A preparation method of a backlight photochromic film

Abstract

The present invention discloses a preparation method of a backlight-induced color change film, which relates to the field of chemical materials. In the present invention, a specific plasticizer dibutyl sebacate (DBS) is used to plasticize a polymethyl methacrylate (PMMA) solution containing a photochromic dye molecule (DASA) to form a film-forming solution, so that the photochromic dye molecules can be more effectively dispersed in the polymer PMMA matrix; then a backlight-induced color change film is prepared by a solution casting method. Compared with traditional color change films, the film prepared by the present invention belongs to a backlight-induced color change film, and improves the fading rate and coloring rate of the film, and significantly enhances the anti-fatigue performance and toughness of the film.

Description

Technical Field

[0001] The present invention relates to a method for preparing a backlight-induced color-changing film, belonging to the field of chemical materials. Background Art

[0002] Organic photochromic materials refer to those organic compounds that can undergo backlight chemical reactions within a specific wavelength range. Due to the charge transfer within and between their molecules, they exhibit a series of special properties. The molecular structure, color, and electromagnetic distribution of such materials can be affected by light radiation within a specific wavelength range and thus change. With their unique light-responsive characteristics, organic photochromic materials show broad development potential in many fields such as optical information storage, optical display, and holographic imaging.

[0003] Currently, photochromic systems based on organic dyes or their derivatives have been widely applied in many fields such as biosensing, chemical sensors, fluorescence detection, and light-emitting devices. However, in the research on backlight-induced color-changing materials, the fading rate, coloring rate, fatigue resistance, and toughness of thin film materials all need to be improved. Therefore, there is an urgent need to develop a backlight-induced color-changing film with excellent fading rate, coloring rate, fatigue resistance, and toughness. Summary of the Invention

[0004] To solve at least one of the above problems, the present invention provides a method for preparing a backlight-induced color-changing film. Specifically, the present invention uses a specific plasticizer dibutyl sebacate (DBS) to plasticize a polymethyl methacrylate (PMMA) solution containing a photochromic dye molecule DASA to form a film-forming solution, and then prepares a backlight-induced color-changing film by solution casting. The backlight-induced color-changing film prepared by the present invention has excellent fading rate, coloring rate, fatigue resistance, and toughness.

[0005] The first object of the present invention is to provide a method for preparing a backlight-induced color-changing film, including the following steps: dissolving a photochromic dye molecule DASA in a polymethyl methacrylate (PMMA) solution to obtain a polymer solution; then adding a plasticizer to the polymer solution and mixing evenly to obtain a film-forming solution; and using the solution casting method to prepare a backlight-induced color-changing film.

[0006] In one embodiment, the molecular weight of the PMMA is 8000 - 200000.

[0007] In one embodiment, the mass fraction of the photochromic dye molecule DASA in the polymer solution is 0.01 - 0.1 wt%, and the PMMA is 1 - 10 wt%.

[0008] In one embodiment, the solvent used in the polymethyl methacrylate (PMMA) solution is one or more of dichloromethane, N,N-dimethylformamide, tetrahydrofuran, and methanol.

[0009] In one embodiment, the mass ratio of the photochromic dye molecule DASA to PMMA is 1:(50 - 100).

[0010] In one embodiment, the plasticizer is dibutyl sebacate (DBS).

[0011] In one embodiment, the addition amount of the plasticizer is 20 - 30 wt% of the polymer solution.

[0012] In one embodiment, the solution casting method is to drop the polymer solution into a plate and leave it at room temperature for 6 - 24 hours to allow the solvent to volatilize, thereby preparing a reverse photochromic film.

[0013] In one embodiment, the amount of the film-forming solution used in the solution casting method is 1 - 20 mL.

[0014] The second object of the present invention is to provide a reverse photochromic film prepared by the above method.

[0015] The third object of the present invention is the application of the reverse photochromic film of the present invention in the fields of biosensing, chemical sensors, fluorescence detection, or light-emitting devices.

