A photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film and a preparation method and application thereof

Abstract

The application provides a photochromic polyvinyl alcohol / branched polyethylene imine / phosphotungstic acid composite film and a preparation method and application thereof. The preparation method of the composite film comprises the following steps: mixing a polyvinyl alcohol (PVA) aqueous solution, a branched polyethylene imine (PEI) aqueous solution and a phosphotungstic acid (PTA) aqueous solution, stirring and reacting, pouring into a film, and obtaining the photochromic polyvinyl alcohol / branched polyethylene imine / phosphotungstic acid composite film. The application solves the problems of single color, slow discoloration response and poor reversibility of existing inorganic photochromic materials. The preparation method is simple; the obtained composite film can realize a stable reversible photochromic process, can realize multicolor discoloration, has a sensitive discoloration response, can automatically discolor at normal temperature and pressure, and has excellent photochromic performance, reversibility, mechanical performance, light transmittance and other performances.

Description

Technical Field

[0001] This invention relates to the field of photochromic thin film technology, specifically to a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, its preparation method, and its application. Background Technology

[0002] Photochromism refers to the chemical reaction that occurs when certain compounds undergo a specific wavelength and intensity of light, causing changes in their molecular structure and color. After further treatment, the compound's color returns to its original state. Photochromic materials have applications in many fields, such as smart windows, information storage, rewritable paper, molecular switches, multiphoton devices, optoelectronic devices, and supramolecular optoelectronics. Thin-film technology allows for the composite of different types and functions of materials in specific proportions, thus endowing composite film materials with new functionalities. Therefore, the preparation and performance study of photochromic composite thin films has always been a research topic of interest and continuous exploration. Developing composite films with excellent photochromic properties has become one of the research hotspots in photochromic materials in recent years.

[0003] There are existing reports on photochromic composite films. For example, Chinese patent document CN1800295A discloses a photochromic material that can be used for blue light storage. It is prepared by weight using the following method: mixing and stirring one or more 1-30% inorganic aqueous solution or sol with 1-20% organic molecular solution, and then casting the resulting sol onto a clean substrate using a casting or spin coating method. However, its reversibility is poor and it cannot undergo coloring-fading cycles, thus affecting its repeatability in response to ultraviolet light. Chinese patent document CN109505065A discloses a method for preparing a photochromic nanofiber film, which includes the following steps: (1) Preparation of electrospinning solution: dissolving 10-20 parts of polymer A in 80-90 parts of distilled water at 50-90°C; adding 2-10 parts of polymer B to the aqueous solution of polymer A at room temperature and stirring at 100-300 rpm for 2-10 hours. (2) Preparation of photochromic nanofiber membrane: 5-20 parts of photochromic nanospheres are added to 20-100 parts of the electrospinning solution in step (1) and then dispersed evenly; then the spinning solution containing the photochromic nanospheres is placed in an electrospinning device, the voltage is adjusted to 10-18kV, and the curing distance is 15-20cm to obtain the photochromic nanofiber membrane. However, this preparation method is relatively complex, the composite amount of photochromic nanospheres is large, and its components are mainly naphthospiroxazine, spiropyran and naphthopyran organic photochromic dyes, which are not environmentally friendly, and organic photochromism has the disadvantages of poor reversibility and high temperature resistance. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present application provides a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film and a preparation method and application thereof.The present application solves the problems of single color, slow discoloration response and poor reversibility of existing inorganic photochromic materials.The preparation method is simple, the obtained composite film can realize a stable reversible photochromic process, multi-color discoloration, sensitive discoloration response, and self-discoloration at normal temperature and pressure, and has excellent photochromic performance, reversibility, mechanical properties, light transmittance and other properties.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, which is composed of polyvinyl alcohol, branched polyethyleneimine and phosphotungstic acid.

[0007] The preparation method of the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film comprises the following steps:

[0008] The polyvinyl alcohol (PVA) aqueous solution, the branched polyethyleneimine (PEI) aqueous solution and the phosphotungstic acid (PTA) aqueous solution are mixed, stirred and reacted, and then poured into a film to obtain the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film.

