Porous composite framework for collecting underwater bubbles and preparation method

Abstract

The invention discloses a porous composite skeleton for collecting underwater bubbles and a preparation method, and belongs to the technical field of new materials, the super-hydrophobic composite skeleton is characterized in that mullite whiskers growing in situ form a skeleton support, and thermocuring silicone oil forms a muscle-like functional phase for capturing underwater bubbles; the composite skeleton shows excellent chemical, thermal and mechanical stability, and still keeps super-hydrophobic performance after being ground into powder; the hybrid skeleton realizes omnibearing underwater bubble trapping, in addition, the aperture of the hybrid skeleton is about 500nm and is more than 100 times smaller than the aperture reported in the past, and the operation depth is enlarged from several centimeters to about 60 meters.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and more specifically, to a porous composite framework for collecting underwater bubbles and a preparation method thereof. Background Art

[0002] Since superhydrophobic surfaces exhibit superaerophilicity in water, this plays a crucial role in the underwater survival of some organisms. For example, rice has a high waterlogging tolerance due to the superhydrophobicity of its leaves, and the air film formed on the leaf surface (referred to as the "air grid") helps with gas exchange with the surrounding water body. Similarly, diving spiders rely on their superhydrophobic abdomens to survive underwater. The abdomen can capture bubbles and form a diving bell to provide them with an air supply. Inspired by these natural systems and driven by application prospects such as collecting methane from water, manipulating Janus particles, water treatment, underwater drag reduction, and energy harvesting, superhydrophobic surfaces with the ability to collect and manipulate underwater bubbles have attracted increasing attention.

[0003] Currently, researchers have developed various geometric forms of superhydrophobic surfaces 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. To manipulate smaller bubbles, a superhydrophobic copper cone is designed, enabling the bubbles to move directionally along the cone from the tip to the base under the drive of the Laplace pressure gradient. Different from these single-bubble strategies, a superhydrophobic sliding surface can simultaneously capture and transport multiple underwater bubbles under the action of buoyancy. To achieve unidirectional bubble transport, a Janus metal mesh has also been developed to manipulate underwater bubbles by constructing a surface wettability gradient. In addition, nano-chitin aerogel has also been used to capture and transport bubbles using buoyancy.

[0004] Chinese Patent with Application No. CN201910588632.7 uses a laser to punch holes in tin foil to manufacture a surface with a micropore diameter of 139 - 142 μm on the upper surface and a micropore diameter of 60 - 62 μm on the lower surface for underwater bubble capture. However, the pore diameter is too large, the puncture strength is very small, and it is easily punctured underwater, and the metal is not corrosion-resistant.

[0005] Chinese Patent with Application No. CN201811621076.0 uses a copper foil and a stearic acid film to prepare a superhydrophobic and superaerophilic surface for collecting underwater bubbles. The diameter of the micropores in the copper foil is 100 - 200 μm. The pore diameter is too large, the puncture strength is small, and the depth of use underwater is very small.

[0006] Chinese Patent with Application No. CN201711224216.6 uses a copper mesh surface-modified with tetradecyl mercaptan to prepare a superaerophilic surface for underwater bubble capture. The pore diameter of the copper mesh is 190 - 540 μm.

[0007] The Chinese patent with the application number CN201911049874.5 uses a superhydrophobic helical cone to achieve the transport of bubbles.

[0008] The above method generally includes the combination of a support substrate and a superhydrophobic coating. Although certain progress has been made in the collection and manipulation of underwater bubbles (especially direction control), due to the insufficient stability of the substrate and the coating, there is still a long way to go before practical applications. Relying solely on the structure of the surface coating is not efficient in the direction of bubble collection, and due to the irreversible transition from the Cassie - Baxter state to the Wenzel state, it often loses its superhydrophobic performance. Currently, common metal and polymer materials used as support substrates are not suitable for harsh water environments such as seawater because they are easily corroded or degraded. In addition, the driving forces for bubbles also have limitations: for small - sized bubbles, buoyancy is not sufficient to overcome the adhesion force; and it is often difficult to continuously form a wetting gradient for a long enough driving distance. Moreover, due to the relatively large pore size of the porous materials used (often larger than 100 microns), the compressive puncture strength of the materials is very small, and the usable depth is limited to a few centimeters to at most dozens of centimeters underwater. Therefore, there is an urgent need to develop small - pore - sized, strong, durable, and superhydrophobic - stable materials to efficiently collect underwater bubbles and promote the progress of practical applications. Summary of the Invention

[0009] 1. Technical problems to be solved: Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a small - pore - sized, high - compressive - puncture - strength, and high - stability composite porous skeleton for underwater bubble collection, so as to solve the problems of poor material chemical stability and poor puncture strength in the above - mentioned background technology.

