Covalently cross-linked room temperature phosphorescent composite film with strong mechanical properties and preparation method thereof

Abstract

The application relates to a kind of room temperature phosphorescence composite films based on covalent cross-linking strong mechanical performance and preparation method, belong to room temperature phosphorescence film preparation technical field.Synthetic and configure inorganic suspension, polymer and phosphorescent molecule solution, make phosphorescent molecule, inorganic and polymer simultaneously occur multiple covalent reaction;Remove solvent to obtain organic-inorganic composite room temperature phosphorescence film with covalent network structure.The covalent rigid network between polymer-phosphorescent molecule-inorganic effectively limits the non-radiative transition of phosphorescent molecule, and high-efficiency room temperature phosphorescence performance is obtained.The external stress received by the composite material can be dissipated or transferred to the inorganic phase through covalent bond, thereby obtaining a composite film with high mechanical strength.The application proposes a method based on multiple covalent interactions between organic and inorganic units to construct a material with mechanical performance and room temperature phosphorescence performance, which can be effectively controlled according to the number of covalent bonds, has high luminous efficiency, good mechanical performance and shows high sensitivity phosphorescence response to mechanical deformation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of room temperature phosphorescent film preparation, and particularly relates to a preparation method for constructing an organic-inorganic composite film with high room temperature phosphorescent performance and strong mechanical performance based on multiple covalent cross-linking between inorganic substances, phosphorescent molecules and a polymer matrix. BACKGROUND

[0002] Polymer-based room temperature phosphorescent materials have attracted much attention due to their large Stokes shift, long lifetime and processability, and have been widely used in optoelectronic devices, information encryption and anti-counterfeiting fields. In order to ensure the practical application of polymer-based room temperature phosphorescent materials, it is increasingly necessary to have thin film materials with excellent room temperature phosphorescent performance and high mechanical strength. In the case of not affecting the high room temperature phosphorescent performance, improving the mechanical properties of the material becomes an important task at present.

[0003] Adding inorganic substances to polymer-based room temperature phosphorescent materials is a feasible method to improve room temperature phosphorescent performance and strengthen mechanical properties. Due to the rigid structure of inorganic substances, not only can the non-radiative transition of phosphorescent molecules be limited to improve room temperature phosphorescent performance, but also the mechanical strength of the polymer matrix can be effectively improved. At present, researchers construct organic-inorganic composite materials through hydrogen bonds, ionic bonds and other interactions, and enhance the interfacial interaction between inorganic substances and polymers. However, hydrogen bonds and ionic bonds usually have hygroscopicity, which can easily lead to phosphorescence quenching and reduce the mechanical properties of the composite material. Therefore, it is still challenging to construct organic-inorganic composite materials with high room temperature phosphorescent performance and strong mechanical performance.

[0004] Covalent bonds have high energy and stability, which can enhance the weak interaction between inorganic phases and organic phases in the composite material, and achieve high mechanical properties. The method of the present application is based on the covalent interaction between inorganic substances, phosphorescent molecules and a polymer matrix, forming a multiple covalent cross-linking network. The organic-inorganic rigid covalent network effectively limits the movement and non-radiative transition of phosphorescent molecules, which can significantly improve the room temperature phosphorescent performance. The external stress on the composite material can be dissipated or transferred to the inorganic phase through covalent bonds, thereby obtaining a composite film with high mechanical strength. The method is simple, fast and has mild reaction conditions, and the constructed composite film has high room temperature phosphorescent performance and strong mechanical performance, which can be mass-produced and has a sensitive phosphorescent response to mechanical deformation, providing a basis for designing practical optical devices with durability and application flexibility. SUMMARY

[0005] In order to meet the demand for organic-inorganic composite materials with high room temperature phosphorescent performance and mechanical properties, the present application provides a preparation method for constructing a room temperature phosphorescent composite film with strong mechanical properties based on covalent cross-linking.