[0009] According to the present application, the weight average molecular weight of the polyvinyl alcohol is 31000-98000, preferably 61000; and the weight average molecular weight of the branched polyethyleneimine is 800-30000, preferably 25000.

[0010] According to the present application, the mass concentration of the polyvinyl alcohol aqueous solution is 5-15%, preferably 10%; the mass concentration of the branched polyethyleneimine aqueous solution is 45-55%, preferably 50%; and the mass concentration of the phosphotungstic acid aqueous solution is 5-15%, preferably 10%.

[0011] According to the present application, the preparation method of the polyvinyl alcohol aqueous solution comprises the following steps: mixing the polyvinyl alcohol with water, and stirring at 60-80 DEG C for 2-3 h to obtain the polyvinyl alcohol aqueous solution.

[0012] According to the present application, the preparation method of the branched polyethyleneimine aqueous solution comprises the following steps: mixing the branched polyethyleneimine with water, and stirring at 60-80 DEG C for 1-2 h to obtain the branched polyethyleneimine aqueous solution.

[0013] According to the present application, the preparation method of the phosphotungstic acid aqueous solution comprises the following steps: mixing the phosphotungstic acid with water, and stirring at 60-80 DEG C for 1-2 h to obtain the phosphotungstic acid aqueous solution.

[0014] According to the application, the mass ratio of polyvinyl alcohol, branched polyethylene imine and phosphotungstic acid is 10:1-4:1.

[0015] According to the application, the polyoxometalate (POM) is also called polyacid, wherein the Keggin type phosphotungstic acid (PTA) has structural diversity, modifiability and tunability, has strong electron and proton transfer / storage capacity, excellent redox performance, high thermal stability, is easily soluble in water and can be directly prepared into an aqueous solution, can realize fast multi-electron transfer reaction under ultraviolet irradiation, has long-term photochemical stability, and has relatively sensitive coloring. However, the PTA cannot perform reversible photochromic reaction without a carrier. The polyvinyl alcohol (PVA) is a water-soluble polymer with excellent performance and wide application. Since the molecular chain contains a large number of side hydroxyl groups, the PVA has good water solubility, good film-forming property, excellent oil and solvent resistance, and the characteristics of natural degradation and environmental friendliness. The branched polyethylene imine (PEI) is a polycation with high ionic charge density and can be crosslinked with the PVA.

[0016] According to the application, the stirring reaction temperature is 70-90 DEG C, and the stirring reaction time is 4-5 h.

[0017] According to the application, the pouring and film-forming temperature is 40 DEG C-90 DEG C, and the pouring and film-forming time is 2-3 h. Preferably, the pouring and film-forming temperature is 50 DEG C-70 DEG C.

[0018] The application of the above photochromic polyvinyl alcohol / branched polyethylene imine / phosphotungstic acid composite film in photochromism.

[0019] According to the application, the composite film can change from transparent and colorless to blue, purple or purple gray under the irradiation of 365 nm ultraviolet light with an intensity of 40-60 mW / cm 2 ; and the composite film can realize discoloration, i.e. change into transparent and colorless, at room temperature or under heating. The sample film without PEI does not have obvious discoloration after ultraviolet irradiation and coloring, and has no reversibility, and the composite film with PEI can realize discoloration at room temperature.

[0020] According to the application, the composite film can be applied to the fields of flexible ultraviolet detection devices or information anti-counterfeiting.

[0021] The technical features and beneficial effects of the application are as follows:

[0022] 1. The application forms a PVA-PEI-PTA high molecular composite film by fully stirring and reacting the branched PEI aqueous solution with high ionic charge density, the PVA aqueous solution and the polyoxometalate PTA aqueous solution, heating and solidifying into a film. The preparation method is simple, green and environment-friendly, the raw materials are cheap and easy to obtain, and the cost is low.

