Polymer brushes, methods of making and use in fluid drag reduction

Abstract

This application provides a polymer brush, its preparation method, and its application in fluid drag reduction. The preparation method includes: preparation of an initiator layer; preparation of a PNIPAM brush: under a nitrogen atmosphere, N-isopropylacrylamide, pentamethyldiethylenetriamine, and acrylic acid are added to a mixed solvent of methanol and deionized water, and then cuprous bromide is added to obtain a polymerization reaction solution. A substrate material coated with an initiator layer is immersed in the polymerization reaction solution to perform a SI-ATRP reaction, and a PNIPAM brush is obtained on the surface of the substrate material. Preparation of a DM-PNIPAM brush: 4-dimethylaminobutamine and an activator are dissolved in N,N-dimethylformamide to obtain a modified solvent. The substrate material grafted with the PNIPAM brush is immersed in the modified solvent and reacted to obtain the polymer brush, i.e., the DM-PNIPAM brush. The polymer brush provided by this application improves its stability and durability as a drag-reducing agent in fluid drag reduction.

Description

Technical Field

[0001] This application relates to the field of solid-liquid interface drag reduction materials, and in particular to a polymer brush, its preparation method, and its application in fluid drag reduction. Background Technology

[0002] The frictional resistance generated by the relative motion between solids and liquids consumes a significant amount of energy. In marine navigation, solid-liquid frictional resistance accounts for 60%-80% of the total resistance experienced by a vehicle (ship, submarine, torpedo, etc.). During fluid transport, the proportion of solid-liquid frictional resistance is even higher, reducing fluid velocity and often requiring multi-stage pumping stations for speed increase and pressurization. Reducing solid-liquid frictional resistance, thereby achieving faster speeds, energy savings, and emission reductions for vehicles or transported fluids, is beneficial to national economic development and the advancement of national carbon neutrality strategies. For these reasons, designing and fabricating interfaces that reduce fluid frictional resistance, thus achieving drag reduction at the solid-liquid interface, has become a key research area of ​​common interest to researchers in the fields of fluid dynamics, interfaces, and materials science.

[0003] Anchoring water-soluble polymers to solid walls to biomimeticly construct a highly hydrophilic, nano- and micro-scale mucus-like polymer layer is one effective method to reduce resistance. Polymer brushes, through their highly extended chain structure, can form a hydrated lubricating layer at the solid-liquid interface, effectively sliding the boundary and thus significantly reducing flow friction resistance. However, in existing technologies, the brush layer has poor durability, making it difficult to achieve long-term effective lubrication. Summary of the Invention

[0004] This application provides a polymer brush, a preparation method thereof, and its application in fluid drag reduction, in order to solve the problems mentioned in the background art.

[0005] In a first aspect, this application provides a method for preparing a polymer brush, the method comprising the following steps: (1) Preparation of initiator layer: Under a nitrogen atmosphere, the initiator and anhydrous toluene are stirred and mixed to obtain an initiator solution. The hydroxylated substrate material is then immersed in the initiator solution and reacted to obtain a substrate material coated with an initiator layer. (2) Preparation of PNIPAM brushes: Under a nitrogen atmosphere, N-isopropylacrylamide, pentamethyldiethylenetriamine and acrylic acid were added to a mixed solvent of methanol and deionized water, stirred, and then cuprous bromide was added and stirred for 10-20 min to obtain a polymerization reaction solution. The substrate material coated with the initiator layer was immersed in the polymerization reaction solution to carry out the SI-ATRP reaction, and a PNIPAM brush was obtained on the surface of the substrate material. (3) Preparation of DM-PNIPAM brush: Under a nitrogen atmosphere, 4-dimethylaminobutyramine and an activator are dissolved in N,N-dimethylformamide to obtain a modified solvent. The substrate material of the grafted PNIPAM brush in step (2) is then immersed in the modified solvent and reacted to obtain a polymer brush, namely the DM-PNIPAM brush.

[0006] Optionally, in the initiator layer preparation step, the initiator is selected from 3-(bromomethyl)phenethyltrimethoxysilane, and the mass ratio of the initiator to anhydrous toluene is 20-25:100.

