Lubricating fluid circulation type bionic super-slip drag reduction surface and preparation method thereof

Abstract

The present invention relates to a lubricating fluid circulation type bionic super-slippery drag reduction surface and a preparation method, belonging to the technical field of drag reduction for ships and underwater vehicles. The bionic super-slippery drag reduction surface includes an asymmetric super-hydrophobic surface structure and a microcirculation channel connecting the upstream and downstream thereof. The lubricating fluid moves directionally downstream along the asymmetric super-hydrophobic surface structure under the action of external shear. The inlet of the microcirculation channel is located downstream of the asymmetric super-hydrophobic surface structure, and the outlet is located upstream of the asymmetric super-hydrophobic surface structure. The outer edges of the inlet and outlet have underwater lubricating fluid repellency properties, so that the lubricating fluid flowing downstream accumulates and enters the microcirculation channel through the inlet under the action of pressure, and then flows back along the microcirculation channel to the upstream outlet, completing a repeated circulation flow process. The present invention can not only effectively seal the lubricating fluid to form a drag reduction and anti-fouling liquid-liquid interface, but also realize automatic replenishment and long-term maintenance of the lubricating fluid, greatly enhancing the durability of the super-slippery surface in underwater drag reduction applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of drag reduction of ships and underwater vehicles, and in particular relates to a lubricating fluid circulation type bionic super-slip drag reduction surface and a preparation method thereof. Background Art

[0002] When operating, ships and underwater vehicles (AUVs) have large areas of direct contact with water. Due to the viscosity of water, this creates significant frictional resistance during navigation. For AUVs in particular, over 80% of their energy consumption is used to overcome frictional resistance. The resulting power loss is a key issue limiting the speed and range of ships and AUVs. Developing efficient drag reduction technologies also contributes to energy conservation, emissions reduction, and environmental protection.

[0003] Inspired by the secretion and storage of mucus by pitcher plants and fish, researchers have developed a biomimetic super-slippery surface that can store lubricating fluids. The lubricating fluid sealed in the microstructure of the super-slippery surface can form a two-phase liquid-liquid interface underwater, generate velocity slip at the liquid-liquid interface, and reduce the contact area between the surface and the water environment, thus having both anti-fouling and drag reduction potential. Artificially prepared super-slippery surfaces usually use water-insoluble lubricating fluids such as silicone oil or liquid alkanes, which give them good pressure resistance and anti-solution properties. Therefore, this type of surface has greater stability and application potential than super-hydrophobic surfaces. However, in actual use, under the action of water flow, the lubricating fluid sealed in the super-slippery surface will still undergo shear loss, resulting in the loss of the drag reduction function of the super-slippery surface. The shear loss of lubricating fluid leads to reduced life and functional failure, which is the bottleneck currently limiting the application of super-slippery surfaces.

[0004] In response to this problem, the prior art discloses a variety of passive and active methods to enhance the stability of lubricating fluids on super-slip surfaces. For example, from the perspective of microstructure design, a spherical pit microstructure that imitates fish glandular cells is constructed on the surface, or a super-hydrophobic surface with a microporous cavity structure is formed as a substrate by adding a pore-forming agent during the coating preparation process. This type of specially designed microstructure can significantly enhance the storage performance of the super-slip surface for lubricating fluids and extend its service life. Obviously, this type of method cannot solve the problem of lubricating fluid loss under long-term flow shear. For this reason, the prior art also discloses super-slip surfaces and systems with active replenishment functions, such as forming a network cross-linked structure through a polymer substrate to store lubricating fluids, which can achieve automatic secretion of lubricating oil, or developing a lubricating fluid active release device based on porous materials. Although these methods can achieve the replenishment of lost lubricating fluids, they have disadvantages such as complex preparation methods, high preparation costs, and the need for additional energy consumption, which limits their scope of application.

