An in-situ observation device and method for the interface contact of underwater soft materials

Abstract

The present invention discloses an in-situ observation device and method for the interface contact of underwater soft materials, belonging to the field of interface observation equipment. The observation device provided by the present invention utilizes the refractive index differences between water and hydrogel materials passing through a transparent prism to distinguish the bright domain interface in contact with the gel from the dark domain interface of the retained water, so as to clearly and accurately observe the evolution process of the true contact area at the interface during the underwater bonding process of the hydrogel, facilitating the exploration of the influence mechanism of the retained water at the interface on the underwater bonding performance of the hydrogel. The principle of the in-situ observation device for the interface contact of underwater soft materials used in the present invention is simple, and the manufacturing cost is low, which can solve the problem that it is difficult to observe the true contact area in the underwater hydrogel bonding experiment.

Description

Technical Field

[0001] The present invention belongs to the field of interface observation devices, and particularly relates to an in-situ observation device and method for underwater soft material interface contact. Background Art

[0002] As an intelligent flexible material, hydrogel is composed of a three-dimensional polymer network and a large amount of water. This wet and soft material not only has a high water content and a simple preparation method, but also can adjust its mechanical properties through diverse polymer network structures. Especially its excellent biocompatibility and structural similarity have attracted wide attention in the field of biomedicine.

[0003] For example, hydrogel can achieve rapid hemostasis on damaged tissues and accelerate wound healing through its controllable drug release function; as a cartilage substitute material, it can provide stable structural support through firm adhesion to bone tissue; it can be used to manufacture micro soft robots, enabling them to climb flexibly on the surface of smooth biological tissues; and in flexible wearable devices, hydrogel can improve skin contact effect and effectively manage sweat excretion problems, etc.

[0004] The actual application of hydrogel often needs to be completed under the synergistic action of multiple materials. Therefore, for such rich and diverse hydrogels with broad application prospects and various functions, how to combine them organically, or form a reliable connection with other interfaces, or even achieve controllable adhesion, is of great significance.

[0005] Due to the high water content of the hydrogel material itself and the hydrophilicity of the polymer chains, etc., at the mesoscopic scale, a permanent "water locking" phenomenon is likely to occur on its surface, resulting in the appearance of a water film layer at the contact interface. The existence of this water film layer not only increases the intermolecular distance, but also greatly weakens the intermolecular force between the bonding materials due to the high dielectric constant of water molecules. Although some researchers currently use some methods to enhance the interface force, when these bonding materials are applied to underwater environment operations, their bonding effect often deteriorates significantly. In order to obtain more obvious advantages during service in the water environment, it is necessary to accurately observe the evolution process of hydrogel interface bonding in the water environment.

[0006] A lot of research has been done on the application of underwater adhesion of hydrogel materials. The invention patent entitled: A method for improving the underwater adhesion ability of hydrogels and related hydrogels and their preparation methods, with publication number CN110358130A, discloses a dynamic hydrogel containing hydrophobic groups prepared by cross-linking with the assistance of a surfactant. The hydrogel can produce a hydrophobic effect underwater and can expel water molecules between interfaces when bonding with a substrate, thereby achieving underwater bonding. However, this method cannot accurately observe the evolution of the real contact area of ​​the interface during the hydrogel bonding process, and cannot quantify the drainage efficiency of the hydrophobic interface. The invention patent entitled: A barnacle bionic water-touch adhesion hydrogel and its preparation method and application, with publication number CN117402292A, also failed to observe the real contact area of ​​the bonding interface when characterizing the underwater adhesion performance.

[0007] Therefore, for hydrogels with high transparency, how to distinguish the contact area and non-contact area in their underwater contact interface is a technical problem that needs to be solved urgently. Summary of the invention

[0008] The purpose of the present invention is to solve the above problems existing in the prior art and to provide an underwater soft material interface contact in-situ observation device and method.

[0009] The specific technical solutions adopted by the present invention are as follows:

[0010] In a first aspect, the present invention provides an underwater soft material interface contact in-situ observation device, which includes a transparent container, a transparent prism, a reflector, a level adjustment platform, a sensor pressure head and an imaging device;

[0011] The transparent container is placed on a horizontal adjustment platform, and the horizontal adjustment platform is used to level the bottom plane of the inner cavity of the transparent container;

[0012] The reflector and the transparent prism are built into the bottom of the inner cavity of the transparent container, the sensor pressure head and the imaging device are located outside the transparent container, the transparent prism is a quadrangular prism whose longitudinal sections are all isosceles trapezoids of the same size, and the isosceles trapezoids are placed inverted, the bottom surface of the prism where the upper base of the isosceles trapezoid is located is in contact with the bottom plane of the inner cavity of the transparent container, and the top surface of the prism where the lower base of the isosceles trapezoid is located is located directly below the sensor pressure head; the top surface of the prism and the two side surfaces of the isosceles trapezoid of the transparent prism are frosted surfaces, and the remaining surfaces are transparent surfaces; the bottom surface of the sensor pressure head is used to fix the hydrogel sample, and can enter the transparent container under the drive of the loading device and apply pressure to the top surface of the prism of the transparent prism;

[0013] The reflector is flatly attached to the inner cavity bottom plane of the transparent container and is located between the transparent prism and the imaging device. The imaging device records the contact interface between the top surface of the prism and the hydrogel sample through the reflector.