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention uses a specific plasticizer, dibutyl sebacate (DBS), to plasticize a polymethyl methacrylate (PMMA) solution containing a photochromic dye molecule DASA to form a film-forming solution, so that the photochromic dye molecules can be more effectively dispersed in the polymer PMMA matrix; then a reverse photochromic film is prepared by the solution casting method. Compared with traditional color-changing films, the film prepared by the present invention is a reverse photochromic film, and the fading rate and coloring rate of the film are improved, and the anti-fatigue performance and toughness of the film are significantly enhanced. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is a graph showing the change of absorbance An / A1 with the number of cycles during ten fading-recoloring cycles of the DASA-PMMA film;

[0020] Figure 2 Absorbance A of DASA-PMMA films and DASA-PMMA films with different DBS contents during ten fading-recoloring cycles n / A 1 Variation diagram with the number of cycles;

[0021] Figure 3 Absorbance A of DASA-PMMA films and DASA-PMMA films with different plasticizers during ten fading-recoloring cycles n / A 1 Variation diagram with the number of cycles;

[0022] Figure 4 First-order kinetic fitting diagram of the coloration process of DASA-PMMA films and DASA-PMMA films with different DBS contents. Detailed implementation manners

[0023] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0024] The phenomenon of photochromism refers to that when compound A is irradiated with light in a specific wavelength range, its molecular structure changes to generate compound B, and an obvious color change is shown during this process. However, in another specific wavelength range or under heating conditions, compound B can be transformed into compound A and return to the original color. The general formula of this photochemical reaction for color change is as follows:

[0025]

[0026] In the formula, A and B are two different substances with different maximum absorption wavelengths, but both can exist stably, and the conversion between the two belongs to a chemical change. The material that changes color due to the change of the light-stimulating wavelength is called a P (Photoactive) type material. In the forward photochromism of the photochromic material, the stable form of the material is colorless or light yellow, and it obtains color under the irradiation of light with a specific wavelength; while in the reverse photochromism, the material shows a stable form in a colored state and turns colorless under the irradiation of light.

[0027] The structure of the photochromic dye molecule DASA used in the examples and comparative examples is as follows in Formula I:

[0028]

[0029] Example 1:

[0030] A preparation method of a reverse photochromic film, comprising the following steps:

[0031] 1.5 g of poly(methyl methacrylate) PMMA with a molecular weight of 100,000 was added to 40 mL of tetrahydrofuran and mixed evenly to obtain a poly(methyl methacrylate) PMMA solution;

[0032] 0.03 g of the photochromic dye molecule DASA was dissolved in the poly(methyl methacrylate) PMMA solution and ultrasonically dispersed and dissolved sufficiently to obtain a polymer solution;

[0033] 6 mL of the polymer solution was taken, and DBS with a mass fraction of 30 wt% was added and mixed evenly to obtain a film-forming solution;

[0034] The film-forming solution was poured into a 4 cm × 4 cm mold and placed in the dark at room temperature for 24 hours to allow the tetrahydrofuran to evaporate sufficiently, forming a reverse photochromic film with a thickness of about 100 μm, denoted as DASA-PMMA-DBS 30.

[0035] Comparative Example 1:

[0036] The amount of DBS was adjusted to 0, 10, 20, 40, 50 wt% of the polymer solution, and the other steps were the same as those in Example 1 to prepare reverse photochromic films, denoted as DASA-PMMA-DBS 0, DASA-PMMA-DBS10, DASA-PMMA-DBS20, DASA-PMMA-DBS 40, and DASA-PMMA-DBS 50, respectively.

[0037] Comparative Example 2:

[0038] The plasticizer was adjusted to tributyl phosphate TBP, trioctyl phosphate TOP, dioctyl phthalate DOP, and dibutyl phthalate DBP, and the other steps were the same as those in Example 1 to prepare reverse photochromic films, denoted as DASA-PMMA-TBP 30 film, DASA-PMMA-TOP 30 film, DASA-PMMA-DOP 30 film, and DASA-PMMA-DBP 30 film, respectively.