[0010] 2. Technical solutions: To achieve the above purpose, the present invention provides the following technical solutions: A porous composite skeleton for collecting underwater bubbles, which is composed of polydimethylsilane and mullite, and its micro - structure is that mullite whiskers form a 3D interlocked porous network structure. The surface of the mullite whiskers is coated with a polydimethylsiloxane film. The pore size of the skeleton is 500 nm - 10 μm, the porosity is 50% - 90%, the mullite whiskers are single - crystal structures, and the composite skeleton has overall superhydrophobicity.

[0011] The preparation method of the porous composite skeleton of the present invention specifically includes the following steps: S1. Place a mixed powder containing 74 - 84 wt% aluminum hydroxide, 14 - 23 wt% diatomite, 1 - 3 wt% aluminum fluoride, and 1 - 3 wt% molybdenum trioxide in a planetary ball mill made of agate and ball - mill for 12 - 48 hours; S2. Load the mixed powder obtained in step S1 into a metal mold and press it into a green body; S3. Place the compacted green body in a glazed ceramic crucible and heat it in an air atmosphere furnace at a heating rate of 5 °C / min to 800 - 1600 °C. After holding for 1 - 3 hours, cool it down with the furnace to obtain a mullite whisker skeleton. S4. Immerse the mullite whisker skeleton in a 1 - 10 wt% polydimethylsiloxane / n - hexane solution for 2 hours. After taking it out, place it in a forced - air drying oven to dry. S5. Place the dried sample in an air atmosphere furnace and heat it at different temperatures to cure the polydimethylsiloxane, hold for 4 hours, and finally obtain a mullite whisker / polydimethylsiloxane composite skeleton material. Further, in the S1 step, the silica content in the diatomite is 95 wt%.

[0012] Further, the pressing pressure in the S2 step is 100 - 600 MPa.

[0013] Further, in the S3 step, use a ceramic crucible with a lid and a glaze layer. At high temperatures, the glaze layer melts to form an airtight seal.

[0014] Further, in the S4 step, the drying temperature is 100 - 160 °C and the drying time is 1 - 8 hours.

[0015] Further, in the S5 step, the temperature for heating and curing is 300 to 450 °C, the time is 1 - 4 h. When the temperature exceeds 450 °C, PDMS is oxidized and loses its hydrophobicity. When the temperature is lower than 300 °C, it is difficult to cure.

[0016] 3. Beneficial effects: Adopting the technical solution provided by the present invention, compared with the prior art, compared with surface - modified materials, the overall super - hydrophobic material still shows hydrophobicity even when ground into powder. Coupled with the single - crystal ceramic material skeleton of the present invention, the material has higher durability and stability. In addition, the pore size of the skeleton of the present invention is as low as 500 nm, which is hundreds of times smaller than the pores in this field, and the puncture strength is increased by hundreds of times. Because the puncture strength formula is: ; Among them, γ l represents the surface tension of the liquid, θ is the liquid - solid contact angle, r max is the maximum pore diameter, and B is a geometric factor determined by the pore structure. Thus, the smaller the pore diameter, the higher the puncture strength, so that the material can collect gas in deeper water.

[0017] 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 using the prior art since they do not involve the design key points and improvement directions of the present invention, and will not be elaborated here. Brief description of the drawings

[0018] Figure 1 These are the photos and scanning electron microscope (SEM) images of the mullite skeleton and the mullite-polydimethylsiloxane composite skeleton of the present invention, where; (a) is the photo of the mullite skeleton; (b, c) are the SEM images of the mullite skeleton at different magnifications; (d) is the photo of the composite skeleton (e, f) are the SEM images of the composite skeleton at different magnifications.