[0014] Preferably, in the first aspect above, the material of the transparent prism is glass or other transparent materials.

[0015] Preferably, in the first aspect above, the included angle between the waist and the lower base of the isosceles trapezoid is 70°.

[0016] Preferably, in the first aspect above, the horizontal adjustment platform adopts a three-axis balancing table.

[0017] Preferably, in the first aspect above, the loading device adopts a universal testing machine, and the sensor indenter moves up and down in the vertical direction driven by the universal testing machine.

[0018] Preferably, in the first aspect above, the sensor indenter is provided with a stress sensor for detecting the stress value between the hydrogel sample and the transparent prism.

[0019] Preferably, in the first aspect above, the position of the imaging device can be adjusted. Before performing the in-situ observation of the underwater soft material interface contact, through preliminary experiments, it is determined that the observation point where the contact interface between the hydrogel sample and the top surface of the prism is a bright area rather than a dark area of the contact interface, and the imaging device is moved and adjusted to the position of the observation point.

[0020] In the second aspect, the present invention provides an in-situ observation method for underwater soft material interface contact using the underwater soft material interface contact in-situ observation device according to any one of the above first aspect solutions, which includes:

[0021] S1. Add water to the transparent container until the water surface submerges the transparent prism and the liquid level is 4 - 5 cm above the top surface of the prism; at the same time, adjust the inner cavity bottom plane of the transparent container through the horizontal adjustment platform to keep the inner cavity bottom plane in a horizontal state;

[0022] S2. Attach the hydrogel sample to the top surface of the transparent prism through preliminary experiments, determine the observation point where the contact interface between the hydrogel sample and the top surface of the prism can be observed as a bright area while the contact interface between water and the top surface of the prism is a dark area, and then move and adjust the imaging device to the position of the observation point;

[0023] S3. Fix the hydrogel sample to be observed at the bottom of the sensor indenter, and start the in-situ observation of the underwater soft material interface contact. First, drive the sensor indenter to move downward uniformly at a preset first rate by the loading device, so that the hydrogel sample enters the transparent container and starts to fit the prism top surface of the transparent prism and apply pressure. After detecting that the stress value between the two reaches the preset stress value, keep the sensor indenter stationary to maintain the pressure between the hydrogel sample and the transparent prism until the contact time meets the preset time value, and then drive the sensor indenter to move upward uniformly at a preset second rate by the loading device, so that the hydrogel sample gradually peels off from the prism top surface of the transparent prism; during the lifting and lowering process of the sensor indenter, record the contact interface between the prism top surface and the hydrogel sample through the reflector to obtain contact interface image frames at different times;

[0024] S4. Perform image recognition on the contact interface image frames at different times, extract the bright region and the dark region in the contact interface image frames. The bright region is the contact interface between the hydrogel sample and the prism top surface, and the dark region is the non-contact interface between the hydrogel sample and the prism top surface due to the existence of retained water, and finally obtain the evolution process of the contact interface of the hydrogel sample to be observed during the underwater bonding process.

[0025] As a preference of the above second aspect, during the lifting and lowering process of the sensor indenter, it is also necessary to record the stress value between the hydrogel sample and the transparent prism in real time through a stress sensor installed on the sensor indenter.

[0026] As a preference of the above second aspect, after obtaining the image recognition results of the contact interface image frames at different times, it is necessary to calculate the contact interface ratio of the hydrogel sample at each time and generate a time-domain curve of the contact interface ratio. The contact interface ratio is the ratio of the area of the bright region to the area of the complete contact surface of the hydrogel sample; at the same time, it is necessary to calculate the nominal stress at each time and generate a time-domain curve of the nominal stress, and extract the negative maximum nominal stress in the curve as the bonding strength of the hydrogel sample; the nominal stress is the ratio of the stress value recorded by the stress sensor to the area of the complete contact surface of the hydrogel sample.