[0007] Optionally, in the initiator layer preparation step, the hydroxylated substrate material is immersed in the initiator solution and reacted at 40-80℃ for 10-12 hours.

[0008] Optionally, in the PNIPAM brush preparation step, the volume ratio of methanol to deionized water is 1:1-1.5, and the concentration of N-isopropylacrylamide in the mixed solvent of methanol and deionized water is 0.5-1.3 mol / L. The molar ratio of cuprous bromide to N-isopropylacrylamide is 1:50-100, the molar ratio of pentamethyldiethylenetriamine to cuprous bromide is 1-1.3:1, and the molar ratio of N-isopropylacrylamide to acrylic acid is 1:18-20.

[0009] Optionally, in the PNIPAM brush preparation step, the SI-ATRP reaction conditions are 25-40℃ for 6-18h.

[0010] Optionally, in the DM-PNIPAM brush preparation step, the concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide is 0.2-0.6 mol / L, and the mass ratio of activator to 4-dimethylaminobutyramine is 1.5-2.2:1.

[0011] Optionally, in the DM-PNIPAM brush preparation step, the activator is a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 1:3-5.

[0012] Optionally, in the DM-PNIPAM brush preparation step, the reaction temperature is 40-60℃ and the reaction time is 12-24h.

[0013] Secondly, this application provides a polymer brush, which is prepared by the above method.

[0014] Thirdly, this application provides a polymer brush for use in the field of fluid drag reduction technology.

[0015] The polymer brush, its preparation method, and its application in fluid drag reduction provided in this application realize the preparation of polymer brushes and have the following advantages compared with the prior art: (1) By hydroxylating the surface of the substrate material, the surface of the substrate material is rich in reactive hydroxyl groups, which activates the surface of the substrate material. The initiator reacts with the hydroxyl groups on the surface of the substrate material to form a stable initiator layer. Using N-isopropylacrylamide as monomer, cuprous bromide as catalyst, and pentamethyldiethylenetriamine as ligand, a uniform PNIPAM brush is "directionally" grown on the surface of the substrate material through SI-ATRP reaction. The generated poly-N-isopropylacrylamide acts as a drag-reducing agent. One end is anchored to the surface of the substrate material, and the long chain is in the water and will combine with a large number of water molecules through hydrogen bonding. This results in a solid-liquid composite interface with superwetting properties in water. That is, when the fluid flows through, the fluid does not directly contact the solid interface, but contacts the hydrated layer of the polymer brush, thereby improving the drag reduction efficiency of the solid-liquid fluid. By introducing 4-dimethylaminobutylamine into the PNIPAM brush, the surface hydrophilicity of the polymer brush is further improved, forming a strong hydration layer on the brush surface, improving the hydration layer structure, and enabling the DM-PNIPAM brush to form a stable hydration layer in water, further reducing frictional resistance.

[0016] (2) The preparation method of the polymer brush provided in this application is simple, easy to obtain and has a wider range of applications. The highly water-soluble macromolecules are directly anchored to the solid-liquid wall surface, so that they are completely in the near-wall fluid layer without the waste of the turbulent core area, which greatly improves its utilization efficiency and reduces its pollution to the fluid medium. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 Water contact angle diagrams of the polymer brushes provided in Examples 1-3 and Comparative Examples 1-3; Figure 2 The graph shows the average coefficient of friction of the polymer brushes provided in Examples 1-3 and Comparative Examples 1-3 in water. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0020] In a first aspect, this application provides a method for preparing a polymer brush, the method comprising the following steps: (1) Preparation of initiator layer: Under a nitrogen atmosphere, the initiator and anhydrous toluene are stirred and mixed to obtain an initiator solution. The hydroxylated substrate material is then immersed in the initiator solution and reacted to obtain a substrate material coated with an initiator layer. (2) Preparation of PNIPAM brushes: Under a nitrogen atmosphere, N-isopropylacrylamide, pentamethyldiethylenetriamine and acrylic acid were added to a mixed solvent of methanol and deionized water, stirred, and then cuprous bromide was added and stirred for 10-20 min to obtain a polymerization reaction solution. The substrate material coated with the initiator layer was immersed in the polymerization reaction solution to carry out the SI-ATRP reaction, and a PNIPAM brush was obtained on the surface of the substrate material. (3) Preparation of DM-PNIPAM brush: Under a nitrogen atmosphere, 4-dimethylaminobutyramine and an activator are dissolved in N,N-dimethylformamide to obtain a modified solvent. The substrate material of the grafted PNIPAM brush in step (2) is then immersed in the modified solvent and reacted to obtain a polymer brush, namely the DM-PNIPAM brush.

