Preparation method of magnetic response hydrophobic array film

Abstract

The invention discloses a preparation method of a magnetic response super-hydrophobic array film, which comprises the following steps: dispersing magnetic particles in a solvent, performing ultrasonic treatment, adding amino silane, stirring and heating to react in a nitrogen atmosphere, separating, washing, and performing vacuum drying to obtain modified magnetic particles; the preparation method comprises the following steps: dissolving stearic acid in a solvent, adding a catalyst, activating, adding modified magnetic beads, stirring for reaction, filtering, washing, drying, uniformly mixing the obtained product with a PDMS prepolymer, a curing agent and a diluent, pouring into a PDMS female die coated with a release agent, carrying out magnetic induction, degassing, curing, and demolding. Amino groups react with carboxyl groups in long-chain fatty acid, so that covalent bonding of the hydrophobic agent is realized, and the hydrophobic durability is improved; due to the formation of the hydrophobic layer, the interface energy between the magnetic particles and the PDMS matrix is reduced, the dispersity of the particles is improved by utilizing a steric hindrance effect, and the problem that the magnetic particles are easy to agglomerate in a polymer matrix is effectively solved.

Description

Technical Field

[0001] This invention relates to a method for preparing a magnetically responsive hydrophobic array thin film, belonging to the field of materials surface engineering technology. Background Technology

[0002] In the field of contemporary microfluidics, non-contact, precise manipulation of microfluidics, droplets, and biological samples has become a core research direction. While traditional closed microfluidic systems perform excellently in continuous flow chemical synthesis and analysis, they have limitations in handling discrete droplets, preventing cross-contamination, and simplifying peripheral pump and valve equipment. Inspired by ciliary movements in nature (such as the cilia that clear mucus from the human respiratory tract or the hydrophoretic cilia on the surface of paramecia), magnetic artificial cilia (magnetically responsive hydrophobic array thin films) have attracted considerable attention as an active micro-mixing and transport structure due to their ability to achieve wireless, programmable, and non-invasive manipulation of fluid properties via external magnetic fields.

[0003] Magnetoresponsive hydrophobic array films are typically constructed from high aspect ratio micropillar arrays of an elastic polymer matrix (such as polydimethylsiloxane PDMS) embedded with magnetic nanoparticles (such as iron(III) oxide (Fe3O4). Their working principle relies on the torque applied to the magnetic particles by an external magnetic field, driving flexible cilia to bend or oscillate. This non-reciprocal motion breaks the reversibility of low Reynolds number flow, resulting in net fluid transport.

[0004] However, in the preparation of existing magnetically responsive hydrophobic array films, magnetic particles are usually directly mixed with PDMS prepolymer, diluent, and curing agent and then poured into a template. After magnetic induction, the array film is cured and demolded. Due to the strong attraction between the magnetic core particles, they will aggregate, which will affect their dispersibility in the mixture.

[0005] Meanwhile, relying solely on magneto-actuation is insufficient for efficient droplet transport. The movement of droplets on solid surfaces is significantly constrained by the wettability of the solid-liquid interface. If the surface adhesion is too high (i.e., severe contact hysteresis), even with vigorous cilia beating, the droplet may remain stuck in place due to the "pinning effect," or leave residual liquid during movement, leading to sample loss and contamination. Therefore, after obtaining the array film, it is immersed in a hydrophobic treatment solution to achieve hydrophobic treatment.

