A method for direct and rapid preparation of ultrathin films on rough macroporous substrates

Abstract

The application discloses a method for directly and rapidly preparing an ultrathin film on a rough macroporous substrate, wherein the rough macroporous substrate is immersed in a solution to form a smooth liquid film on the surface of the rough macroporous substrate; the two-phase interface formed on the surface of the rough macroporous substrate with the smooth liquid film is utilized to directly prepare the ultrathin film, thereby shortening the preparation process; compared with a general film preparation process, the method does not have a film transfer process, and the problem of film breaking is avoided; the prepared ultrathin film can be directly used in a subsequent separation process, and the integration of preparation and application is realized; the thickness of the film can be directly regulated by changing film preparation conditions, and the requirements and limitations of the film transfer process on the thickness of the film are avoided, thereby shortening the period of ultrathin film preparation, reducing the preparation cost and technical threshold, and being not limited by a film forming method, and being more conducive to industrial scale production.

Description

Technical Field

[0001] This invention belongs to the field of organic membrane materials and relates to a method for preparing organic thin films, specifically a method for directly and rapidly preparing ultrathin films on a rough macroporous substrate. Background Technology

[0002] High-performance separation membranes can achieve rapid and highly selective separation of target substances and are a key focus in the field of membrane research, as mentioned in reference [1]. Among them, the preparation technology of ultrathin separation membranes belongs to the intersection of cutting-edge nanomaterials and advanced processing technology, and faces the dual challenges of material design and structural optimization.

[0003] Separation processes in industrial production account for a significant portion of global energy consumption. Developing low-energy, high-efficiency separation technologies can effectively reduce production costs and alleviate the energy crisis. Compared to traditional separation technologies (such as cryogenic separation, amine absorption, and low-temperature distillation), membrane separation technology offers advantages such as compact equipment, simple operation, no phase change, and environmental friendliness. Therefore, it is increasingly used in separation processes related to water, environment, energy, healthcare, and chemical production. In membrane separation, higher permeability of the target substance per unit time results in lower energy consumption per unit time. Membrane permeability and membrane thickness are generally inversely correlated; thin films have shorter transport paths and lower transport resistance, thus enabling faster material transport. Reducing membrane thickness is a highly effective method to improve membrane permeability; therefore, the preparation of ultrathin films has become a research hotspot in the field of membrane separation.

[0004] With the advent of the reverse phase method for preparing asymmetric membranes in the 1960s and the interfacial polymerization method for preparing composite thin films in the 1970s (see reference [2]), the thickness of thin films has been reduced to the micrometer and submicrometer scale, and the membrane flux has been increased by several orders of magnitude. The huge commercial value of separation membranes has driven the rapid development of related technologies, and the preparation of ultrathin films based on nanomaterials and nanotechnology has become a revolutionary technology in the field of membrane separation in the 21st century. The preparation of 15nm silica gel film in 2007 marked the beginning of this new era (see reference [3]). Subsequently, a series of experiments realized the use of graphene (thickness 0.34nm) (see reference [4]), graphene oxide (GO, as low as 1.8nm), zeolite imidazole framework (ZIF, <10nm) (see reference [5]), and polyamide (PA) (<10nm) and other nanoporous atomic films (NATMs, ≈0.335nm) for separation. The preparation technology of ultrathin films can be roughly divided into two categories: chemical assembly and physical assembly. Chemical assembly, such as in-situ growth (see reference [6]) and interfacial synthesis (see reference [7]), refers to the process of forming a thin film directly on the surface of a porous substrate or at the interface of two immiscible solutions through relatively strong non-covalent bonds such as covalent bonds (hundreds of kJ / mol) or metal coordination bonds (≈300 kJ / mol). The thickness of the film grown in situ is usually on the micrometer scale, while the film synthesized through the interface needs to be further transferred to the porous substrate for use. Physical assembly means that the separation membrane formed on a smooth substrate or in solution through relatively weak intramolecular non-covalent bonds, such as van der Waals forces and π-π stacking (tens of kJ / mol), is transferred, coated or stacked onto a porous substrate. Although there are multiple pathways to prepare ultrathin films, there are still many challenges in the rapid, large-area, controllable preparation of ultrathin films.

