A porous composite skeleton for collecting underwater bubbles and its preparation method

Abstract

The present invention discloses a porous composite skeleton for collecting underwater bubbles and a preparation method, belonging to the field of new material technology. The super-hydrophobic composite skeleton is composed of in-situ grown mullite whiskers forming a skeleton support and heat-cured silicone oil forming a muscle-like functional phase, and is used for underwater bubble capture. The composite skeleton exhibits excellent chemical, thermal and mechanical stability, and when ground into powder, it still maintains super-hydrophobic properties. The hybrid skeleton realizes all-round underwater bubble capture. In addition, the pore size of the hybrid skeleton is about 500nm, which is more than 100 times smaller than the pore size previously reported, expanding the operating depth from a few centimeters to about 60 meters.

Description

Technical Field

[0001] The present invention relates to the field of new material technology, and more particularly to a porous composite skeleton for collecting underwater bubbles and a preparation method thereof. Background Art

[0002] Because superhydrophobic surfaces exhibit superaerophilicity in water, this plays a key role in the underwater survival of some organisms. For example, rice plants are highly resistant to waterlogging due to the superhydrophobicity of their leaves. The air film formed on the leaf surface (called an "air barrier") facilitates gas exchange with the surrounding water. Similarly, diving spiders survive underwater thanks to their superhydrophobic abdomens, which capture air bubbles and form a diving bell, providing them with an air supply. Inspired by these natural systems and driven by promising applications such as methane collection from water, manipulation of Janus particles, water treatment, underwater drag reduction, and energy harvesting, superhydrophobic surfaces with the ability to capture and manipulate underwater bubbles have attracted increasing attention.

[0003] At present, researchers have developed superhydrophobic surfaces of various geometric forms for the collection and manipulation of underwater bubbles. For example, a superhydrophobic copper spiral structure is used to control the movement of bubbles. Under the combined action of buoyancy and adhesion, the bubbles will rotate with the copper spiral. In order to manipulate smaller bubbles, a superhydrophobic copper cone is designed so that the bubbles move directionally from the tip to the base along the cone driven by the Laplace pressure gradient. Unlike these single bubble strategies, the superhydrophobic sliding surface can capture and transport multiple underwater bubbles at the same time under the action of buoyancy. In order to achieve unidirectional transport of bubbles, a Janus metal mesh was also developed to achieve the manipulation of underwater bubbles by constructing a surface wettability gradient. In addition, nano-chitin aerogel is also used to capture and transport bubbles using buoyancy.

[0004] Chinese patent application number CN201910588632.7 uses laser perforation of tin foil to create micropores with diameters of 139 to 142 μm on the upper surface and 60 to 62 μm on the lower surface, intended for underwater bubble capture. However, the large pore diameters result in low penetration strength, making it easy to penetrate underwater, and the metal is not corrosion-resistant.

[0005] The Chinese patent application number CN201811621076.0 uses copper foil and stearic acid film to prepare a super-hydrophobic and super-aerophilic surface to collect underwater bubbles. The diameter of the copper foil micropores is 100μm to 200μm. The pore size is too large, the penetration strength is small, and the depth of underwater use is very small.

[0006] According to the Chinese patent application number CN201711224216.6, a copper mesh is surface-modified with tetradecyl mercaptan to prepare a superaerophilic surface for underwater bubble capture. The pore size of the copper mesh is 190 to 540 μm.

[0007] The Chinese patent application number is CN201911049874.5, which uses a super-hydrophobic spiral cone to achieve bubble transport.

[0008] These methods typically combine a support substrate with a superhydrophobic coating. While some progress has been made in underwater bubble collection and manipulation (particularly directional control), practical application remains a long way off due to the limited robustness of both the substrate and the coating. Structures relying solely on surface coatings are inefficient in terms of bubble collection direction and often lose their superhydrophobic properties due to the irreversible transition from the Cassie-Baxter state to the Wenzel state. Currently, common metal and polymer materials used as support substrates are unsuitable for harsh aqueous environments such as seawater due to their susceptibility to corrosion and degradation. Furthermore, the forces used to propel the bubbles are limited: for smaller bubbles, buoyancy is insufficient to overcome adhesion forces, and wettability gradients often struggle to maintain a sufficiently long propulsion distance. Furthermore, the large pore sizes of the porous materials used (often greater than 100 microns) result in low compressive strength, limiting their practical application to depths of a few centimeters to tens of centimeters underwater. Therefore, the development of robust, small-pore materials with high durability and superhydrophobic stability is urgently needed to efficiently collect underwater bubbles and promote practical applications. Summary of the Invention

[0009] 1. Technical problems to be solved:

[0010] In response to the problems existing in the prior art, the purpose of the present invention is to provide a small-pore, high-compression-penetration strength, and high-stability composite porous skeleton for underwater bubble collection, so as to solve the problems of poor chemical stability and poor compression-penetration strength of the materials existing in the above-mentioned background technology.