[0027] The present invention has the following beneficial effects compared with the prior art:

[0028] The present invention provides an in-situ observation device for the interface contact of underwater soft materials. This device utilizes the refractive index differences between water and hydrogel materials passing through a transparent prism to distinguish the bright domain interface in contact with the gel from the dark domain interface of the retained water, thereby clearly and accurately observing the evolution process of the true contact area during the underwater bonding process of the hydrogel, facilitating the exploration of the influence mechanism of the retained water at the interface on the underwater bonding performance of the hydrogel. The principle of the in-situ observation device for the interface contact of underwater soft materials used in the present invention is simple and the manufacturing cost is low, which can solve the problem that it is difficult to observe the true contact area in the underwater hydrogel bonding experiment. Description of the Drawings

[0029] Figure 1 Fig. is a schematic structural diagram of the in-situ observation device for the interface contact of underwater soft materials;

[0030] Figure 2 Fig. is a schematic diagram of the interface observation principle of the transparent prism;

[0031] Figure 3 Fig. is a schematic diagram of the usage state of the in-situ observation device for the interface contact of underwater soft materials after water injection;

[0032] Figure 4 Fig. is the relationship curve of contact area ratio - contact time obtained in the embodiment;

[0033] Figure 5 Fig. is the nominal stress - time curve during the underwater bonding process of the hydrogel obtained in the embodiment.

[0034] The reference numerals in the figures are as follows: transparent container 1, transparent prism 2, reflecting mirror 3, horizontal adjustment platform 4, sensor indenter 5, imaging device 6, hydrogel sample 7, liquid level 8, retained water 9, bright domain A, dark domain B. Detailed Embodiments

[0035] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is provided in conjunction with the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined correspondingly without conflict.

[0036] In the description of the present invention, it should be understood that when an element is considered to be "connected" to another element, it can be directly connected to the other element or indirectly connected, i.e., there is an intermediate element. On the contrary, when an element is referred to as being "directly" connected to another element, there is no intermediate element.

[0037] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for distinguishing and describing purposes, and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features.

[0038] In a preferred embodiment of the present invention, an in-situ observation device for the interface contact of underwater soft materials is provided. The components of the device include a transparent container 1, a transparent prism 2, a reflector 3, a horizontal adjustment platform 4, a sensor indenter 5, and an imaging device 6. Based on this device, the evolution process of the true contact area at the interface during the underwater bonding process of hydrogels can be clearly and accurately observed, and it can be used to explore the influence mechanism of the retained water at the interface on the underwater bonding performance of hydrogels. The specific structure and working principle of this device will be introduced in detail below.

[0039] In the in-situ observation device of the present invention, the transparent container 1 is a container made of a transparent material with an open inner cavity. The transparent container 1 is placed on the horizontal adjustment platform 4, and the horizontal adjustment platform 4 is used to level the bottom plane of the inner cavity of the transparent container 1.

[0040] It should be noted that the specific form of the horizontal adjustment platform 4 is not limited, and any device capable of three-axis adjustment can be used. In the embodiment of the present invention, the horizontal adjustment platform 4 adopts a three-axis balancing table.

[0041] The above reflector 3 and transparent prism 2 are built into the bottom of the inner cavity of the transparent container 1, while the sensor indenter 5 and the imaging device 6 are located outside the transparent container 1. The transparent prism 2 is a quadrangular prism with an isosceles trapezoid in both longitudinal sections, and the isosceles trapezoid is placed upside down. According to the definition of an isosceles trapezoid, there are two bases and two waists. The shorter base is called the upper base, and the longer base is called the lower base. In a normally placed isosceles trapezoid, the upper base is above the lower base, but in the present invention, the isosceles trapezoid is placed upside down, so the lower base is above the upper base. Thus, for the upside-down transparent prism 2, the prism bottom surface where the upper base of the isosceles trapezoid is located fits the bottom plane of the inner cavity of the transparent container 1, and the prism top surface where the lower base of the isosceles trapezoid is located is directly below the sensor indenter 5. In addition, the prism top surface and the two side surfaces in the shape of an isosceles trapezoid of the transparent prism 2 are all frosted surfaces, and the remaining surfaces (including the prism bottom surface and the two rectangular side surfaces) are all transparent surfaces.

[0042] The above sensor indenter 5 is a test indenter that can carry a sensor. The sensor indenter 5 can be connected to a loading device for operation. The bottom surface of the sensor indenter 5 is used to fix the hydrogel sample 7, and it can enter the transparent container 1 under the drive of the loading device and gradually approach and fit to the prism top surface of the above transparent prism 2, so as to apply pressure to the prism top surface of the transparent prism 2.

[0043] In an embodiment of the present invention, a universal testing machine can be used as the loading device for installing the sensor indenter 5. Generally, the universal testing machine comes with a sensor indenter 5. Of course, if necessary, a sensor indenter 5 can also be added. The sensor indenter 5 is driven by the universal testing machine to move up and down in the vertical direction, thereby controlling the entire observation process.

