Polyimide matrix co-doped nanocrystal thin film and method of making same

Abstract

The present application relates to the field of high-temperature-resistant film, co-doped nanocrystals and surface matrix material, and particularly relates to a polyimide matrix co-doped nanocrystal film and a preparation method thereof. A co-doped nanocrystal precursor modified reverse-phase fine emulsion is prepared first, and then a dispersion containing the co-doped nanocrystal precursor and polyamic acid is prepared; then, the dispersion containing the co-doped nanocrystal precursor and polyamic acid is spin-coated on a clean quartz glass sheet, and is placed in a replaceable air oven for drying to obtain a polymer matrix co-doped film; finally, after sintering and cooling, a polyimide matrix co-doped film is obtained. The thickness of the polyimide matrix co-doped film can be controlled within 80-500 nanometers, and the base film is flat; the co-doped nanocrystals are uniformly distributed in the form of nanodots on the matrix film; the film can be used at high temperature, the base film does not deform, and the co-doped nanodots have good adhesion.

Description

Technical Field

[0001] This invention relates to the fields of high-temperature resistant thin films, co-doped nanocrystals, and surface substrate materials, and particularly to a polyimide matrix co-doped nanocrystal thin film and its preparation method. Background Technology

[0002] Polyimide refers to a class of polymers containing imide rings in their main chain. It has a high temperature resistance exceeding 400℃ and a long-term operating temperature range of -200 to 300℃. As a special engineering material, polyimide has been widely used in aerospace, microelectronics, nanotechnology, liquid crystals, separation membranes, and lasers. Polyimide films, including pyromellitic dianhydride films and biphenyl dianhydride films, are a new type of high-temperature resistant organic polymer film. They are produced by polycondensation and casting of pyromellitic dianhydride and diaminodiphenyl ether in the extremely strong solvent dimethylacetamide, followed by imidization. There are two main synthesis processes: one is thermal imidization, suitable for producing polyimide films below the electronic grade; the other is chemical imidization, suitable for producing polyimide films above the electronic grade. Compared to thermal imidization, chemical imidization produces polyimide films with superior performance and stronger market competitiveness. Dimethylformamide, a crucial solvent in the chemical imidization process for high-end polyimide films, has stricter requirements, particularly regarding moisture content, which must be controlled below 100 ppm. Currently, 90% of domestic manufacturers use thermal imidization, while internationally, chemical imidization has largely replaced thermal imidization.

[0003] Co-doping is a commonly used method in materials modification, involving the simultaneous introduction of two or more different types of impurity atoms into a material to alter its electrical properties. Co-doping can modulate the band structure, light absorption properties, and distribution of photogenerated carriers. This technique allows for precise control of material properties by adjusting the proportions and types of different impurity atoms. Co-doping methods include sol-gel methods, co-precipitation methods, and ion exchange methods. Appropriate doping ratios can improve light absorption performance and increase the residence time of photogenerated carriers.

[0004] Fine emulsions are transitional emulsion dispersions with droplet sizes between those of general emulsions and microemulsions. Fine emulsions are thermodynamically metastable systems that cannot form spontaneously; mechanical work is required to overcome the cohesive energy of the oil phase and the surface energy for droplet formation, thus dispersing them in water. Due to the low efficiency of mechanical dispersion, high-intensity homogenizers must be used when preparing submicron fine emulsions. Commonly used homogenizers include rotary shear homogenizers, ultrasonic homogenizers, and high-pressure homogenizers. Reverse fine emulsions are dispersions in which the oil phase is the continuous phase and the aqueous phase is the dispersed phase. Summary of the Invention

[0005] The purpose of this invention is to prepare polyimide matrix co-doped films using modified reverse microemulsions, which is carried out according to the following steps:

[0006] (1) Preparation of reverse microemulsion modified by co-doped nanocrystalline precursor

[0007] At room temperature, a measured amount of oil-soluble matrix metal salt is dissolved in a measured amount of mixed solvent to form an oil phase; a measured amount of alkaline aqueous solution capable of forming matrix nanocrystals is weighed as the aqueous phase. After mixing the oil and water phases, the mixture is rapidly transferred to an ultrasonic pulverizer and pulverized at a certain temperature for a set time. Aqueous solutions of the doped metal salt and co-doped metal salt are added at once, and ultrasonic pulverization is maintained for a certain time. Subsequently, the temperature is increased and the pressure is reduced for a fixed time to complete the separation of low-boiling-point liquids. The system is then cooled to room temperature and vented, completing the preparation of a modified reverse-phase fine emulsion containing a co-doped nanocrystal precursor.