[0021] Specifically, after hydroxylation treatment, the substrate surface is rich in reactive silanol groups (Si-OH) or other hydroxyl groups (M-OH). The initiator undergoes a condensation reaction with the hydroxyl groups on the substrate surface, forming stable covalent bonds. This firmly anchors the ATRP-initiating initiator to the substrate surface, forming a monolayer or multilayer initiator layer suitable for surface polymerization. This initiates polymer chain growth on the substrate surface, achieving surface grafting and yielding a brush-like polymer. The Si-O-Si covalent bonds anchor the initiator to the substrate, ensuring that the subsequent growth of the entire polymer brush layer is chemically bonded to the substrate, rather than physically adsorbed. This significantly improves the stability and durability of the polymer brush layer, enabling it to withstand subsequent solvent washing, swelling, shrinkage, and other physicochemical changes during use.

[0022] The substrate material is selected from silicon wafers, glass, Fe, Al, organic coatings, etc., and in this application, it is selected from silicon wafers.

[0023] The preparation method of hydroxylated substrate material includes: immersing the substrate material in Piranha solution for 5-8 hours, rinsing it 3-4 times with ultrapure water, and drying it in a vacuum oven at 100-120℃ for 2-4 hours to obtain the hydroxylated substrate material. Hydroxylation removes organic contaminants from the surface of the substrate material, exposing sufficient hydroxyl active sites and creating reaction sites for subsequent coupling initiators.

[0024] Piranha solution is a mixture of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 3:1.

[0025] In the preparation of PNIPAM brushes, N-isopropylacrylamide is used as a monomer, cuprous bromide as a catalyst, and pentamethyldiethylenetriamine as a ligand. A uniform PNIPAM brush is directionally grown on a silicon surface via SI-ATRP (surface-initiated atom transfer radical polymerization). The resulting poly(N-isopropylacrylamide) is a water-soluble polymer that acts as a drag-reducing agent. One end is anchored to the substrate surface, while the long chain and the other end are in water and will combine with a large number of water molecules through hydrogen bonding to form a hydrated extended state. This results in a superwetting solid-liquid composite interface in water. When fluid flows through, the high hydration of the polymer brush leads to a highly flexible interface, further reducing the interface roughness. The fluid does not directly contact the solid interface but rather the hydrated layer of the polymer brush, thus improving the drag reduction efficiency for the solid-liquid fluid.

[0026] DM-PNIPAM brushes were prepared by modifying the PNIPAM polymer chain with 4-dimethylaminobutyramine after the SI-ATRP reaction, which resulted in carboxyl groups. After the reaction, the brush was washed sequentially with DMF, methanol, and deionized water, and then dried in a vacuum oven at 100-120℃ for 1-3 hours to obtain the DM-PNIPAM brush. The introduction of 4-dimethylaminobutyramine formed a covalent structure, further improving the surface hydrophilicity of the polymer brush and creating a robust hydration layer on the brush surface. This improved the hydration layer structure, allowing the DM-PNIPAM brush to form a stable hydration layer in water, enhancing the durability and stability of the hydration layer, and further reducing frictional resistance.

[0027] Furthermore, after the reaction is complete, the brush is washed with deionized water until neutral, and then dried in a vacuum oven at 100-120℃ for 1-3 hours to obtain the DM-PNIPAM brush.

[0028] The thickness of the DM-PNIPAM brush is 40-110nm.