[0039] Test Example 1:

[0040] The film DASA-PMMA-DBS 30 prepared in Example 1 was subjected to a fatigue resistance test. During the test, the film was irradiated under a D65 standard daylight light source for 10 min, and then its absorbance was measured at 560 nm. Then the film was placed in the dark and allowed to recover for 24 h before measuring its absorbance, and 10 cycles of testing were carried out in sequence. The results are shown in Figure 1 。

[0041] Through Figure 1It can be found that the absorbance of the film in its initial state is relatively high, about 1.60. After being irradiated by the D65 standard light source for the first time, the absorbance decreases to 0.63. As the number of cycles increases, the absorbance of the film before illumination gradually decreases from 1.60 to 1.40, and the absorbance after illumination increases from 0.63 to 0.75. During the ten fading-recoloring cycles, the difference in the maximum absorbance of the film shows a downward trend. This phenomenon is due to the irreversible photodegradation reaction of the color-changing molecules as the number of irradiations by the D65 standard light source increases.

[0042] The films prepared in Comparative Example 1 and Comparative Example 2 were tested for fatigue resistance. The same test method as described above was used for the fatigue resistance test. The fatigue attenuation rate of the film was calculated by the change value of the absorbance before and after ten irradiations by the D65 standard light source relative to the maximum change value. The test results are as Figure 2 shown.

[0043] According to Figure 2 the results, the attenuation rate of the DASA-PMMA-DBS 0 film is 72.5%. However, after adding the plasticizer DBS, the attenuation rate of the film decreases. As the content of DBS increases, the attenuation rate of the film decreases, from 44.8% to 37%. When the DBS content is 30 wt%, the attenuation rate of the film is the lowest. Subsequently, when the DBS content continues to increase, the attenuation rate of the film rises to 60%. Therefore, adding the DBS plasticizer can improve the fatigue performance of DASA in the film. This may be because DBS is a compound with flexible chain segments, which can interact with the PMMA molecular chain, increasing the flexibility and ductility of the film, thus slowing down the fatigue damage of the film. In addition, DBS can also form a phase-separated structure in the film, forming an aggregated structure with good mechanical strength and fatigue resistance, thereby improving the anti-fatigue ability of the film. However, when the content of DBS is too high (>20 wt%), the fatigue resistance of the film will begin to decline. This is because an excessive amount of plasticizer may reduce the mechanical strength of the film, making it more fragile and brittle, and increasing the voids between the molecules inside the film, resulting in the formation of fatigue damage. Therefore, the content of the plasticizer needs to be controlled within a certain range to achieve the best fatigue resistance.

[0044] Figure 3 is the graph of the change in absorbance A n / A 1 with the number of cycles during the ten fading-recoloring cycles of the DASA-PMMA film and the DASA-PMMA films with different types of plasticizers. According to Figure 3 it can be seen that when the plasticizer is DBS, the fatigue resistance of the film is significantly better than that of the films prepared with other plasticizers added.

[0045] Test Example 2:

[0046] The coloration behaviors of the thin films prepared in Example 1 and Comparative Examples 1 and 2 were measured.

[0047] Under dark conditions, the molecular size and polarity of the DASA photochromic dye molecule change, and isomerization occurs from a colorless ring shape to a colored linear shape, returning to the thermodynamically stable colored open-ring isomer.

[0048] To quantitatively describe the coloration behavior of the thin film, the thin film was first irradiated under a D65 standard light source for 10 min, and then placed in a dark field condition. Absorbances were measured at several unequal time points within the wavelength range of 450 nm to 650 nm.

[0049] Kinetic fitting was performed on the coloration processes of the DASA-PMMA-DBS 0 thin film prepared without adding DBS and the DASA-PMMA thin films with different contents of DBS. Let A 0 be the absorbance of the thin film before being placed in the dark (t = 0), A t be the absorbance at time t after being placed in the dark, A ∞ be the absorbance at time t = ∞ after being placed in the dark, and k be the first-order reaction rate constant of photochromism.