[0008] In step (1), the oil-soluble matrix metal salt is a metal salt of acetic acid, stearic acid, naphthenic acid, or isooctanoic acid, such as cobalt acetate, zinc acetate, calcium stearate, zinc stearate, copper naphthenate, manganese naphthenate, cadmium isooctanoate, or molybdenum isooctanoate; the mixed solvent is an oily solvent formed by the first solvent (N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone, etc.) and the second solvent (cyclohexane, n-heptane, or isoheptane) in a mass ratio of 8:1; the water-soluble alkaline solution is an aqueous solution with pH>7, such as ammonia, sodium hydroxide, potassium hydroxide, potassium sulfide, or sodium sulfide; the doped metal salt and co-doped metal salt are functional water-soluble nitric acid, chloride, or sulfate metal salts, such as lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, yttrium nitrate, europium nitrate, or samarium nitrate, etc.

[0009] In step (1), the mass ratio of the oil-soluble matrix metal salt, the mixed solvent (first solvent and second solvent), the 0.1% mass concentration alkaline aqueous solution, the 0.01% mass concentration doped metal salt aqueous solution and the 0.01% mass concentration co-doped metal salt aqueous solution is 0.1-0.5:100:0.1:0.01:0.005.

[0010] In step (1), the aqueous phase and oil phase are mixed and then ultrasonically pulverized at room temperature with a power of 200W for 10 minutes. After adding the aqueous solution of the doped metal salt, the ultrasonic treatment is continued for another 10 minutes. The temperature is then raised to 50°C and the system is depressurized to 1000Pa. The low-boiling-point liquid begins to separate and this condition is maintained for 60 minutes.

[0011] (2) Preparation of dispersions containing co-doped nanocrystalline precursors and polyamic acid

[0012] At room temperature, the modified reverse fine emulsion containing co-doped nanocrystal precursor from step (1) was added to a commercially available polyamic acid solution. After being mixed evenly, the mixture was subjected to high-pressure nano-sizing in a high-pressure homogenizer to prepare a dispersion containing co-doped nanocrystal precursor and polyamic acid.

[0013] In step (2), the commercially available polyamic acid solution is a 10-20% mass concentration poly(pyromellitic dianhydride-co-4,4'-diaminodiphenyl ether)amic acid, and the ratio of the co-doped nanocrystalline precursor colloid to the commercially available polyamic acid solution in step (1) is 10-20:100. The high-pressure homogenizer uses a high pressure of 10-20 MPa and a temperature control of 20-50℃.

[0014] (3) Preparation of polyimide matrix co-doped thin films

[0015] At room temperature, the dispersion prepared in step (2) is spin-coated onto a clean quartz glass slide and dried in a ventilated oven at a certain temperature for a fixed time. The spin-coating and drying processes can be repeated to obtain polymer matrix co-doped films of different thicknesses. The films are then transferred to a sintering furnace and sintered at a fixed temperature for a certain time. After sintering and cooling, the polyimide matrix co-doped films can be peeled off from the quartz glass.

[0016] In step (3), the ventilated oven is ventilated with nitrogen, and the oven drying temperature is 200℃ for 90-120 minutes. After drying, the spin coating can be repeated and the oven dried again to obtain polyimide matrix co-doped films of different thicknesses, repeated 1-5 times. The sintering furnace sintering temperature is 400℃ for 240-300 minutes.

[0017] This invention prepares polyimide-based co-doped thin films by modifying a reverse-phase fine emulsion using a high-pressure homogenizer. The films prepared by this method have potential applications in optoelectronics and separation membranes. This invention has the following advantages:

[0018] 1. Co-doped nanocrystals with a size of 3-10 nanometers can be obtained by dispersing colloids using a high-pressure homogenizer and by solvent heat treatment.