[0011] 2. Technical solution:

[0012] To achieve the above objectives, the present invention provides the following technical solution: a porous composite skeleton for collecting underwater bubbles, composed of polydimethylsilane and mullite, with a microstructure of a porous network structure formed by 3D interlocking mullite whiskers, the surface of the mullite whiskers being covered with a polydimethylsiloxane film, the skeleton pore size being 500nm ~ 10um, the porosity being 50% ~ 90%, the mullite whiskers being a single crystal structure, and the composite skeleton having overall superhydrophobicity.

[0013] The preparation method of the porous composite skeleton of the present invention specifically comprises the following steps:

[0014] S1. Place a mixed powder containing 74-84 wt% aluminum hydroxide, 14-23 wt% diatomaceous earth, 1-3 wt% aluminum fluoride and 1-3 wt% molybdenum trioxide in an agate planetary ball mill and ball mill for 12-48 hours;

[0015] S2, placing the mixed powder obtained in step S1 into a metal mold and pressing it into a green body;

[0016] S3, placing the pressed green body in a glazed ceramic crucible, heating it to 800-1600° C. at a heating rate of 5° C. / min in an air atmosphere furnace, keeping it at that temperature for 1-3 hours, and then cooling it with the furnace to obtain a mullite whisker skeleton;

[0017] S4, immersing the mullite whisker skeleton in a 1-10 wt% polydimethylsiloxane / n-hexane solution for 2 hours, taking it out and drying it in a blast drying oven;

[0018] S5, the dried sample was placed in an air atmosphere furnace, heated at different temperatures to solidify the polydimethylsiloxane, and kept warm for 4 hours to finally obtain a mullite whisker / polydimethylsiloxane composite skeleton material. Further, the silica content in the diatomaceous earth in step S1 was 95wt%.

[0019] Furthermore, the pressing pressure of the metal mold in step S2 is 100-600 MPa.

[0020] Furthermore, in the step S3, a ceramic crucible with a lid and a glaze layer is used, and the glaze layer melts at high temperature to form an airtight seal.

[0021] Furthermore, in the step S4, the drying temperature is 100-160° C., and the drying time is 1-8 hours.

[0022] Furthermore, in the step S5, the temperature for heating and curing is 300 to 450°C for 1 to 4 hours. If the temperature exceeds 450°C, the PDMS is oxidized and loses its hydrophobicity. If the temperature is below 300°C, it is difficult to cure.

[0023] 3. Beneficial effects:

[0024] The technical solution provided by the present invention, compared with the existing technology, is that the overall super-hydrophobic material, even when ground into powder, still exhibits hydrophobicity compared to surface-modified materials. Combined with the single-crystal ceramic material skeleton of the present invention, the material has higher durability and stability. Furthermore, the skeleton pore size of the present invention is as low as 500nm, which is hundreds of times smaller than the pores in the field, and the penetration strength is increased by hundreds of times, because the penetration strength formula is:

[0025] ;

[0026] Among them, γ l represents the surface tension of the liquid, θ is the liquid-solid contact angle, r max is the maximum pore size, and B is a geometric factor determined by the pore structure. Therefore, the smaller the pore size, the higher the penetration strength, which enables the material to collect gas in deeper water.

[0027] It should be noted that the structures not introduced in the present invention are the same as those in the prior art or can be implemented by using the prior art, and are not described in detail here because they do not involve the design points and improvement directions of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The following are photos and scanning electron microscope (SEM) images of the mullite skeleton and the mullite-polydimethylsiloxane composite skeleton of the present invention, wherein;

[0029] (a) is a photo of the mullite skeleton;

[0030] (b, c) are SEM images of mullite skeleton at different magnifications;

[0031] (d) is a photo of the composite skeleton

[0032] (e, f) are SEM images of the composite skeleton at different magnifications.

