Reversible regulation method for refractive index of nano titanium dioxide film

Abstract

The invention discloses a refractive index reversible regulation and control method of a nano titanium dioxide film. The method specifically comprises the following steps: step 1, modifying titanium dioxide with acrylic acid; step 2, preparing a polymer with a reversible structure; step 3, preparing titanium dioxide with a reversible refractive index according to products obtained in the step 1 and the step 2; and 4, preparing the titanium dioxide film with the reversible refractive index according to the product obtained in the step 3. The titanium dioxide-based thin film material with high refractive index is obtained by constructing valence bond compounding of conjugated sulfur macromolecules and nano titanium dioxide, and reversible regulation and control of the refractive index of the thin film are realized by utilizing reversible change of an anthracene structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials and relates to a method for reversibly regulating the refractive index of a nano-titanium dioxide thin film. Background Art

[0002] High refractive index materials have been widely used in optical lenses, waveguide materials, light trapping in solar cells, light extraction in OLEDs, etc., and have attracted people's attention in recent years. Inorganic nano materials have a high refractive index, but their film-forming properties are poor. Usually, inorganic nano materials are compounded with organic polymer materials to improve the film-forming properties of the materials. However, the refractive index of organic polymer materials is relatively low. When inorganic nano materials are compounded with organic polymer materials, the higher the content of organic polymer materials, the better the film-forming properties, but the refractive index drops sharply. In order to obtain a high refractive index titanium dioxide thin film material, the polymer material also needs to have a high refractive index during compounding. Secondly, when organic-inorganic materials are compounded, the compatibility between organic and inorganic materials also needs to be considered to avoid phase separation during processing. In recent years, with the development of electro-optic modulation technology, people use the refractive index to modulate the propagation of light. Achieving the cyclic reversibility of the refractive index of materials is a necessary condition for the reversible modulation of light propagation. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for reversibly regulating the refractive index of a nano-titanium dioxide thin film. This method constructs a valence bond complex of conjugated sulfur-containing polymers and nano-titanium dioxide to obtain a titanium dioxide-based thin film material with a high refractive index, and at the same time realizes the reversible regulation of the refractive index of the thin film by using the reversible change of the anthracene structure.

[0004] The technical solution adopted by the present invention is a method for reversibly regulating the refractive index of a nano-titanium dioxide thin film, which specifically includes the following steps:

[0005] Step 1, modifying titanium dioxide with acrylic acid;

[0006] Step 2, preparing a polymer with a reversible structure;

[0007] Step 3, preparing reversibly refractive-indexed titanium dioxide according to the products obtained in Step 1 and Step 2;

[0008] Step 4, preparing a reversibly refractive-indexed titanium dioxide thin film according to the product obtained in Step 3.

[0009] The characteristics of the present invention also lie in:

[0010] The specific process of Step 1 is as follows:

[0011] Step 1.1: Take 10 - 15 g of titanium dioxide powder, add 30 - 40 mL of phosphate ester type dispersant, put it into a nano ball mill, and mill for 48 - 72 h at room temperature. After the milling is completed, filter it and wash it 3 - 5 times with 50 - 75 mL of dimethyl sulfoxide, then wash it 3 - 5 times with 50 - 75 mL of ethanol and deionized water, and dry it for 12 - 18 h at 45 - 60 °C to obtain activated nano titanium dioxide;

[0012] Step 1.2: Take 5 - 10 g of the activated nano carbon dioxide obtained in Step 1.1, add 0.5 - 1 mL of acrylic acid and 0.1 - 0.15 g of nitroxide piperidone, raise the temperature to 80 - 90 °C, then add 0.02 - 0.04 g of phosphoric acid and react for 30 - 45 min to obtain acrylic acid modified titanium dioxide.

[0013] The specific process of Step 2 is as follows:

[0014] Take 3.61 - 7.22 g of 2,7 - anthracenedithiol and 2.83 - 5.66 g of 3,7 - dichlorodibenzo[b,d]thiophene 5,5 - dioxide and dissolve them in 10 - 20 mL of sulfolane solution, add 0.2 - 0.3 g of potassium carbonate, react under a nitrogen protection atmosphere at 180 - 190 °C for 15 - 20 min. After the reaction is completed, add 1 - 1.2 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, impregnate and wash it with 100 - 150 mL of industrial alcohol for three times, and dry the washed product at 45 - 60 °C for 12 - 18 h to obtain a structure - reversible polymer.