[0019] 2. The thickness of the polyimide matrix co-doped film can be controlled between 80-500 nanometers, and the base film is flat; moreover, the co-doped nanocrystals are uniformly distributed as nanodots on the matrix film;

[0020] 3. Co-doped films on polyimide matrix can be used at high temperatures (below 300℃) without deformation of the base film and with good adhesion of co-doped nanodots. Attached Figure Description

[0021] Figure 1 Transmission electron scanning microscope image (-10 nm) of the polyimide matrix co-doped thin film prepared in Example 1 of the present invention. Detailed Implementation

[0022] The invention will now be described in further detail with reference to examples.

[0023] Example 1

[0024] (1) Preparation of reverse microemulsion modified by co-doped nanocrystalline precursor

[0025] At room temperature, 0.1 g of cobalt acetate was dissolved in a mixed solvent of 80 g of N,N-dimethylacetamide and 20 g of cyclohexane to form an oil phase. 0.1 g of a 0.1% ammonia solution was weighed as the aqueous phase. The oil and water phases were mixed and quickly transferred to an ultrasonic pulverizer. The mixture was ultrasonically pulverized at 200 W at room temperature for 10 minutes. Then, 0.01 g of a 0.01% strontium nitrate aqueous solution and 0.005 g of a 0.01% yttrium nitrate aqueous solution were added, and ultrasonication continued for another 10 minutes. The temperature was then raised to 50 °C and the system pressure reduced to 1000 Pa, initiating the separation of low-boiling-point liquids. This condition was maintained for 60 minutes. The system was then cooled to room temperature and vented, completing the preparation of the modified reverse-phase fine emulsion containing the co-doped nanocrystalline precursor.

[0026] (2) Preparation of dispersions containing co-doped nanocrystalline precursors and polyamic acid

[0027] At room temperature, 10 g of the modified reverse-phase fine emulsion containing the co-doped nanocrystalline precursor from step (1) was added to 100 g of a commercially available 10% (w / w) poly(pyromellitic dianhydride-co-4,4'-diaminodiphenyl ether) ammonium acid solution. After mixing thoroughly, the mixture was subjected to high-pressure nano-sizing in a high-pressure homogenizer. The high-pressure homogenizer was used at 10 MPa and the temperature was controlled at 50 °C. A dispersion containing the co-doped nanocrystalline precursor and polyamic acid was prepared, yielding co-doped nanocrystals with a size of 3 nm.

[0028] (3) Preparation of polyimide matrix co-doped thin films

[0029] At room temperature, the dispersion prepared in step (2) was spin-coated onto a clean quartz glass slide and dried in a nitrogen-filled oven at 200°C for 90 minutes. It was then transferred to a sintering furnace and sintered at 400°C for 240 minutes. A polyimide matrix co-doped film could be peeled off from the quartz glass. The polyimide matrix co-doped film was 80 nm thick, with a smooth substrate; the co-doped nanocrystals were uniformly distributed as nanodots on the substrate film; the polyimide matrix co-doped film could be used below 300°C without deformation of the substrate film, and the co-doped nanodots exhibited good adhesion.

[0030] Example 2

[0031] (1) Preparation of reverse microemulsion modified by co-doped nanocrystalline precursor

[0032] At room temperature, 0.5 g of zinc stearate was dissolved in a mixed solvent of 80 g of N-methylpyrrolidone and 20 g of isoheptane to form an oil phase; 0.1 g of 0.1% potassium hydroxide solution was weighed as the aqueous phase. After mixing the oil and water phases, the mixture was quickly transferred to an ultrasonic pulverizer and ultrasonically pulverized at 200 W at room temperature for 10 minutes. Then, 0.01 g of 0.01% samarium nitrate aqueous solution and 0.005 g of 0.01% europium nitrate aqueous solution were added, and ultrasonication was continued for another 10 minutes. The temperature was then raised to 50 °C and the system was depressurized to 1000 Pa, at which point the low-boiling-point liquid began to separate, and this condition was maintained for 60 minutes. The system was then cooled to room temperature and vented, completing the preparation of the modified reverse fine emulsion containing the co-doped nanocrystalline precursor.