[0006] The technical scheme of the present application is: synthesizing and configuring inorganic suspension, configuring polymer and phosphorescent molecule solution, making phosphorescent molecules, inorganic matter and polymer covalently react, and constructing multiple covalent cross-linking structure. Solvent evaporation method is used to remove solvent to obtain organic-inorganic composite film, which not only has strong room temperature phosphorescent signal and phosphorescent afterimage visible to naked eye for 12s, but also has strong mechanical property, and the tensile strength is close to 100MPa. By adjusting the number of functional groups in inorganic matter and polymer participating in reaction, the content of covalent bond in the composite material can be adjusted, so that the room temperature phosphorescent performance and mechanical property of the composite film can be effectively controlled. The method is suitable for large-scale preparation of composite film, and the constructed organic-inorganic composite film has certain flexibility, bendability and mechanical deformation phosphorescent responsiveness, which greatly expands the application range of room temperature phosphorescent film.

[0007] The present application provides a method for constructing organic-inorganic composite room temperature phosphorescent film with high room temperature phosphorescence and strong mechanical property based on covalent cross-linking, which is simple, efficient and suitable for large-scale preparation. The constructed composite film has strong mechanical property, good phosphorescent performance, adjustable structure and performance, and wide application range, which provides a new method for constructing efficient room temperature phosphorescent material.

[0008] A preparation method of a room temperature phosphorescent composite film with strong mechanical property based on covalent cross-linking, characterized in that it comprises the following steps:

[0009] (1) Synthesizing inorganic matter with rich hydroxyl groups and preparing suspension;

[0010] (2) Dissolving phosphorescent molecules modified by boronic acid groups at both ends and preparing alkaline solution to hydrolyze boronic acid groups;

[0011] (3) Dissolving polymer and preparing aqueous solution: selecting hydroxyl-rich polymer such as polyvinyl alcohol (PVA) as the polymer. PVA powder is added to deionized water and stirred at 85℃ for 2 hours to completely dissolve and obtain transparent solution, which is cooled to room temperature for standby.

[0012] (4) Measuring a certain amount of inorganic matter suspension with rich hydroxyl groups and alkaline solution of phosphorescent molecules containing boronic acid groups at both ends, stirring for 30 minutes to make them fully dispersed and react. Then a certain amount of polymer solution is added dropwise to the above mixture, and stirred for 1 hour to make them fully react.

[0013] (5) Transferring the reacted solution to a watch glass, eliminating bubbles, and placing it in a constant temperature drying oven to dry to obtain a composite film, and taking out the film and placing it in a desiccator for storage.

[0014] The method is suitable for constructing composite material with covalent cross-linking of phosphorescent molecules, inorganic matter and polymer matrix.

[0015] In step (1), the inorganic substance rich in hydroxyl groups can be selected from montmorillonite (MMT), layered double hydroxides (LDHs), and silicon dioxide, and the inorganic substance is preferably hydrotalcite (LDHs); the MgAl-LDHs are synthesized by a urea method in the application, and magnesium nitrate, aluminum nitrate and urea are used as raw materials (molar ratio of 2:1:12), and hydrotalcite with different metal elements in the layer, different sizes and different morphologies can also be synthesized by different methods.

[0016] In step (2), the phosphorescent molecule is a substance modified by boronic acid groups at both ends, the number of boronic acid groups in a single molecule is greater than 1, and the intermediate light-emitting part can be selected from biphenyl, phenyl, tetraphenylstyryl and preferably 4,4'-biphenyldiboronic acid molecule (BPBA).

[0017] A K2CO3 / KHCO3 buffer solution with pH = 10.5 is prepared, and a solution of dimethyl sulfoxide:buffer solution = 4:1 (volume ratio) is used to hydrolyze the phosphorescent molecule and prepare an alkaline solution.

[0018] In step (3), the hydroxyl-containing polymer is selected from polyvinyl alcohol, cellulose and chitosan, and polyvinyl alcohol is preferred, the alcoholysis degree of which is > 50%, and further preferably 72%-98%, and the polyvinyl alcohol with alcoholysis degrees of 98% and 87% (denoted as PVA98 and PVA87) is selected in the application.

[0019] In step (4), the amount relationship of the inorganic substance, the phosphorescent molecule and the polymer for constructing the composite material is: the inorganic substance is 0%-15% of the mass of the polymer, and the phosphorescent molecule is 0.1%-10% of the mass content of the polymer.

[0020] In step (4), the stirring time is 10 min-4 h, and the stirring temperature is room temperature, and the reaction degree can be improved by heating appropriately, and the temperature range is room temperature-80℃.