[0029] The above scheme enables the preparation of polymer brushes. By hydroxylating the surface of the substrate material, which enriches the surface with reactive hydroxyl groups, the substrate material surface is activated. The initiator undergoes a condensation reaction with the hydroxyl groups on the substrate material surface to form a stable initiator layer. Using N-isopropylacrylamide as a monomer, cuprous bromide as a catalyst, and pentamethyldiethylenetriamine as a ligand, uniform PNIPAM brushes are directionally grown on the substrate material surface via SI-ATRP reaction. The generated poly(N-isopropylacrylamide) acts as a drag-reducing agent, with one end anchored to the substrate material surface and the long chain connected to the other end in water. It binds a large number of water molecules through hydrogen bonding, resulting in a superwetting solid-liquid composite interface in water. That is, when the fluid flows through it, the fluid does not directly contact the solid interface, but rather contacts the hydrated layer of the polymer brush, thereby improving the drag reduction efficiency of the solid-liquid fluid. By introducing 4-dimethylaminobutylamine into the PNIPAM brush, the surface hydrophilicity of the polymer brush is further improved, forming a strong hydration layer on the brush surface, improving the hydration layer structure, and enabling the DM-PNIPAM brush to form a stable hydration layer in water, further reducing frictional resistance.

[0030] Optionally, in the initiator layer preparation step, the initiator is selected from 3-(bromomethyl)phenethyltrimethoxysilane, and the mass ratio of the initiator to anhydrous toluene is 20-25:100.

[0031] Specifically, controlling the mass ratio of initiator to anhydrous toluene is beneficial for controlling the uniformity and thickness of the initiator layer. Too high an initiator concentration can easily lead to multilayer adsorption, while too low a concentration will result in insufficient initiation site density, which in turn affects the growth of the polymer brush.

[0032] Optionally, in the initiator layer preparation step, the hydroxylated substrate material is immersed in the initiator solution and reacted at 40-80℃ for 10-12 hours.

[0033] Optionally, in the PNIPAM brush preparation step, the volume ratio of methanol to deionized water is 1:1-1.5, and the concentration of N-isopropylacrylamide in the mixed solvent of methanol and deionized water is 0.5-1.3 mol / L. The molar ratio of cuprous bromide to N-isopropylacrylamide is 1:50-100, the molar ratio of pentamethyldiethylenetriamine to cuprous bromide is 1-1.3:1, and the molar ratio of N-isopropylacrylamide to acrylic acid is 1:18-20.

[0034] Optionally, in the PNIPAM brush preparation step, the SI-ATRP reaction conditions are 25-40℃ for 6-18h.

[0035] Optionally, in the DM-PNIPAM brush preparation step, the concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide is 0.2-0.6 mol / L, and the mass ratio of activator to 4-dimethylaminobutyramine is 1.5-2.2:1.

[0036] Optionally, in the DM-PNIPAM brush preparation step, the activator is a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 1:3-5.

[0037] Optionally, in the DM-PNIPAM brush preparation step, the reaction temperature is 40-60℃ and the reaction time is 12-24h.

[0038] Secondly, this application provides a polymer brush, which is prepared by the above method.

[0039] Thirdly, this application provides a polymer brush for use in the field of fluid drag reduction technology.

[0040] Specifically, the polymer brush provided in this application, as a water-based drag-reducing agent, anchors water-soluble polymers to a solid wall surface. This means the drag-reducing agent macromolecules are directly positioned in the near-wall flow field region. Poly(N-isopropylacrylamide) serves as the drag-reducing agent, with one end anchored to the substrate surface and the long chain connected to the other end in water. Through hydrogen bonding, a large number of water molecules are bound together, resulting in a superwetting solid-liquid composite interface in water. This means that when fluid flows through, it does not directly contact the solid interface but rather the hydrated layer of the polymer brush, thereby improving the drag-reducing efficiency for the solid-liquid fluid. Simultaneously, the polymer brush allows it to directly suppress turbulent pulsations and reduce turbulent shear stress in the near-wall layer. This reduces unnecessary waste of drag-reducing agent in the turbulent core region, improves the utilization rate of the drag-reducing agent, and also reduces contamination of the fluid medium by the drag-reducing agent molecules.

[0041] The technical solutions of this application are illustrated in detail below with specific embodiments, but they should not be construed as limiting the scope of protection of this invention. Example 1

[0042] A method for preparing a polymer brush, the method comprising the following steps: (1) Preparation of initiator layer: Under a nitrogen atmosphere, the initiator and anhydrous toluene were stirred and mixed to obtain an initiator solution. The hydroxylated silicon wafer was then immersed in the initiator solution and reacted at 40°C for 12 hours to obtain a substrate material coated with an initiator layer. The initiator is selected from 3-(bromomethyl)phenylethyltrimethoxysilane, and the mass ratio of the initiator to anhydrous toluene is 20:100.