[0033] (2) Preparation of co-doped nanocrystalline precursors and polyamic acid dispersions

[0034] At room temperature, 20 g of the modified reverse-phase fine emulsion containing the co-doped nanocrystalline precursor from step (1) was added to 100 g of a commercially available 20% (w / w) poly(pyromellitic dianhydride-co-4,4'-diaminodiphenyl ether) ammonium acid solution. After mixing thoroughly, the mixture was subjected to high-pressure nano-sizing in a high-pressure homogenizer. The high-pressure homogenizer was used at 20 MPa and the temperature was controlled at 20 °C. A dispersion containing the co-doped nanocrystalline precursor and polyamic acid was prepared, yielding co-doped nanocrystals with a size of 10 nm.

[0035] (3) Preparation of polyimide matrix co-doped thin films

[0036] At room temperature, the dispersion prepared in step (2) was spin-coated onto a clean quartz glass slide and dried in a nitrogen-filled oven at 200°C for 120 minutes. After drying, the spin-coating and oven drying were repeated twice to obtain a polyisoimide matrix co-doped film. The film was then transferred to a sintering furnace and sintered at 400°C for 270 minutes. The polyimide matrix co-doped film could be peeled off from the quartz glass. The thickness of the polyimide matrix co-doped film can be controlled to 200 nm, the base film is flat, and the co-doped nanocrystals are uniformly distributed as nanodots on the matrix film. The polyimide matrix co-doped film can be used below 300°C without deformation of the base film, and the co-doped nanodots have good adhesion.

[0037] Example 3

[0038] (1) Preparation of reverse microemulsion modified by co-doped nanocrystalline precursor

[0039] At room temperature, 0.3 g of cadmium isooctanoate was dissolved in a mixed solvent of 80 g of N-methylpyrrolidone and 20 g of isoheptane to form an oil phase; 0.1 g of 0.1% sodium sulfide solution was weighed as the aqueous phase. After mixing the oil and water phases, the mixture was quickly transferred to an ultrasonic pulverizer and ultrasonically pulverized at 200 W at room temperature for 10 minutes. Then, 0.01 g of 0.01% lanthanum nitrate aqueous solution and 0.005 g of praseodymium nitrate aqueous solution were added, and ultrasonication was continued for another 10 minutes. The temperature was then raised to 50 °C and the system pressure was reduced to 1000 Pa, at which point the low-boiling-point liquid began to separate, and this condition was maintained for 60 minutes. The system was then cooled to room temperature and vented, completing the preparation of the modified reverse fine emulsion containing the co-doped nanocrystalline precursor.

[0040] (2) Preparation of dispersions containing co-doped nanocrystalline precursors and polyamic acid

[0041] At room temperature, 15 g of the modified reverse fine emulsion containing the co-doped nanocrystalline precursor from step (1) was added to 100 g of a commercially available 15% (w / w) poly(pyromellitic dianhydride-co-4,4'-diaminodiphenyl ether) ammonium acid solution. After mixing thoroughly, the mixture was subjected to high-pressure nano-sizing in a high-pressure homogenizer. The high-pressure homogenizer was operated at 15 MPa and the temperature was controlled at 30 °C. A dispersion containing the co-doped nanocrystalline precursor and polyamic acid was prepared, yielding co-doped nanocrystals with a size of 5 nm.

[0042] (3) Preparation of polyimide matrix co-doped thin films

[0043] At room temperature, the dispersion prepared in step (2) was spin-coated onto a clean quartz glass slide and dried in a nitrogen-filled oven at 200°C for 100 minutes. After drying, the spin-coating and oven drying were repeated to obtain a polyisoimide matrix co-doped film, repeated 5 times; then transferred to a sintering furnace and sintered at 400°C for 300 minutes. The polyimide matrix co-doped film can be peeled off from the quartz glass. The polyimide matrix co-doped film is 500 nm thick, with a smooth base film; and the co-doped nanocrystals are uniformly distributed as nanodots on the matrix film; the polyimide matrix co-doped film can be used below 300°C without deformation of the base film, and the co-doped nanodots have good adhesion.