[0044] The above-mentioned mirror 3 is flatly attached to the inner cavity bottom plane of the transparent container 1 and is located between the transparent prism 2 and the imaging device 6. The imaging device 6 can be a camera, a high-speed industrial camera, etc. Its function is to record the contact interface between the top surface of the prism and the hydrogel sample 7 through the mirror 3. The purpose of setting the mirror 3 is to meet the requirement of the inversion of the above-mentioned transparent prism 2 because

[0045] During actual testing, different microstructures can be processed on the surface of the hydrogel sample 7 to be tested. By pre-injecting water into the transparent container 1 to submerge the top surface of the transparent prism 2, an underwater bonding test environment for the hydrogel sample 7 can be created. The hydrogel sample 7 can be directly bonded to the bottom surface of the sensor indenter 5 and then driven by the loading device to move downward, fit to the top surface of the transparent prism 2 in water and gradually increase the pressure. During this fitting process, the water layer between the hydrogel sample 7 and the transparent prism 2 will be gradually squeezed out, but there may be retained water in local areas, resulting in a contact interface between the hydrogel sample 7 and the top surface of the prism and a non-contact interface on the final contact interface. During this process, the imaging device 6 records the contact interface between the top surface of the prism and the hydrogel sample 7 through the mirror 3. In addition, after maintaining the pressure for a certain period of time, the transparent prism 2 can be lifted upward again to peel it off from the top surface of the transparent prism 2. During this process, the imaging device 6 can continue to record the contact interface between the top surface of the prism and the hydrogel sample 7 through the mirror 3 to observe the change of the release interface during the peeling process. The ideal contact state between the hydrogel sample 7 and the top surface of the prism is complete contact between the two without a retained water area, but actual samples are often difficult to reach this state. Therefore, the observation device based on the present invention can observe the underwater interface contact state of hydrogel samples 7 with different preparation processes or different surface microstructures, and can be used to explore the influence mechanism of interface retained water on the underwater hydrogel bonding performance.

[0046] In addition, in general hydrogel performance testing requirements, it is also necessary to record the stress value between the hydrogel sample 7 and the transparent prism 2. Therefore, a stress sensor for detecting the stress value between the hydrogel sample 7 and the transparent prism 2 can be further installed on the above-mentioned sensor indenter 5.

[0047] It should be specifically noted that the position of the above imaging device 6 should be movable and adjustable. Before performing in-situ observation of the underwater soft material interface contact, a pre-experiment is conducted to determine the observation point where the contact interface between the hydrogel sample 7 and the top surface of the prism can be observed as the bright region A rather than the dark region B, and the imaging device 6 is moved and adjusted to the position of the observation point.

[0048] In Figure 2 , taking the case where the transparent prism 2 is placed upright as an example, the schematic diagram of the principle that the above transparent prism 2 can be used for in-situ observation of the evolution of the hydrogel contact interface underwater is illustrated. Since the refractive indices of the hydrogel material and water for light are different, there is a slight difference in the refraction angles of the light refracted into the glass prism 2 through these two materials. It is to distinguish whether the interface contact is water or the hydrogel material. In Figure 2 , θ w is the critical refraction angle of water, and θ g is the critical refraction angle of the hydrogel. When the observation point falls between the two included angle regions, if the observed target point is in contact with the hydrogel sample 7, the light can be refracted into the human eye, so what is seen is the bright region A; conversely, if it is in contact with the stagnant water 9, since total internal reflection of the light occurs and no light enters the human eye, what is seen is the dark region B, thus distinguishing the true contact area on the surface. Using such a strategy, the imaging device 6 is set between the two included angle regions and is oriented towards the glass prism 2 to record the evolution process of the entire underwater contact interface. Similarly, after the transparent prism 2 is inverted, its shape in the transparent container 1 after adding water is as shown in Figure 3 . At this time, since there is a reflector 3 that changes the light path, the imaging device 6 can record the contact interface between the top surface of the prism and the hydrogel sample 7 through the reflector 3, and its principle is similar to that in Figure 2 .

[0049] The material of the transparent prism 2 of the present invention is glass. In addition, the included angle between the waist and the lower base of the isosceles trapezoid needs to be optimized according to the actual situation. In the embodiment of the present invention, the optimal included angle between the waist and the lower base of the isosceles trapezoid is 70°. Of course, the transparent prism 2 can also be replaced with other transparent materials except glass, and the actual size can be adjusted to ensure that the observable angle on the side is greater than the included angle between the critical refraction angle of water and the critical refraction angle of the hydrogel.

[0050] In the present invention, further based on the underwater soft material interface contact in-situ observation device shown in the above Figure 1 , an underwater soft material interface contact in-situ observation method is provided, and the specific method is as follows:

[0051] S1. Add water to the transparent container 1 until the water surface submerges the transparent prism 2 and the liquid level 8 is 4 - 5 cm above the top surface of the prism. At the same time, adjust the bottom plane of the inner cavity of the transparent container 1 through the horizontal adjustment platform 4 to keep the bottom plane of the inner cavity in a horizontal state.