[0005] The fabrication of ultrathin films with a thickness of less than 100 nanometers is mainly achieved through interfacial synthesis in chemical assembly or in-situ growth and transfer in physical assembly. To ensure the uniformity of the fabricated film, both methods require a smooth liquid / solid substrate as a support, allowing the film to spread uniformly on the substrate. Therefore, fabricating nanometer-thick films requires a smooth substrate with a surface roughness of at least the nanometer level. In the application stage, smooth solid substrates cannot meet the separation requirements, necessitating the transfer of the film to a porous substrate. The smoother the surface and the denser the pores of the porous substrate, the higher the integrity of the film transfer, and the greater the impact of the substrate on the material separation efficiency. Therefore, traditional separation film fabrication requires at least two steps: film preparation on a smooth substrate and transfer of the film from the smooth substrate to the porous substrate. The different requirements for substrate smoothness and porosity in film preparation and separation applications pose significant challenges to film research. The cost and time issues associated with substrate replacement and transfer processes also severely hinder the industrialization of ultrathin film fabrication.

[0006] Literature description:

[0007] [1]S.Zhang,L.Shen,H.Deng,Q.Liu,X.You,J.Yuan,Z.Jiang and S.Zhang,AdvMater 2022,34,e2

[0008] [2]a)JECadotte,RJPetersen,RELarson and EEErickson,Desalination 1980,32,25-31;b)L.Rozelle,J.Cadotte,B.Nelson and C.Kopp,Polymeric materials for unusual service conditions 1973,223-239.

[0009] [3]CCStriemer,TRGaborski,JLMcGrath and PMFauchet,Nature 2007,445,749-753.

[0010] [4]JSBunch,SSVerbridge,JSAlden,Avan der Zande,JMParpia,HGCraighead and PLMcEuen,Nanotechnology 2008,8,2458-2462.

[0011] [5]K.Varoon,XYZhang,B.Elyassi,DDBrewer,M.Gettel,S.Kumar,JALee,S.Maheshwari,A.Mittal,CYSung,M.Cococcioni,LFFrancis,AVMcCormick,KAMkhoyan and M.Tsapatsis,Science 2011,334,72-75.

[0012] [6]I.-C.Kim,J.Jegal and K.-H.Lee,Journal of Polymer Science Part B:Polymer Physics 2002,40,2151-2163.

[0013] [7]Y.Zhong,B.Cheng,C.Park,A.Ray,S.Brown,F.Mujid,JULee,H.Zhou,J.Suh,KHLee,AJMannix,K.Kang,SJSibener,DAMuller and J.Park,Science 2019,366,1379-1384.

[0014] [8] Guo Haiyan, Peng Donglai, Feng Xiaoquan, Jin Yehao, Tian Zhihong, Wang Jing and Zhang Yatao, Chemical Industry Progress 2021, 40, 5577-5589. Summary of the Invention

[0015] To address the shortcomings of existing technologies, the present invention aims to provide a method for directly and rapidly preparing ultrathin films on rough, macroporous substrates, which shortens the ultrathin film preparation process, improves film quality, and reduces costs.

[0016] A method for directly and rapidly preparing ultrathin films on rough, macroporous substrates includes the following steps:

[0017] 1) Prepare the thin film precursor solution;

[0018] 2) Smoothing liquid film treatment of rough, large-pore substrates;

[0019] After immersing the rough, macroporous substrate in the solution for a period of time, remove it while ensuring that the smooth liquid film on the substrate surface is not damaged, and remove excess liquid droplets from the substrate surface for later use.