[0050] Absorbance data A 0 , A t , A ∞ at 560 nm wavelength of the DASA-PMMA thin film and the DASA-PMMA thin films with different DBS contents were collected. According to the first-order kinetic equation of the photochromic reaction:

[0051] Plots of ln[(A ∞ - A 0 ) / (A ∞ - A t )] vs. t were made, and the photochromic kinetic curves of the thin films prepared in Example 1 and Comparative Example 1 were obtained respectively, as shown in Figure 4 . By calculating the slope of the straight line, the photochromic rate constant k (min -1 ) of the sample can be obtained.

[0052] Table 1 Fitting data of the coloration rates of DASA-PMMA thin films with different DBS contents

[0053]

[0054] According to Figure 4and the data in Table 1, the color rendering behavior of each thin film sample after irradiation with a D65 standard light source conforms more to the first-order kinetic curve (the correlation coefficients are 0.99379, 0.99402, 0.9971, 0.9979, 0.99912, 0.98459 respectively). Among them, k 10 (0.00389 min -1 ) < k 0 (0.00391 min -1 ) < k 50 (0.00771 min -1 ) < k 20 (0.00825 min -1 ) < k 40 (0.00841 min -1 ) < k 30 (0.00981 min -1 ). This indicates that the influence of 10 wt% DBS on the color rendering rate of DASA-PMMA-DBS is not obvious. However, with the increase in the content of DBS, the color rendering rate of the thin film significantly accelerates until the content of DBS exceeds a certain range, and the color rendering rate of the DASA-PMMA-DBS thin film begins to decline. The addition of the plasticizer DBS will change the physical and chemical properties of the thin film of PMMA doped with DASA, thereby affecting the color rendering rate of the thin film. With the increase in the concentration of DBS, the color rendering rate of the thin film of PMMA doped with DASA will first increase and then decrease. This is because when the concentration of DBS is low, the addition of the plasticizer will promote the diffusion of dye molecules in the thin film, thereby increasing the color rendering rate of the thin film. However, when the concentration of DBS is too high, the plasticizer will form a certain barrier effect on the dye molecules in the thin film, hindering the diffusion of dye molecules, thereby decreasing the color rendering rate of the thin film.

[0055] Test Example 3:

[0056] Measure the tensile strength and elongation at break of the thin films prepared in Example 1 and Comparative Examples 1 and 2.

[0057] To ensure that the thin film material has a wide range of application prospects, it must possess a certain mechanical strength. Adding a plasticizer to DASA-PMMA can increase the fading rate of the thin film. However, the addition of the plasticizer will inevitably reduce the mechanical properties of the thin film. To evaluate the mechanical properties of the thin film, a tensile test was conducted in this test example.

[0058] Table 2 Tensile Strength and Elongation at Break of DASA-PMMA Thin Films with Different DBS Contents

[0059]

[0060] According to the data in Table 2, as the DBS content increases from 0 wt% to 50 wt%, the tensile strength of the film decreases from 24.5 MPa to 4.02 MPa, and the mechanical properties of the film deteriorate. PMMA is a hard and brittle plastic with an elongation at break of only 2.07%. When the DBS content in the film is low, the increase in elongation at break is small. When the DBS content reaches 30 wt%, the elongation at break of the film rapidly increases to 19.1%. However, after continuing to increase the DBS content, the elongation at break of the film begins to decrease. This is because an appropriate amount of DBS can increase the flexibility and plasticity of the film, thereby increasing the elongation at break. However, when the DBS concentration is too high, a large number of voids and cracks will form inside the film, destroying the integrity and strength of the film, resulting in a decrease in tensile strength and elongation at break.

[0061] Table 3 Tensile Strength and Elongation at Break of DASA-PMMA Films with Different Types of Plasticizers

[0062]

[0063] As shown in Table 3, different types of plasticizers also have a certain influence on the tensile strength and elongation at break of the film. Among them, only when using DBS plasticizer, the tensile strength and elongation at break of the prepared film are better.