[0005] Therefore, in order to promote the practical application of bionic super-slippery surfaces in underwater drag reduction applications, it is urgent to develop solutions that can overcome the shear loss problem of lubricating fluids. Summary of the Invention

[0006] Technical issues to be solved:

[0007] To overcome the shortcomings of the prior art, the present invention provides a lubricating fluid circulating bionic super-slip drag-reducing surface and a preparation method. The bionic super-slip drag-reducing surface is designed with reference to the asymmetric stepped cross-sectional structure of fish epidermal scales. This surface facilitates the directional movement of the lubricating fluid downstream of the surface under external shearing. Combined with a microcirculation channel opposite to the incoming flow direction, when the lubricating fluid is sheared and moves downstream along the surface and accumulates, the Laplace pressure difference generated by the asymmetric structure is used to drive the downstream accumulated lubricating fluid through the bottom microcirculation channel to the upstream of the super-slip surface, thereby achieving the circulation and recycling of the lubricating fluid. The super-slip surface of the present invention can not only effectively seal the lubricating fluid to form a drag-reducing and anti-fouling liquid-liquid interface, but also realize the automatic replenishment and long-term maintenance of the lubricating fluid, greatly enhancing the durability of the super-slip surface in underwater drag reduction applications.

[0008] The technical solution of the present invention is: a lubricating fluid circulating bionic super-lubricating drag-reducing surface, including an asymmetric super-hydrophobic surface structure and a microcirculation channel connecting the upstream and downstream thereof. The lubricating fluid moves directionally downstream along the asymmetric super-hydrophobic surface structure under the action of external shear; the inlet of the microcirculation channel is located downstream of the asymmetric super-hydrophobic surface structure, and the outlet is located upstream of the asymmetric super-hydrophobic surface structure. The outer edges of the inlet / outlet have underwater lubricating fluid-repelling properties, so that the lubricating fluid flowing downstream accumulates and enters the microcirculation channel through the inlet under pressure, and then flows in reverse along the microcirculation channel to the upstream outlet, completing a repeated circulation flow process.

[0009] A further technical solution of the present invention is that the upper surface of the asymmetric super-hydrophobic surface structure is an asymmetric stepped micron-scale microstructure with a periodic array along the flow direction, and the cross-section of a single microstructure unit is an asymmetric triangle.

[0010] A further technical solution of the present invention is: the design limitation conditions of the size of the single microstructure unit are:

[0011] L≤0.2×(γ1 / ρg)^0.5

[0012] L1>L2

[0013] L=L1+L2

[0014] Wherein, L is the flow length of a single microstructure unit, γ1 is the surface tension of the lubricating fluid, ρ is the density of the lubricating fluid, g is the acceleration of gravity, L1 is the flow length of the incoming flow surface of a single microstructure unit, and L2 is the flow length of the back flow surface of a single microstructure unit.

[0015] A further technical solution of the present invention is that the length of the single microstructure unit along the flow direction is 0.1 to 0.6 mm, and the height perpendicular to the flow direction is 0.1 to 0.6 mm.

[0016] A further technical solution of the present invention is: the microcirculation channel is formed by the gap between the substrate and the asymmetric super-hydrophobic surface structure; the asymmetric super-hydrophobic surface structure is semi-encapsulated at the opening on the top surface of the substrate, that is, the two side walls of the asymmetric super-hydrophobic surface structure parallel to the fluid flow direction are sealedly connected to the two side walls of the substrate, and a gap is left between its upstream / downstream and the other two side walls of the substrate; the part of the substrate located below the asymmetric super-hydrophobic surface structure is a lubricating fluid storage cavity, which connects the upstream / downstream gaps to form a microcirculation channel.

[0017] A further technical solution of the present invention is: the flow direction width of the microcirculation channel inlet is equal to the sum of the side wall gap and the flow direction length of the back flow surface of a single microstructure unit; the flow direction width of the microcirculation channel outlet is equal to the sum of the side wall gap and the flow direction length of the outflow surface of a single microstructure unit.

[0018] A further technical solution of the present invention is that the lubricating fluid is a lubricating oil that is insoluble in water and has low viscosity and surface tension.

