the interface deformation caused by the liquid film pressure will only appear within the range of surface force; at the medium Reynolds number and large Reynolds number (free bubble) scale, the influence of hydrodynamic pressure on the drainage process gradually increases. At this time, hydrodynamic pressure will also cause interface deformation, which will jointly dominate the liquid film thinning process with surface force. The piezoelectric ceramic displacement mechanism used in the prior art has a stroke of only 18μm and a maximum displacement rate of 12μm / s. Although the high-precision displacement adjustment mechanism can realize the detailed study of the separation pressure, the movement rate limits the two to the study of wetting behavior at low Reynolds numbers. In this embodiment, the cantilever beam stress measurement system can use a high-precision piezoelectric ceramic positioning table and a high-precision stepper motor in series to achieve graded control of displacement and speed, achieve micron-level positioning accuracy and a wide range of positioning speed settings, covering the medium Reynolds number range. The piezoelectric ceramic positioning table can use a piezoelectric ceramic displacement mechanism with a positioning accuracy of 0.6nm and a maximum displacement of 20μm (such as NFL5DP20S / M). The stepper motor can use a high-precision stepper motor with a minimum repeatability of 1.6μm, a maximum speed of 50mm / s, and a maximum displacement of 25mm (such as DRV250).

[0059] It should be understood that the deformation of the piezoelectric ceramic positioning stage is positively correlated with the voltage intensity, so the voltage signal of the piezoelectric ceramic positioning stage can be read in real time by the sensor to obtain the position coordinates of the substrate. The stepper motor can be adjusted to initially control the relative position of the cantilever beam and the bubble, and the piezoelectric ceramic controller boost rate can be set to make the bubble approach the cantilever beam at a preset speed. This achieves graded control of displacement and speed.

[0060] Furthermore, the optical path system includes: a dual-band light source 50, a collimating lens 60, a dichroic mirror 70, a half-reflecting half-mirror 80 and two long-distance working objective lenses 90. The two beams of light of different wavelengths emitted by the dual-band light source 50 pass through the collimating lens 60, and then are reflected on the liquid film of the bubble 30 and the surface of the substrate 20 through the half-reflecting half-mirror 80. The reflected light passes through the half-reflecting half-mirror 80 and the dichroic mirror 70 and enters the long-distance working objective lens 90, and is recorded by the visualization system.

[0061] It should be noted that the dual-band light source 50 can adopt a dual LED light source of a blue light source and a red light source. The blue light source can emit light with a wavelength of 430-480nm (refer to B in the figure), for example, a blue light source with a wavelength of 455nm can be selected. The red light source can emit light with a wavelength of 620-760nm (refer to R in the figure), for example, a red light source with a wavelength of 625nm can be selected. The collimating lens 60 can be an optical instrument that can convert an incident light beam into a parallel collimated light beam, which is composed of a single lens or a combination of multiple lenses, and converts a divergent or converging light beam into a parallel light beam. The blue light and red light generated by the dual-band light source 50 are collimated in parallel by the collimating lens 60 and then enter the semi-reflecting half-mirror 80. The semi-reflecting half-mirror can be an optical element with a reflectivity and a transmittance of 50% each. When the light beam is irradiated on the semi-reflecting half-mirror, a part of the light beam is reflected, while the other part of the light beam passes through the lens. The light beam reflected by the semi-reflecting half-mirror enters the contact surface of the bubble and the substrate. One side of the cantilever beam can be coated with a high-reflectivity gold reflective layer using electron beam physical vapor deposition to reflect the light beam. When the optical path difference between the two beams of light is within the coherence length of the light source, interference occurs. The light beam reflected by the cantilever beam passes through a semi-reflective and semi-transmissive mirror and enters the dichroic mirror 70. The dichroic mirror 70 can be an optical element with different reflection or transmission characteristics at two different wavelengths. For example, blue light can pass through the dichroic mirror while red light will be reflected by the dichroic mirror. Therefore, two long-distance working objective lenses 90 are set in the two light path directions of reflection and transmission of the dichroic mirror and then enter the visualization system. Using lasers can obtain a larger coherence length, and interference fringes can be formed at a longer distance (millimeter to centimeter level) between the wetting interface and the wall surface. However, it is precisely because of its large coherence length that the background environment, gas-liquid interface fluctuations or container walls may form interference ripples to cause interference, reducing the signal-to-noise ratio of the measurement. The coherence length of monochrome LEDs or white light LEDs is in the micrometer level, which can well meet the observation requirements.