[0020] 3) Preparation of ultrathin films;

[0021] Ultrafilms are prepared on rough macroporous substrates with smooth liquid films coated on the surface treated in step 2) using the thin film precursor solution prepared in step 1).

[0022] Furthermore, in step 3), ultrathin films are prepared by spin coating, spray coating, or casting.

[0023] Furthermore, in step 3), an ultrathin film is prepared using a spin coating process. The rough, macroporous substrate is fixed on a spin coater, and an appropriate amount of spin coating solution is added at a rotation speed of 3000 rpm to prepare the ultrathin film.

[0024] Furthermore, in step 2), an ultrathin film is prepared using a spraying process with a spraying temperature of 25°C, a nozzle diameter of 1 mm, a spraying distance of 300 mm, an atomization pressure of 0.1 MPa, and a spraying time of 1 second.

[0025] Furthermore, in step 2), the rough macroporous substrate is divided into ceramic film, polymer film and fiber film.

[0026] Furthermore, the ceramic film includes, but is not limited to, anodized aluminum film; polymer film includes, but is not limited to, polyvinylidene fluoride film; and fiber film includes, but is not limited to, qualitative filter paper.

[0027] Furthermore, the solution in step 2) is water, methanol, n-hexane, pentane, or diethyl ether.

[0028] Furthermore, the film precursor solution in step 1) is prepared by a film-forming substance and a solvent; the film-forming substance is a self-porous polymer, rubber, silicone rubber, polyolefin polymer, polyamide polymer, polysulfone polymer or aromatic heterocyclic polymer.

[0029] Furthermore, the solvent is chloroform, acetonitrile, benzene, dichloroethane, toluene, or tetrahydrofuran; the concentration of the prepared film precursor solution is 0.1wt%-5wt%.

[0030] This invention has the following features and advantages:

[0031] This invention involves immersing a rough, macroporous substrate in a solution to form a smooth liquid film on its surface. The two-phase interface formed on the surface of the rough, macroporous substrate coated with the smooth liquid film is used as the smooth substrate to prepare an ultrathin film. After the liquid film dries, the ultrathin film adheres to the rough, macroporous substrate and can be directly used for material separation, achieving direct preparation of ultrathin films. This shortens the preparation process and, compared to conventional membrane fabrication processes, eliminates the need for membrane transfer, avoiding the problem of membrane breakage. The prepared ultrathin film can be directly used in subsequent separation processes, achieving integration of preparation and application.

[0032] In addition, the thickness of the film can be directly controlled by changing the film preparation conditions, without being subject to the requirements and limitations of the film transfer process on the film thickness, thus shortening the cycle of the entire preparation process and reducing the preparation cost and technical threshold.

[0033] Compared to a smooth solid substrate, the roughness of the two-phase insolubilized interface is reduced to the angstrom level, which not only improves the uniformity of the film, but also reduces the use of additional substrates and etching processes, thus significantly reducing costs.

[0034] The method of the present invention can be used to rapidly prepare ultrathin films with adjustable thickness directly on the surface of a rough macroporous substrate treated with liquid film by means of spin coating, spraying, casting, etc., without being limited by film formation methods, which is more conducive to industrial-scale production. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope image of the anodic aluminum oxide surface used in Example 1, magnified 50,000 times.

[0036] Figure 2This is a scanning electron microscope image, magnified 10,000 times, of the microporous polymer ultrathin film in Example 1 on the surface of anodized aluminum on a rough macroporous substrate;

[0037] Figure 3 This is a scanning electron microscope image, magnified 100,000 times, of the cross-section of the microporous polymer ultrathin film in Example 1 on the surface of anodized aluminum on a rough macroporous substrate;

[0038] Figure 4 This is an atomic force microscope image of the self-porous polymer ultrafilm in Example 1;

[0039] Figure 5 This is an atomic force microscope image of the self-porous polymer ultrafilm in Example 2.