[0019] A further technical solution of the present invention is: the upper surface of the asymmetric super-hydrophobic surface structure is a super-hydrophobic surface with underwater lubricating fluid properties; the end surface at the base opening is a super-hydrophilic surface with underwater lubricating fluid properties.

[0020] A method for preparing a lubricating fluid circulating bionic super-slip drag-reducing surface, comprising the following specific steps:

[0021] Processing a mold casting template; processing an asymmetric stepped structure on the bottom surface of the template of the box structure as a casting template for the upper surface of the asymmetric super-hydrophobic surface structure;

[0022] Placing a soluble template; using a water-soluble high molecular polymer to prepare a soluble template of a microcirculation channel, and bonding it to the center position of the flip casting template to obtain an integral mold;

[0023] pouring liquid polymer to prepare the base;

[0024] Curing, demoulding and mask spraying of super hydrophobic coating;

[0025] Fill with lubricating fluid.

[0026] A further technical solution of the present invention is: the method of curing, demoulding and masking and spraying the super-hydrophobic coating is:

[0027] The poured liquid polymer is placed together with the mold and heated and cured at a set temperature;

[0028] The solidified substrate is removed from the template, immersed in hot water and ultrasonically cleaned to completely dissolve the soluble template inside the substrate;

[0029] The cleaned substrate is dried, and a nano-superhydrophobic coating is sprayed on the area with the asymmetric microstructure using a mask spraying method, while the substrate and edge areas remain smooth and have the original wettability.

[0030] A further technical solution of the present invention is: the method of injecting lubricating fluid is:

[0031] The substrate with the asymmetric superhydrophobic surface structure is immersed in a lubricating fluid;

[0032] Evacuate and let it stand to ensure that the microcirculation channel and the super-hydrophobic surface microstructure are filled with lubricating fluid;

[0033] The soaked substrate is taken out and placed on oil-absorbing paper to absorb excess lubricating fluid, completing the preparation of the bionic super-slippery surface.

[0034] A surface hull has a bottom surface provided with the lubricating fluid circulation type bionic super-slip drag reduction surface.

[0035] Working principle: In the initial state, the microcirculation channels and the super-hydrophobic surface microstructure are filled with lubricating fluid. Under the shear action of the external flow, the lubricating fluid in the microstructure flows downstream and eventually accumulates at the entrance of the downstream microcirculation channel. During this process, the asymmetric stepped microstructure can ensure the unidirectional flow of the lubricating fluid downstream, and the smooth substrate surrounding the super-hydrophobic surface forms a wettability step to prevent the loss of the lubricating fluid. Then, the liquid-liquid interface at the entrance of the microcirculation channel changes from the initial flat state to a convex state, and the liquid-liquid interface at the outlet of the upstream microcirculation channel changes to a concave state. At this time, the Laplace pressure generated by the liquid-liquid interface at the entrance of the downstream microcirculation channel is greater than the Laplace pressure generated by the liquid-liquid interface at the outlet of the upstream microcirculation channel. Driven by the pressure difference, the lubricating fluid accumulated at the entrance of the downstream microcirculation channel automatically flows through the downstream microchannel, the lubricating fluid storage chamber and the upstream microchannel to be replenished to the super-hydrophobic surface. Under the action of flow shear, the lubricating fluid upstream of the super-hydrophobic surface continues to move downstream, realizing the automatic replenishment of the lubricating fluid lost by shear.

[0036] Beneficial effects

[0037] The beneficial effects of the present invention are:

[0038] (1) The present invention designs a bionic super-slippery drag-reducing surface with lubricating fluid circulation. On the basis of the traditional super-slippery surface sealing lubricating fluid to form a liquid-liquid interface and underwater drag reduction function, the lubricating fluid can be automatically replenished by circulating the lubricating fluid on the surface and inside. The replenishment process is spontaneous and does not require additional energy consumption, thereby improving the maintenance effect of the super-slippery surface lubricating fluid and the overall service life of the system.