[0021] The thickness size of the constructed thin film is adjustable, and the self-supporting thin film with a thickness of 30-1000 μm.

[0022] The room temperature phosphorescent composite thin film of the application, especially 6% LDHs-0.1% BPBA-PVA, exhibits obvious strong phosphorescent emission at 495 nm; under 280 nm ultraviolet light, it exhibits strong fluorescence, and after the ultraviolet lamp is turned off, it shows strong phosphorescent emission, and the afterglow time is as long as 12 seconds; with the increase of the alcoholysis degree of PVA, the phosphorescent intensity increases obviously, and the afterglow time increases from 4 s to 12 s. With the deformation increasing, the phosphorescence is more and more obvious.

[0023] The organic-inorganic composite material constructed by the application is a self-supporting film, smooth and transparent, with adjustable size, and can be prepared on a large scale, with a thickness of 30-1000 μm. The phosphorescent molecules are significantly enhanced in room-temperature phosphorescent performance under the covalent interaction with the inorganic and polymer matrix, and the phosphorescent lifetime can reach the order of seconds. Under the action of the inorganic rigid filler and the strong covalent crosslinking network, the tensile strength of the composite film is greatly enhanced.

[0024] The application is based on the simultaneous covalent crosslinking of the phosphorescent molecules modified at both ends with the inorganic and polymer matrix to form a multiple covalent bond network. On the one hand, the rigid covalent network restricts the movement of the phosphorescent molecules, suppresses the non-radiative transition, and blocks water, oxygen and the like which quench the phosphorescence, greatly improving the phosphorescent performance; on the other hand, the covalent bond enhances the phase interface of the organic and inorganic phases and plays a role in dissipating stress, and the rigid inorganic filler plays a role in bearing stress, so that the mechanical performance is significantly improved. Therefore, the method successfully constructs an organic-inorganic composite film with high-efficiency room-temperature phosphorescent performance and strong mechanical performance. The room-temperature phosphorescent film constructed by the method has long phosphorescent lifetime, good mechanical performance, can be prepared on a large scale, the phosphorescent performance is adjustable, and has a phosphorescent response to mechanical deformation, which can provide a new method for developing strong, durable and flexible room-temperature phosphorescent materials for application in the fields of anti-counterfeiting and information storage. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A is the phosphorescent spectrum of LDHs, phosphorescent molecule BPBA and composite materials 0.1% BPBA-PVA and 6% LDHs-0.1% BPBA-PVA; B is the corresponding phosphorescent intensity.

[0026] Figure 2 It is the phosphorescent lifetime curve of 6% LDHs-0.1% BPBA-PVA.

[0027] Figure 3 It is the photo of the composite materials 0.1% BPBA-PVA and 6% LDHs-0.1% BPBA-PVA under 280 nm ultraviolet lamp and after the ultraviolet lamp is turned off.

[0028] Figure 4 It is the Fourier transform infrared spectrum of LDHs, BPBA, PVA and the composite material 6% LDHs-0.1% BPBA-PVA.

[0029] Figure 5 It is the tensile strength of the composite film 6% LDHs-0.1% BPBA-PVA (the content of LDHs is 0%, 1%, 3%, 6%, 10% and 15% of the mass ratio of PVA).

[0030] Figure 6A is the phosphorescence emission photo of 6% LDHs-0.1% BPBA-PVA composite film after bending and folding; B is the photo of large size 6% LDHs-0.1% BPBA-PVA composite film under visible light, under ultraviolet lamp and after the ultraviolet lamp is turned off, respectively. Figure 7 The phosphorescence spectrum of 6% LDHs-0.1% BPBA-PVA (PVA98), 6% LDHs-0.1% BPBA-PVA (PVA87) and SDS@6% LDHs-0.1% BPBA-PVA (PVA98) composite film after the surface of LDHs is modified with 15 mg of SDS.

[0031] Figure 8 The photo of 6% LDHs-0.1% BPBA-PVA (PVA98), 6% LDHs-0.1% BPBA-PVA (PVA87) and SDS@6% LDHs-0.1% BPBA-PVA (PVA98) composite film under 280 nm ultraviolet lamp and after the ultraviolet lamp is turned off.