[0040] Figure 6 This is a scanning electron microscope image, magnified 90,000 times, of the microporous polymer ultrathin film on the surface of a rough macroporous anodic aluminum oxide substrate in Example 3.

[0041] Figure 7 This is a scanning electron microscope image, magnified 1000 times, of the microporous polymer ultrafilm on the surface of qualitative filter paper in Example 4. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0043] The film-forming substance in this invention can be selected from the following types:

[0044] Self-contained microporous polymers (PIM), see reference [8];

[0045] Rubber and silicone rubber (PTMSP, PDMS, etc.);

[0046] Polyolefin polymers (PE, etc.);

[0047] Polyamide polymers (PI, NY-66, etc.);

[0048] Polysulfone polymers (PES, etc.);

[0049] Aromatic heterocyclic polymers (PBI, etc.)

[0050] Terminology Explanation:

[0051] PIM (polymer of intrinsic microporosity): Polymers with inherent micropores. Due to the presence of various rigid and tortuous structures within the molecule, the polymer cannot effectively stack when forming close packing, thus generating a large number of micropores (most of which have a pore size of less than 2 nm).

[0052] PTMSP (Poly(1-trimethylsilyl-1-propyne): Poly(1-trimethylsilyl-1-propyne)

[0053] PDMS (Polydimethylsiloxane): Polydimethylsiloxane

[0054] PE (Polyethylene): Polyethylene

[0055] PI (Polyimide): Polyimide

[0056] NY-66: Nylon 66

[0057] PES (Polyethersulfone): Polyethersulfone

[0058] PBI (polybenzimidazoles): Polybenzimidazole

[0059] Example 1

[0060] A method for rapidly and controllably fabricating microporous polymer ultrathin films on rough macroporous ceramic substrates of anodic alumina, comprising the following steps:

[0061] Dissolve 0.05g of the self-porous polymer in 10g of chloroform solution, sonicate for 10min, and filter to obtain a uniform and transparent solution for later use.

[0062] Immerse the anodized aluminum substrate in water for 10 minutes. Fix the immersed anodized aluminum on a spin coater, set the program to 1500 rpm and hold for 10 seconds to remove residual solvent from the surface of the anodized aluminum.

[0063] An appropriate amount of spin-coating solution was dropped onto the surface of anodized aluminum, and the program was set to 4000 rpm and held for 50 s to obtain an ultrathin film on the surface of anodized aluminum. The film thickness was measured to be 30 nm.

[0064] Figure 1 This is a scanning electron microscope image of the surface of the anodic aluminum oxide used in this embodiment, magnified 50,000 times. The scale bar is 1 μm. It can be seen from the image that the anodic aluminum oxide substrate is covered with large pores with a diameter of about 200 nm and has protrusions on the surface, which is relatively rough compared with smooth substrates such as silicon wafers.

[0065] Figure 2 This is a scanning electron microscope image magnified 10,000 times on the surface of the microporous polymer ultrathin film on the rough macroporous anodic aluminum substrate in this embodiment. The scale bar is 5 μm. As can be seen from the image, a microporous polymer film is covered on the surface of the anodic aluminum substrate. The film is uniform and undamaged, and the macropores on the anodic aluminum can still be seen through the film.

[0066] Figure 3 This is a scanning electron microscope image magnified 100,000 times on the cross-section of the microporous polymer ultrathin film on the rough macroporous substrate anodic aluminum oxide surface in this embodiment. The scale bar is 500 nm. As can be seen from the image, the microporous polymer film is flatly covered on the anodic aluminum oxide substrate and the thickness is less than 50 nm, which proves that the ultrathin film was successfully prepared on the rough macroporous substrate.

[0067] Figure 4 This is an atomic force microscope (AFM) image of the microporous polymer ultrathin film in this embodiment, with a scale bar of 20 μm. The film thickness was measured to be 30 nm. The actual thickness of the film was measured using an AFM, which is more reliable than the thickness estimate obtained by an electron microscope, further demonstrating the successful fabrication of the ultrathin film on a rough, macroporous substrate.