[0015] The specific process of Step 3 is as follows:

[0016] Take 2 - 4 g of acrylic acid modified titanium dioxide and disperse it in 10 - 15 mL of anhydrous N - methylpyrrolidone solution, then sequentially add 0.1 - 0.15 mL of isocyanate ethyl acrylate, 1.5 - 3 g of 2 - iodostyrene and 0.02 - 0.03 g of azobisisobutyronitrile, and react under nitrogen conditions at 65 - 85 °C for 12 - 18 h; then, lower the reaction temperature to 45 - 50 °C, add 4 - 8 g of the structure - reversible polymer obtained in Step 2, and continue to stir for 3 - 6 h. After the reaction is completed, add anhydrous ethanol to quench the reaction, and at the same time, colorless solid powder precipitates. Collect the solid powder and dry it at 45 - 50 °C for 12 - 18 h to obtain titanium dioxide with reversible refractive index.

[0017] The specific process of Step 4 is as follows: Take 100 - 150 mg of titanium dioxide with reversible refractive index and disperse it in 20 - 30 mL of a mixed solution of dichlorotoluene and N - methylpyrrolidone to obtain a mixed solution. Spin - coat this mixed solution on the surface of a single - crystal silicon wafer at a rotational speed of 3000 - 4000 r / min, and the thickness of the spin - coated film is 25 - 30 μm, thus obtaining a film with reversible refractive index.

[0018] The beneficial effect of the present invention is that the present invention is prepared by compounding a polymer with high refractive index and nano - titanium dioxide, obtaining a high - refractive - index thin - film material. When the mass ratio of the inorganic component titanium dioxide is less than 30%, the refractive index can reach 1.98. Since the mass ratio of the organic component is more than 70%, as a polymer material, its refractive index is much higher than that of traditional polymer materials (1.3 - 1.65). And by using the reversible change of the anthracene structure in the material, the reversible regulation of the refractive index is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the UV oxidation and heating deoxidation processes of the thin - film material in the method for reversibly regulating the refractive index of the nano - titanium dioxide thin film of the present invention;

[0020] Figure 2 It is a schematic diagram of the initial refractive index of the thin film in Example 1 and the reversible cyclic change of the refractive index during UV oxidation and heating deoxidation in the method for reversibly regulating the refractive index of the nano - titanium dioxide thin film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0022] The method for reversibly regulating the refractive index of the nano - titanium dioxide thin film of the present invention specifically includes the following:

[0023] Step 1, acrylic - modified titanium dioxide, specifically:

[0024] Take titanium dioxide powder (10 - 15 g) with a nano - size specification of 20 - 30 nm, add 30 - 40 mL of a phosphate - type dispersant, put it into a nano - ball mill, and ball - mill at room temperature for 48 - 72 h. After the ball - milling is completed, filter and wash it 3 - 5 times with 50 - 75 mL of dimethyl sulfoxide, and then wash it 3 - 5 times with 50 - 75 mL of ethanol and deionized water (v:v = 1:1), and further dry it at 45 - 60 °C for 12 - 18 h to obtain activated nano - titanium dioxide. Take 5 - 10 g of the activated nano - titanium dioxide, add 0.5 - 1 mL of acrylic acid and 0.1 - 0.15 g of nitroxide piperidone, raise the temperature to 80 - 90 °C, and then add 0.02 - 0.04 g of catalyst phosphoric acid and continuously react for 30 - 45 min to obtain acrylic - modified titanium dioxide.

[0025] Step 2, Preparation of the structurally reversible polymer, specifically:

[0026] Take 3.61 - 7.22 g (in excess) of 2,7 - anthracenedithiol and 2.83 - 5.66 g of 3,7 - dichlorodibenzo[b,d]thiophene 5,5 - dioxide and dissolve them in 10 - 20 mL of sulfolane solution. Further add 0.2 - 0.3 g of potassium carbonate. Under a nitrogen - protection atmosphere, react at 180 - 190 °C for 15 - 20 min. After the reaction, add 1 - 1.2 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, further impregnate and wash it with 100 - 150 mL of industrial alcohol three times, and dry the sample at 45 - 60 °C for 12 - 18 h for standby.

