Stress-regulated surface wettability switching thin film and preparation method and application thereof

Abstract

The application belongs to the field of micro-nano processing, and particularly relates to a stress-regulated surface wettability switching film and a preparation method and application thereof. The film is prepared from an elastic material; the film comprises a plurality of micro-column units connected to the root of the main part of the film after being annularly cut from any one side or both sides along the thickness direction. The top and side of the micro-column unit are provided with a hydrophobic modification layer; the surface of the main part of the film except the micro-column unit is provided with a hydrophilic modification layer; when the film is stretched and extended by external force parallel to the film, each micro-column unit protrudes from the main part; at this time, the surface of the film is in a super-hydrophobic state. When the film returns to the natural state, each micro-column unit is flush with or in a concave state with the main part; at this time, the surface of the film is in a super-hydrophilic state. The application solves the problems of existing wettability-controllable materials, such as complex operation, large energy consumption, insufficient durability, lack of scalability and universality, etc.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of micro-nano processing, and particularly relates to a stress-regulated surface wettability switching film and a preparation method and application thereof. BACKGROUND

[0002] Wettability-controllable material is a new type of material that can regulate the wettability of the material surface through technical means. The existing surface property switching methods of wettability-controllable materials include temperature regulation method, light regulation method and electric field regulation method. Among them, the temperature regulation type wettability switching material refers to a material that can adjust the surface wettability by changing the temperature to realize the switching of superhydrophilicity and superhydrophobicity. Common materials are heat-sensitive polymers, polyurethane and the like. The light regulation type wettability switching material refers to a material that can adjust the wettability by activating the surface chemical or physical reaction through laser irradiation such as ultraviolet light or visible light. For example, some special materials can change the surface structure through light-sensitive chemicals to achieve the effect of wettability regulation. The electric field regulation type wettability switching material refers to a material that can adjust the wettability by changing the surface structure through the application of an electric field. For example, some materials can use electrostatic force to displace the surface micro-nano structure to change the wettability of the material surface.

[0003] However, the existing various wettability switching materials still have many defects and limited practical value. Among them, the temperature regulation type wettability switching material has the characteristics of slow response speed, large energy consumption and high temperature control precision. For example, it takes a long time for temperature change to achieve the expected effect, and it is difficult to realize fast switching; temperature regulation usually requires heating or cooling equipment, which consumes a lot of energy and reduces the efficiency of the system; the temperature needs to be accurately controlled during wettability switching, otherwise it may affect the performance of the material or cause the material to age. The light regulation type wettability switching material has the shortcomings of dependence on external light source, sensitivity to environmental light and fast material loss. For example, it needs to be matched with a specific light source during use, and the light intensity and wavelength need to be accurately controlled; in actual application, the interference of environmental light may cause unstable wettability switching; long-term light irradiation may cause material degradation or performance degradation, limiting its long-term application. The electric field regulation type wettability switching material has the shortcomings of high complexity, electric field strength limitation and limited application range. For example, an additional electric field control system is required during application, which is complicated to operate; an excessively strong electric field may damage the material and affect its sustainability; it can only be applied to the surface of materials with certain electrical conductivity, limiting its application range, etc.

[0004] In summary, the existing wettability-controllable materials generally have the problems of complex operation, large energy consumption, insufficient durability, lack of scalability and universality, and slow response speed. SUMMARY

[0005] In order to solve the problems of the existing wetting degree adjustable material, such as many defects and limited practical value, the application provides a stress regulation type surface wetting switching film and a preparation method and application thereof.

[0006] The technical scheme provided by the application is:

[0007] The stress regulation type surface wetting switching film is prepared from an elastic material. The film comprises a plurality of micro-column units which are connected to the root of the main part of the film after being annularly cut from any side or both sides along the thickness direction. The top and side surface of the micro-column unit are provided with a hydrophobic modification layer; and the surface of the main part of the film except the micro-column unit is provided with a hydrophilic modification layer.

[0008] When the film is stretched by an external force parallel to the film and is extended, each micro-column unit protrudes from the main part; at this time, the surface of the film is in a super-hydrophobic state. Conversely, when the external force is removed and the film returns to the natural state, each micro-column unit is flush with or recessed from the main part; at this time, the surface of the film is in a super-hydrophilic state.

[0009] As a further improvement of the application, the maximum cutting depth of the micro-column unit is equal to 40%-80% of the thickness of the film.

[0010] As a further improvement of the application, the specified thickness part of the top of the cut micro-column unit is removed first, and then the hydrophobic modification layer is formed, so that the film is flush with or recessed from the main part when it returns to the natural state.