[0039] (2) The present invention adopts an asymmetric microstructure that imitates fish scales. The size of the microstructure ensures that the lubricating fluid will not be lost due to gravity when the device is tilted or inverted. On the one hand, the asymmetric structure allows the lubricating fluid to flow in one direction under shear without backflow. On the other hand, a size difference is generated at the front and rear microchannel openings, generating a Laplace pressure difference and driving the circulation of the lubricating fluid.

[0040] (3) The present invention has a simple structure and high reliability, and the preparation method is economical and efficient, and can achieve rapid and large-scale preparation, which can greatly promote the application of bionic super-slippery surfaces in the field of underwater drag reduction of ships and underwater vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of a lubricating fluid circulation type bionic super-slip drag reduction surface in an embodiment of the present invention, (a) a three-dimensional schematic diagram, and (b) a surface micrograph;

[0042] Figure 2a Schematic diagram of the cross-sectional structure of the present invention; in the figure, l1 is the length of the upstream and downstream microchannels, l2 and h are the length and height of the lubricating fluid storage chamber respectively;

[0043] Figure 2b Schematic diagram of the upstream microchannel structure of the present invention; in the figure, D1 is the size of the upstream microchannel mouth, and d is the width of the upstream microchannel;

[0044] Figure 2c Schematic diagram of the asymmetric stepped microstructure of the present invention; in the figure, L is the size of the stepped microstructure unit, H is the height of a single microstructure, L1 and L2 are the front and rear dimensions of the microstructure unit respectively;

[0045] Figure 2d Schematic diagram of the downstream microchannel structure of the present invention; in the figure, D2 is the size of the downstream microchannel mouth, and d is the size of the downstream microchannel;

[0046] Figure 3 Schematic diagram of the working process of the present invention; in the figure, θ1 and θ2 are the contact angles of the liquid-liquid interface of the lubricating fluid at the upstream microchannel and downstream microchannel openings, respectively;

[0047] Figure 4 Schematic diagram of the preparation steps of the present invention;

[0048] Explanation of the reference numerals: 1 - lubricating fluid 2 - downstream microchannel 3 - substrate 4 - lubricating fluid storage chamber 5 - upstream microchannel 6 - asymmetric superhydrophobic surface structure. DETAILED DESCRIPTION

[0049] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0050] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0051] In response to the problem in the prior art that lubricating fluid on bionic super-slippery surfaces is prone to loss under shear, as well as the limitations of existing active and passive lubricating fluid maintenance and replenishment technologies, the present invention provides a lubricating fluid circulating bionic super-slippery surface, comprising a super-hydrophobic surface structure, a lubricating fluid, an upstream microchannel, a downstream microchannel, a lubricating fluid storage cavity and a substrate, wherein the upstream microchannel, the lubricating fluid storage cavity and the downstream microchannel constitute a microcirculation flow channel.

[0052] The upper surface of the super-hydrophobic surface structure has an asymmetric stepped micron-scale microstructure, and at the same time, there is a nano-scale super-hydrophobic coating on the micron-scale structure, which has the characteristics of underwater lubricating fluid affinity, can bind and seal the lubricating fluid underwater to form a super-slippery surface, and form a liquid-liquid interface with a drag reduction effect; upstream microchannels and downstream microchannels are formed between the upstream and downstream walls of the asymmetric super-hydrophobic surface structure and the inner wall of the substrate, and a lubricating fluid storage cavity is formed in the substrate below the super-hydrophobic surface structure; under the action of flow shear, the lubricating fluid moves directionally downstream along the super-hydrophobic surface and accumulates at the downstream microchannel entrance; due to the super-hydrophobic microstructure The method is asymmetric, with the size of the downstream microchannel mouth being smaller than that of the upstream microchannel mouth. The lubricating fluid forms a curved liquid-liquid interface at the microchannel mouth and generates a Laplace pressure difference. The Laplace pressure difference drives the lubricating fluid accumulated downstream of the super-hydrophobic surface to pass through the downstream microchannel, the lubricating fluid storage cavity and the upstream microchannel in sequence, and finally flows out from the upstream microchannel outlet to the super-hydrophobic surface, realizing the circulation and automatic replenishment of the lubricating fluid. This method can realize the automatic replenishment of the lubricating fluid on the bionic super-slippery surface without consuming additional energy, effectively overcoming the problem of lubricating fluid loss during use and extending its service life.