[0032] Figure 9 The phosphorescence photo of 6% LDHs-0.1% BPBA-PVA film dumbbell-shaped sample under different stretching lengths to deformation after the ultraviolet lamp is turned off. DETAILED DESCRIPTION

[0033] The application is further described below in combination with examples, but the application is not limited to the following examples.

[0034] Example 1:

[0035] (1) Synthesis of Mg-Al LDHs

[0036] 5.128 g of magnesium nitrate, 3.751 g of aluminum nitrate and 7.207 g of urea were weighed, added into 80 mL of deionized water, stirred until uniformly mixed, then placed into a blast drying oven for constant temperature at 100 ℃ for 24 h, taken out and cooled, then centrifuged in a centrifuge at a speed of 5000 r / min for five minutes, washed with deionized water for 3-4 times until pH=7, to obtain MgAl-LDHs colloid. The colloid was prepared into a suspension, and its concentration was quantified by inductively coupled plasma emission spectrometer (ICP), and the MgAl-LDHs colloid was sealed for use.

[0037] (2) Preparation of phosphorescent molecule BPBA and polymer PVA solution

[0038] A K2CO3 / KHCO3 buffer solution with pH 10.5 was prepared. BPBA (2 mg) was dissolved in DMSO and diluted with the above buffer solution to obtain a basic solution (0.5 mg / mL). PVA (3 g) was dissolved in 100 mL of deionized water, and stirred at 85°C for 1 h to obtain a PVA solution, and then cooled to room temperature.

[0039] (3) Preparation of 6% LDHs-0.1% BPBA-PVA composite film

[0040] The LDHs suspension (30 mg) was added to the BPBA solution (0.25 mL) and stirred for 30 min. Then the PVA aqueous solution (16.7 mL) was added to the above mixture and stirred for 1 h. The mixture was then poured into a petri dish and placed in an oven at 60°C for 4 h to dry. A 6% LDHs-0.1% BPBA-PVA composite film was obtained. Finally, the film was peeled off and stored in a desiccator. A 0.1% BPBA-PVA film was prepared without the addition of LDHs.

[0041] Similarly, a 6% LDHs-0.1% BPBA-PVA (PVA87) composite film was prepared using PVA with an alcoholysis degree of 87% (referred to as PVA87) according to the above procedure. In addition, 15 mg of sodium dodecyl sulfate (SDS) was added to the LDHs suspension and ultrasonically treated for 1 h to obtain LDHs nanosheets with reduced surface hydroxyl groups, and then a SDS@6% LDHs-0.1% BPBA-PVA composite film was prepared according to the same procedure.

[0042] (4) Study on the phosphorescent properties of 6% LDHs-0.1% BPBA-PVA composite film

[0043] As shown in Figure 1 , the phosphorescent spectrum test was performed on the original components of the composite film. LDHs had no phosphorescent emission, and the original BPBA also had extremely weak phosphorescent emission. The 0.1% BPBA-PVA composite film had weak phosphorescent emission at 495 nm, while the 6% LDHs-0.1% BPBA-PVA composite film showed obvious strong phosphorescent emission at 495 nm, and the emission intensity was significantly higher than that of BPBA and 0.1% BPBA-PVA film, which was 5 times that of 0.1% BPBA-PVA. The phosphorescent lifetime decay curve is shown in Figure 2 , and the phosphorescent lifetime of the 6% LDHs-0.1% BPBA-PVA film was 1.45 s after fitting. As shown in Figure 3 , the 6% LDHs-0.1% BPBA-PVA film showed strong fluorescence under 280 nm ultraviolet light, and after the ultraviolet lamp was turned off, it showed strong phosphorescent emission with a long afterglow time of 12 s, while the 0.1% BPBA-PVA film only had an afterglow time of 7 s.

[0044] (5) Structure study of 6% LDHs-0.1% BPBA-PVA composite films

[0045] Figure 4 To characterize the LDHs, BPBA, PVA and the composite materials after reaction, PVA shows a characteristic peak at 3260 cm -1 -1, which is attributed to O-H stretching vibration. After reaction with LDHs and BPBA, this peak of PVA is red-shifted, indicating that the hydroxyl groups are used to form covalent bonds and thus the number is reduced. In addition, the absorption peak of 6% LDHs-0.1% BPBA-PVA composite film in the range of 1310-1430 cm -1 -1 is enhanced, which is attributed to B-O stretching vibration; and a new peak attributed to B-O-C bond appears at 1030 cm -1 -1. The above results prove that B-O covalent crosslinking reaction occurs between BPBA, LDHs and PVA in the composite film, and a rigid network of multiple covalent bonds is established.