[0023] 2、The present application realizes the preparation of multi-color composite film, i.e. deep blue, light purple, deep purple, purple gray and the like, by regulating the proportion of PEI in the composite film under ultraviolet irradiation. Under ultraviolet irradiation, the transition metal in PTA undergoes reduction reaction, its valence state changes, d-d transition and valence electron transfer between metals occur, thereby producing colored mixed valence substances, realizing the change of color of the composite film. PTA has good water solubility due to its negative surface charge, is easy to be compounded with positively charged materials; it can tolerate certain electron gain and loss, and keeps the molecular structure stable, which enables it to realize stable and reversible photochromic process. PVA in the present application mainly serves as a matrix, the main role of PEI in the composite film is to adjust the color change, PVA and PEI can provide electrons for PTA, electron transfer occurs under the irradiation of ultraviolet light, the valence state of tungsten changes, thereby producing color change. After the coloring process is completed, the film can fade at room temperature, the main component acting is oxygen in the air, which re-oxidizes the reduced low-valence tungsten ion into hexavalent tungsten ion, completing the fading process. The process can be repeated, and has good reversibility. The components of the composite film in the present application act together as a whole to realize the effect of the present application.

[0024] 3、The molecular weight of polyvinyl alcohol (PVA) needs to be appropriate, and low PVA molecular weight will affect the mechanical properties of the sample film. The branched polyethyleneimine is selected in the application, compared with the ordinary linear polyethyleneimine, the branched polyethyleneimine has a more complex molecular structure, has multiple amino groups, and the number and length of the branched chains are more diversified; the branched polyethyleneimine has very good solubility and heat resistance, and has good antioxidant and ultraviolet resistance; at the same time, the molecular weight of the branched polyethyleneimine is larger than that of the ordinary linear polyethyleneimine, and the viscosity is also higher, which can increase the mechanical strength of the composite film. Moreover, the ratio of PVA and PEI in the application also has a certain influence on the photochromic performance of the composite film. The amount of PTA needs to be appropriate, if the amount of PTA is too small, the color change effect will not be obvious, and if the amount is too high, the color will change to near black, and it is not easy to realize the color transition by adjusting the ratio of PEI. Without PVA and PEI, the PTA alone will not change color under ultraviolet light irradiation, because there is no electron-providing matrix to change the valence of tungsten. The PVA-PTA composite film without PEI will only turn blue after ultraviolet light irradiation, and the color transition from blue to purple cannot be realized by adjusting the ratio of the two. If PEI is replaced by polyimide, there is no group to provide protons, and the valence electron transfer cannot be completed, so the color change by adjusting the ratio cannot be realized. If PEI is replaced by polypropylene imine, although there are amino groups, they are connected with carbonyl groups, the reactivity is greatly reduced, and the color change effect is not obvious. In addition, the film forming temperature needs to be appropriate, and the film forming temperature is too low will affect the transparency of the film, and the color change effect is better under dry conditions. From the above, the raw material composition and the preparation method of the application are as a whole, and they work together to realize the excellent effect of the application.

[0025] 4、The composite film obtained by the method has excellent photochromic performance, reversibility, mechanical properties, light transmittance and other properties. The composite film of the application has a sensitive fading response and can fade automatically at normal temperature and pressure, improving the photochromic reversibility. The photochromic composite film can be applied to flexible ultraviolet detection devices, information anti-counterfeiting and other fields. The portable flexible material is used as the substrate and the packaging layer, and underwater ultraviolet detection can be realized at the same time, which provides the possibility for real-time detection of ultraviolet intensity in various scenes. The photochromic composite film is easy to manufacture into a device, such sensor does not need additional electronic components, and can be directly visually measured by colorimetry, and the photochromic composite film material can be integrated into flexible materials, which expands the application range and promotes the research and development of photochromic materials. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The absorption curve of the photochromic composite film prepared in Comparative Example 1 after color change.

[0027] Figure 2Absorption curve after discoloration of the photochromic composite film prepared in Example 1.

[0028] Figure 3 Absorption curve after discoloration of the photochromic composite film prepared in Example 2.

[0029] Figure 4 Absorption curve after discoloration of the photochromic composite film prepared in Example 3.

[0030] Figure 5 Absorption curve after discoloration of the photochromic composite film prepared in Example 4.