[0053] The above technical solution is further described below with reference to the accompanying drawings:

[0054] In one embodiment, referring to Figure 1 As shown in the figure, this embodiment provides a lubricating fluid circulation biomimetic super-slip drag-reducing surface, comprising an asymmetric super-hydrophobic surface structure 6, a lubricating fluid 1, an upstream microchannel 5, a downstream microchannel 2, a lubricating fluid storage chamber 4, and a substrate 3. The super-hydrophobic surface structure has an asymmetric stepped periodic micron-scale microstructure similar to fish scales. The cross-section of a single microstructure unit is an asymmetric triangle. The flow direction length L of a single microstructure unit ranges from 0.1 to 0.6 mm, and the height H ranges from 0.1 to 0.6 mm.

[0055] Specifically, the asymmetric stepped micron-scale structure is provided with a nano-scale super-hydrophobic coating, forming a micro-nano composite structure to enhance the binding effect on the lubricating fluid.

[0056] In one embodiment, referring to Figure 2c As shown, the flow length L of a single microstructure unit of the asymmetric stepped micron-scale structure satisfies L≤0.2×(γ1 / ρg)^0.5, where γ1 is the surface tension of the lubricating fluid, ρ is the density of the lubricating fluid, and g is the acceleration of gravity. Meeting this condition is conducive to the stable retention of the lubricating fluid under the action of surface tension in the superhydrophobic microstructure, enhancing its stability. When the length of a single microstructure unit does not meet this condition, the gravity acting on the lubricating fluid stored in the microstructure is greater than the surface tension generated by the interface. When the surface is tilted or inverted, the lubricating fluid resistance cannot be effectively maintained, and the lubricating fluid is easily lost.

[0057] Taking the incoming flow during use as a reference, the front length L1 of a single microstructure unit is greater than the rear length L2, satisfying L1+L2=L.

[0058] In one embodiment, the lubricating fluid is a lubricating oil that is insoluble in water and has low viscosity and surface tension, such as dimethyl silicone oil, long-chain alkanes, and electronic fluorinated liquid.

[0059] Reference Figure 2a As shown, the upstream microchannel and the downstream microchannel are respectively located upstream and downstream of the asymmetric superhydrophobic microstructure. Taking the incoming flow during use as a reference, water flows from upstream to downstream of the superhydrophobic surface.

[0060] In one embodiment, referring to Figure 2b and Figure 2dAs shown, due to the existence of micron-scale microstructures with an asymmetric stepped shape, the size of the upstream microchannel mouth d + L1 is larger than the size of the downstream microchannel mouth d + L2, where d is the internal size of the upstream and downstream microchannels, and it should satisfy d < L2. Otherwise, under the action of gravity, the surface tension is less than gravity, and lubricating fluid loss is likely to occur. Refer to Figure 2a As shown, the length of the microchannel is l1.

[0061] Refer to Figure 3 As shown, the working process of the above embodiment is as follows: At the outlet of the upstream microchannel, the Laplace pressure generated by the bending of the liquid-liquid interface is P1 = 0.5×sinθ1×γ2 / (d + L1), and at the inlet of the downstream microchannel, the Laplace pressure generated by the bending of the liquid-liquid interface is P2 = 0.5×sinθ2×γ2 / (d + L2), where θ1 and θ2 are the contact angles formed by the liquid-liquid interfaces of water and lubricating fluid at the rear of the upstream microchannel and the mouth of the downstream microchannel, respectively, with a range of -30° to 60°. The upwardly convex liquid-liquid interface is defined as positive, and the downwardly concave liquid-liquid interface is defined as negative. γ2 is the surface tension of the lubricating fluid under water.