[0027] Step 3, Preparation of the titanium dioxide with reversible refractive index, specifically:

[0028] Take 2 - 4 g of acrylic - acid - modified titanium dioxide and disperse it in 10 - 15 mL of anhydrous N - methylpyrrolidone solution. Then add 0.1 - 0.15 mL of isocyanate ethyl acrylate, 1.5 - 3 g of 2 - iodostyrene, and 0.02 - 0.03 g of azobisisobutyronitrile. React under nitrogen conditions at 65 - 85 °C for 12 - 18 h. Then, lower the reaction temperature to 45 - 50 °C, add 4 - 8 g of the structurally reversible polymer, and continue stirring for 3 - 6 h. After the reaction, add anhydrous ethanol to quench the reaction, and at the same time, colorless solid powder precipitates. Collect the solid powder and dry it at 45 - 50 °C for 12 - 18 h.

[0029] Step 4, Preparation of the thin film with reversible refractive index, specifically:

[0030] Take 100 - 150 mg of the titanium dioxide with reversible refractive index and disperse it in 20 - 30 mL of a mixed solution of dichlorotoluene and N - methylpyrrolidone (v:v = 1:1). Spin - coat this mixed solution on the surface of a 4 - cm - diameter single - crystal silicon wafer at 3000 - 4000 r / min, and the thickness of the spin - coated thin film is 25 - 30 μm. Then, use an ellipsometer to measure the refractive index of the thin film.

[0031] As Figure 1 shown, for the reversible refractive - index test, first irradiate the material under an O 2 atmosphere and 365 - nm ultraviolet lamp for 2 - 3 min, and then measure its refractive index. Then heat it at 65 - 80 °C under a nitrogen atmosphere for 12 - 24 h, and then measure its refractive index. The ultraviolet - irradiation oxidation and heating - reduction processes are repeated, and the refractive - index change is measured.

[0032] Example 1

[0033] Step 1, Acrylic - acid - modified titanium dioxide, specifically:

[0034] Take titanium dioxide powder (10 g) with a nano-size specification of 20 nm, add 30 mL of a phosphate ester-type dispersant, put it into a nano ball mill, and ball mill for 48 h at room temperature. After the ball milling is completed, filter and wash 3 times with 50 mL of dimethyl sulfoxide, then wash 3 times with 50 mL of ethanol and deionized water (v:v = 1:1), and further dry at 45 °C for 12 h to obtain activated nano titanium dioxide. Take 5 g of the activated nano titanium dioxide, add 0.5 mL of acrylic acid and 0.1 g of nitroxide piperidone, raise the temperature to 80 °C, and then add 0.02 g of catalyst phosphoric acid and continue the reaction for 30 min to obtain acrylic acid-modified titanium dioxide.

[0035] Step 2, preparation of a structure-reversible polymer, specifically:

[0036] Take 3.61 g (in excess) of 2,7-anthracenedithiol and 2.83 g of 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide and dissolve them in 10 mL of a sulfolane solution. Further add 0.2 g of potassium carbonate. React at 180 °C for 15 min under a nitrogen protection atmosphere. After the reaction is completed, add 1 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, and further impregnate and wash with 100 mL of industrial alcohol three times. Dry the washed sample at 45 °C for 12 h for standby.

[0037] Step 3, preparation of titanium dioxide with reversible refractive index, specifically:

[0038] Take 2 g of acrylic acid-modified titanium dioxide and disperse it in 10 mL of anhydrous N-methylpyrrolidone solution. Then add 0.1 mL of isocyanate ethyl acrylate, 1.5 g of 2-iodostyrene, and 0.02 g of azobisisobutyronitrile. React at 65 °C for 12 h under a nitrogen condition. Then, lower the reaction temperature to 45 °C, add 4 g of the structure-reversible polymer (prepared in Step 2), and continue stirring for 3 h. After the reaction is completed, add anhydrous ethanol to quench the reaction, and at the same time, a colorless solid powder precipitates. Collect the solid powder and dry it at 45 °C for 12 h.

[0039] Step 4, preparation of a refractive-index-reversible thin film, specifically:

[0040] Take 100 mg of titanium dioxide with reversible refractive index and disperse it in a mixed solution of 20 mL of dichlorotoluene and N-methylpyrrolidone (v:v = 1:1). Spin-coat this mixed solution on the surface of a 4-cm-diameter single-crystalline silicon wafer at 3000 r / min, with the thickness of the spin-coated thin film being 25 μm, and then measure the refractive index of the thin film using an ellipsometer.