[0043] (2) Preparation of PNIPAM brushes: Under a nitrogen atmosphere, N-isopropylacrylamide, pentamethyldiethylenetriamine and acrylic acid were added to a mixed solvent of methanol and deionized water and stirred for 10 min. Then cuprous bromide was added and stirred for 10 min to obtain a polymerization reaction solution. The substrate material coated with the initiator layer was immersed in the polymerization reaction solution for SI-ATRP reaction and reacted at 25°C for 18 h to obtain a PNIPAM brush on the surface of the substrate material. The volume ratio of methanol to deionized water is 1:1, and the concentration of N-isopropylacrylamide in the mixed solvent of methanol and deionized water is 0.5 mol / L; the molar ratio of cuprous bromide to N-isopropylacrylamide is 1:50, the molar ratio of pentamethyldiethylenetriamine to cuprous bromide is 1:1, and the molar ratio of N-isopropylacrylamide to acrylic acid is 1:18.

[0044] (3) Preparation of DM-PNIPAM brush: Under a nitrogen atmosphere, 4-dimethylaminobutyramine and an activator were dissolved in N,N-dimethylformamide to obtain a modified solvent. The substrate material of the grafted PNIPAM brush in step (2) was then immersed in the modified solvent and reacted at 40°C for 24 hours to obtain a polymer brush, namely the DM-PNIPAM brush.

[0045] The concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide was 0.2 mol / L, and the mass ratio of activator to 4-dimethylaminobutyramine was 1.5:1. The activator was a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 1:3. Example 2

[0046] A method for preparing a polymer brush, the method comprising the following steps: (1) Preparation of initiator layer: Under a nitrogen atmosphere, the initiator and anhydrous toluene were stirred and mixed to obtain an initiator solution. The hydroxylated substrate material was then immersed in the initiator solution and reacted at 60°C for 11 hours to obtain a substrate material coated with an initiator layer. The initiator is selected from 3-(bromomethyl)phenylethyltrimethoxysilane, and the mass ratio of the initiator to anhydrous toluene is 22:100.

[0047] (2) Preparation of PNIPAM brushes: Under a nitrogen atmosphere, N-isopropylacrylamide, pentamethyldiethylenetriamine and acrylic acid were added to a mixed solvent of methanol and deionized water and stirred for 10 min. Then cuprous bromide was added and stirred for 16 min to obtain a polymerization reaction solution. The substrate material coated with the initiator layer was immersed in the polymerization reaction solution for SI-ATRP reaction and reacted at 30°C for 12 h to obtain a PNIPAM brush on the surface of the substrate material. The volume ratio of methanol to deionized water was 1:1.2, and the concentration of N-isopropylacrylamide in the mixed solvent of methanol and deionized water was 0.8 mol / L; the molar ratio of cuprous bromide to N-isopropylacrylamide was 1:70, the molar ratio of pentamethyldiethylenetriamine to cuprous bromide was 1.2:1, and the molar ratio of N-isopropylacrylamide to acrylic acid was 1:19.

[0048] (3) Preparation of DM-PNIPAM brush: Under a nitrogen atmosphere, 4-dimethylaminobutyramine and an activator were dissolved in N,N-dimethylformamide to obtain a modified solvent. The substrate material of the grafted PNIPAM brush in step (2) was then immersed in the modified solvent and reacted at 50°C for 18 hours to obtain a polymer brush, namely the DM-PNIPAM brush.

[0049] The concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide was 0.4 mol / L, and the mass ratio of activator to 4-dimethylaminobutyramine was 1.8:1. The activator was a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 1:4. Example 3

[0050] A method for preparing a polymer brush, the method comprising the following steps: (1) Preparation of initiator layer: Under a nitrogen atmosphere, the initiator and anhydrous toluene were stirred and mixed to obtain an initiator solution. The hydroxylated substrate material was then immersed in the initiator solution and reacted at 80°C for 10 hours to obtain a substrate material coated with an initiator layer. The initiator is selected from 3-(bromomethyl)phenylethyltrimethoxysilane, and the mass ratio of the initiator to anhydrous toluene is 25:100.