[0011] As a further improvement of the application, the film is made of silica gel, rubber, PDMS or other elastic polymers.

[0012] The application also includes a preparation method of the stress regulation type surface wetting switching film, which comprises:

[0013] (1) uniformly stretching the elastic material film to the maximum elastic deformation state, and performing the subsequent procedures in the stretched state.

[0014] (2) scanning the target area of the film surface by femtosecond laser to form a roughened surface.

[0015] (3) using any kind of hydrophilic modifier to modify the surface of the film to form a hydrophilic modification layer.

[0016] (4) forming a mask layer which can be specifically removed on the surface of the hydrophilic modification layer of the film.

[0017] (5) annularly scanning the target area according to the preset shape, depth and space by femtosecond laser, and then cutting a plurality of micro-column units which are connected to the root of the main part of the film.

[0018] (6) The top of the micro-pillar unit is scanned by femtosecond laser to remove the mask layer, the hydrophilic modification layer and a specified thickness of the thin film material, and a rough surface is formed.

[0019] (7) The side of the thin film containing the micro-pillar unit is modified by any hydrophobic modifier to form a hydrophobic modification layer.

[0020] (8) The mask layer is specifically removed by a specified means, and the hydrophobic modification layer on it is peeled off; then the thin film is restored to the natural state, and the desired product is obtained.

[0021] As a further improvement of the present application, in steps (2) and (6), a network of grooves with a depth of 10-20 μm and a pitch of 20-50 μm is machined by femtosecond laser, and a rough surface is formed.

[0022] As a further improvement of the present application, in step (4), a PET film is used as a mask layer, and in step (8), the mask layer is specifically removed by mechanical peeling or solvent dissolution.

[0023] As a further improvement of the present application, in step (3), the thin film is immersed in a hydrophilic reagent solution to form a hydrophilic modification layer. In step (7), hydrophobic silica particles are sprayed onto the surface of the thin film to form a hydrophobic modification layer.

[0024] The present application also includes the use of a stress-regulated surface wettability switching thin film as described above in the separation of liquid-phase components. A plurality of stress-regulated surface wettability switching thin films are unfolded and immersed in a suspension liquid containing water-phase and oil-phase components, and adsorb the water-phase components contained therein; then the stress-regulated surface wettability switching thin films are taken out and stretched horizontally to the super-hydrophobic state, and the adsorbed water-phase components are caused to slide off the thin films; the above process is repeated to realize the separation of components in the suspension liquid.

[0025] The present application also includes a liquid-phase component separator for realizing the separation of water-phase and oil-phase substances in a suspension liquid. The liquid-phase component separator comprises a movable support and a plurality of stress-regulated surface wettability switching thin films as described above. The movable support has a switchable natural state and an expanded state; the stress-regulated surface wettability switching thin films are installed on the movable support, and satisfy: when the movable support is in the natural state, each stress-regulated surface wettability switching thin film is unfolded and in the super-hydrophilic state; when the movable support is in the expanded state, each stress-regulated surface wettability switching thin film is stretched and in the super-hydrophobic state.

[0026] The application also comprises an application of the stress-regulated surface wettability switching film as previously described in controllable chemical reactions. The stress-regulated surface wettability switching film is used as a container for reactions between liquid-phase chemicals, and the wettability state of the switching film is switched to regulate the chemical reactions between the liquid-phase chemicals.

[0027] The technical solution provided by the application has the following beneficial effects:

[0028] The application combines the surface microstructure processing of femtosecond lasers with the surface modification process of materials, and then designs a new material that can reversibly regulate the surface wettability of the film under the influence of stress. Through the synergistic effect of the surface microstructure and the chemical coating of the material in the stretched state and the relaxed state, the reversible wettability regulation of the material from superhydrophilic to superhydrophobic is realized. This dynamic regulation characteristic has broad application prospects in the fields of flexible sensors, intelligent surfaces, microfluidic devices, etc. And can be applied to intelligent control of liquid flow and distribution, adjustable surface optical properties, dynamic information display, antifouling and waterproof surface design, droplet capture and release device, etc. It shows significant cross-field adaptability.

[0029] The surface wettability regulation material designed by the application switches states through stress, so it can effectively overcome many defects of traditional temperature regulation method, light regulation method, and electric field regulation method in terms of energy consumption, response characteristics, and anti-interference characteristics. The manufacturing process of the product provided by the application is simple, and the production cost is low, so it has higher practical value.