[0052] S2. Through preliminary experiments, attach the hydrogel sample 7 to the top surface of the transparent prism 2, determine the observation point where the contact interface between the hydrogel sample 7 and the top surface of the prism can be observed as the bright region A and the contact interface between water and the top surface of the prism as the dark region B, and then move and adjust the imaging device 6 to the position of the observation point.

[0053] S3. Fix the hydrogel sample 7 to be observed at the bottom of the sensor indenter 5, and start performing in - situ observation of the underwater soft material interface contact. First, drive the sensor indenter 5 to move downward uniformly at a preset first rate by the loading device, so that the hydrogel sample 7 enters the transparent container 1 and starts to attach to the top surface of the transparent prism 2 and apply pressure. After detecting that the stress value between the two reaches the preset stress value, keep the sensor indenter 5 stationary to maintain the pressure between the hydrogel sample 7 and the transparent prism 2 until the contact time meets the preset time value, and then drive the sensor indenter 5 to move upward uniformly at a preset second rate by the loading device, so that the hydrogel sample 7 gradually peels off from the top surface of the transparent prism 2. During the up - and - down movement of the sensor indenter 5, record the contact interface between the top surface of the prism and the hydrogel sample 7 through the reflector 3 to obtain contact interface image frames at different times.

[0054] S4. Perform image recognition on the contact interface image frames at different times, extract the bright region and the dark region in the contact interface image frames. The bright region is the contact interface between the hydrogel sample 7 and the top surface of the prism, and the dark region is the non - contact interface between the hydrogel sample 7 and the top surface of the prism due to the presence of stagnant water 9. Finally, obtain the evolution process of the contact interface of the hydrogel sample 7 to be observed during the underwater bonding process.

[0055] It should be noted that the above - mentioned first rate, preset stress value, and second rate can all be set according to the actual test plan requirements, and no limitation is made in this regard.

[0056] It should be noted that in the above S2 step, for the determination of the observation point, it can be observed by the naked eye or the imaging device 6, or determined through theoretical calculation of θ w and θ g, and then determine the optional range of the observation point according to geometric relationships. However, in the present invention, visual observation is preferably adopted, which has higher efficiency. Additionally, during the pre-experiment, when determining the observation point, the hydrogel sample 7 needs to be attached to the prism top surface of the transparent prism 2. At this time, the hydrogel sample 7 can be attached to the prism top surface of the transparent prism 2 alone, or the hydrogel sample 7 can be directly fixed on the sensor indenter 5 and then driven by the sensor indenter 5 to be attached to the prism top surface of the transparent prism 2. Both methods are acceptable.

[0057] It should be noted that when performing image recognition on the contact interface image frames at different times, manual recognition can be used, or image processing software (such as Image-J) or an automatic recognition program can be used for recognition, as long as the bright domain area and the dark domain area can be distinguished based on the brightness difference in the image.

[0058] In an embodiment of the present invention, according to the test requirements, during the lifting and lowering process of the above-mentioned sensor indenter 5, the stress value between the hydrogel sample 7 and the transparent prism 2 is recorded in real time by a stress sensor installed on the sensor indenter 5.

[0059] Based on the recorded various image information and stress information, corresponding analysis can be further carried out. One optional analysis method is as follows: after obtaining the image recognition results of the contact interface image frames at different times, it is necessary to calculate the contact interface occupancy ratio of the hydrogel sample 7 at each time and generate a time-domain curve of the contact interface occupancy ratio; at the same time, it is necessary to calculate the nominal stress at each time and generate a time-domain curve of the nominal stress, and extract the negative maximum nominal stress in the curve as the bonding strength of the hydrogel sample 7.

[0060] It should be noted that the above-mentioned contact interface occupancy ratio in the present invention is defined as the ratio of the area of the bright domain area in the contact interface image frame to the area of the complete contact surface of the hydrogel sample 7. The area of the complete contact surface of the hydrogel sample 7 here refers to the contact area corresponding to when the hydrogel sample 7 is completely attached to the prism top surface of the transparent prism 2, that is, the area of this contact surface of the hydrogel sample 7 itself used for attachment to the transparent prism 2. Additionally, the above-mentioned nominal stress in the present invention is defined as the ratio of the stress value recorded by the stress sensor to the area of the complete contact surface of the hydrogel sample 7.

[0061] The following shows the above of the present invention through a specific embodiment Figure 1 The specific implementation and technical effects of the in-situ observation device for underwater soft material interface contact shown, and the in-situ observation method for underwater soft material interface contact shown in S1~S4.