[0062] The visualization system may include a first high-speed camera 101 and a second high-speed camera 102; the first high-speed camera 101 is arranged in the direction of the transmission light path of the dichroic mirror 70, and is used to receive and record the reflected light of the blue light source (430-480nm); the second high-speed camera 102 is arranged in the direction of the reflection light path of the dichroic mirror 70, and is used to receive and record the reflected light of the red light source (620-760nm). The high-speed camera can have a maximum time resolution of 600fps when the image resolution is 1600*1600, a recording bit depth of 10bit, and a maximum time resolution of 204100fps. It can be triggered synchronously by software and TTL to record the interference fringes generated by the contact between the bubble and the liquid film, and calculate the thickness of the bubble liquid film according to the interference fringes.

[0063] Furthermore, the visualization system further comprises: an illumination light source and a third high-speed camera 103. The illumination light source and the third high-speed camera are arranged on the horizontal side between the lower side of the substrate and the apex of the bubble.

[0064] It should be noted that the illumination light source can be used to provide white light in combination with ambient light for illumination; the third high-speed camera 103 can be used to record the liquid film contact process between the substrate and the bubble. The third high-speed camera can detect the liquid film wetting process from a lateral perspective. At the micron level of coherence length, the spatial distribution size of the interference fringes formed by the wetting interface and the wall surface is about tens to hundreds of microns, so it is necessary to be equipped with a microscopic coaxial illumination system, using Navitar variable magnification coaxial microscopic illumination light path, the illumination light source is white light, combined with ambient light illumination, to record the wetting behavior near the contact line during the wetting process.

[0065] It should be understood that when bubbles or non-polar oil droplets are close to the surface of the cantilever beam, when the distance between them is less than the coherence length of the light source, the reflected light at the wetting interface and the reflected light on the cantilever beam surface meet the coherence condition. Adjust the relative position of the bubble and the cantilever beam to align with the impact area. At the same time, adjust the relative position of the microscope light path so that the cantilever beam impact area, the bubble / oil droplet vertex, and the center of the microscope light path field of view are on the same axis. The displacement of the bubble and the trough body can be adjusted by the cantilever beam stress measurement system. The distance between the top of the bubble and the cantilever beam can be controlled to about 15μm first. At this time, the distance can be measured by the side-view microscope illumination light path. Subsequently, adjust the focus plane of the microscope illumination light path to confirm the focus area of ​​the lower surface of the cantilever beam and the upper surface of the bubble. Because the reflected interference image is near the upper surface of the bubble, adjust the focal plane to the bubble surface to obtain a clear interference image. Finally, the piezoelectric ceramic controller boost rate is set to make the bubble / droplet approach the cantilever beam at a preset speed. At this time, three high-speed cameras are set in trigger mode and use a high frame rate to record the final stage of liquid film thinning and the initial stage of three-phase contact line expansion after the liquid film ruptures, and analyze the change of liquid film thickness with time and spatial position. The side-view camera records the whole process. The optical path for monitoring the change of liquid film thickness uses 455nm and 625nm dual-wavelength LED light sources for synchronous illumination. For each optical path, the relationship between pixel brightness and thickness in the interference fringe image can be calculated by the following formula:

[0066]

[0067] in,

[0068] In the formula, h is the thickness of the liquid film corresponding to a pixel point at a certain position in the interference image, Imax and Imin are the brightest and darkest values ​​in the same interference level, and I is the brightness value of the pixel at the desired position. λ is the wavelength of the incident light, m ​​is the interference level, and n1, n2, and n3 are the refractive indices of bubbles, water, and cantilever beam surface (silicon dioxide), respectively. Due to the use of a dual-wavelength optical path, the value of m in the formula can be obtained by trial and error or least squares estimation through dual-wavelength interference information to obtain the absolute interference level, and then the absolute liquid film thickness is obtained. In the liquid film rupture stage, the liquid film thickness near the three-phase contact line is measured using the same method, and information such as the wetting line retreat speed and the rate of change of the dewetting area can be obtained at the same time. Information such as the late stage of contact line extension and the equilibrium contact angle can be obtained by the side-view camera.