[0031] Figure 6 Stress-strain curve of the photochromic composite film prepared in Comparative Example 1.

[0032] Figure 7 Stress-strain curve of the photochromic composite film prepared in Example 1.

[0033] Figure 8 Stress-strain curve of the photochromic composite film prepared in Example 2.

[0034] Figure 9 Stress-strain curve of the photochromic composite film prepared in Example 3.

[0035] Figure 10 Stress-strain curve of the photochromic composite film prepared in Example 4.

[0036] Figure 11 Reversibility test curve of the composite film prepared in Comparative Example 1.

[0037] Figure 12 Reversibility test curve of the photochromic composite film prepared in Example 3. DETAILED DESCRIPTION

[0038] The present application is further illustrated by the following specific examples, but is not limited thereto.

[0039] The raw materials used in the examples are conventional raw materials, which are commercially available, unless otherwise specified; the methods used in the examples are prior art, unless otherwise specified.

[0040] Comparative Example 1

[0041] A method for preparing a composite film, comprising the steps of:

[0042] Step 1. Polyvinyl alcohol (Mw = 61000, degree of hydrolysis 98% ~ 98.8%, viscosity 9-11 mPa.s) was mixed with water, and stirred at 70°C for 3h to prepare a polyvinyl alcohol aqueous solution with a mass concentration of 10%;

[0043] Step 2. Phosphotungstic acid was mixed with water and stirred at 70°C for 2h to obtain a 10% phosphotungstic acid aqueous solution.

[0044] Step 3. The polyvinyl alcohol aqueous solution and the phosphotungstic acid aqueous solution were mixed at a mass ratio of polyvinyl alcohol to phosphotungstic acid of 10:1 and stirred at 80°C for 4h.

[0045] Step 4. The mixed film solution in Step 3 was poured into a culture dish, which was placed on a heating plate and heated at 70°C for 2h to solidify, obtaining a polyvinyl alcohol / phosphotungstic acid composite film, i.e. Sample No. 1 film.

[0046] The composite film obtained in the present comparative example was placed under a 365nm wavelength, 60mW / cm 2 UV lamp for irradiation to cause discoloration.

[0047] The absorption curve of the composite film prepared in the present comparative example after discoloration is shown in Figure 1 The figure shows that the composite film prepared in Comparative Example 1 has absorption peaks at 490nm and 730nm after discoloration, corresponding to the d-d transition of tungsten ions and the valence electron transfer between metals (W 6+ → W 5+ ), and the composite film becomes dark blue.

[0048] The stress-strain curve of the composite film prepared in the present comparative example is shown in Figure 6 The figure shows that the strain of the composite film obtained by doping PVA with PTA is 110%.

[0049] The composite film prepared in the present comparative example has high transparency, and the transmittance can reach 94%.

[0050] The composite film of Comparative Example 1 was irradiated with 365nm UV light at a light power density of 60mW / cm 2 for 20min to cause discoloration to dark blue, and absorbance test was performed; then it was left to stand in air at room temperature, and absorbance test was performed after standing for 1h, 3h and 5h, respectively; the test results are shown in Figure 11 The figure shows that the sample film of Comparative Example 1 has no obvious discoloration and the absorbance has almost no change with time (5h).

[0051] Example 1

[0052] A preparation method of a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, comprising the steps of:

[0053] Step 1. Polyvinyl alcohol (Mw=61000, hydrolysis degree 98%~98.8%, viscosity 9-11mPa.s) was mixed with water and stirred at 70°C for 3h to obtain a 10% polyvinyl alcohol aqueous solution;

[0054] Step 2. Branched polyethyleneimine (Mw ~ 25,000, viscosity at 50℃ 13,000-18,000, density at 25℃ 1.030 g / mL) was mixed with water, stirred at 70℃ for 2h to obtain a branched polyethyleneimine aqueous solution with a mass concentration of 50%;

[0055] Step 3. Phosphotungstic acid was mixed with water, stirred at 70℃ for 2h to obtain a phosphotungstic acid aqueous solution with a mass concentration of 10%.