[0041] Refractive-index-reversible test. First, place the material in O 2Under an atmosphere and irradiated with a 365 nm ultraviolet lamp for 2 min, and then its refractive index was measured. Then it was heated at 65 °C for 12 h under a nitrogen atmosphere, and then its refractive index was measured. The processes of ultraviolet irradiation oxidation and heating reduction were repeated, and the change in refractive index was measured.

[0042] Comparative Example 1 (The titanium dioxide was not modified, and the refractive index of the prepared film was uneven, mainly due to the large density of titanium dioxide)

[0043] Step 1, Preparation of a structurally reversible polymer, specifically:

[0044] Take 3.61 g (in excess) of 2,7-anthracenedithiol and 2.83 g of 3,7-dichlorodibenzothiophene 5,5-dioxide and dissolve them in 10 mL of sulfolane solution. Further add 0.2 g of potassium carbonate. Under a nitrogen protection atmosphere, react at 180 °C for 15 min. After the reaction, add 1 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, and further impregnate and wash it with 100 mL of industrial alcohol three times. Dry the washed sample at 45 °C for 12 h for standby.

[0045] Step 2, Preparation of titanium dioxide with reversible refractive index, specifically:

[0046] Take 2 g of titanium dioxide and disperse it in 10 mL of anhydrous N-methylpyrrolidone solution. Then add 0.1 mL of isocyanate ethyl acrylate, 1.5 g of 2-iodostyrene, and 0.02 g of azobisisobutyronitrile. React under nitrogen conditions and at 65 °C for 12 h. Then, lower the reaction temperature to 45 °C, add 4 g of the structurally reversible polymer, and continue stirring for 3 h. After the reaction, add anhydrous ethanol to quench the reaction, and at the same time, colorless solid powder precipitates. Collect the solid powder and dry it at 45 °C for 12 h.

[0047] Step 3, Preparation of a film with reversible refractive index, specifically:

[0048] Take 100 mg of titanium dioxide with reversible refractive index and disperse it in a mixed solution of 20 mL of dichlorotoluene and N-methylpyrrolidone (v:v = 1:1). Spin-coat this mixed solution on the surface of a 4-cm-diameter single-crystalline silicon wafer at 3000 r / min. The thickness of the spin-coated film is 25 μm, and then use an ellipsometer to measure the refractive index of the film.

[0049] Reversible refractive index test. First, place the material in an O 2 Under an atmosphere and irradiated with a 365 nm ultraviolet lamp for 2 min, and then its refractive index was measured. Then it was heated at 65 °C for 12 h under a nitrogen atmosphere, and then its refractive index was measured. The processes of ultraviolet irradiation oxidation and heating reduction were repeated, and the change in refractive index was measured.

[0050] Comparative Example 2 (Ethyl acrylate is substituted for ethyl isocyanate acrylate in the titanium dioxide structure with reversible refractive index. Since there is no isocyanate structural unit, it cannot react with the mercapto group in the reversibly structured polymer, resulting in uneven refractive index)

[0051] Step 1, Acrylic acid modified titanium dioxide, specifically:

[0052] Take titanium dioxide powder (10 g) with a nano-size specification of 20 nm, add 30 mL of phosphate ester type dispersant, put it into a nano ball mill, and ball mill at room temperature for 48 h. After the ball milling is completed, filter and wash it 3 times with 50 mL of dimethyl sulfoxide, then wash it 3 times with 50 mL of ethanol and deionized water (v:v = 1:1), and further dry it at 45 °C for 12 h to obtain activated nano titanium dioxide. Take 5 g of the activated nano titanium dioxide, add 0.5 mL of acrylic acid and 0.1 g of nitroxide piperidone, raise the temperature to 80 °C, then add 0.02 g of catalyst phosphoric acid and continue the reaction for 30 min to obtain acrylic acid modified titanium dioxide.

[0053] Step 2, Preparation of the reversibly structured polymer, specifically:

[0054] Take 3.61 g (in excess) of 2,7-anthracenedithiol and 2.83 g of 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide and dissolve them in 10 mL of sulfolane solution. Further add 0.2 g of potassium carbonate. Under the protection of nitrogen atmosphere, react at 180 °C for 15 min. After the reaction is completed, add 1 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, and further impregnate and wash it with 100 mL of industrial alcohol three times. Dry the sample at 45 °C for 12 h for standby.