[0019] Figure 2 These are the transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis diagrams of the composite skeleton of the present invention, where; (a, b) are the TEM images of the composite skeleton at different magnifications; (c) is the XRD pattern of the composite skeleton; (d) is the FTIR analysis diagram of the composite skeleton.

[0020] Figure 3 In (a, b) is the schematic diagram of the mullite skeleton: it shows superhydrophilicity in air and superaerophobicity in water; In (c, d) is the schematic diagram of the composite skeleton: it shows superhydrophobicity in air and aerophilicity in water; In (e, f) are the optical photos of the mullite skeleton: it is superhydrophilic in air and superaerophobic in water; In (g, h) are the optical photos of the composite skeleton: it is superhydrophobic in air and aerophilic in water.

[0021] Figure 4 These are the schematic diagrams of all-directional underwater bubble collection of the present invention, where; In (a, d) is bottom collection: a hybrid skeleton with a diameter of 30 mm and a thickness of about 3 mm floats on the water surface of a cubic quartz water tank, and its bottom captures and adsorbs bubbles; In (b, e) is side collection: the hybrid skeleton disk is vertically placed in the water tank, the top of the disk communicates with the atmosphere, and the syringe needle is about 1 mm away from the side; In (c, f) is top collection (anti-buoyancy collection): the bubbles are captured and fixed by the top surface of the disk.

[0022] Figure 5 These are the schematic diagrams of superhydrophobicity after the composite skeleton of the present invention is ground into powder. Detailed implementation mode

[0023] To facilitate the 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 given 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, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0024] A porous composite skeleton for collecting underwater bubbles and a preparation method thereof, comprising the following steps: The first step: ball-mill a mixed powder containing aluminum hydroxide (74 - 84 wt%), diatomite (14 - 23 wt%), aluminum fluoride (AlF3, 1 - 3 wt%), and molybdenum trioxide (MoO3, 1 - 3 wt%) in a planetary ball mill for 12 - 48 hours (both the grinding balls and the grinding jar are made of agate); The second step: use a metal mold to press the ball-milled powder into a green body at 100 - 600 MPa; The third step: put the pressed green body into a ceramic crucible with a glazed 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, with a heating and cooling rate of 5°C / minute; The fourth step: immerse the obtained mullite whisker skeleton in a 1 - 10 wt% PDMS / n-hexane solution for 2 hours, and then place it in a blast drying oven for drying. The drying temperature is 100 - 160°C, and the drying time is 1 - 8 hours; The fifth step: place the sample in an air atmosphere furnace, and heat it at 300 to 450°C for 1 - 4 h to cure the PDMS.

[0025] Organisms composed of multiple materials usually have multifunctionality and high stability. Inspired by the bone - muscle structure of organisms, the present invention aims to construct a composite skeleton with bulk superhydrophobicity for capturing and transporting underwater bubbles. Compared with surface-modified materials, bulk superhydrophobic materials maintain their hydrophobic properties throughout the entire service life, and thus have higher durability and stability. For this reason, the present invention designs mullite whiskers similar to bones and cured silicone oil to simulate muscles. Mullite is a high-strength ceramic that can still maintain 90% of its room temperature strength at 1500°C and can resist the corrosion of molten sodium chloride or high-temperature alkali metal oxides for a long time. In addition, mullite whiskers with a single crystal structure are stronger due to fewer defects. As for the driving force for bubble collection, the present invention abandons the traditional methods based on buoyancy or wettability gradient and attempts to use hydrostatic pressure as the driving force. Therefore, the greater the water depth, the stronger the driving force, and the higher the bubble collection efficiency.

[0026] Example 1: Step 1: Ball mill the mixed powder containing aluminum hydroxide (74 wt%), diatomaceous earth (22 wt%), aluminum fluoride (AlF3, 3 wt%), and molybdenum trioxide (MoO3, 1 wt%) in a planetary ball mill for 12 hours; Step 2: Use a metal mold to press the ball-milled powder into a green body at 100 MPa; Step 3: Place the pressed green body into a ceramic crucible with a glazed lid, put it into an air atmosphere furnace, heat it to 1300 °C, and hold for 3 hours to obtain a porous mullite whisker skeleton, with a heating and cooling rate of 5 °C / minute; Step 4: Immerse the obtained mullite whisker skeleton in a 1 wt% PDMS / n-hexane solution for 2 hours, then place it in a forced-air drying oven to dry, with a drying temperature of 150 °C and a drying time of 8 hours; Step 5: Place the sample in an air atmosphere furnace and heat it at 300 °C for 4 h to cure the PDMS.