[0030] The product provided by the application effectively improves the accuracy and uniformity of microstructure preparation through stress-induced microstructure morphology changes. The silicone surface structure and functional coating can still maintain stable wettability switching performance after multiple stretching and relaxing cycles, which reflects excellent durability and reliability. This performance advantage lays the foundation for long-term use of the product. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The structural schematic diagram of the stress-regulated surface wettability switching film provided in Embodiment 1 of the application in the relaxed state.

[0032] Figure 2 The structural schematic diagram of the stress-regulated surface wettability switching film provided in Embodiment 1 of the application in the stretched state.

[0033] Figure 3 The cross-sectional structural schematic diagram of the stress-regulated surface wettability switching film provided in Embodiment 1 of the application, in which the microcolumn units can protrude to both sides.

[0034] Figure 4This is a flow chart of the method for preparing a stress-regulated surface wettability switching film provided in Example 2 of the present invention.

[0035] Figure 5 This is a schematic structural diagram of the liquid phase component separator provided in Example 3 of the present invention.

[0036] Figure 6 To verify the micromorphology and line profile analysis of the samples in the tensile state in the experiment.

[0037] Figure 7 To verify the micromorphology and line profile analysis of the sample in the relaxed state in the experiment.

[0038] Figure 8 To verify the micromorphology and line profile analysis of the sample in the experimental state after 20 stretching cycles.

[0039] Figure 9 To verify the changing curves of contact angle and rolling angle of the sample surface under different strain conditions in the experiment. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] Example 1

[0042] This embodiment provides a stress-regulated surface wettability switching film made of an elastic material. The film comprises a plurality of microcolumnar units connected to the base of the main body of the film, produced by circular cuts along the thickness direction from either or both sides. The top and sides of the microcolumnar units are provided with a hydrophobic modification layer; the surface of the main body of the film, excluding the microcolumnar units, is provided with a hydrophilic modification layer. In practical applications, the hydrophobic and hydrophilic modification layers can be obtained by physically or chemically modifying the original film material.

[0043] In natural state, Figure 1 As shown, the microcolumns in this embodiment of the film are tightly "embedded" within the main body, with each microcolumn unit positioned flush with or slightly lower than the main body, forming a recessed state. Therefore, when liquid contacts the surface of the film material, the droplet primarily contacts the main body. Because the main body's surface includes a hydrophilic modification layer, forming a network-like structure, the film exhibits a predominantly superhydrophilic state under these conditions.

[0044] Furthermore, after conducting stress analysis on the film material with this specific structure and material surface characteristics, it can be found that: when this type of film is subjected to tensile stress along the water surface, the part other than the micro-column units constitutes a complete grid-like main body. This part will undergo elastic deformation and be gradually stretched under the tensile action of the external force. In this process, the area of ​​the main body gradually expands and the thickness gradually becomes thinner. As for the independent micro-column units "embedded" in the main body, since they are basically not affected by external stress except for the roots, their shapes will remain in their original state. Therefore, if Figure 2 As shown in the figure, external stretching causes the main body to thin, while also causing the individual microcolumns to protrude upward along the main body. In this state, when liquid contacts the surface of the film material, the droplet primarily contacts the tops of the protruding microcolumns. Because the tops of the main cells contain a hydrophobic modification layer, the film exhibits a predominantly superhydrophobic state under these conditions.

[0045] Furthermore, because the film provided in this embodiment is made of an elastic material, such as silicone, rubber, PDMS, or other elastic polymers, deformation of the main portion within the elastic limit is reversible. When the tensile stress acting on the film is removed, the main portion of the film shrinks and thickens, allowing the individual microcolumns to re-embed into the main portion. At this point, the film surface returns to a superhydrophilic state.

[0046] In summary, the film material provided in this embodiment can undergo elastic deformation under stress. Combined with the surface property differences of the different structures after deformation, the wettability of the film surface can be freely switched between hydrophilic and hydrophobic properties. In other words, the film material provided in this embodiment is a stress-controlled surface wettability film.

[0047] An analysis of the inherent principle of the stress-regulated surface wettability switching performance generated by the thin film material provided in this embodiment reveals that: after the material is divided, the thin film material comprises two parts, the main body and the microcolumn unit, which are only connected at the root; and the surfaces of these two parts in the film exhibit different wettabilities. When the film is subjected to tensile stress, the main body parts connected to each other will undergo obvious strain, while the strains on the independent microcolumn units will be relatively slight. Based on the characteristic that elastic films will become thinner under tension, the relative height between the main body and the microcolumn unit of the film of this embodiment will change with the magnitude of the tensile stress; when the microcolumn unit is higher than the main body, the surface of the film will be hydrophobic corresponding to the top of the microcolumn unit, and when the microcolumn unit is flush with or shorter than the main body, the surface of the film will be hydrophilic corresponding to the main body.