[0006] In this method, the hydrophobic agent adheres to the micropillars solely through physical adsorption, and the magnetic micropillars undergo high-frequency, large-deformation bending motions during operation. This deformation generates significant shear stress between the hydrophobic coating and the flexible substrate. Due to modulus mismatch (hard coating covering a soft substrate), the coating is prone to cracking or peeling, resulting in a rapid decline in hydrophobic properties over time. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a magnetically responsive hydrophobic array film. By modifying the amino group, the magnetic particles are given the same charge. The repulsion effect of like charges is used to improve the dispersion of the magnetic particles. Then, the amino group reacts with the carboxyl group in the long-chain fatty acid to achieve covalent bonding of the hydrophobic agent, thereby improving the hydrophobic durability. Furthermore, the formation of the hydrophobic layer reduces the interfacial energy between the magnetic particles and the PDMS matrix, and the steric hindrance effect is used to improve the dispersion of the particles, effectively solving the problem of easy aggregation of magnetic particles in the polymer matrix.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a magnetically responsive hydrophobic array thin film includes the following steps: S1. After dispersing the magnetic particles in a solvent, ultrasonic treatment is performed. Then, aminosilane is added, and the mixture is stirred and heated under a nitrogen atmosphere. After separation, washing, and vacuum drying, modified magnetic particles are obtained. S2. Stearic acid is dissolved in a solvent, activated by adding a catalyst, and then modified magnetic beads are added. After stirring and reacting, the mixture is filtered, washed, and dried. The resulting product is then mixed evenly with PDMS prepolymer, curing agent, and diluent and poured into a PDMS mold coated with a release agent. A permanent magnet is placed under the PDMS mold for magnetic induction. After degassing, the product is cured and demolded.

[0009] Preferably, the magnetic particles are iron(III) oxide; the aminosilane is 3-aminopropyltriethoxysilane or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; and the hydrophobic agent is a long-chain fatty acid.

[0010] Preferably, the hydrophobic agent is stearic acid or palmitic acid.

[0011] Preferably, in step S1, the ratio of magnetic particles to aminosilane is 1g:(2-3)mL.

[0012] Preferably, in step S1, the stirring and heating reaction conditions are: 200-500 rpm, 70-80℃, and reflux reaction for 6-12 hours.

[0013] Preferably, in step S2, the mass ratio of PDMS prepolymer, curing agent, diluent, modified magnetic beads and hydrophobic agent is 10:1:(1-10):(10-50):(1-10).

[0014] Preferably, in step S2, the stirring reaction conditions are: 35-40℃, 3-5h; the curing conditions are: 80-90℃, 2-3h.

[0015] Preferably, in step S2, demolding is performed in anhydrous ethanol and with ultrasonic assistance.

[0016] Preferably, in step S2, the method for preparing the PDMS concave mold is as follows: first, a micro-column array master mold is prepared using 3D printing technology; then, the PDMS prepolymer and curing agent are mixed evenly and poured into the micro-column array master mold coated with a release agent, followed by curing and demolding; and finally, the groove is cut out.

[0017] Preferably, the mass ratio of PDMS prepolymer to curing agent is 10:1; the curing conditions are: 70-90℃, 2-3h; demolding is carried out in anhydrous ethanol with ultrasonic assistance.

[0018] The beneficial effects of this invention are as follows: 1. A dual modification strategy of "first modifying with aminosilane coupling agent, then grafting with long-chain fatty acid" is adopted. First, active amino groups are introduced on the surface of magnetic particles to improve the dispersibility between magnetic particles (like charges repel each other) and provide chemical anchors for subsequent hydrophobic agents. Then, the carboxyl groups of long-chain fatty acids (stearic acid / palmitic acid) are used to react with the amino groups on the surface of magnetic particles to undergo an amidation reaction.

[0019] This chemical bonding is stronger than physical adhesion, effectively forming a dense hydrophobic protective layer on the surface of magnetic particles. The formation of the hydrophobic protective layer reduces the interfacial energy between the magnetic particles and the PDMS matrix, and improves the dispersion of particles by utilizing the steric hindrance effect. This effectively solves the problem of easy aggregation of magnetic particles in the polymer matrix, ensuring uniform distribution of magnetic materials, as well as hydrophobic uniformity and durability within the array film.

[0020] 2. Commonly used materials such as iron(II,III) oxide, PDMS, and biocompatible fatty acids (stearic acid / palmitic acid) are selected, avoiding the use of expensive or highly toxic fluorinated modifiers, thus reducing costs and making the product more environmentally friendly.