[0027] The porous composite skeleton prepared according to the above steps has a pore diameter of 1 μm and a porosity of 80%. The mullite whiskers are single-crystalline structures. The composite skeleton has overall superhydrophobicity, with a water droplet contact angle (WCA) of 151° and an underwater bubble contact angle (BCA) of 47°, and can capture bubbles in all directions such as the lower surface, upper surface, and side surface.

[0028] Example 2: Step 1: Ball mill the mixed powder containing aluminum hydroxide (78 wt%), diatomaceous earth (20 wt%), aluminum fluoride (AlF3, 1 wt%), and molybdenum trioxide (MoO3, 1 wt%) in a planetary ball mill for 24 hours; Step 2: Use a metal mold to press the ball-milled powder into a green body at 200 MPa; Step 3: Place the pressed green body into a ceramic crucible with a glazed lid, put it into an air atmosphere furnace, heat it to 1000 °C, and hold for 2 hours to obtain a porous mullite whisker skeleton, with a heating and cooling rate of 5 °C / minute; Step 4: Immerse the obtained mullite whisker skeleton in a 5 wt% PDMS / n-hexane solution for 2 hours, then place it in a forced-air drying oven to dry, with a drying temperature of 150 °C and a drying time of 4 hours; Step 5: Place the sample in an air atmosphere furnace and heat it at 400 °C for 6 h to cure the PDMS.

[0029] The porous composite skeleton prepared according to the above steps has a pore diameter of 500 nm and a porosity of 70%. The mullite whiskers are single-crystalline structures. The composite skeleton has overall superhydrophobicity, with a water droplet contact angle (WCA) of 150° and an underwater bubble contact angle (BCA) of 36°, and can capture bubbles in all directions such as the lower surface, upper surface, and side surface.

[0030] Example 3: First step: Ball mill a mixed powder containing aluminum hydroxide (84 wt%), diatomaceous earth (14 wt%), aluminum fluoride (AlF3, 1 wt%), and molybdenum trioxide (MoO3, 1 wt%) in a planetary ball mill for 48 hours; Second step: Use a metal mold to press the ball-milled powder into a green body at 600 MPa; Third step: Place the pressed green body into a ceramic crucible with a glazed lid, put it into an air atmosphere furnace, heat it to 1600 °C, and hold for 1 hour to obtain a porous mullite whisker skeleton. The heating and cooling rate is 5 °C / minute; Fourth step: Immerse the obtained mullite whisker skeleton in a 10 wt% PDMS / n-hexane solution for 2 hours, then place it in a blast drying oven to dry. The drying temperature is 160 °C and the drying time is 1 hour; Fifth step: Place the sample in an air atmosphere furnace and heat it at 450 °C for 1 h to cure the PDMS.

[0031] The porous composite skeleton prepared according to the above steps has a pore diameter of 10 um, a porosity of 90%, the mullite whiskers are single crystal structures, the composite skeleton has overall superhydrophobicity, the water contact angle (WCA) is 158°, and the underwater bubble contact angle (BCA) is 4°. It can capture bubbles in all directions such as the lower surface, upper surface, and side surface.

[0032] Example 4: First step: Ball mill a mixed powder containing aluminum hydroxide (74 wt%), diatomaceous earth (20 wt%), aluminum fluoride (AlF3, 3 wt%), and molybdenum trioxide (MoO3, 3 wt%) in a planetary ball mill for 48 hours; Second step: Use a metal mold to press the ball-milled powder into a green body at 600 MPa; Third step: Place the pressed green body into a ceramic crucible with a glazed lid, put it into an air atmosphere furnace, heat it to 1400 °C, and hold for 3 hours to obtain a porous mullite whisker skeleton. The heating and cooling rate is 5 °C / minute; Fourth step: Immerse the obtained mullite whisker skeleton in a 10 wt% PDMS / n-hexane solution for 2 hours, then place it in a blast drying oven to dry. The drying temperature is 160 °C and the drying time is 4 hours; Fifth step: Place the sample in an air atmosphere furnace and heat it at 300 °C for 4 h to cure the PDMS.