[0048] Based on the working principle described above, it can be known that the cutting depth of the micro-column unit in the stress-regulated surface wettability switching film provided in the embodiment has an influence on the performance of the product. In actual application, when the cutting depth of the micro-column unit part is too shallow, the change in the relative height difference between the micro-column unit and the main part of the film is not obvious when the film is stretched, and it is difficult to achieve a good wettability switching effect. When the cutting depth of the micro-column unit part is too deep, the difference in the strain effect between the main part and the micro-column unit part of the film when the film is stretched may cause the root part of the two to be torn, and thus the wettability regulation characteristics of the film are invalid. Therefore, in a more optimized scheme, the cutting depth of the micro-column unit should be equal to 40%-80% of the overall thickness of the film.

[0049] The stress-regulated surface wettability switching film provided in the embodiment is formed by locally circularly cutting a completed elastic film to form a main part and a micro-column unit part with root adhesion. In this process condition, it is difficult to achieve the technical effect that the height of the micro-column unit is lower than that of the main part. In view of this situation, the embodiment removes a specified thickness part of the top of the cut micro-column unit first, and then forms a hydrophobic modification layer, so that the film returns to a concave state relative to the main part when the film returns to a natural state.

[0050] In addition, it should be additionally explained that the above content mainly introduces a scheme of cutting along one side of the film, so that the micro-column unit will "pop out" from the corresponding side in the stretched state, and thus the wettability of the surface of the film on the side is changed. Figure 3 As shown in the figure, in other more optimized schemes, the film can also be cut simultaneously along both sides, the middle part of the micro-column unit is connected to the main part of the film, and the surfaces of the micro-column unit on both sides and the main part of the film are modified. In this film structure, when the film is stretched, the embedded micro-column unit will pop out from both sides at the same time, and thus the wettability of the surfaces of the film on both sides is changed.

[0051] Embodiment 2

[0052] The embodiment provides a preparation method of a stress-regulated surface wettability switching film, which is used to prepare the stress-regulated surface wettability switching film in Embodiment 1. Specifically, the preparation method of the embodiment combines femtosecond laser processing technology and functional surface coating treatment, so that the surface wettability of the elastic film can be reversibly switched in the stretched and relaxed states. As shown in the figure, the preparation method provided in the embodiment includes: Figure 4

[0053] (1) uniformly stretch the elastic material film to the maximum elastic deformation state, and perform the subsequent procedures in the stretched state.

[0054] ​The embodiment selects silica gel as the elastic film. Of course, in actual applications, other materials that can withstand stretching and have obvious thickness changes during stretching can be used as the required elastic base material. The specific material can be selected according to actual needs. In addition, the thickness of the silica gel film can also be adjusted according to the actual application requirements to meet different functional requirements. During processing, the embodiment can clamp the elastic film along the edge through the holding device, and then expand the clamping device outward synchronously to stretch the elastic film in the middle. In the embodiment, in order to ensure better processing effect and avoid damage to the material, the film should be stretched to the maximum elastic deformation state.

[0055] (2) Scanning the target area on the surface of the film by femtosecond laser to form a roughened surface.

[0056] According to the needs of the application scenario, the embodiment can choose to process the entire surface of the film material so that it has the switchable wetting property, or choose to process only part of the surface of the film material and make the processed part have the switchable wetting property.

[0057] The first femtosecond laser scanning processing of the surface of the film material is to obtain a roughened interface that can make the hydrophilic modification layer more stable, which can make the final film have a longer service life in frequent "stretching-recovery" cycles and is not easy to lose hydrophilic properties. Specifically, the embodiment selects to process a regular groove structure to form the required roughened surface. For example, a network of grooves with a depth of 10-20 μm and a pitch of 20-50 μm is processed by femtosecond laser to form the required roughened surface.

[0058] (3) Using any kind of hydrophilic modifier to modify the surface of the film to form a hydrophilic modification layer.

[0059] Specifically, the silica gel film after surface roughening processing in the stretched state is immersed in a hydrophilic reagent solution for chemical modification, so that the inside of the groove and the surface of the substrate both exhibit superhydrophilicity, and then the required hydrophilic modification layer is obtained. Of course, in actual applications, the hydrophilic reagent can be selected according to actual needs, and even a reagent with high surface energy can be used, or the silica gel surface can be made hydrophilic by surface treatment technology.