[0044] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and any modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A polyimide matrix co-doped thin film, characterized in that, The polyimide matrix co-doped film is obtained by spin-coating a dispersion containing co-doped nanocrystal precursor and polyamic acid onto a clean quartz glass slide, drying it in an air-ventilated oven, and then transferring it to a sintering furnace for sintering and cooling. The method for preparing the dispersion containing co-doped nanocrystalline precursor and polyamic acid is as follows: at room temperature, the modified reverse phase fine emulsion containing co-doped nanocrystalline precursor is added to the polyamic acid solution, mixed evenly, and then subjected to high pressure nano-sizing in a high-pressure homogenizer to prepare the dispersion containing co-doped nanocrystalline precursor and polyamic acid. The method for preparing the modified reverse fine emulsion of the co-doped nanocrystalline precursor is as follows: at room temperature, an oil-soluble matrix metal salt is dissolved in a mixed solvent to form an oil phase; an alkaline aqueous solution that can form matrix nanocrystals is weighed as the aqueous phase; after the oil and water phases are mixed, they are quickly transferred to an ultrasonic pulverizer and pulverized according to the set method; then, an aqueous solution of the doped metal salt and the co-doped metal salt is added at one time and ultrasonic pulverization is maintained; after heating, the pressure is reduced to complete the separation of low-boiling-point liquids; the system is cooled to room temperature and vented to obtain the modified reverse fine emulsion containing the co-doped nanocrystalline precursor. The oil-soluble matrix metal salt is: cobalt acetate, zinc acetate, calcium stearate, zinc stearate, copper naphthenate, manganese naphthenate, cadmium isooctanoate, or molybdenum isooctanoate; the doped metal salt and co-doped metal salt are lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, yttrium nitrate, and europium nitrate.

2. The polyimide matrix co-doped thin film as described in claim 1, characterized in that, The polyamic acid solution is a 10-20% mass concentration of poly(pyromellitic dianhydride-co-4,4'-diaminodiphenyl ether) amic acid. The mass ratio of the modified reverse fine emulsion containing co-doped nanocrystalline precursor to the polyamic acid solution is 10-20:

100. The high-pressure homogenizer uses a high pressure of 10-20 MPa and the temperature is controlled at 20-50℃.

3. The polyimide matrix co-doped thin film as described in claim 1, characterized in that, The mixed solvent is an oily solvent formed by the first solvent and the second solvent in a mass ratio of 8:2; the alkaline aqueous solution is an aqueous solution of ammonia, sodium hydroxide, potassium hydroxide, potassium sulfide, or sodium sulfide with a pH > 7.

4. The polyimide matrix co-doped thin film as described in claim 3, characterized in that, The first solvent is N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone; the second solvent is cyclohexane, n-heptane, or isoheptane.

5. The polyimide matrix co-doped thin film as described in claim 1, characterized in that, The mass ratio of the oil-soluble matrix metal salt, mixed solvent, alkaline aqueous solution, doped metal salt aqueous solution, and co-doped metal salt aqueous solution is 0.1-0.5:100:0.1:0.01:0.005; the mass concentration of the alkaline aqueous solution is 0.1%, and the mass concentrations of the doped metal salt and co-doped metal salt aqueous solutions are both 0.01%.

6. The polyimide matrix co-doped thin film according to claim 1, characterized in that, The aqueous and oil phases are mixed and then ultrasonically pulverized at room temperature with a power of 200W for 10 minutes. After adding an aqueous solution of doped metal salt, the ultrasonication continues for another 10 minutes. The temperature is raised to 50°C and the system is depressurized to 1000Pa to begin separating the low-boiling-point liquid, and this condition is maintained for 60 minutes.

7. The polyimide matrix co-doped thin film according to claim 1, characterized in that, The ventilated oven uses nitrogen for ventilation, and the drying temperature is 200℃ for 90-120 minutes.

8. The polyimide matrix co-doped thin film as described in claim 1, characterized in that, After drying, it can be spin-coated again and dried in an oven, repeated 1-5 times; the sintering temperature in the sintering furnace is 400℃, and the time is 240-300 minutes.

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