[0055] Step 3, Preparation of titanium dioxide with reversible refractive index, specifically:

[0056] Take 2 g of acrylic acid modified titanium dioxide and disperse it in 10 mL of anhydrous N-methylpyrrolidone solution. Then add 0.1 mL of ethyl acrylate, 1.5 g of 2-iodostyrene and 0.02 g of azobisisobutyronitrile. React at 65 °C under nitrogen conditions for 12 h. Then, lower the reaction temperature to 45 °C, add 4 g of the reversibly structured polymer, and continue stirring for 3 h. After the reaction is completed, add anhydrous ethanol to quench the reaction, and at the same time, colorless solid powder precipitates. Collect the solid powder and dry it at 45 °C for 12 h.

[0057] Step 4, Preparation of the refractive index reversible film, specifically:

[0058] Disperse 100 mg of titanium dioxide with reversible refractive index in a mixed solution of 20 mL of dichlorotoluene and N-methylpyrrolidone (v:v = 1:1). Spin-coat this mixed solution on the surface of a 4-cm-diameter single-crystal silicon wafer at 3000 r / min. The thickness of the spin-coated film is 25 μm, and then use an ellipsometer to measure the refractive index of the film.

[0059] For the reversible refractive index test, first irradiate the material with a 365-nm ultraviolet lamp in an O 2 atmosphere for 2 min, and then measure its refractive index. Then heat it at 65 °C in a nitrogen atmosphere for 12 h, and then measure its refractive index. The processes of ultraviolet irradiation oxidation and heating reduction are repeated, and the change in refractive index is measured.

[0060] Comparative Example 3 (When synthesizing the structure-reversible polymer, 2,7-anthracenedithiol is replaced with 1,4-benzenedithiol, there is no reversible response in the refractive index, and at the same time the refractive index decreases)

[0061] Step 1, Modify titanium dioxide with acrylic acid, specifically:

[0062] Take 10 g of titanium dioxide powder with a nanometer size specification of 20 nm, add 30 mL of a phosphate ester dispersant, put it into a nanosphere mill, and mill it at room temperature for 48 h. After the milling is completed, filter it and wash it 3 times with 50 mL of dimethyl sulfoxide, and then wash it 3 times with 50 mL of ethanol and deionized water (v:v = 1:1), and further dry it at 45 °C for 12 h to obtain activated nanometer titanium dioxide. Take 5 g of the activated nano-carbon dioxide, add 0.5 mL of acrylic acid and 0.1 g of nitroxide piperidone, raise the temperature to 80 °C, and then add 0.02 g of catalyst phosphoric acid and continue the reaction for 30 min to obtain acrylic acid-modified titanium dioxide.

[0063] Step 2, Preparation of the structure-reversible polymer, specifically:

[0064] Dissolve 2.13 g (in excess) of 1,4-benzenedithiol and 2.83 g of 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide in 10 mL of sulfolane solution, and further add 0.2 g of potassium carbonate. Under a nitrogen protection atmosphere, react at 180 °C for 15 min. After the reaction is completed, add a 1 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, further immerse and wash it with 100 mL of industrial alcohol three times, and dry the sample at 45 °C for 12 h for standby.

[0065] Step 3, Preparation of titanium dioxide with reversible refractive index, specifically:

[0066] Take 2 g of acrylic acid modified titanium dioxide and disperse it in 10 mL of anhydrous N-methylpyrrolidone solution. Then add 0.1 mL of isocyanate ethyl acrylate, 1.5 g of 2-iodostyrene and 0.02 g of azobisisobutyronitrile. React under nitrogen conditions at 65 °C for 12 h. Then, lower the reaction temperature to 45 °C, add 4 g of a structurally reversible polymer, and continue stirring for 3 h. After the reaction is completed, add anhydrous ethanol to quench the reaction, and at the same time, colorless solid powder precipitates. Collect the solid powder and dry it at 45 °C for 12 h.

[0067] Step 4, Preparation of the refractive index reversible film, specifically:

[0068] Take 100 mg of refractive index reversible titanium dioxide and disperse it in a mixed solution of 20 mL of dichlorotoluene and N-methylpyrrolidone (v:v = 1:1). Spin-coat this mixed solution on the surface of a 4 cm diameter single crystal silicon wafer at 3000 r / min, with the spin-coated film thickness being 25 μm, and then use an ellipsometer to measure the refractive index of the film.

[0069] Refractive index reversible test. First, irradiate the material with a 365 nm ultraviolet lamp in an O 2 atmosphere for 2 min, and then measure its refractive index. Then heat it at 65 °C in a nitrogen atmosphere for 12 h, and then measure its refractive index. The ultraviolet irradiation oxidation and heating reduction processes are repeated, and the change in refractive index is measured.