[0033] Figure 2 Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis diagrams of the composite skeleton of the present invention, wherein;

[0034] (a, b) TEM images of the composite skeleton at different magnifications;

[0035] (c) XRD pattern of the composite framework;

[0036] (d) FTIR analysis of the composite skeleton.

[0037] Figure 3 (a, b) are schematic diagrams of the mullite skeleton: it is superhydrophilic in air and superaerophobic in water;

[0038] (c, d) Schematic diagram of the composite skeleton: it is superhydrophobic in air and aerophilic in water;

[0039] (e, f) Optical photos of the mullite skeleton: superhydrophilic in air and superaerophobic in water;

[0040] (g, h) Optical photographs of the composite framework: superhydrophobic in air and aerophilic in water.

[0041] Figure 4 Schematic diagram of omnidirectional underwater bubble collection according to the present invention, wherein;

[0042] (a, d) Bottom-surface collection: A hybrid framework with a diameter of 30 mm and a thickness of approximately 3 mm floats on the water surface of a cubic quartz tank, and its bottom surface captures and adsorbs bubbles;

[0043] (b, e) Side collection: The hybrid skeleton disk was placed vertically in a water tank, with the top of the disk open to the atmosphere, and the syringe needle was about 1 mm away from the side;

[0044] (c, f) Top surface collection (anti-buoyancy collection): the bubbles are captured and fixed by the top surface of the dish.

[0045] Figure 5 Schematic diagram of the super-hydrophobicity of the composite skeleton of the present invention after being ground into powder. DETAILED DESCRIPTION

[0046] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0047] A porous composite skeleton for collecting underwater bubbles and a preparation method thereof, comprising the following steps:

[0048] Step 1: A mixed powder containing aluminum hydroxide (74-84 wt%), diatomaceous earth (14-23 wt%), aluminum fluoride (AlF3, 1-3 wt%), and molybdenum trioxide (MoO3, 1-3 wt%) was ball milled in a planetary ball mill (both the grinding balls and the grinding jar were made of agate) for 12-48 hours.

[0049] Step 2: Use a metal mold to press the mixed powder into a green body after ball milling at 100~600MPa;

[0050] Step 3: Place the pressed green body into a ceramic crucible with a glaze layer on the lid, place it in an air atmosphere furnace, heat it to 800°C~1600°C, and keep it warm for 1~3 hours to obtain a porous mullite whisker skeleton. The heating and cooling rate is 5°C / min.

[0051] Step 4: Immerse the prepared mullite whisker skeleton in a 1-10 wt% PDMS / n-hexane solution for 2 hours, and then dry it in a blast drying oven at a temperature of 100-160° C. for 1-8 hours.

[0052] Step 5: Place the sample in an air atmosphere furnace and heat at 300 to 450°C for 1 to 4 hours to cure the PDMS.

[0053] Organisms composed of multiple materials are typically multifunctional and highly stable. Inspired by the skeletal-muscle structure of organisms, the present invention aims to construct a composite skeleton with bulk superhydrophobicity for capturing and transporting underwater bubbles. Compared to surface-modified materials, bulk superhydrophobic materials maintain their hydrophobic properties throughout their entire lifespan, thus offering greater durability and stability. To this end, the present invention designs bone-like mullite whiskers and muscle-mimicking cured silicone oil. Mullite is a high-strength ceramic that retains 90% of its room-temperature strength at 1500°C and offers long-term corrosion resistance to molten sodium chloride or high-temperature alkali metal oxides. Furthermore, mullite whiskers, with their single-crystal structure, are stronger due to their reduced defects. As for the driving force for bubble collection, the present invention abandons traditional methods based on buoyancy or wettability gradients and instead utilizes hydrostatic pressure as the driving force. Therefore, the greater the water depth, the stronger the driving force and the higher the bubble collection efficiency.

[0054] Example 1:

[0055] Step 1: A mixed powder containing aluminum hydroxide (74 wt%), diatomaceous earth (22 wt%), aluminum fluoride (AlF3, 3 wt%), and molybdenum trioxide (MoO3, 1 wt%) was ball milled in a planetary ball mill for 12 h;

[0056] Step 2: Use a metal mold to press the mixed powder into a green body after ball milling at 100 MPa;

[0057] Step 3: Place the pressed green body into a ceramic crucible with a glaze layer on the lid, place it in an air atmosphere furnace, heat it to 1300°C, and keep it warm for 3 hours to obtain a porous mullite whisker skeleton. The heating and cooling rate is 5°C / min.