[0051] (2) Preparation of PNIPAM brushes: Under a nitrogen atmosphere, N-isopropylacrylamide, pentamethyldiethylenetriamine and acrylic acid were added to a mixed solvent of methanol and deionized water and stirred for 10 min. Then cuprous bromide was added and stirred for 20 min to obtain a polymerization reaction solution. The substrate material coated with the initiator layer was immersed in the polymerization reaction solution to carry out the SI-ATRP reaction. The reaction was carried out at 40°C for 6 h to obtain a PNIPAM brush on the surface of the substrate material. The volume ratio of methanol to deionized water is 1:1.5, the concentration of N-isopropylacrylamide in the mixed solvent of methanol and deionized water is 1.3 mol / L, the molar ratio of cuprous bromide to N-isopropylacrylamide is 1:100, the molar ratio of pentamethyldiethylenetriamine to cuprous bromide is 1.3:1, and the molar ratio of N-isopropylacrylamide to acrylic acid is 1:20.

[0052] (3) Preparation of DM-PNIPAM brush: Under a nitrogen atmosphere, 4-dimethylaminobutyramine and an activator were dissolved in N,N-dimethylformamide to obtain a modified solvent. The substrate material of the grafted PNIPAM brush in step (2) was then immersed in the modified solvent and reacted at 60°C for 12 hours to obtain a polymer brush, namely the DM-PNIPAM brush.

[0053] The concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide was 0.6 mol / L, and the mass ratio of activator to 4-dimethylaminobutyramine was 2.2:1. The activator was a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 1:5.

[0054] Comparative Example 1 A method for preparing a polymer brush, the method comprising the following steps: The differences from Example 2 include: (3) The concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide is 0.7 mol / L.

[0055] Comparative Example 2 A method for preparing a polymer brush, the method comprising the following steps: The differences from Example 2 include: (3) The concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide is 0.1 mol / L.

[0056] Comparative Example 3 A method for preparing a polymer brush, the method comprising the following steps: The differences from Example 2 include: In this embodiment, the reaction in step (3) is not performed, and the PNIPAM brush obtained in step (2) is used directly.

[0057] Experimental Example 1 DM-PNIPAM brushes were successfully prepared in Examples 1-3. The water contact angles of the polymer brushes provided in Examples 1-3 and Comparative Examples 1-3 were tested. Measurements were performed using a contact angle goniometer (DECCA-100) fitted with the Laplace-Young algorithm, and the results are as follows. Figure 1As shown.

[0058] Figure 1 The figures show the water contact angles of the polymer brushes provided in Examples 1-3 and Comparative Examples 1-3. As can be seen from the figures, the contact angles of Examples 1-3 are significantly lower than those of Comparative Examples 1-3, indicating that the polymer brushes provided in Examples 1-3 have excellent hydrophilicity. That is, the polymer brushes bind a large number of water molecules in water through hydrogen bonding, obtaining a solid-liquid composite interface with superwetting properties in water. By introducing 4-dimethylaminobutyramine onto the PNIPAM brush, the surface hydrophilicity of the polymer brush is further improved, forming a strong hydration layer on the brush surface and improving the hydration layer structure. This allows the DM-PNIPAM brush to form a stable hydration layer in water, thereby reducing the frictional resistance of the fluid. In Comparative Example 3, without the use of 4-dimethylaminobutyramine to modify the PNIPAM brush, the hydrophilicity of the polymer brush was significantly reduced. Meanwhile, in Comparative Examples 1 and 2, the reaction concentration of 4-dimethylaminobutyramine changed, indicating that the modification with 4-dimethylaminobutyramine can significantly improve the hydrophilicity of the polymer brush, which helps to stabilize the formation of the hydration layer on the surface of the polymer brush, thereby improving the drag reduction performance of the polymer brush.

[0059] Experiment Example 2 The average coefficient of friction of the polymer brushes provided in Examples 1-3 and Comparative Examples 1-3 was tested using a ball-and-socket reciprocating friction testing machine (CSM, TRB3) under a wet environment, a load of 2N, and a frequency of 2Hz for 10,000 cycles of reciprocating friction. A 6mm diameter polydimethylsiloxane (PDMS) elastomer hemisphere was used as the upper friction pair. The results are as follows: Figure 2 As shown.