[0056] Step 4. The polyvinyl alcohol aqueous solution, the branched polyethyleneimine aqueous solution and the phosphotungstic acid aqueous solution were mixed, and the mass ratio of polyvinyl alcohol, branched polyethyleneimine and phosphotungstic acid was 10:1:1, and the mixture was stirred at 80℃ for 4h.

[0057] Step 5. The film solution after being fully mixed in step 4 was poured into a culture dish, and the culture dish was placed on a heating plate and heated at 70℃ for 2h to solidify, to obtain a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, i.e. sample film No. 2.

[0058] The composite film obtained in this example was placed under a 365nm wavelength, 60mW / cm 2 UV lamp to irradiate and discolor.

[0059] The absorption curve of the composite film prepared in this example after discoloration is shown in Figure 2 The figure shows that the composite film prepared in Example 1 has absorption peaks at 380nm and 610nm after discoloration, and the peak at 730nm is obviously inhibited after the addition of PEI, and the composite film becomes light blue.

[0060] The stress-strain curve of the composite film prepared in this example is shown in Figure 7 The figure shows that the strain can reach 320%, showing good tensile properties.

[0061] The composite film prepared in this example has high light transmittance, which can reach 94.5%.

[0062] Example 2

[0063] A preparation method of a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, comprising the steps of:

[0064] Step 1. Polyvinyl alcohol (Mw ~ 61000, hydrolysis degree 98%-98.8%, viscosity 9-11 mPa.s) was mixed with water, stirred at 70℃ for 3h to obtain a polyvinyl alcohol aqueous solution with a mass concentration of 10%;

[0065] Step 2. Branched polyethyleneimine (Mw~25,000, viscosity at 50℃ 13,000-18,000, density at 25℃ 1.030 g / mL) was mixed with water, stirred at 70℃ for 2h to obtain a branched polyethyleneimine aqueous solution with a mass concentration of 50%;

[0066] Step 3. Phosphotungstic acid was mixed with water, stirred at 70℃ for 2h to obtain a phosphotungstic acid aqueous solution with a mass concentration of 10%.

[0067] Step 4. The polyvinyl alcohol aqueous solution, the branched polyethyleneimine aqueous solution and the phosphotungstic acid aqueous solution were mixed, and the mass ratio of polyvinyl alcohol, branched polyethyleneimine and phosphotungstic acid was 10:2:1, and the mixture was stirred at 80℃ for 4h.

[0068] Step 5. The film solution after sufficient mixing in step 4 was poured into a culture dish, and the culture dish was placed on a heating plate and heated at 70℃ for 2h to solidify, to obtain a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, which was sample film No. 3.

[0069] The composite film obtained in this example was placed under a 365nm wavelength, 60mW / cm 2 The color change was observed under UV light.

[0070] The absorption curve of the composite film prepared in this example after color change is shown in Figure 3 As can be seen from the figure, the composite film prepared in Example 2 has an absorption peak at 525nm after color change, and the composite film becomes light purple.

[0071] The stress-strain curve of the composite film prepared in this example is shown in Figure 8 As can be seen from the figure, the strain can reach 436%, and the tensile properties of the sample film are further improved with the increase of the amount of PEI composite.

[0072] The composite film prepared in this example has high light transmittance, which can reach 94.7%.

[0073] Example 3

[0074] A preparation method of a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, comprising the steps of:

[0075] Step 1. Polyvinyl alcohol (Mw~61000, hydrolysis degree 98%-98.8%, viscosity 9-11 mPa.s) was mixed with water, stirred at 70℃ for 3h to obtain a polyvinyl alcohol aqueous solution with a mass concentration of 10%;

[0076] Step 2. A branched polyethyleneimine (Mw~25,000, viscosity at 50℃ of 13,000-18,000, density at 25℃ tested of 1.030 g / mL) was mixed with water and stirred at 70℃ for 2h to obtain a 50% mass concentration branched polyethyleneimine aqueous solution;

[0077] Step 3. Phosphotungstic acid was mixed with water and stirred at 70℃ for 2h to obtain a 10% mass concentration phosphotungstic acid aqueous solution.