[0062] Embodiment

[0063] In this embodiment, to solve the problem of difficult observation of the contact interface between the hydrogel and the adhesive in the water environment, the following was built asFigure 1 The in-situ observation device for underwater soft material interface contact is shown. The transparent container 1 is a rectangular transparent experimental box. The rectangular transparent experimental box is a box-shaped structure without a lid surrounded by 5 acrylic plates. The bottom is a square acrylic plate with a thickness of 5 mm and a side length of 210 mm. The four sides are surrounded by rectangular acrylic plates with a size of 210 mm*100 mm*5 mm. The transparent prism 2 is an isosceles trapezoidal glass prism, which is a quadrangular prism glass prism with an isosceles trapezoidal cross section. The glass prism is made of borosilicate glass. The dimensions of the isosceles trapezoid are: upper base 50 mm, lower base 66 mm, height 22.08 mm, angle 70°, of which the prism bottom surface where the 50 mm upper base is located and the two trapezoidal side surfaces are frosted, and the remaining surfaces are all smooth. The reflector 3 is a rectangular reflector with a size of 150 mm*80 mm*3 mm. The horizontal adjustment platform 4 is a three-axis adjustable horizontal platform. The three-axis adjustable horizontal platform is a commercial xyz three-axis adjustable platform with a table size of 200mm*200mm. The hydrogel sample 7 is a pre-prepared polyampholyte hydrogel. The universal material testing machine uses instron 5965. The sensor pressure head 5 uses the sensor pressure head provided by the universal material testing machine, and the pressure head is provided with a stress sensor, which is controlled by the universal material testing machine and records the stress data of the sensor. The imaging device 6 uses an industrial camera.

[0064] The construction sequence of the above-mentioned underwater soft material interface contact in-situ observation device is as follows: first, place the three-axis adjustable horizontal platform under the force arm of the instron 5965 test machine, and then place the rectangular transparent experimental box on the three-axis adjustable horizontal platform. Place the rectangular reflector flat on the bottom of the experimental box and align it with the side. Then invert the isosceles trapezoidal glass prism (with the large square bottom facing up), with the rectangular side facing the reflector, and place it 1~2cm away from the reflector to ensure that the refracted light of the glass prism can be reflected by the reflector, which is convenient for the experimenter to observe. Adjust the xyz axis of the horizontal platform so that the upper surface of the isosceles trapezoidal glass prism is perpendicular to the force sensor of the test machine. According to the needs of the test environment, water can be injected into the experimental box to explore the underwater contact situation.

[0065] like Figure 2 As shown in the in-situ observation device for underwater soft material interface contact, due to the refractive index of water n w ≈1.33, and the refractive index of the hydrogel n g ≈1.35. When light is refracted from water or hydrogel into a glass prism (nglass ≈1.52), according to the law of refraction shown in formula (1), the refracted light will deviate toward the normal line of the prism interface.

[0066] n 1 *sinθ 1 = n 2 *sinθ2 (1)

[0067] Therefore, when the incident angle of light is greater than the critical angle θ c , total internal reflection will occur, and in this case, the situation of the contact interface cannot be seen. Therefore, by using the difference in the refractive indices of the two materials, water and hydrogel, the difference in the critical angles of the two can be calculated to determine the optimal viewing angle. According to the total internal reflection formula

[0068] sinθ c = n 2 / n 1 (2)

[0069] In this embodiment, the critical angle θ w of water can be calculated to be approximately 62°, and the critical angle θ g of the hydrogel is approximately 64°. Then, a glass prism is used to refract the light of the underwater contact interface to the side of the isosceles trapezoid, so that the experimenter can observe the evolution of the underwater contact interface in situ from the side. As Figure 2 shown, θ w is the critical refraction angle of water, and θ g is the critical refraction angle of the hydrogel. When the observation point of the camera is placed in the area between the two angles θ w and θ g , if the observed target point is in contact with the hydrogel, the light can be refracted into the human eye, so what is seen is the bright area; on the contrary, if it is in contact with water, since total internal reflection occurs and no light enters the human eye, what is seen is the dark area, thus distinguishing the true contact area of the surface.

[0070] Using the above-built in-situ observation device for the contact of the underwater soft material interface, the experimental steps for the in-situ observation of the contact of the underwater soft material interface are as follows:

[0071] First, adjust the direction of the cuboid experimental box so that the rectangular mirror at the bottom of the box is in front of the experimenter, and ensure that the upper surface of the isosceles trapezoid glass prism can be observed through the mirror;

[0072] Then, pour water into the experimental box. The water flows along the side wall of the experimental box to prevent the displacement of the isosceles trapezoid glass prism and the rectangular mirror caused by the impact of the water flow. Stop adding water when the liquid level exceeds the upper surface of the isosceles trapezoid glass prism by 4 - 5 cm. Note that the liquid level should not be too high to prevent submerging the entire stress sensor in subsequent experiments and causing damage to the instrument;

[0073] Then, adjust the xyz axes of the three-axis horizontal platform so that the upper surface of the isosceles trapezoid glass prism is completely perpendicular to the indenter of the stress sensor, ensuring that only normal stress and no shear stress are generated on the upper surface during the subsequent pressing process;