[0062] Specifically, the upstream microchannel, the downstream microchannel, and the lubricating fluid storage cavity are connected to form a microcirculation flow channel. The lubricating fluid storage cavity is between the superhydrophobic surface and the substrate, with a height of h, a length of l2, and a width of w.

[0063] Specifically, the substrate surrounds the superhydrophobic surface, and its upper surface is flush with the superhydrophobic surface. The upper surface is smooth and does not have superhydrophobicity. <s

[0064] The working process of this embodiment is as follows: In the initial state, the lubricating fluid storage cavity, the upstream microchannel, the downstream microchannel, and the microstructures on the superhydrophobic surface are filled with lubricating fluid. Under the shear action of the external flow, the lubricating fluid in the microstructures flows downstream and finally accumulates at the mouth of the downstream microchannel. The liquid-liquid interface at the mouth of the downstream microchannel changes from the initial flat state to an upwardly convex state, and the liquid-liquid interface at the mouth of the upstream microchannel changes to a downwardly concave state. At this time, the Laplace pressure P2 generated by the liquid-liquid interface on the downstream microchannel is greater than the Laplace pressure P1 generated by the liquid-liquid interface at the mouth of the upstream microchannel. Under the driving action of the pressure difference, the lubricating fluid accumulated at the mouth of the downstream microchannel automatically flows through the downstream microchannel, the lubricating fluid storage cavity, and the upstream microchannel and then is replenished to the superhydrophobic surface. Under the action of the flow shear, the lubricating fluid upstream of the superhydrophobic surface continues to move downstream, realizing the automatic replenishment of the lubricating fluid lost by shear. During this process, the flow rate of the lubricating fluid in the upstream and downstream microchannels and the lubricating fluid storage cavity is Q = w×d^3×h^3×(P2 - P1) / 12μ / (2l1×h^3 + l2×d^3), where μ is the viscosity of the lubricating fluid.

[0065] In one embodiment, refer to Figure 4As shown in FIG. 1 , this embodiment provides a method for preparing a lubricating fluid circulation type bionic ultra-slip drag reducing surface based on a soluble template remolding method, and the specific steps are as follows:

[0066] Step 1: Process the mold template. Use machining or laser engraving technology to process an asymmetric stepped structure on the bottom of the template. The characteristic parameter range of the microstructure is selected according to the selected lubricating fluid.

[0067] Step 2: Place the soluble template. Prepare the microchannel and lubricating fluid storage cavity template using a water-soluble polymer, such as maltose, polyethylene glycol, or maltodextrin. Place the soluble template in the center of the remolding template and secure it to the bottom of the remolding template with a small amount of low-concentration polyethylene glycol solution or maltose solution.

[0068] Step 3: Pour liquid polymer. Pour the liquid polymer into the mold to prepare a base. Epoxy resin, polydimethylsiloxane, or polyurethane can be used as the base material, and then place it in a vacuum environment to remove gas.

[0069] Step 4: Curing and demoulding, mask spraying super-hydrophobic coating. The poured liquid polymer is left to stand together with the mold and heated at a certain temperature for a sufficient time to solidify. The solidified substrate is then removed from the template, placed in 60-80 degrees Celsius hot water and ultrasonically cleaned to completely dissolve the soluble template inside the substrate. The cleaned substrate is dried and the nano-super-hydrophobic coating is sprayed on the microstructured area using a mask spraying method, while the substrate and edge areas remain smooth and have the original wettability.

[0070] Step 5: Infusing the lubricating fluid. The prepared substrate is immersed in a lubricating fluid, such as dimethyl silicone oil, liquid alkane, or electronic fluoride. The substrate is then placed in a vacuum for a period of time to ensure that the microchannels, lubricating fluid storage chamber, and superhydrophobic surface microstructure are filled with the lubricating fluid. Remove the immersed substrate and place it on blotting paper to absorb any excess lubricating fluid. This completes the preparation of the biomimetic superslippery surface.