[0060] (4) Forming a mask layer that can be specifically removed on the surface of the hydrophilic modification layer of the film.

[0061] In this embodiment, a PET film with a thickness of 10-20 μm is used as a mask layer on the super-hydrophilic substrate surface. The mask layer can be used for the subsequent selective "growth" of micro-pillar units and hydrophobic modification of the material surface at specific locations.

[0062] It should be noted that the mask layer in this embodiment should be made of a material that can be removed specifically. For example, when a PET film is used as a mask layer, the PET film can be removed directly to remove the material at the specific location. In other embodiments, a material that can be removed specifically by chemical solvents or light, such as photoresist, can be used to form the mask layer. In practical applications, the mask material can be selected to be no more than 100 microns thick, insoluble in water, and non-reactive with silica gel to ensure the accuracy and stability during processing.

[0063] (5) The target area is scanned in a ring shape according to the preset shape, depth, and space by femtosecond laser, and then a plurality of micro-pillar units connected to the root of the main part of the film are cut out.

[0064] This step is mainly used for ring cutting of the film material to form the required micro-pillar units. As known, before the ring-shaped femtosecond laser ring scanning, the film is an integral whole and is subjected to tensile stress to cause overall strain. When the femtosecond laser processes a ring groove with a certain depth on the film, the elastic material in the middle of the ring groove is no longer in contact with the elastic material on the periphery. At this time, most of the elastic material on the periphery is still subjected to tensile stress and deformed, while the local elastic material in the middle is no longer affected by the tensile stress and returns to the natural state (i.e., shrinks and thickens). Macroscopically, it is equivalent to "growing" a micro-pillar unit protruding upward from the middle of the film.

[0065] Finally, the ring groove of the corresponding shape is cut according to the shape of the required micro-pillar unit, for example, a circular groove is cut when a cylindrical column is required, but a square groove is cut when a square column is required. In combination with the spatial distribution of the required micro-pillar units, a micro-pillar array composed of a plurality of micro-pillar units is cut out. The height of the processed micro-pillar unit (the depth of the ring groove) is mainly controlled by adjusting the laser power and the number of scans during femtosecond laser processing. In practical applications, the laser power, scanning speed, micro-pillar spacing, number of scans, and micro-pillar diameter, etc. processing parameters can be adjusted according to actual needs to optimize the surface structure.

[0066] (6) The top of the formed micro-pillar unit is scanned by femtosecond laser to remove the mask layer, the hydrophilic modification layer, and the film material with a specified thickness, and a roughened surface is formed.

[0067] In the order from bottom to top, each micro-column unit cut out in the previous step includes a base made of the original elastic material, the hydrophilic modification layer generated in step (3), and the mask layer generated in step (4). In this step, the top of each micro-column unit processed is scanned by femtosecond laser, and the mask layer and the hydrophilic modification layer can be removed respectively, so as to hydrophobically modify the micro-column unit in the subsequent step. In addition, it needs to be emphasized that, in order to make the thickness of the micro-column unit corresponding area of the film be flush with other parts or present a concave structure when the external force is removed, the scanning in this step will continue to scan downward after removing the hydrophilic modification layer to remove the specified thickness of the elastic material. In addition, in order to ensure that the surface of the micro-column unit can form a more firm hydrophobic modification layer in the subsequent step, the top of the micro-column unit in this embodiment also needs to be roughened. The roughening of the top of the micro-column unit is still realized by the way of forming grid micro-grooves by cross scanning of femtosecond laser.

[0068] (7) Surface modification of the side of the film containing the micro-column unit by using any one of the hydrophobic modification agents to form a hydrophobic modification layer.

[0069] In this step, the hydrophobic silica particles are uniformly sprayed onto the surface of the micro-column array composed of micro-column units, especially the top structure, and then the super-hydrophobic performance is realized through the self-assembly effect of the particles. It should be noted that in this embodiment, when the hydrophobic modification agent is sprayed onto the micro-column unit, the hydrophobic modification agent will inevitably be sprayed onto the corresponding area of the main part, and this area is currently covered by the mask layer, that is, the hydrophobic modification layer will be formed on the mask layer of the main part and the surface of the elastic material of the micro-column unit. Of course, in the scheme of this embodiment, the hydrophobic reagent can be reasonably selected according to actual needs, or even a low surface energy reagent can be used, or the silica gel surface can be made hydrophobic by surface treatment technology

[0070] (8) The mask layer is specifically removed by using a specified means, and the hydrophobic modification layer on the mask layer is peeled off; then the film is restored to the natural state, and then the desired product is obtained.