[0060] Figure 2 The graph shows the average coefficient of friction of the polymer brushes provided in Examples 1-3 and Comparative Examples 1-3 in water. Figure 2 It can be seen that the polymer brushes provided in Examples 1-3 have the lowest average coefficient of friction, with a minimum value of 0.02, indicating that the polymer brushes provided in this application have excellent drag reduction effect in water. A strong hydration layer is formed on the surface of the polymer brush through hydrogen bonding, resulting in a super-wetting solid-liquid composite interface in water. When fluid flows through it, the fluid does not directly contact the solid interface, but rather contacts the hydration layer of the polymer brush, thereby improving the drag reduction efficiency for solid-liquid fluids.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a polymer brush, characterized in that, The preparation method includes the following steps: (1) Preparation of initiator layer: Under a nitrogen atmosphere, an initiator and anhydrous toluene are stirred and mixed to obtain an initiator solution. The hydroxylated substrate material is then immersed in the initiator solution and reacted to obtain a substrate material coated with an initiator layer. (2) Preparation of PNIPAM brushes: Under a nitrogen atmosphere, N-isopropylacrylamide, pentamethyldiethylenetriamine and acrylic acid are added to a mixed solvent of methanol and deionized water, stirred, and then cuprous bromide is added and stirred for 10-20 min to obtain a polymerization reaction solution. The substrate material coated with the initiator layer is immersed in the polymerization reaction solution to carry out the SI-ATRP reaction, and a PNIPAM brush is obtained on the surface of the substrate material. (3) Preparation of DM-PNIPAM brush: Under a nitrogen atmosphere, 4-dimethylaminobutyramine and an activator are dissolved in N,N-dimethylformamide to obtain a modified solvent. The substrate material grafted with the PNIPAM brush in step (2) is then immersed in the modified solvent and reacted to obtain a polymer brush, namely a DM-PNIPAM brush.

2. The method for preparing the polymer brush according to claim 1, characterized in that, In the initiator layer preparation step, the initiator is selected from 3-(bromomethyl)phenylethyltrimethoxysilane; The mass ratio of the initiator to anhydrous toluene is 20-25:

100.

3. The method for preparing the polymer brush according to claim 1, characterized in that, In the initiator layer preparation step, the hydroxylated substrate material is immersed in the initiator solution and reacted at 40-80°C for 10-12 hours.

4. The method for preparing the polymer brush according to claim 1, characterized in that, In the PNIPAM brush preparation step, the volume ratio of methanol to deionized water is 1:1-1.5, and the concentration of N-isopropylacrylamide in the mixed solvent of methanol and deionized water is 0.5-1.3 mol / L. The molar ratio of cuprous bromide to N-isopropylacrylamide is 1:50-100, the molar ratio of pentamethyldiethylenetriamine to cuprous bromide is 1-1.3:1, and the molar ratio of N-isopropylacrylamide to acrylic acid is 1:18-20.

5. The method for preparing a polymer brush according to claim 1, characterized in that, In the PNIPAM brush preparation step, the SI-ATRP reaction conditions are 25-40℃ for 6-18h.

6. The method for preparing a polymer brush according to claim 1, characterized in that, In the DM-PNIPAM brush preparation step, the concentration of 4-dimethylaminobutyramine in N,N-dimethylformamide is 0.2-0.6 mol / L, and the mass ratio of the activator to the 4-dimethylaminobutyramine is 1.5-2.2:

1.

7. The method for preparing a polymer brush according to claim 1, characterized in that, In the preparation step of the DM-PNIPAM brush, the activator is a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 1:3-5.

8. The method for preparing a polymer brush according to any one of claims 1-7, characterized in that, In the preparation step of the DM-PNIPAM brush, the reaction temperature is 40-60℃ and the reaction time is 12-24h.

9. A polymer brush, characterized in that, The polymer brush is prepared by the method described in any one of claims 1-8.

10. A polymer brush as described in claim 9, applied in the field of fluid drag reduction technology.

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