[0021] 3. The method of using 3D printing to prepare the master mold combined with PDMS casting greatly reduces the equipment threshold and preparation cost compared with traditional micro-nano processing technologies such as photolithography and etching, making it suitable for rapid preparation and potential large-scale production. Attached Figure Description

[0022] Figure 1 The fabrication process for magnetically responsive hydrophobic array thin films; Figure 2 The static contact angle of the array thin film obtained in Example 1; Figure 3 This is a schematic diagram of droplet transport in the air. Detailed Implementation

[0023] Example 1: This example provides a method for preparing a magnetically responsive hydrophobic array thin film. The preparation flowchart is as follows. Figure 1 As shown, it includes the following steps: A micropillar array master mold was prepared using 3D printing technology. Then, PDMS prepolymer and curing agent were mixed evenly at a mass ratio of 10:1 and poured into the micropillar array master mold coated with a release agent. The mixture was then placed in a vacuum chamber and degassed at room temperature for 15 minutes. Next, the degassed micropillar array master mold was placed in a forced-air drying oven and heated and dried at 70°C for 3 hours. The cured micropillar array master mold was then placed in anhydrous ethanol and ultrasonically vibrated to detach the PDMS concave preform from the micropillar array master mold. Finally, grooves were cut to form the PDMS concave mold.

[0024] 10g of iron(III) oxide (particle size 20nm) was dispersed in 200mL of ethanol and then sonicated. Then 20mL of 3-aminopropyltriethoxysilane was added, and the mixture was refluxed at 75℃ for 8h under a nitrogen atmosphere at 300rpm. After magnetic separation, washing and vacuum drying, modified magnetic particles were obtained.

[0025] Stearic acid was dissolved in a solvent (95% ethanol by volume), and a catalyst (0.8g EDC·HCl and 0.5g NHS per 1g stearic acid) was added. The mixture was then stirred and activated at room temperature for 15 minutes. Modified magnetic beads were then added, and the mixture was stirred at 35°C and 300 rpm for 5 hours. After filtration, washing, and drying, the resulting product was mixed evenly with PDMS prepolymer, curing agent, and diluent to obtain a composite material, which was then cast into a PDMS mold coated with a release agent. In the above steps, the mass ratio of PDMS prepolymer, curing agent, diluent, modified magnetic beads, and stearic acid was 10:1:5:30:5.

[0026] A Nd-Fe-B permanent magnet was placed directly beneath the PDMS mold for magnetic induction. The magnetic induction distance was approximately 5 mm, and the magnetic field strength of the Nd-Fe-B permanent magnet was approximately 300 mT. The magnetic poles were facing upwards, and the magnetic field direction was perpendicular to the mold surface. The mold was left to stand under this magnetic field for 30 minutes for magnetic induction. Subsequently, the mold was placed in a vacuum chamber and degassed at room temperature for 30 minutes. Then, it was heated and cured at 80°C for 3 hours. After curing, the PDMS mold was placed in anhydrous ethanol and ultrasonically vibrated to detach the array film from the PDMS mold. The resulting array film micropillars had a vertical drop of 0.8 mm, a center-to-center distance of 1.9 mm between adjacent micropillars, and a height of 3 mm.

[0027] Under the action of an external magnetic field of 285mT, the initial static contact angle of the array thin film is 145°. Figure 2 After 150 days of use, the static contact angle of the array film was 140°.

[0028] Example 2: Manipulating droplets in air (e.g.) Figure 3 (As shown).

[0029] First, the array film obtained in Example 1 is placed on a horizontal glass plate, ensuring that the array film does not slip. Then, an Nd-Fe-B permanent magnet is placed below the glass plate. As the permanent magnet approaches, the upright micropillars completely align themselves with the permanent magnet. Then, as the center of the permanent magnet moves to the bottom of the structure, the micropillars on both sides bend and converge under the magnetic driving force to form a peak-shaped structure. As the permanent magnet moves, the micropillars follow the movement to transport the liquid.