[0058] Step 4: Immerse the prepared mullite whisker skeleton in a 1 wt% PDMS / n-hexane solution for 2 hours, and then dry it in a blast drying oven at a temperature of 150° C. for 8 hours.

[0059] Step 5: Place the sample in an air atmosphere furnace and heat at 300°C for 4 hours to cure the PDMS.

[0060] The porous composite skeleton prepared according to the above steps has a pore size of 1 μm and a porosity of 80%. The stone whiskers have a single crystal structure. The composite skeleton has overall superhydrophobicity, a water drop angle (WCA) of 151°, and an underwater bubble contact angle (BCA) of 47°. It can capture bubbles in various directions such as the bottom surface, top surface, and side surface.

[0061] Example 2:

[0062] Step 1: A mixed powder containing aluminum hydroxide (78 wt%), diatomaceous earth (20 wt%), aluminum fluoride (AlF3, 1 wt%), and molybdenum trioxide (MoO3, 1 wt%) was ball milled in a planetary ball mill for 24 h;

[0063] Step 2: Use a metal mold at 200 MPa to press the mixed powder into a green body.

[0064] Step 3: Place the pressed green body into a ceramic crucible with a glaze layer on the lid, place it in an air atmosphere furnace, heat it to 1000°C, and keep it warm for 2 hours to obtain a porous mullite whisker skeleton. The heating and cooling rate is 5°C / min.

[0065] Step 4: Immerse the prepared mullite whisker skeleton in a 5wt% PDMS / n-hexane solution for 2 hours, and then dry it in a blast drying oven at a temperature of 150°C for 4 hours;

[0066] Step 5: Place the sample in an air atmosphere furnace and heat at 400°C for 6 hours to cure the PDMS.

[0067] The porous composite skeleton prepared according to the above steps has a pore size of 500nm, a porosity of 70%, and a single-crystal structure of mullite whiskers. The composite skeleton has overall superhydrophobicity, a water drop angle (WCA) of 150°, and an underwater bubble contact angle (BCA) of 36°, which can capture bubbles in various directions such as the bottom surface, top surface, and side surface.

[0068] Example 3:

[0069] Step 1: A mixed powder containing aluminum hydroxide (84 wt%), diatomaceous earth (14 wt%), aluminum fluoride (AlF3, 1 wt%), and molybdenum trioxide (MoO3, 1 wt%) was ball milled in a planetary ball mill for 48 h;

[0070] Step 2: Use a metal mold at 600 MPa to press the mixed powder into a green body.

[0071] Step 3: Place the pressed green body into a ceramic crucible with a glaze layer on the lid, place it in an air atmosphere furnace, heat it to 1600°C, and keep it warm for 1 hour to obtain a porous mullite whisker skeleton. The heating and cooling rate is 5°C / min.

[0072] Step 4: Immerse the prepared mullite whisker skeleton in a 10 wt% PDMS / n-hexane solution for 2 hours, and then dry it in a blast drying oven at a temperature of 160° C. for 1 hour.

[0073] Step 5: Place the sample in an air atmosphere furnace and heat at 450°C for 1 hour to cure the PDMS.

[0074] The porous composite skeleton prepared according to the above steps has a pore size of 10 μm, a porosity of 90%, and a single-crystal structure of mullite whiskers. The composite skeleton has overall superhydrophobicity, a water droplet angle (WCA) of 158°, and an underwater bubble contact angle (BCA) of 4°. It can capture bubbles in various directions, including the bottom surface, top surface, and side surface.

[0075] Example 4:

[0076] Step 1: A mixed powder containing aluminum hydroxide (74 wt%), diatomaceous earth (20 wt%), aluminum fluoride (AlF3, 3 wt%), and molybdenum trioxide (MoO3, 3 wt%) was ball milled in a planetary ball mill for 48 h;

[0077] Step 2: Use a metal mold at 600 MPa to press the mixed powder into a green body.

[0078] Step 3: Place the pressed green body into a ceramic crucible with a glaze layer on the lid, place it in an air atmosphere furnace, heat it to 1400°C, and keep it warm for 3 hours to obtain a porous mullite whisker skeleton at a heating and cooling rate of 5°C / min;

[0079] Step 4: Immerse the prepared mullite whisker skeleton in a 10 wt% PDMS / n-hexane solution for 2 hours, and then dry it in a blast drying oven at a temperature of 160° C. for 4 hours.