[0074] Next, fix the hydrogel sample to be explored on the sensor indenter of a universal material testing machine. After determining through the aforementioned preliminary experiment the observation point where the contact interface between the hydrogel sample and the top surface of the prism can be observed as a bright area and the contact interface between water and the top surface of the prism as a dark area, place an industrial camera at the observation point position and record the interface image through a rectangular reflector. Control the hydrogel sample on the sensor indenter by the universal material testing machine to slowly approach the isosceles trapezoidal glass prism at a rate of 10 μm / s and adhere to the top surface of the prism until the stress detected by the stress sensor on the sensor indenter reaches the preset load of 15 N, then stop pressing down and maintain a certain contact time;

[0075] Then, reverse the tensile of the sensor indenter at a speed of 10 μm / s to peel the hydrogel from the adhesion substrate. When the hydrogel is completely separated from the top surface of the prism, the experiment is completed.

[0076] It should be noted that during the experiment, the industrial camera is set at the observation point position and parameters such as the viewing angle and focal length remain unchanged, and clear videos are recorded throughout the process from contact to peeling for subsequent analysis and calculation of the pictures using Image-J software to quantify the evolution process of the contact interface.

[0077] Read the data of the stress sensor from the universal material testing machine and read the contact interface image frames at different times from the industrial camera. Perform image recognition on the contact interface image frames at different times, extract the bright area and the dark area in the contact interface image frames. The bright area is the contact interface between the hydrogel sample 7 and the top surface of the prism, and the dark area is the non-contact interface between the hydrogel sample 7 and the top surface of the prism due to the presence of retained water 9. Finally, obtain the evolution process of the contact interface of the hydrogel sample 7 to be observed during the underwater bonding process. At the same time, after obtaining the image recognition results of the contact interface image frames at different times, it is necessary to calculate the contact interface ratio of the hydrogel sample 7 at each time and generate a time-domain curve of the contact interface ratio; at the same time, it is necessary to calculate the nominal stress at each time and generate a time-domain curve of the nominal stress, and extract the negative maximum nominal stress in the curve as the bonding strength of the hydrogel sample 7.

[0078] It should be noted that in order to achieve a better underwater bonding effect, different microstructural designs are usually carried out on the hydrogel surface to improve the interface drainage efficiency. Therefore, if there are multiple groups of hydrogel samples, the above experimental process can be repeated.

[0079] In this embodiment, use Image-J software to calculate the contact area in the contact image at different time points, and divide the contact area A by the complete contact surface area A 0 to obtain the contact area ratio A / A 0。The curve of the contact area ratio varying with time can be plotted to clarify the interface drainage efficiency. Taking the hydrogel with a hexagonal microstructure on the surface as an example, in order to compare the bonding strengths of different microstructures, regular hexagonal convex patterns with a height of 0.5 mm and side lengths of 8 mm, 4 mm, and 3 mm were designed on the hydrogel surface (denoted as 8 mm - 0.5 mm, 4 mm - 0.5 mm, and 3 mm - 0.5 mm respectively). Figure 4 shows the curve of the contact area ratio - contact time relationship between the gel with the surface microstructure design obtained in this embodiment and the gel without the microstructure design, Figure 5 shows the nominal stress - time curve of the underwater bonding process of the hydrogel obtained in this embodiment. Thus, the underwater interface bonding performance of the hydrogel under different microstructure designs can be intuitively compared.