[0030] Comparative Example 1: This comparative example provides a method for preparing a magnetically responsive hydrophobic array thin film, which is basically the same as that in Example 1, except that the iron(III) oxide was not modified. The specific steps include the following: A micropillar array master mold was prepared using 3D printing technology. Then, PDMS prepolymer and curing agent were mixed evenly at a mass ratio of 10:1 and poured into the micropillar array master mold coated with a release agent. The mixture was then placed in a vacuum chamber and degassed at room temperature for 15 minutes. Next, the degassed micropillar array master mold was placed in a forced-air drying oven and heated and dried at 70°C for 3 hours. The cured micropillar array master mold was then placed in anhydrous ethanol and ultrasonically vibrated to detach the PDMS concave preform from the micropillar array master mold. Finally, grooves were cut to form the PDMS concave mold.

[0031] Stearic acid was dissolved in a solvent (95% ethanol by volume), and a catalyst (0.8g EDC·HCl and 0.5g NHS per 1g stearic acid) was added. The mixture was then stirred and activated at room temperature for 15 min. Ferric oxide (20nm particle size) was then added, and the mixture was stirred at 35℃ and 300rpm for 5 h. After filtration, washing, and drying, the resulting product was mixed uniformly with PDMS prepolymer, curing agent, and diluent to obtain a composite material, which was then cast into a PDMS mold coated with a release agent. In the above steps, the mass ratio of PDMS prepolymer, curing agent, diluent, ferric oxide, and stearic acid was 10:1:5:30:5.

[0032] A Nd-Fe-B permanent magnet was placed directly beneath the PDMS mold for magnetic induction. The magnetic induction distance was approximately 5 mm, and the magnetic field strength of the Nd-Fe-B permanent magnet was approximately 300 mT, with the magnetic poles facing upwards so that the magnetic field direction was perpendicular to the mold surface. The mold was left to stand under this magnetic field for 30 minutes for magnetic induction. Then, the mold was placed in a vacuum chamber and degassed at room temperature for 30 minutes. It was then heated and cured at 80°C for 3 hours. Finally, the cured PDMS mold was placed in anhydrous ethanol and ultrasonically vibrated to detach the array film from the PDMS mold.

[0033] Under the action of an external magnetic field of 285mT, the initial static contact angle of the array film is 140°. Due to the non-covalent bond between stearic acid and iron oxide, the static contact angle of the array film is 130° after 150 days of use.

[0034] Comparative Example 2: This comparative example provides a method for preparing a magnetically responsive hydrophobic array thin film, which is basically the same as that in Example 1, except that hydrophobic treatment is performed after the array thin film is prepared. Specifically, it includes the following steps: A micropillar array master mold was prepared using 3D printing technology. Then, PDMS prepolymer and curing agent were mixed evenly at a mass ratio of 10:1 and poured into the micropillar array master mold coated with a release agent. The mixture was then placed in a vacuum chamber and degassed at room temperature for 15 minutes. Next, the degassed micropillar array master mold was placed in a forced-air drying oven and heated and dried at 70°C for 3 hours. The cured micropillar array master mold was then placed in anhydrous ethanol and ultrasonically vibrated to detach the PDMS concave preform from the micropillar array master mold. Finally, grooves were cut to form the PDMS concave mold.

[0035] 10g of iron(III) oxide (particle size 20nm) was dispersed in 200mL of ethanol and then sonicated. Then 20mL of 3-aminopropyltriethoxysilane was added, and the mixture was refluxed at 75℃ for 8h under a nitrogen atmosphere at 300rpm. After magnetic separation, washing and vacuum drying, modified magnetic particles were obtained.

[0036] The modified magnetic beads, PDMS prepolymer, curing agent, and diluent are mixed evenly to obtain a composite material, which is then poured into a PDMS mold coated with a release agent (the mass ratio of PDMS prepolymer, curing agent, diluent, and modified magnetic beads is 10:1:5:30).