[0068] Example 2

[0069] The amount of the self-porous polymer in step 1) of Example 1 was changed to 0.02 g, while other experimental conditions remained the same as in Example 1. The thickness of the ultrafilm was measured to be 13 nm.

[0070] Figure 5 This is an atomic force microscope image of the microporous polymer ultrafilm in this embodiment, with a scale bar of 36 μm. The film thickness is approximately 13 nm, demonstrating that the film thickness can be controllably adjusted by changing the solution concentration.

[0071] Example 3

[0072] Replace the water in step 2) of Example 1 with methanol, and keep the other experimental conditions the same as in Example 1.

[0073] Figure 6 This is a scanning electron microscope image (SEM) image of a microporous polymer ultrathin film on a rough macroporous substrate of anodic aluminum oxide, magnified 90,000 times in this embodiment. The scale bar is 500 nm. This proves that ultrathin films can still be prepared on rough macroporous substrates by changing different solutions, and the thickness of ultrathin films prepared by using different solutions is different.

[0074] Example 4

[0075] The substrate in step 2) of Example 1 was changed to fiber-based qualitative filter paper, and other experimental conditions were the same as in Example 1.

[0076] Figure 7 This is a scanning electron microscope image (SEM) image of the self-porous polymer ultrathin film on the surface of qualitative filter paper in this embodiment, magnified 1000 times. The scale bar is 50 μm. This proves that the method can still achieve the preparation of ultrathin films using substrates with different roughness and pore size, and that the preparation of ultrathin films using this method has universality.

[0077] The rough, macroporous substrate can be made of ceramic film, polymer film, or fiber film, such as polyvinylidene fluoride film or glass fiber. The solution in step 2) can also be replaced with n-hexane, pentane, or diethyl ether.

Claims

1. A method for directly and rapidly preparing ultrathin films on rough, macroporous substrates, characterized in that... Includes the following steps: 1) Prepare the thin film precursor solution; The self-porous polymer was dissolved in chloroform solution, and then ultrasonically dispersed and filtered to obtain a uniform and transparent solution for later use. 2) Smoothing liquid film treatment of rough, large-pore substrates; After soaking the rough macroporous substrate in water for a period of time, remove it and fix the soaked rough macroporous substrate on a spin coater. Set the program to 1500 rpm and hold for 10 seconds to ensure that the smooth liquid film on the substrate surface is not damaged while removing excess liquid droplets from the substrate surface. Set aside for later use. The rough macroporous substrate is a ceramic film or a fiber film. The ceramic film includes, but is not limited to, anodized aluminum film, and the fiber film includes, but is not limited to, qualitative filter paper. 3) Preparation of ultrathin films; Ultrafilms are prepared on rough, macroporous substrates with smooth liquid films coated on the surface treated in step 2) using spin coating, spray coating, or casting methods, based on the thin film precursor solution prepared in step 1).

2. The method for directly and rapidly preparing ultrathin films on a rough, macroporous substrate as described in claim 1, characterized in that: In step 3), an ultrathin film is prepared using a spin coating process. The rough, macroporous substrate is fixed on a spin coater, and an appropriate amount of spin coating solution is added to prepare the ultrathin film at a speed of 3000 rpm.

3. The method for directly and rapidly preparing ultrathin films on a rough, macroporous substrate as described in claim 1, characterized in that: In step 3), an ultrathin film is prepared by spraying. The spraying temperature is 25°C, the nozzle diameter is 1 mm, the spraying distance is 300 mm, the atomization pressure is 0.1 MPa, and the spraying time is 1 second.

4. The method for directly and rapidly preparing ultrathin films on a rough, macroporous substrate as described in claim 1, characterized in that: The concentration of the prepared film precursor solution is 0.1wt%-5wt%.

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