[0064] Test Example 4:

[0065] The free volume theory states that the volume of a polymer consists of two parts: the volume occupied by molecules and the unoccupied free volume, and the latter exists in the form of "holes". The existence of free volume provides space for the isomerization reaction of photochromic molecules. As the temperature decreases, the free volume gradually decreases. When the temperature drops below a certain critical temperature, the free volume will reach the minimum value and remain unchanged, and this critical temperature is called the glass transition temperature of the polymer. The glass transition temperature refers to the temperature at which the polymer undergoes a glass transition, reflecting the ease of movement of polymer molecular segments and the heat resistance of the polymer, and can be used to characterize the properties of the polymer. At a temperature T above the glass transition temperature (T g ), the free volume fraction f T of the polymer can be expressed as:

[0066] f T = f g + a f (T - T g ) T > T g )

[0067] where f g is the free volume fraction of the glassy polymer, and a f is the free volume expansion coefficient.

[0068] Adding a plasticizer to a polymer causes a dilution effect, thereby reducing the interaction between polymer chains and increasing the free volume fraction f of the polymer. T As a result, the glass transition temperature of the polymer is significantly reduced. At the same time, after adding the plasticizer DBS, the free volume increases, the segments are more likely to move, there is more space for the isomerization reaction of the photochromic molecule LDMN, and the fading rate of the photochromic molecule increases.

[0069] The glass transition temperatures of the films prepared in each example and each comparative example were measured, and the results are shown in Table 4 below:

[0070] Table 4 Glass transition temperatures of DASA-PMMA films with different plasticizers and different DBS contents

[0071]

[0072] The T of the film g is listed in Table 4. According to the data in Table 4, after adding 10 wt% of the plasticizer DBS to the DASA-PMMA film, the T of the film g decreases from 108.8 to 80.8, indicating that DBS has a plasticizing effect on LDMN-PMMA, and the plasticizing effect is significant. When 20 wt% of DBS is added, the T of the film g further decreases to 78.5. Continuing to increase the content of DBS, the T of the film g increases. This is because the main function of the plasticizer is to form a phase compatible with the polymer chains in the polymer and act as a lubricant between the molecular chains. When a plasticizer is added, the plasticizer molecules interact with the polymer chains, reducing the interaction force between the polymer chains, thereby lowering the glass transition temperature. The addition of the plasticizer can increase the mobility of the polymer segments, making it easier for the polymer chains to undergo conformational adjustment, resulting in a decrease in the glass transition temperature. However, when the content of the plasticizer reaches a certain level, the interaction between the plasticizer molecules may increase, forming a mutual blocking effect. This may limit the mobility of the polymer chains and cause the glass transition temperature to rise slightly.

[0073] According to Table 4, the plasticizing effect is the best only when the plasticizer is DBS and the addition amount is 20 - 30 wt%.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a backlight photochromic film, characterized in that, it comprises the following steps: Add 1.5 g of poly(methyl methacrylate) PMMA with a molecular weight of 100,000 to 40 mL of tetrahydrofuran and mix evenly to obtain a poly(methyl methacrylate) PMMA solution; Dissolve 0.03 g of the photochromic dye molecule DASA in the poly(methyl methacrylate) PMMA solution and use ultrasonic waves to fully disperse and dissolve it to obtain a polymer solution; Take 6 mL of the polymer solution, add DBS with a mass fraction of 30 wt%, mix evenly to obtain a film-forming solution; use the solution casting method to prepare a backlight photochromic film.

2. The preparation method according to claim 1, characterized in that, the solution casting method is to drop the film-forming solution into a plate and place it at room temperature for 6 to 24 hours to allow the solvent to volatilize, thereby preparing a backlight photochromic film.

3. The preparation method according to claim 1, characterized in that, the amount of the film-forming solution used in the solution casting method is 1 to 20 mL.

4. A backlight photochromic film prepared by the method according to any one of claims 1 to 3.

5. Application of the backlight photochromic film according to claim 4 in the fields of biosensing, chemical sensors, fluorescence detection or light-emitting devices.

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