[0078] Step 4. The polyvinyl alcohol aqueous solution, the branched polyethyleneimine aqueous solution and the phosphotungstic acid aqueous solution were mixed, with the mass ratio of polyvinyl alcohol, branched polyethyleneimine and phosphotungstic acid being 10:3:1, and stirred at 80℃ for 4h.

[0079] Step 5. The film solution after being mixed thoroughly in Step 4 was poured into a culture dish, and the culture dish was placed on a heating plate and heated at 70℃ for 2h to solidify, to obtain a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, i.e. Sample No. 4 film.

[0080] The composite film obtained in this example was placed under a 365nm wavelength, 60mW / cm 2 UV lamp to irradiate and colorize.

[0081] The absorption curve of the composite film prepared in this example after colorization is shown in Figure 4 The figure shows that the composite film prepared in Example 3 has an absorption peak at 525nm after colorization, and the composite film becomes dark purple. Under the same environment and the same irradiation conditions, the experimentally measured absorbance intensity is higher than that of Example 2.

[0082] The stress-strain curve of the composite film prepared in this example is shown in Figure 9 The figure shows that the strain can reach 606%, and with the increase of the amount of PEI composite, the tensile properties of the sample film are further improved, and the flexibility is good.

[0083] The composite film prepared in this example has high light transmittance, which can reach 97%.

[0084] The composite film prepared in this example was irradiated with 365nm UV light with a light power density of 60mW / cm 2 for 10min to colorize and become dark purple, and then the composite film was placed on a 60℃ heating plate in air to accelerate the color fading process. After 15min, the composite film can fade to transparent colorless. The reversibility was tested for 10 times. The reversibility test curve of the composite film prepared in this example is shown in Figure 12 The figure shows that the absorbance of the sample of Example 3 does not change much after 10 times of colorization-fading cycle, proving that the reversibility is good.

[0085] Example 4

[0086] A preparation method of a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, comprising the steps of:

[0087] Step 1. Polyvinyl alcohol (Mw ~ 61000, hydrolysis degree 98% ~ 98.8%, viscosity 9-11 mPa.s) was mixed with water to prepare a 10% polyvinyl alcohol aqueous solution, which was stirred at 70°C for 3h;

[0088] Step 2. Branched polyethyleneimine (Mw ~ 25,000, viscosity 13,000-18,000 at 50°C, density 1.030 g / mL at 25°C) was mixed with water to prepare a 50% branched polyethyleneimine aqueous solution, which was stirred at 70°C for 2h;

[0089] Step 3. Phosphotungstic acid was mixed with water to prepare a 10% phosphotungstic acid aqueous solution, which was stirred at 70°C for 2h.

[0090] Step 4. The polyvinyl alcohol aqueous solution, the branched polyethyleneimine aqueous solution and the phosphotungstic acid aqueous solution were mixed, and the mass ratio of polyvinyl alcohol, branched polyethyleneimine and phosphotungstic acid was 10:4:1, and the mixture was stirred at 80°C for 4h.

[0091] Step 5. The film solution after being fully mixed in step 4 was poured into a culture dish, and the culture dish was placed on a heating plate and heated at 70°C for 2h to solidify, to obtain a photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, which was sample film No. 5.

[0092] The composite film obtained in this example was placed under a 365nm wavelength, 60mW / cm 2 UV lamp to irradiate and change color.

[0093] The absorption curve of the composite film prepared in this example after color change is shown in Figure 5 The figure shows that the composite film prepared in Example 4 has an absorption peak at 525nm after color change, and the composite film becomes purple gray. Under the same environment and the same irradiation conditions, the experimental measurement shows that the absorbance intensity is lower than that of Example 3.

[0094] The stress-strain curve of the composite film prepared in this example is shown in Figure 10 The figure shows that the strain can reach 740%, and with the increase of the composite amount of PEI, the tensile properties of the sample film are further improved. The sample is 6.72 times the strain of the comparative example 1 composite film sample.

[0095] The composite film prepared in this example has high light transmittance, which can reach 91.1%.