[0046] (6) Study on the mechanical properties of 6% LDHs-0.1% BPBA-PVA composite films

[0047] Figure 5 The tensile strength test was carried out on 6% LDHs-0.1% BPBA-PVA composite films with different LDHs content, and the tensile strength of 0.1% BPBA-PVA was 48.1 MPa. With the addition of inorganic rigid filler LDHs, the mechanical properties of 6% LDHs-0.1% BPBA-PVA composite material were significantly enhanced, and the tensile strength of 6% LDHs-0.1% BPBA-PVA reached 97.9 MPa, which was twice that of 0.1% BPBA-PVA. The reason for the enhancement of the mechanical properties of the composite film is that the rich covalent bonds in the multiple covalent crosslinking network can dissipate stress, and LDHs plays a role in bearing stress, and the tensile load can be transferred from the polymer matrix to the rigid LDHs through the covalent bond.

[0048] (7) Flexibility and large-scale preparation of 6% LDHs-0.1% BPBA-PVA composite films

[0049] As shown in A of Figure 6 , 6% LDHs-0.1% BPBA-PVA composite films have mechanical flexibility, and these films can be bent, folded into a ring, fan-shaped, etc. At the same time, the film can be made into an expandable size (9x5.5 cm 2 ) as shown in B of Figure 6 , and bright phosphorescence can be observed in the entire area.

[0050] (8) Covalent bonding and phosphorescence performance regulation of 6% LDHs-0.1% BPBA-PVA composite films

[0051] The key to achieving high-efficiency room-temperature phosphorescence performance in the 6% LDHs-0.1% BPBA-PVA composite material lies in its internal multiple covalent cross-linking. Therefore, the room-temperature phosphorescence performance of the film can be adjusted by regulating the covalent interactions within the composite film. Since hydroxyl groups are the main reaction sites for this covalent cross-linking reaction, we controlled the number of covalent bonds by adjusting the number of hydroxyl groups in PVA and LDHs. First, we changed the degree of alcoholysis of PVA, using PVA with a degree of alcoholysis of 98% (containing 98% hydroxyl groups and 2% ester groups) and 87% (containing 87% hydroxyl groups and 13% ester groups), denoted as PVA98 and PVA87, respectively. Figure 7 As shown, when the degree of PVA hydrolysis decreased from 98% to 87%, the phosphorescence intensity of the 6%LDHs-0.1%BPBA-PVA composite film significantly decreased, with the signal dropping to approximately 35% of its original value. Furthermore, the afterglow time of 6%LDHs-0.1%BPBA-PVA87 was shortened from 12 seconds to 4 seconds compared to 6%LDHs-0.1%BPBA-PVA98. Figure 8 Furthermore, sodium dodecyl sulfate (SDS) was used to modify the surface of LDHs. Some hydroxyl sites in the LDHs were partially occupied by SDS, preventing them from reacting with the borate groups in the chromophores. With the addition of SDS, the phosphorescence intensity and afterglow time of the 6% LDHs-0.1% BPBA-PVA98 composite film were significantly reduced. The phosphorescence signal of SDS@6% LDHs-0.1% BPBA-PVA (PVA98) decreased to 40% of that of 6% LDHs-0.1% BPBA-PVA98, and the afterglow time shortened from 12 s to 4 s. Therefore, the phosphorescence intensity and lifetime can be adjusted by regulating the number of hydroxyl groups in LDHs and PVA.

[0052] (9) Phosphorescence response of 6% LDHs-0.1% BPBA-PVA composite film to mechanical deformation

[0053] like Figure 9 As shown, dumbbell-shaped 6% LDHs-0.1% BPBA-PVA films were prepared and then artificially stretched. The original film, with a length of 2.5 cm, exhibited phosphorescence after UV lamp removal. When the 6% LDHs-0.1% BPBA-PVA film was stretched from 2.5 cm to 3.6 cm, a significant enhancement in phosphorescence emission was observed in the deformed region of the film. The longer the stretching length, the more pronounced the phosphorescence enhancement. Therefore, the enhanced phosphorescence emission can visualize the deformation, providing a valuable opportunity for visual monitoring of material deformation and early damage detection.