[0070] Comparative Example 4 (Replace 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide with p-dichlorobenzyl, refractive index decreases)

[0071] Step 1, Acrylic acid modified titanium dioxide, specifically:

[0072] Take titanium dioxide powder (10 g) with a nanosize specification of 20 nm, add 30 mL of a phosphate ester type dispersant, put it into a nanosphere mill, and ball mill at room temperature for 48 h. After the ball milling is completed, filter and wash it 3 times with 50 mL of dimethyl sulfoxide, and then wash it 3 times with 50 mL of ethanol and deionized water (v:v = 1:1), and further dry it at 45 °C for 12 h to obtain activated nanometer titanium dioxide. Take 5 g of the activated nano-carbon dioxide, add 0.5 mL of acrylic acid and 0.1 g of nitroxide piperidone, raise the temperature to 80 °C, and then add 0.02 g of catalyst phosphoric acid and continue the reaction for 30 min to obtain acrylic acid modified titanium dioxide.

[0073] Step 2, Preparation of the structurally reversible polymer, specifically:

[0074] 3.61 g (excess) of 2,7-anthracenedithiol and 1.75 g of p-dichlorobenzyl were dissolved in 10 mL of sulfolane solution, and 0.2 g of potassium carbonate was further added. Under a nitrogen protection atmosphere, the reaction was carried out at 180 °C for 15 min. After the reaction, 1 mol / L acetic acid solution was added to neutralize the reaction, the precipitate was collected, and it was further impregnated and washed with 100 mL of industrial alcohol three times. The sample was dried at 45 °C for 12 h for standby.

[0075] Step 3, preparation of titanium dioxide with reversible refractive index, specifically:

[0076] 2 g of acrylic acid-modified titanium dioxide was dispersed in 10 mL of anhydrous N-methylpyrrolidone solution, and then 0.1 mL of isocyanate ethyl acrylate, 1.5 g of 2-iodostyrene and 0.02 g of azobisisobutyronitrile were added. The reaction was carried out at 65 °C for 12 h under nitrogen conditions. Then, the reaction temperature was lowered to 45 °C, 4 g of a structurally reversible polymer was added, and stirring was continued for 3 h. After the reaction, anhydrous ethanol was added to quench the reaction, and a colorless solid powder precipitated out. The solid powder was collected and dried at 45 °C for 12 h.

[0077] Step 4, preparation of a thin film with reversible refractive index, specifically:

[0078] 100 mg of titanium dioxide with reversible refractive index was dispersed in 20 mL of a mixed solution of dichlorotoluene and N-methylpyrrolidone (v:v = 1:1). This mixed solution was spin-coated on the surface of a 4-cm-diameter single-crystalline silicon wafer at 3000 r / min, and the thickness of the spin-coated film was 25 μm. Then, an ellipsometer was used to measure the refractive index of the film.

[0079] Reversible refractive index test. First, the material was irradiated with a 365-nm ultraviolet lamp for 2 min in an O 2 atmosphere, and then its refractive index was measured. Then, it was heated at 65 °C for 12 h in a nitrogen atmosphere, and then its refractive index was measured. The processes of ultraviolet irradiation oxidation and heating reduction were repeated, and the refractive index changes were measured.

[0080] Result discussion

[0081] Table 1 Comparison of optical properties of Example 1 and Comparative Examples 1-4

[0082]

[0083]

[0084] Refractive index uniformity aTesting. The testing method is that the relative difference in refractive index at the center point of the circular film, at a radius of 1 cm, and at a radius of 2 cm is less than 5% for uniformity, and greater than % for non-uniformity. At the same time, the refractive index value corresponds to a wavelength of 589 nm. Examples 1 and Comparative Examples 1-4 are all colorless transparent materials, which is beneficial for their application in the optical field.

[0085] Nano-titanium dioxide is an inorganic powder material and cannot form a film by itself. It is necessary to introduce a polymer to form a film, but the addition of the polymer will cause a decrease in the overall refractive index. As shown in Table 1, Examples 1 and Comparative Examples 1-2 have relatively high refractive indices: on the one hand, titanium dioxide itself has a relatively high refractive index (2.4 - 2.6); on the other hand, the polymers used also have a high refractive index because the polymer materials all contain highly conjugated aromatic rings (anthracene, biphenyl) and sulfur (sulfide, dioxythiophene sulfur), which endow them with a high refractive index.