[0080] The above-described embodiments are only some preferred implementation solutions of the present invention, but are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting the means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. An underwater soft material interface contact in-situ observation method using an underwater soft material interface contact in-situ observation device, characterized in that: The observation device comprises a transparent container (1), a transparent prism (2), a reflector (3), a level adjustment platform (4), a sensor pressure head (5) and an imaging device (6); The transparent container (1) is placed on a horizontal adjustment platform (4), and the horizontal adjustment platform (4) is used to level the bottom plane of the inner cavity of the transparent container (1); The reflector (3) and the transparent prism (2) are built into the bottom of the inner cavity of the transparent container (1); the sensor pressure head (5) and the imaging device (6) are located outside the transparent container (1); the transparent prism (2) is a quadrangular prism whose longitudinal sections are all isosceles trapezoids of the same size, and the isosceles trapezoids are placed upside down, the prism bottom surface where the upper base of the isosceles trapezoid is located is in contact with the bottom plane of the inner cavity of the transparent container (1), and the prism top surface where the lower base of the isosceles trapezoid is located is located directly below the sensor pressure head (5); the prism top surface and two isosceles trapezoidal side surfaces of the transparent prism (2) are frosted surfaces, and the remaining surfaces are transparent surfaces; the bottom surface of the sensor pressure head (5) is used to fix the hydrogel sample (7), and can enter the transparent container (1) under the drive of a loading device and apply pressure to the prism top surface of the transparent prism (2); The reflector (3) is flatly attached to the bottom plane of the inner cavity of the transparent container (1) and is located between the transparent prism (2) and the imaging device (6); the imaging device (6) records the contact interface between the top surface of the prism and the hydrogel sample (7) through the reflector (3); The underwater soft material interface contact in-situ observation method comprises: S1, adding water to the transparent container (1) until the water surface submerges the transparent prism (2) and the liquid surface (8) is located 4 to 5 cm above the top surface of the prism; at the same time, adjusting the bottom plane of the inner cavity of the transparent container (1) through the horizontal adjustment platform (4) so ​​that the bottom plane of the inner cavity remains in a horizontal state; S2. Through a preliminary experiment, the hydrogel sample (7) is attached to the top surface of the transparent prism (2), and an observation point is determined at which the contact interface between the hydrogel sample (7) and the top surface of the prism is observed as a bright area (A) and the contact interface between water and the top surface of the prism is observed as a dark area (B), and then the imaging device (6) is moved and adjusted to the position of the observation point; S3, fixing the hydrogel sample (7) to be observed at the bottom of the sensor pressure head (5), and starting to perform underwater soft material interface contact in-situ observation, first, the sensor pressure head (5) is driven by the loading device to move downward at a constant speed according to a preset first rate, so that the hydrogel sample (7) enters the transparent container (1) and begins to fit the prism top surface of the transparent prism (2) and apply pressure, after detecting that the stress value between the two reaches a preset stress value, the sensor pressure head (5) is kept stationary to maintain the pressure between the hydrogel sample (7) and the transparent prism (2) until the contact time meets the preset time value, and then the sensor pressure head (5) is driven by the loading device to move upward at a constant speed according to a preset second rate, so that the hydrogel sample (7) is gradually peeled off from the prism top surface of the transparent prism (2); during the lifting and lowering process of the sensor pressure head (5), the contact interface between the prism top surface and the hydrogel sample (7) is recorded by the reflector (3), and contact interface image frames at different times are obtained; S4. Perform image recognition on the contact interface image frames at different times, and extract the bright area and dark area in the contact interface image frames, wherein the bright area is the contact interface between the hydrogel sample (7) and the top surface of the prism, and the dark area is the non-contact interface between the hydrogel sample (7) and the top surface of the prism due to the presence of retained water (9), and finally obtain the evolution process of the contact interface of the hydrogel sample (7) to be observed during the underwater bonding process.

2. The in-situ observation method of underwater soft material interface contact according to claim 1, characterized in that: The transparent prism (2) is made of glass or other transparent materials.

3. The in-situ observation method of underwater soft material interface contact according to claim 1, characterized in that: The angle between the waist and the lower base of the isosceles trapezoid is 70°.

4. The in-situ observation method of underwater soft material interface contact according to claim 1, characterized in that: The horizontal adjustment platform (4) adopts a three-axis balancing platform.

5. The in-situ observation method of underwater soft material interface contact according to claim 1, characterized in that: The loading device is a universal testing machine, and the sensor pressure head (5) is driven by the universal testing machine to move up and down in the vertical direction.

6. The in-situ observation method of underwater soft material interface contact according to claim 1, characterized in that: The sensor pressure head (5) is provided with a stress sensor for detecting the stress value between the hydrogel sample (7) and the transparent prism (2).

7. The in-situ observation method of underwater soft material interface contact according to claim 1, characterized in that: The position of the imaging device (6) can be moved and adjusted, and before performing in-situ observation of underwater soft material interface contact, an observation point at which the contact interface between the hydrogel sample (7) and the top surface of the prism can be observed as a bright area (A) and the non-contact interface as a dark area (B) is determined through preliminary experiments, and the imaging device (6) is moved and adjusted to the observation point position.

8. The in-situ observation method of underwater soft material interface contact according to claim 1, characterized in that: During the lifting and lowering process of the sensor pressure head (5), it is also necessary to record the stress value between the hydrogel sample (7) and the transparent prism (2) in real time through a stress sensor installed on the sensor pressure head (5).

9. The in-situ observation method of underwater soft material interface contact according to claim 8, characterized in that: After obtaining the image recognition results of the contact interface image frames at different times, it is necessary to calculate the contact interface ratio of the hydrogel sample (7) at each time, and generate a time domain curve of the contact interface ratio, wherein the contact interface ratio is the ratio of the bright domain area to the complete contact surface area of ​​the hydrogel sample (7); at the same time, it is necessary to calculate the nominal stress at each time, and generate a time domain curve of the nominal stress, and the negative maximum nominal stress in the extracted curve is the bonding strength of the hydrogel sample (7); the nominal stress is the ratio of the stress value recorded by the stress sensor to the complete contact surface area of ​​the hydrogel sample (7).

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