[0033] The porous composite framework prepared according to the above steps has a framework pore size of 500 nm, a porosity of 50%, the mullite whiskers are in single crystal structure, the composite framework has overall superhydrophobicity, the water droplet contact angle (WCA) is 150°, and the underwater bubble contact angle (BCA) is 29°. Bubbles can be trapped in all directions such as the lower surface, upper surface, and side surface.

[0034] Example 5: First step: Ball-mill the mixed powder containing aluminum hydroxide (74 wt%), diatomite (23 wt%), aluminum fluoride (AlF3, 2 wt%), and molybdenum trioxide (MoO3, 1 wt%) in a planetary ball mill for 12 hours; Second step: Use a metal mold to press the ball-milled powder into a green body at 100 MPa; Third step: Load the pressed green body into a ceramic crucible with a glazed lid, place it in an air atmosphere furnace, heat it to 800 °C, and hold for 3 hours to obtain a porous mullite whisker framework. The heating and cooling rate is 5 °C / minute; Fourth step: Immerse the obtained mullite whisker framework in a 1 wt% PDMS / n-hexane solution for 2 hours, and then place it in a blast drying oven for drying. The drying temperature is 100 °C and the drying time is 8 hours; Fifth step: Place the sample in an air atmosphere furnace and heat it at 450 °C for 3 h to cure the PDMS.

[0035] The porous composite framework prepared according to the above steps has a framework pore size of 2 m, a porosity of 73%, the mullite whiskers are in single crystal structure, the composite framework has overall superhydrophobicity, the water droplet contact angle (WCA) is 153°, and the underwater bubble contact angle (BCA) is 40°. Bubbles can be trapped in all directions such as the lower surface, upper surface, and side surface.

[0036] The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0037] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A porous composite framework for collecting underwater bubbles, characterized in that: It includes a porous network skeleton composed of mullite whiskers and a polydimethylsiloxane film coating its surface; Among them, the mullite whiskers are in single crystal structure and form a skeleton with a pore size of 500 nm to 10 μm and a porosity of 50% to 90% through three-dimensional interlocking; The polydimethylsiloxane film endows the skeleton with overall superhydrophobicity, and the water contact angle is greater than 150°; The composite skeleton can collect bubbles simultaneously from the lower surface, side surface and upper surface in an underwater environment.

2. The preparation method of a porous composite skeleton for collecting underwater bubbles according to claim 1, wherein, It includes the following steps: S1. Place the mixed powder containing 74 - 84 wt% aluminum hydroxide, 14 - 23 wt% diatomite, 1 - 3 wt% aluminum fluoride and 1 - 3 wt% molybdenum trioxide in a planetary ball mill made of agate and ball mill for 12 - 48 hours; S2. Load the mixed powder obtained in step S1 into a metal mold and press it into a green body; S3. Place the pressed green body in a glazed ceramic crucible, heat it to 800 - 1600 °C at a heating rate of 5 °C / min in an air atmosphere furnace, hold for 1 - 3 hours and then cool with the furnace to obtain a mullite whisker skeleton; S4. Immerse the mullite whisker skeleton in a 1 - 10 wt% polydimethylsiloxane / n - hexane solution for 2 hours, take it out and dry it in a blast drying oven; S5. Place the dried sample in an air atmosphere furnace to heat and cure the polydimethylsiloxane, hold for 4 hours, and finally obtain a mullite whisker / polydimethylsiloxane composite skeleton material.

3. The preparation method of a porous composite skeleton for collecting underwater bubbles according to claim 2, wherein In step S1, the silicon dioxide content in the diatomite is 95 wt%.

4. The preparation method of a porous composite framework for collecting underwater bubbles according to claim 2, characterized in that, The pressing pressure of the metal mold in step S2 is 100 - 600 MPa.

5. The preparation method of a porous composite framework for collecting underwater bubbles according to claim 2, wherein, The drying temperature in step S4 is 100 - 160 °C, and the drying time is 1 - 8 hours.

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

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