[0086] Examples 1 and Comparative Examples 1-2, 4 all contain anthracene compounds in their film structures. Under UV and O2 conditions, the anthracene ring is oxidized as Figure 1 shown, resulting in a decrease in conjugation and a decrease in refractive index; while under nitrogen conditions and heating, after removing O2, the conjugation increases and the refractive index increases.

[0087] In Comparative Example 3, 2,7-anthracenedithiol is replaced with 1,4-benzenedithiol. The decrease in conjugation of the polymer component leads to a low refractive index. At the same time, due to the lack of anthracene structure, refractive index regulation cannot be achieved under UV and heating conditions. In Comparative Example 4, 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide is replaced with p-dichlorobenzyl. The conjugation decreases without the biphenyl structure, and there is no dioxythiophene sulfur, resulting in the lowest refractive index.

[0088] It should be noted that the refractive indices of Comparative Examples 1-2 are not uniform in different regions. The main reason is that in Comparative Examples 1 and 2, the titanium dioxide component and the polymer component do not react. Therefore, the spin coating solution during film preparation is a physical mixture of the titanium dioxide component and the polymer component. However, the density of the titanium dioxide (about 41.4 g·cm -1 ) component is much higher than that of the polymer component (about 1.4 g·cm -1 ). Due to the relatively high rotation speed (3000 r / min) during spin coating, the centrifugal force and inertia are different, and the two undergo phase separation, resulting in non-uniform refractive index distribution.

[0089] As Figure 2 shown, the film material of Example 1 undergoes 5 cycles of UV oxidation and heating deoxidation processes. The refractive index change rule corresponds one-to-one with UV oxidation and heating deoxidation, and the cyclic change rule is obvious. Importantly, after five cycles, the refractive index is almost unchanged from the refractive index in the first cycle, maintaining a relatively high refractive index of 1.96.

[0090] Example 2

[0091] Step 1: Acrylic acid modified titanium dioxide, specifically:

[0092] Take 12 g of titanium dioxide powder with a nanosize specification of 25 nm, add 35 mL of phosphate ester type dispersant, put it into a nanosphere mill, and ball mill for 65 h at room temperature. After the ball milling is completed, filter and wash 4 times with 60 mL of dimethyl sulfoxide, then wash 4 times with 60 mL of ethanol and deionized water (v:v = 1:1), and further dry at 55 °C for 16 h to obtain activated nanometer titanium dioxide. Take 8 g of activated nanometer carbon dioxide, add 0.8 mL of acrylic acid and 0.12 g of nitroxide piperidone, raise the temperature to 85 °C, then add 0.03 g of catalyst phosphoric acid and continue the reaction for 40 min to obtain acrylic acid modified titanium dioxide.

[0093] Step 2: Preparation of a structurally reversible polymer, specifically:

[0094] Take 4.82 g (in excess) of 2,7-anthracenedithiol and 3.68 g of 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide and dissolve them in 15 mL of sulfolane solution. Further add 0.25 g of potassium carbonate. React at 185 °C for 18 min under a nitrogen protection atmosphere. After the reaction is completed, add 1.15 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, and further impregnate and wash with 120 mL of industrial alcohol three times. Dry the washed sample at 55 °C for 16 h for standby.

[0095] Step 3: Preparation of titanium dioxide with reversible refractive index, specifically:

[0096] Take 3 g of acrylic acid modified titanium dioxide and disperse it in 12 mL of anhydrous N-methylpyrrolidone solution, then add 0.12 mL of isocyanate ethyl acrylate, 2 g of 2-iodostyrene, and 0.025 g of azobisisobutyronitrile. React at 75 °C for 16 h under nitrogen conditions. Then, lower the reaction temperature to 48 °C, add 6 g of the structurally reversible polymer (prepared in Step 2), and continue stirring for 4 h. After the reaction is completed, add anhydrous ethanol to quench the reaction, and at the same time, colorless solid powder precipitates. Collect the solid powder and dry it at 48 °C for 16 h.

[0097] Step 4: Preparation of a thin film with reversible refractive index, specifically:

[0098] Take 120 mg of titanium dioxide with reversible refractive index and disperse it in a mixed solution of 25 mL of dichlorotoluene and N-methylpyrrolidone (v:v = 1:1). Spin-coat this mixed solution on the surface of a 4-cm diameter single-crystalline silicon wafer at 3500 r / min, and the thickness of the spin-coated film is 28 μm. Then, use an ellipsometer to measure the refractive index of the film.