[0037] A Nd-Fe-B permanent magnet was placed directly beneath the PDMS mold for magnetic induction. The magnetic induction distance was approximately 5 mm, and the magnetic field strength of the Nd-Fe-B permanent magnet was approximately 300 mT, with the magnetic poles facing upwards so that the magnetic field direction was perpendicular to the mold surface. The mold was left to stand under this magnetic field for 30 minutes for magnetic induction. Then, the mold was placed in a vacuum chamber and degassed at room temperature for 30 minutes. It was then cured at 80°C for 3 hours. Finally, the cured PDMS mold was placed in anhydrous ethanol and ultrasonically vibrated to detach the array film from the PDMS mold.

[0038] Prepare an ethanol solution of stearic acid with a concentration of 0.1 mol / L; place the obtained array film in the stearic acid ethanol solution and heat in a water bath at 70°C for 2 hours; remove and wash, then place in a forced-air drying oven and dry at 110°C for 2.5 hours.

[0039] Under the action of an external magnetic field of 285mT, the initial static contact angle of the array film is 150° (the presence of micropillars on the hydrophobic layer leads to a higher initial static contact angle). However, since the hydrophobic agent is only physically adsorbed onto the micropillars, the deformation of the magnetic micropillars during operation will cause the coating to crack or peel off, resulting in a rapid decay of hydrophobic performance over time. After 150 days of use, the static contact angle of the array film is 125°.

Claims

1. A method for preparing a magnetically responsive hydrophobic array thin film, characterized in that, Includes the following steps: S1. After dispersing the magnetic particles in a solvent, ultrasonic treatment is performed. Then, aminosilane is added, and the mixture is stirred and heated under a nitrogen atmosphere. After separation, washing, and vacuum drying, modified magnetic particles are obtained. S2. Stearic acid is dissolved in a solvent, activated by adding a catalyst, and then modified magnetic beads are added. After stirring and reacting, the mixture is filtered, washed, and dried. The resulting product is then mixed evenly with PDMS prepolymer, curing agent, and diluent and poured into a PDMS mold coated with a release agent. A permanent magnet is placed under the PDMS mold for magnetic induction. After degassing, the product is cured and demolded.

2. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 1, characterized in that, The magnetic particles are iron(III) oxide (Fe3O4). The aminosilane is 3-aminopropyltriethoxysilane or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; The hydrophobic agent is a long-chain fatty acid.

3. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 2, characterized in that, The hydrophobic agent is stearic acid or palmitic acid.

4. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 1, characterized in that, In step S1, the ratio of magnetic particles to aminosilane is 1 g:(2-3) mL.

5. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 1, characterized in that, In step S1, the stirring and heating reaction conditions are: 200-500 rpm, 70-80℃, and reflux reaction for 6-12 hours.

6. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 1, characterized in that, In step S2, the mass ratio of PDMS prepolymer, curing agent, diluent, modified magnetic beads and hydrophobic agent is 10:1:(1-10):(10-50):(1-10).

7. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 1, characterized in that, In step S2, the stirring reaction conditions are: 35-40℃, 3-5h; The curing conditions are: 80-90℃, 2-3h.

8. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 1, characterized in that, In step S2, demolding is performed in anhydrous ethanol with ultrasonic assistance.

9. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 1, characterized in that, In step S2, the method for preparing the PDMS concave mold is as follows: first, a micro-column array master mold is prepared using 3D printing technology; then, the PDMS prepolymer and curing agent are mixed evenly and poured into the micro-column array master mold coated with a release agent, followed by curing and demolding; and finally, the groove is cut out.

10. The method for preparing a magnetically responsive hydrophobic array thin film according to claim 9, characterized in that, The mass ratio of PDMS prepolymer to curing agent is 10:1; The curing conditions are: 70-90℃, 2-3 hours; Demolding was performed in anhydrous ethanol with ultrasonic assistance.

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