[0069] Reference Figure 2 , Figure 2 FIG. 1 is a schematic diagram of the thinning process of the liquid film between the substrate and the bubble according to the first embodiment of the present invention. The thinning process of the liquid film between the substrate and the bubble is visualized by using a hydrophilic substrate and a hydrophobic substrate respectively. Figure 2 As shown, the thinning curve of the liquid film on the hydrophilic substrate refers to L1 in the figure, and the thinning curve of the liquid film on the hydrophobic substrate refers to L2 in the figure. The horizontal axis is the recording time of the thinning process, and the vertical axis is the measured liquid film thickness. In the case of the hydrophilic substrate, the bubble has not burst, and the distance between the bubble and the substrate is stable at about 100 nanometers due to the presence of the liquid. In the case of the hydrophobic substrate, the bubble bursts at about 100 nanometers from the substrate at 12 to 13 seconds.

[0070] In this embodiment, the device for measuring the thinning of the liquid film between the substrate and the bubble includes: a cantilever stress measurement system, a visualization system and an optical path system; the cantilever stress measurement system, the bubble and the optical path system are arranged in order from top to bottom, and the collision area of ​​the cantilever stress measurement system and the bubble, the vertex of the bubble and the field of view center of the optical path system are adjusted to be located on the same axis; the cantilever stress measurement system is used to adjust the spatial position of the bubble; the optical path system forms interference fringes based on the spatial position of the bubble; the visualization system is used to record the interference fringes and calculate the thickness of the liquid film of the bubble according to the interference fringes. By collecting the interference image during the contact between the bubble liquid film and the wall, the study of the wetting behavior of the liquid film in different chemical environments can greatly improve the selectivity and efficiency of the flotation process.

[0071] In addition, the present invention also provides a method for measuring liquid film thinning. Figure 3 , Figure 3 The figure is a flow chart of an embodiment of a method for measuring thinning of a liquid film proposed by the present invention.

[0072] In this embodiment, the liquid film thinning measurement method includes the following steps:

[0073] Step S10: adjusting the separation distance between the bubble and the substrate by adjusting the spatial position of the bubble.

[0074] It should be noted that a precision syringe pump can be used to pump out bubbles according to a given volume so that they adhere to the bottom of the surface-treated quartz container in a hemispherical shape. A cantilever beam stress measurement system is used to adjust the separation distance between the bubble and the substrate, and the bubble is aligned with the impact area of ​​the substrate, so that the impact area of ​​the cantilever beam, the bubble vertex, and the field of view center of the optical path system are on the same axis.

[0075] In one possible implementation, the spatial position of the bubble can be obtained through a piezoelectric ceramic positioning table; a visualization system is used to calculate the target position of the bubble, and a control signal of the target position is generated to drive a stepper motor to adjust the position of the substrate, thereby adjusting the separation distance between the bubble and the substrate.

[0076] Step S20: Recording the change of interference fringes based on the separation distance.

[0077] Step S30: calculating the thickness of the bubble liquid film according to the change of the interference fringes.

[0078] It should be noted that during the test, the substrate displacement speed can be controlled to 800nm / s to approach the top of the bubble, and the recording frame rate of the high-speed camera can be set to 500fps to record the changes in the interference fringes. For the monitoring of the liquid film thickness, the reflected light between the wetting interface and the wall is required to interfere to form interference fringes for measurement. The use of lasers can obtain a larger coherence length, and interference fringes can be formed at a longer distance (millimeter to centimeter level) between the wetting interface and the wall. The high-speed camera of the visualization system is used to record the late stage of liquid film thinning and the initial stage of three-phase line expansion after the liquid film ruptures, analyze the changes in liquid film thickness with time and spatial position, and calculate the bubble liquid film thickness based on the interference fringe image.

[0079] It should be understood that after calculating the thickness of the bubble liquid film according to the change of the interference fringes, the change time of the thickness of the liquid film being lower than the preset rupture thickness (e.g., 100 nanometers) can also be recorded. The whole process is recorded with low time resolution from a side view, combined with the measurement of the initial formation stage of the three-phase line with high time resolution, to complete the cross-scale dynamic analysis of the contact line formation process.

[0080] In this embodiment, the separation distance between the bubble and the substrate is adjusted by adjusting the spatial position of the bubble; the change of the interference fringes is recorded based on the separation distance; and the thickness of the bubble liquid film is calculated according to the change of the interference fringes. By improving the liquid film thinning measurement method and combining it with dynamic fitting, the influence mechanism of the chemical environment on the liquid film wetting process is explored. It has the characteristics of high measurement accuracy and can be used for droplets or bubbles within medium Reynolds numbers and millimeter scale.

[0081] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or system including the element.