[0071] In step (7), the hydrophobic modification material covers the main part of the film, and in this step, the mask layer is removed, and the hydrophobic modification layer above the mask layer is simultaneously peeled off, exposing the hydrophilic modification layer below, so that the surface of the micro-column unit of the final obtained film material is covered with a hydrophobic modification layer, and the main part except the micro-column unit is covered with a hydrophilic modification layer. Since the mask layer used in this embodiment is a PET film, the mask layer can be removed by mechanical peeling. In other embodiments, when the mask layer is made of other materials, methods such as light, chemical reagents and solvents can be used to specifically remove the corresponding mask layer material.

[0072] After the structure design and surface modification of the above-mentioned material are completed, the stress applied to the film material is removed, and a new material similar in overall appearance to a conventional film but capable of reversibly adjusting the wettability of the material surface after the action of tensile stress is obtained.

[0073] Embodiment 3

[0074] The film material provided in Embodiments 1 and 2 having the wettability reversibility switching performance has broad application prospects in the fields of flexible sensors, smart surfaces, microfluidic devices, etc. This embodiment develops the functions of the product and further provides two typical application scenarios. Specifically, (1) application of the stress-regulated surface wettability switching film as described above in liquid-phase component separation; and (2) application of the stress-regulated surface wettability switching film as described above in controllable chemical reactions. In the former, a plurality of stress-regulated surface wettability switching films are unfolded and immersed in a suspension liquid containing water-phase and oil-phase components, and the hydrophilic property of the films in the natural state is used to adsorb the water-phase components contained therein. Then the stress-regulated surface wettability switching films are taken out and stretched horizontally to the super-hydrophobic state, so that the adsorbed water-phase components fall off the films; the above process is repeated to realize the separation of components in the suspension liquid. In this application, the film is used as a water-phase material specific extraction material in the suspension liquid, thereby replacing the traditional chromatography, distillation and other complex and energy-consuming material purification processes. The latter refers to using the stress-regulated surface wettability switching film as a container for reactions between liquid-phase chemicals, and controlling the chemical reactions between liquid-phase chemicals by switching the wettability state of the film.

[0075] In combination with the first application mentioned above, this embodiment further provides a liquid-phase component separator for separating water-phase substances and oil-phase substances in a suspension liquid. As shown in Figure 5 the liquid-phase component separator includes a movable support and a plurality of stress-regulated surface wettability switching films as described above. The movable support has a switchable natural state and an expanded state; the stress-regulated surface wettability switching films are installed on the movable support and satisfy the following conditions: when the movable support is in the natural state, each of the stress-regulated surface wettability switching films is unfolded and in a super-hydrophilic state; when the movable support is in the expanded state, each of the stress-regulated surface wettability switching films is stretched and in a super-hydrophobic state.

[0076] Verification experiment

[0077] To verify the stress-regulated surface wettability switching film provided by the present application, the skilled person uses silica gel material and a femtosecond laser processing system to prepare a corresponding sample, and tests the performance of the film.

[0078] I. Product manufacturing

[0079] (1) Four-axis stretching and groove processing

[0080] Install the silica gel substrate on the four-axis stretching device, apply uniform tensile stress in four directions, and cause uniform deformation of the silica gel surface.

[0081] Use a femtosecond laser to process regular groove microstructures on the stretched silica gel substrate, and the groove depth and pitch can be adjusted according to requirements. Generally, the recommended depth is 10-20 μm, and the pitch is 20-50 μm.

[0082] (2) Preparation of super-hydrophilic substrate

[0083] Soak the processed silica gel substrate in the stretched state in a hydrophilic reagent solution for chemical modification, so that the inside of the groove and the surface of the substrate exhibit super-hydrophilic properties.

[0084] (3) Mask covering

[0085] Cover a layer of PET film with a thickness of 10-20 μm on the surface of the super-hydrophilic substrate as a mask layer for the selective growth of the micro-pillar structure in the subsequent step.

[0086] (4) Self-growth and modification of micro-pillar array

[0087] Use a femtosecond laser to scan the stretched silica gel surface in a circular path, and use the synergistic effect of laser processing and stress to form a regular micro-pillar array on the silica gel surface.

[0088] Continue to scan fine groove structures at the top of the micro-pillars, which can not only accurately remove the mask layer, but also enhance the adhesion effect of the hydrophobic coating.