[0080] Step 5: Place the sample in an air atmosphere furnace and heat at 300°C for 4 hours to cure the PDMS.

[0081] The porous composite skeleton prepared according to the above steps has a pore size of 500nm, a porosity of 50%, and a single-crystal structure of mullite whiskers. The composite skeleton has overall superhydrophobicity, a water droplet contact angle (WCA) of 150°, and an underwater bubble contact angle (BCA) of 29°. It can capture bubbles in various directions, including the bottom surface, top surface, and side surface.

[0082] Example 5:

[0083] Step 1: A mixed powder containing aluminum hydroxide (74 wt%), diatomaceous earth (23 wt%), aluminum fluoride (AlF3, 2 wt%), and molybdenum trioxide (MoO3, 1 wt%) was ball milled in a planetary ball mill for 12 h;

[0084] Step 2: Use a metal mold to press the mixed powder into a green body after ball milling at 100 MPa;

[0085] Step 3: Place the pressed green body into a ceramic crucible with a glaze layer on the lid, place it in an air atmosphere furnace, heat it to 800°C, and keep it warm for 3 hours to obtain a porous mullite whisker skeleton at a heating and cooling rate of 5°C / min;

[0086] Step 4: Immerse the prepared mullite whisker skeleton in a 1 wt% PDMS / n-hexane solution for 2 hours, and then dry it in a blast drying oven at a temperature of 100° C. for 8 hours.

[0087] Step 5: Place the sample in an air atmosphere furnace and heat at 450°C for 3 hours to cure the PDMS.

[0088] The porous composite skeleton prepared according to the above steps has a pore size of 2 μm and a porosity of 73%. The stone whiskers have a single crystal structure. The composite skeleton has overall superhydrophobicity, a water drop angle (WCA) of 153°, and a bubble contact angle (BCA) of 40°, which can capture bubbles in all directions such as the bottom surface, top surface, and side surface.

[0089] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0090] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A porous composite skeleton for collecting underwater bubbles, characterized by: It includes a porous network skeleton composed of mullite whiskers and a polydimethylsiloxane film covering the surface of the porous network skeleton; The mullite whiskers are in a single crystal structure and form a skeleton with a pore size of 500nm to 10μm and a porosity of 50% to 90% through three-dimensional interlocking; The polydimethylsiloxane film imparts superhydrophobicity to the entire skeleton, with a water contact angle greater than 150°; The composite skeleton can collect bubbles from the bottom surface, side surface and top surface simultaneously in an underwater environment.

2. The method for preparing a porous composite skeleton for collecting underwater bubbles according to claim 1, characterized in that: The following steps are involved: S1. Place a mixed powder containing 74-84 wt% aluminum hydroxide, 14-23 wt% diatomaceous earth, 1-3 wt% aluminum fluoride and 1-3 wt% molybdenum trioxide in an agate planetary ball mill and ball mill for 12-48 hours; S2, placing the mixed powder obtained in step S1 into a metal mold and pressing it into a green body; S3, placing the pressed green body in a glazed ceramic crucible, heating it to 800-1600° C. at a heating rate of 5° C. / min in an air atmosphere furnace, keeping it at that temperature for 1-3 hours, and then cooling it with the furnace to obtain a mullite whisker skeleton; S4, immersing the mullite whisker skeleton in a 1-10 wt% polydimethylsiloxane / n-hexane solution for 2 hours, taking it out and drying it in a blast drying oven; S5. The dried sample is placed in an air atmosphere furnace to heat and cure the polydimethylsiloxane, and the temperature is kept for 4 hours to finally obtain a mullite whisker / polydimethylsiloxane composite skeleton material.

3. The method for preparing a porous composite skeleton for collecting underwater bubbles according to claim 2, characterized in that: The silicon dioxide content in the diatomaceous earth in step S1 is 95 wt %.

4. The method for preparing a porous composite skeleton for collecting underwater bubbles according to claim 2, characterized in that: The metal mold pressing pressure in the step S2 is 100~600MPa.

5. The method for preparing a porous composite skeleton for collecting underwater bubbles according to claim 2, characterized in that: The drying temperature in step S4 is 100-160° C., and the drying time is 1-8 hours.

6. The method for preparing a porous composite skeleton for collecting underwater bubbles according to claim 2, characterized in that: The temperature for heating and curing in the step S5 is 300 to 450°C.

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