[0082] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A device for measuring thinning of a liquid film between a substrate and a bubble, characterized in that: The device for measuring thinning of liquid film between substrate and bubble comprises: a cantilever beam stress measurement system, a visualization system and an optical path system; The cantilever beam stress measurement system, the bubble and the optical path system are arranged in sequence from top to bottom, and the collision area of ​​the cantilever beam stress measurement system and the bubble, the apex of the bubble and the field of view center of the optical path system are adjusted to be located on the same axis; The cantilever beam stress measurement system is used to adjust the spatial position of the bubble; The optical path system forms interference fringes based on the spatial position of the bubble; The visualization system is used to record the interference fringes and calculate the liquid film thickness of the bubble according to the interference fringes.

2. The device for measuring thinning of a liquid film between a substrate and a bubble as claimed in claim 1, characterized in that: The cantilever beam stress measurement system comprises: a cantilever beam and a substrate; The cantilever beam is connected to the upper side of the substrate, and the lower side of the substrate is close to the apex of the bubble; The cantilever beam is used to adjust the displacement of the substrate to adjust the collision area between the substrate and the bubble; The cantilever beam is also used to adjust the distance between the lower side of the substrate and the apex of the bubble.

3. The device for measuring thinning of a liquid film between a substrate and a bubble as claimed in claim 2, characterized in that: The cantilever beam stress measurement system further includes: a stepping motor and a piezoelectric ceramic positioning table; The stepper motor and the piezoelectric ceramic positioning platform are connected in series to control the cantilever beam, and the stepper motor is electrically connected to the piezoelectric ceramic positioning platform; The piezoelectric ceramic positioning stage generates a corresponding position voltage signal based on the position coordinates of the bubble, and transmits the position voltage signal to the stepping motor; The stepping motor adjusts the position of the substrate to a target position according to the position voltage signal.

4. The device for measuring thinning of a liquid film between a substrate and a bubble as claimed in claim 2, characterized in that: The optical path system comprises: a dual-band light source, a collimating lens, a dichroic mirror, a half-reflecting half-mirror and two long-distance working objective lenses; The two beams of light of different wavelengths emitted by the dual-band light source pass through the collimating lens and then through the half-reflecting half-mirror to be reflected on the liquid film of the bubble and the surface of the substrate. The reflected light passes through the half-reflecting half-mirror and the dichroic mirror and enters the long-distance working objective lens to be recorded by the visualization system respectively.

5. The device for measuring thinning of a liquid film between a substrate and a bubble as claimed in claim 4, characterized in that: The dual-band light source adopts a dual LED light source of a blue light source (430-480nm) and a red light source (620-760nm).

6. The device for measuring thinning of a liquid film between a substrate and a bubble as claimed in claim 5, characterized in that: The visualization system includes: a first high-speed camera and a second high-speed camera; The first high-speed camera is arranged in the transmission light path direction of the dichroic mirror, and is used to receive and record the reflected light of the blue light source (430-480nm); The second high-speed camera is arranged in the direction of the reflected light path of the dichroic mirror, and is used to receive and record the reflected light of the red light source (620-760nm).

7. The device for measuring thinning of a liquid film between a substrate and a bubble as claimed in claim 6, characterized in that: The visualization system further comprises: an illumination light source and a third high-speed camera; The illumination light source and the third high-speed camera are arranged on a horizontal side between the lower side of the substrate and the apex of the bubble; The lighting source is used to provide white light to cooperate with ambient light for lighting; The third high-speed camera is used to record the liquid film contact process between the substrate and the bubble.

8. A method for measuring thinning of a liquid film, applied to the device for measuring thinning of a liquid film between a substrate and a bubble as claimed in any one of claims 1 to 7, characterized in that: The measuring method comprises the following steps: The separation distance between the bubble and the substrate is adjusted by adjusting the spatial position of the bubble; recording changes in interference fringes based on the separation distance; The thickness of the bubble liquid film is calculated according to the change of the interference fringes.

9. The method for measuring thinning of a liquid film according to claim 8, characterized in that: The step of adjusting the separation distance between the bubble and the substrate by adjusting the spatial position of the bubble comprises: Acquiring the spatial position of the bubble by a piezoelectric ceramic positioning stage; The target position of the bubble is calculated using a visualization system, and a control signal of the target position is generated to drive a stepping motor to adjust the position of the substrate to adjust the separation distance.

10. The method for measuring thinning of a liquid film according to claim 8, characterized in that: After the step of calculating the thickness of the bubble liquid film according to the change of the interference fringes, the method further includes: The time during which the thickness of the liquid film is lower than the preset rupture thickness is recorded.

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