[0089] (5) Formation of hydrophobic coating

[0090] Use a spraying device to uniformly spray hydrophobic silica particles onto the surface of the micro-pillar array, especially the top structure, to achieve super-hydrophobic properties through the self-assembly effect of the particles.

[0091] (6) Removal of mask and realization of wettability switching

[0092] Use mechanical peeling or solvent dissolution methods to remove the PET film mask, leaving the micro-pillar structure and the bottom hydrophilic substrate.

[0093] II. Analysis of performance morphology and cycle effect

[0094] The film samples manufactured in the experiment were stretched and relaxed multiple times, and the surface morphology of the film in different states was observed by confocal microscope. The height change of different areas on the film surface was measured, and the line profile analysis of the longitudinal section of the film was completed. After taking and measuring the three-dimensional morphology of the silica gel material under different strain states, this analysis result provides a detailed structural background for the subsequent wetting test, helping technicians to understand how the surface microstructure changes with deformation and changes the wetting performance.

[0095] The microstructure and line profile analysis diagram of the film material in the stretched state are shown in Figure 6 , and the microstructure and line profile analysis diagram in the relaxed state are shown in Figure 7 . After 20 stretching cycles, the microstructure and line profile analysis diagram of the film material in the stretched state are shown in Figure 8 .

[0096] Comparing Figure 6 and Figure 7 , it can be found that in the stretched state, the microcolumn height increases significantly, showing a clear periodic arrangement, which helps to form the surface superhydrophobic performance. In the relaxed state, the microcolumn is partially embedded in the substrate, and the surface tends to be flat, resulting in superhydrophilic properties. Further comparison of Figure 6 and Figure 8 , it can be found that even after 20 stretching cycles, the microcolumn morphology and its profile height of the film material prepared in the experiment do not change significantly, which shows that the microstructure has excellent stability and durability under multiple mechanical loads.

[0097] III. Wetting regulation effect

[0098] In the stretching cycle, the experiment further measures the contact angle and rolling angle of the sample surface under different strains, and then discusses the specific influence of stress on the surface wetting of the film material. The contact angle and rolling angle variation curve of the sample surface under different strain conditions according to the experimental results is shown in Figure 9 .

[0099] Analyzing the experimental data in Figure 9 , it can be found that when the film is stretched less than 20mm, the silica gel surface is superhydrophilic, and the liquid droplet added on the surface will spread rapidly, showing a contact angle close to 0°. This is because when the stretching is small, the microcolumn has not yet appeared, and the surface characteristics are dominated by the superhydrophilic property of the substrate.

[0100] When the stretching is more than 20mm, the height of the micro-column structure is enough, the surface of the silica gel turns into super-hydrophobic state, at this time, the contact angle is more than 150°, the rolling angle is less than 10°, and the typical "Cassie-Baxter" state is shown. The super-hydrophobicity is derived from the appearance of the micro-column structure, which makes the contact area of the liquid drop and the surface significantly reduced, forms the air pocket effect, and reduces the adhesion of the liquid drop.

[0101] Therefore, the above results show that the thin film material provided by the present application can realize the dynamic switching from super-hydrophilic to super-hydrophobic through the micro-structure change in the stretching state, and the new material characteristics can provide a new research direction for the intelligent surface design.

[0102] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A stress-regulated surface wettability switching film, characterized in that: It is made of elastic material; the film contains a plurality of micro-column units connected to the root of the main part of the film after circular cutting from any one or both sides along the thickness direction; the top and side of the micro-column units are provided with a hydrophobic modification layer; the surface of the main part of the film other than the micro-column units is provided with a hydrophilic modification layer; When the film is stretched by an external force parallel to the film, each microcolumn unit protrudes from the main body; at this time, the surface of the film is in a superhydrophobic state; when the film returns to its natural state, each microcolumn unit is flush with the main body or is in a concave state; at this time, the surface of the film is in a superhydrophilic state; The film is prepared by a stress-regulated surface wettability switching film preparation method: (1) Uniformly stretching the elastic material film to the maximum elastic deformation state, and performing subsequent processes in the stretched state; (2) Scanning the target area of ​​the film surface by femtosecond laser to form a roughened surface; (3) using any hydrophilic modifier to modify the surface of the film to form a hydrophilic modified layer; (4) forming a mask layer that can be specifically removed on the surface of the hydrophilic modified layer of the film; (5) Using a femtosecond laser, the target area is scanned in a circular manner according to a preset shape, depth, and space, thereby cutting out a plurality of microcolumn units connected to the root of the main part of the film; (6) Scanning the top of the formed microcolumn unit by femtosecond laser to remove the mask layer, the hydrophilic modification layer, and the thin film material of a specified thickness, and forming a roughened surface; (7) using any hydrophobic modifier to modify the surface of one side of the film containing the microcolumn units to form a hydrophobic modified layer; (8) Using a specified means to specifically remove the mask layer and peel off the hydrophobic modified layer thereon; then restoring the film to its natural state to obtain the desired product; In steps (2) and (6), a mesh groove with a depth of 10-20 μm and a spacing of 20-50 μm is machined by femtosecond laser to form the desired roughened surface.