[0071] In one embodiment, this example is the application of a lubricating fluid circulating bionic super-slip drag reduction surface on the surface of a small water surface vessel. The vessel is a box-type structure with a relatively flat bottom and side structure. Therefore, the lubricating fluid circulating bionic super-slip drag reduction surface of the present invention is directly pasted on the surface of the applied vessel in the form of a skin patch.

[0072] First, a lubricating fluid circulation type bionic super-slippery surface was prepared. The preparation steps were as shown in the attached Figure 4 As shown, the specific steps are:

[0073] Step 1: Process the mold template. A pointed milling cutter with a tip diameter of 0.1 mm was used to machine an asymmetric stepped structure on the bottom of the aluminum alloy template. The length L of a single microstructure unit was 300 μm, and the height H was 150 μm. The lengths L1 and L2 of the front and back halves of the microstructure unit were 100 μm and 200 μm, respectively. The internal dimensions of the mold were 10 mm × 20 mm × 3 mm.

[0074] Step 2: Place a soluble template at the bottom of the mold. Prepare the microchannel and lubricant storage cavity template using the water-soluble polymer polyethylene glycol. Set the lubricant storage cavity height h to 0.8 mm and length l2 to 18 mm. Set the upstream and downstream microchannel dimensions d to 80 μm and length l1 to 1 mm. Place the soluble template at the center of the overmold template and secure it to the bottom of the overmold template with a small amount of low-concentration polyethylene glycol solution. Apply a small amount of liquid release agent to the assembled mold.

[0075] Step 3: Pouring liquid polydimethylsiloxane. Mix a certain amount of polydimethylsiloxane prepolymer and curing agent in a mass ratio of 10:1. After thorough stirring, pour the liquid polymer into the mold template, which is then placed in a vacuum environment to remove gas.

[0076] Step 4: Curing and demoulding, mask spraying super hydrophobic coating. The cast polydimethylsiloxane is left to stand together with the mold and heated at a certain temperature for a sufficient time to solidify it. The solidified substrate is then removed from the template, placed in 60-80 degrees Celsius hot water and soaked and ultrasonically cleaned to completely dissolve the soluble template inside the substrate. The cleaned substrate is dried and the mask spraying method is used to spray the nano super hydrophobic coating on the area with the microstructure, while the substrate and edge areas remain smooth and do not have super hydrophobicity.

[0077] Step 5: Infuse the lubricating fluid. The prepared substrate is immersed in a lubricating fluid, preferably dimethyl silicone oil with a viscosity of 10 cSt. The substrate is then placed in a vacuum for a period of time to ensure that the microchannels, lubricating fluid storage chambers, and superhydrophobic surface microstructures are filled with the lubricating fluid. Remove the soaked substrate and place it on oil-absorbing paper to absorb any excess lubricating fluid. This completes the preparation of the biomimetic superslippery surface.

[0078] Then, the batch-prepared bionic drag-reducing super-slippery surface is pasted and spread all over the hull surface. During the navigation of the ship, the bound liquid-liquid interface on the super-slippery surface can produce speed slip, thereby producing a drag reduction effect, achieving energy conservation and emission reduction of the ship. At the same time, the present invention can realize the circulation and automatic replenishment of the lubricating fluid, thereby increasing the service life of the drag-reducing super-slippery surface.

[0079] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A lubricating fluid circulation type bionic super-slip drag reduction surface, characterized by: The invention comprises an asymmetric super-hydrophobic surface structure and a microcirculation channel connecting the upstream and downstream thereof. The lubricating fluid moves directionally downstream along the asymmetric super-hydrophobic surface structure under the action of external shear. The inlet of the microcirculation channel is located downstream of the asymmetric super-hydrophobic surface structure, and the outlet is located upstream of the asymmetric super-hydrophobic surface structure. The outer edges of the inlet and outlet have underwater lubricating fluid repelling properties, so that the lubricating fluid flowing downstream accumulates and enters the microcirculation channel through the inlet under the action of pressure, and then flows in the opposite direction along the microcirculation channel to the upstream outlet, completing the flow process of repeated circulation.

2. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 1, characterized in that: The upper surface of the asymmetric super-hydrophobic surface structure is an asymmetric stepped micron-scale microstructure arranged in a periodic array along the flow direction, and the cross-section of a single microstructure unit is an asymmetric triangle.

3. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 2, characterized in that: The design limitation conditions for the size of the single microstructure unit are: L≤0.2×(γ1 / ρg)^0.5 L1>L2 L=L1+L2 Wherein, L is the flow length of a single microstructure unit, γ1 is the surface tension of the lubricating fluid, ρ is the density of the lubricating fluid, g is the acceleration of gravity, L1 is the flow length of the incoming flow surface of a single microstructure unit, and L2 is the flow length of the back flow surface of a single microstructure unit.

4. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 3, characterized in that: The microcirculation channel is formed by the gap between the substrate and the asymmetric super-hydrophobic surface structure; the asymmetric super-hydrophobic surface structure is semi-encapsulated at the opening on the top surface of the substrate, that is, the two side walls of the asymmetric super-hydrophobic surface structure parallel to the fluid flow direction are sealedly connected to the two side walls of the substrate, and a gap is left between the upstream / downstream and the other two side walls of the substrate; the part of the substrate located below the asymmetric super-hydrophobic surface structure is a lubricating fluid storage cavity, which connects the upstream / downstream gaps to form a microcirculation channel.

5. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 4, characterized in that: The flow direction width of the microcirculation channel inlet is equal to the sum of the side wall gap and the flow direction length of the back flow surface of a single microstructure unit; the flow direction width of the microcirculation channel outlet is equal to the sum of the side wall gap and the flow direction length of the outflow surface of a single microstructure unit.

6. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 4, characterized in that: The upper surface of the asymmetric super-hydrophobic surface structure is a super-hydrophobic surface with underwater lubricating fluid properties; the end surface at the base opening is a super-hydrophilic surface with underwater lubricating fluid properties.

7. A method for preparing a lubricating fluid circulating bionic ultra-slip drag reducing surface according to any one of claims 1 to 6, characterized in that The specific steps are as follows: Processing a mold casting template; processing an asymmetric stepped structure on the bottom surface of the template of the box structure as a casting template for the upper surface of the asymmetric super-hydrophobic surface structure; Placing a soluble template; using a water-soluble high molecular polymer to prepare a soluble template of a microcirculation channel, and bonding it to the center position of the flip casting template to obtain an integral mold; pouring liquid polymer to prepare the base; Curing, demoulding and mask spraying of super hydrophobic coating; Fill with lubricating fluid.

8. The method for preparing a lubricating fluid circulating bionic super-slip drag-reducing surface according to claim 7, characterized in that: The method of curing, demoulding and mask spraying super hydrophobic coating is: The poured liquid polymer is placed together with the mold and heated and cured at a set temperature; The solidified substrate is removed from the template, immersed in hot water and ultrasonically cleaned to completely dissolve the soluble template inside the substrate; The cleaned substrate is dried, and a nano-superhydrophobic coating is sprayed on the area with the asymmetric microstructure using a mask spraying method, while the substrate and edge areas remain smooth and have the original wettability.

9. The method for preparing a lubricating fluid circulating bionic super-slip drag reducing surface according to claim 8, characterized in that: The method of injecting lubricating fluid is as follows: The substrate with the asymmetric superhydrophobic surface structure is immersed in a lubricating fluid; Evacuate and let it stand to ensure that the microcirculation channel and the super-hydrophobic surface microstructure are filled with lubricating fluid; The soaked substrate is taken out and placed on oil-absorbing paper to absorb excess lubricating fluid, completing the preparation of the bionic super-slippery surface.

10. A surface vessel, characterized in that: The bottom surface of the ship is provided with a lubricating fluid circulation type bionic super-slip drag reduction surface as described in any one of claims 1 to 6.

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