[0096] Comparative Example 2

[0097] A method for preparing a composite film, comprising the steps of:

[0098] Step 1. Polyvinyl alcohol (Mw ~ 61000, degree of hydrolysis 98% ~ 98.8%, viscosity 9-11 mPa.s) was mixed with water, stirred at 70°C for 3h to prepare a 10% polyvinyl alcohol aqueous solution;

[0099] Step 2. Branched polyethyleneimine (Mw ~ 25,000, viscosity 13,000-18,000 at 50°C, density 1.030 g / mL at 25°C) was mixed with water, stirred at 70°C for 2h to prepare a 50% branched polyethyleneimine aqueous solution;

[0100] Step 3. Phosphotungstic acid was mixed with water, stirred at 70°C for 2h to prepare a 10% phosphotungstic acid aqueous solution.

[0101] Step 4. The polyvinyl alcohol aqueous solution, branched polyethyleneimine aqueous solution and phosphotungstic acid aqueous solution were mixed, and the mass ratio of polyvinyl alcohol, branched polyethyleneimine and phosphotungstic acid was 10:5:1, and the mixture was stirred at 80°C for 4h.

[0102] Step 5. The well-mixed film solution in step 4 was poured into a culture dish, and the culture dish was placed on a heating plate and heated at 70°C for 2h to solidify.

[0103] In this example, PEI has a high mass fraction and high viscosity, and cannot form a film.

Claims

1. A photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film, characterized in that, The composite membrane is composed of polyvinyl alcohol, branched polyethyleneimine, and phosphotungstic acid; the mass ratio of polyvinyl alcohol, branched polyethyleneimine, and phosphotungstic acid is 10:1-4:1; the weight-average molecular weight of polyvinyl alcohol is 31,000-98,000; and the weight-average molecular weight of branched polyethyleneimine is 25,000-30,000.

2. The method for preparing the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film as described in claim 1, comprising the steps of: A photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film is obtained by mixing polyvinyl alcohol aqueous solution, branched polyethyleneimine aqueous solution and phosphotungstic acid aqueous solution, stirring and reacting, and then casting into a film.

3. The method for preparing the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film according to claim 2, characterized in that, The mass concentration of the polyvinyl alcohol aqueous solution is 5-15%; the mass concentration of the branched polyethyleneimine aqueous solution is 45-55%; and the mass concentration of the phosphotungstic acid aqueous solution is 5-15%.

4. The method for preparing the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film according to claim 2, characterized in that, Includes one or more of the following conditions: i. The preparation method of polyvinyl alcohol aqueous solution includes the following steps: mixing polyvinyl alcohol with water and stirring at 60-80 ℃ for 2-3 h to obtain polyvinyl alcohol aqueous solution; ii. The preparation method of branched polyethyleneimine aqueous solution includes the following steps: mixing branched polyethyleneimine with water and stirring at 60-80 °C for 1-2 h to obtain branched polyethyleneimine aqueous solution; iii. The preparation method of phosphotungstic acid aqueous solution includes the following steps: mixing phosphotungstic acid with water and stirring at 60-80 °C for 1-2 h to obtain phosphotungstic acid aqueous solution.

5. The method for preparing the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film according to claim 2, characterized in that, The stirring reaction temperature is 70-90℃, and the stirring reaction time is 4-5h.

6. The method for preparing the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film according to claim 2, characterized in that, The casting temperature is 40-90 ℃, and the casting time is 2-3 hours.

7. The application of the photochromic polyvinyl alcohol / branched polyethyleneimine / phosphotungstic acid composite film as described in claim 1 in photochromism.

8. The application according to claim 7, characterized in that, The composite film changes from transparent and colorless to blue, purple, or purplish-gray under 365 nm ultraviolet light irradiation; the ultraviolet light intensity is 40-60 mW / cm². 2 The composite film fades at room temperature or under heating, becoming transparent and colorless.

9. The application according to claim 8, characterized in that, The composite film is used in flexible ultraviolet detection devices or information anti-counterfeiting fields.

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