Claims

1. A method for preparing a covalently cross-linked, strong mechanical performance room temperature phosphorescent composite thin film, characterized in that, It comprises the following steps: (1) Synthesis of hydroxyl-rich inorganic material and preparation of suspension; (2) Dissolution of phosphorescent molecules modified by boronic acid groups at both ends and preparation of alkaline solution for hydrolysis of boronic acid groups; (3) Dissolution of polymer and preparation of aqueous solution: the polymer is selected from hydroxyl-rich polymers; (4) A certain amount of hydroxyl-rich inorganic material suspension and alkaline solution of phosphorescent molecules containing boronic acid groups at both ends are stirred for 30 minutes to allow sufficient dispersion and reaction; then a certain amount of polymer solution is added dropwise to the above mixture, and stirred for 1 hour to allow sufficient reaction; (5) The reacted solution is transferred to a watch glass to eliminate bubbles, and then placed in a constant temperature drying oven for drying to obtain a composite film, which is taken out and stored in a desiccator; In step (4), the amount of inorganic material, phosphorescent molecules and polymer for building the composite material is as follows: the inorganic material is 0%-15% of the mass of the polymer and is not 0, and the phosphorescent molecules are 0.1%-10% of the mass of the polymer; In step (1), the hydroxyl-rich inorganic material is selected from montmorillonite MMT, layered double hydroxide LDHs and hydroxyl-rich silicon dioxide; and in step (3), the hydroxyl-rich polymer is selected from polyvinyl alcohol, cellulose and chitosan.

2. The method for preparing a covalent cross-linking based strong mechanical performance room temperature phosphorescent composite film according to claim 1, characterized in that, In step (2), the phosphorescent molecules are substances modified by boronic acid groups at both ends, the number of boronic acid groups in a single molecule is greater than 1, and the intermediate light-emitting part is selected from biphenyl, phenyl and tetraphenylstyryl; the boronic acid molecules are hydrolyzed by using an alkaline buffer solution, and the alkaline buffer solution is selected from a K2CO3 / KHCO3 buffer system.

3. The method for preparing a room-temperature phosphorescent composite film with strong mechanical properties based on covalent crosslinking according to claim 1, characterized in that, The alcoholysis degree of the polyvinyl alcohol is greater than 50%.

4. The method for preparing a room-temperature phosphorescent composite film with strong mechanical properties based on covalent crosslinking according to claim 1, characterized in that, The alcoholysis degree of the polyvinyl alcohol is 72%-98%.

5. The method for preparing a room-temperature phosphorescent composite film with strong mechanical properties based on covalent crosslinking according to claim 1, characterized in that, The stirring temperature ranges from room temperature to 80°C.

6. The method for preparing a room-temperature phosphorescent composite film with strong mechanical properties based on covalent crosslinking according to claim 1, characterized in that, The thickness of the built film can be adjusted, and the self-supporting film has a thickness of 30-1000 μm.

7. A covalently cross-linked organic-inorganic composite film with high-efficiency room-temperature phosphorescent performance and strong mechanical performance prepared by the method according to any one of claims 1-6.

8. A covalently cross-linked organic-inorganic composite film with high-efficiency room-temperature phosphorescent performance and strong mechanical performance prepared by the method according to any one of claims 1-6, which exhibits obvious strong phosphorescent emission at 495 nm and strong fluorescence under 280 nm ultraviolet light, and shows strong phosphorescent emission with a long afterglow time of 12 seconds after the ultraviolet light is turned off; as the alcoholysis degree of PVA increases, the phosphorescent intensity and the afterglow time increase, from 4 s to 12 s; the greater the deformation, the more obvious the phosphorescent enhancement.

9. Application of a covalently cross-linked organic-inorganic composite film with high-efficiency room-temperature phosphorescent performance and strong mechanical performance prepared by the method according to any one of claims 1-6, which visualizes deformation through enhanced phosphorescent emission, and provides a technology for visual monitoring and early damage monitoring of material deformation.

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