2. The stress-regulated surface wettability switching film according to claim 1, wherein: The maximum cutting depth of the microcolumn unit is equal to 40-80% of the thickness of the film.

3. The stress-regulated surface wettability switching film according to claim 2, wherein: First, a portion of a specified thickness at the top of the cut microcolumn unit is removed, and then a hydrophobic modification layer is formed, so that the film is flush with the main body or concave when it returns to its natural state.

4. The stress-regulated surface wettability switching film according to claim 2, wherein: The film is made of rubber or PDMS.

5. The stress-regulated surface wettability switching film according to claim 2, wherein: The film is made of silica gel.

6. A method for preparing a stress-regulated surface wettability switching film, characterized in that: The film used for stress-regulated surface wettability switching according to any one of claims 1 to 5 comprises: (1) Uniformly stretching the elastic material film to the maximum elastic deformation state, and performing subsequent processes in the stretched state; (2) Scanning the target area of ​​the film surface by femtosecond laser to form a roughened surface; (3) using any hydrophilic modifier to modify the surface of the film to form a hydrophilic modified layer; (4) forming a mask layer that can be specifically removed on the surface of the hydrophilic modified layer of the film; (5) Using a femtosecond laser, the target area is scanned in a circular manner according to a preset shape, depth, and space, thereby cutting out a plurality of microcolumn units connected to the root of the main part of the film; (6) Scanning the top of the formed microcolumn unit by femtosecond laser to remove the mask layer, the hydrophilic modification layer, and the thin film material of a specified thickness, and forming a roughened surface; (7) using any hydrophobic modifier to modify the surface of one side of the film containing the microcolumn units to form a hydrophobic modified layer; (8) Using a specified means to specifically remove the mask layer and peel off the hydrophobic modified layer thereon; then restoring the film to its natural state to obtain the desired product; In steps (2) and (6), a mesh groove with a depth of 10-20 μm and a spacing of 20-50 μm is machined by femtosecond laser to form the desired roughened surface.

7. The method for preparing a stress-regulated surface wettability switching film according to claim 6, wherein: In step (4), a PET film is used as a mask layer, and in step (8), the mask layer is specifically removed by mechanical stripping or solvent dissolution; In step (3), the film is immersed in a hydrophilic reagent solution to form the hydrophilic modified layer; in step (7), hydrophobic silica particles are sprayed onto the surface of the film to form the hydrophobic modified layer.

8. Use of the stress-regulated surface wettability switching film according to any one of claims 1 to 5 in liquid phase component separation, characterized in that: After unfolding, multiple stress-regulated surface wettability switching films are immersed in a suspension containing aqueous and oily phase components to adsorb the aqueous phase components contained therein; then, the stress-regulated surface wettability switching films are removed and horizontally stretched to a superhydrophobic state, thereby allowing the adsorbed aqueous phase components to slide off the films; the above process is repeated to achieve the separation of the components in the suspension.

9. A liquid phase separator for separating aqueous and oily phases in a suspension, characterized in that: It comprises a movable support and a plurality of stress-regulated surface wettability switching films according to any one of claims 1 to 5; the movable support has a switchable natural state and an expanded state; The stress-regulated surface wettability switching film is installed on a movable bracket and meets the following requirements: when the movable bracket is in a natural state, each stress-regulated surface wettability switching film is unfolded and presents a superhydrophilic state; when the movable bracket is in an expanded state, each stress-regulated surface wettability switching film is stretched and presents a superhydrophobic state.

10. Use of the stress-regulated surface wettability switching film according to any one of claims 1 to 5 in a controllable chemical reaction, characterized in that: The stress-regulated surface wettability switching film is used as a container for reactions between liquid-phase chemicals, and the chemical reactions between liquid-phase chemicals are regulated by switching the wettability state of the film.

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