[0099] Reversible refractive index test. First, the material is irradiated with a 365 nm ultraviolet lamp in an O 2 atmosphere for 2.5 min, and then its refractive index is measured. Then, it is heated at 70 °C for 18 h in a nitrogen atmosphere, and then its refractive index is measured. The processes of ultraviolet irradiation oxidation and heating reduction are repeated, and the change in refractive index is measured.

[0100] Example 3

[0101] Step 1: Acrylic acid modified titanium dioxide, specifically:

[0102] Take titanium dioxide powder (15 g) with a nanoscale specification of 30 nm, add 40 mL of phosphate ester type dispersant, put it into a nanosphere mill, and mill it at room temperature for 72 h. After the milling is completed, filter it and wash it 5 times with 75 mL of dimethyl sulfoxide, then wash it 5 times with 75 mL of ethanol and deionized water (v:v = 1:1), and further dry it at 60 °C for 18 h to obtain activated nanoscale titanium dioxide. Take 10 g of the activated nano-carbon dioxide, add 1 mL of acrylic acid and 0.15 g of nitroxide piperidone, raise the temperature to 90 °C, and then add 0.04 g of catalyst phosphoric acid and continue the reaction for 45 min to obtain acrylic acid modified titanium dioxide.

[0103] Step 2: Preparation of a structurally reversible polymer, specifically:

[0104] Take 7.22 g (in excess) of 2,7-anthracenedithiol and 5.66 g of 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide and dissolve them in 20 mL of sulfolane solution. Further add 0.3 g of potassium carbonate. Under a nitrogen protection atmosphere, react at 190 °C for 20 min. After the reaction is completed, add 1.2 mol / L acetic acid solution to neutralize the reaction, collect the precipitate, further impregnate and wash it with 150 mL of industrial alcohol three times, and dry the washed sample at 60 °C for 18 h for standby.

[0105] Step 3: Preparation of titanium dioxide with reversible refractive index, specifically:

[0106] Take 4 g of acrylic acid modified titanium dioxide and disperse it in 15 mL of anhydrous N-methylpyrrolidone solution, then add 0.15 mL of isocyanate ethyl acrylate, 3 g of 2-iodostyrene, and 0.03 g of azobisisobutyronitrile. React at 85 °C for 18 h under a nitrogen condition. Then, lower the reaction temperature to 50 °C, add 8 g of the structurally reversible polymer (prepared in Step 2), and continue stirring for 6 h. After the reaction is completed, add anhydrous ethanol to quench the reaction, and at the same time, colorless solid powder precipitates. Collect the solid powder and dry it at 50 °C for 18 h.

[0107] Step 4: Preparation of a thin film with reversible refractive index, specifically:

[0108] 150 mg of titanium dioxide with reversible refractive index was dispersed in 30 mL of a mixed solution of dichlorotoluene and N-methylpyrrolidone (v:v = 1:1). The mixed solution was spin-coated on the surface of a 4-cm-diameter single-crystalline silicon wafer at 4000 r / min, and the thickness of the spin-coated film was 30 μm. Then, an ellipsometer was used to measure the refractive index of the film.

[0109] For the reversible refractive index test, first, the material was irradiated with a 365-nm ultraviolet lamp in an O 2 atmosphere for 3 min, and then its refractive index was measured. Then, it was heated at 80 °C for 24 h in a nitrogen atmosphere, and then its refractive index was measured. The processes of ultraviolet irradiation oxidation and heating reduction were repeated, and the change in refractive index was measured.

Claims

1. A method for reversibly controlling the refractive index of a nano-titanium dioxide film, characterized in that: The specific steps include: Step 1, using acrylic acid to modify titanium dioxide; Step 2, preparing a structurally reversible polymer; Step 3, preparing titanium dioxide with reversible refractive index according to the products obtained in step 1 and step 2; Step 4, preparing a titanium dioxide film with reversible refractive index according to the product obtained in step 3.

2. The method for reversibly controlling the refractive index of a nano-titanium dioxide film according to claim 1, characterized in that: The specific process of step 1 is as follows: Step 1.1, taking 10-15g of titanium dioxide powder, adding 30-40mL of phosphate dispersant, putting it into a nano ball mill, and ball milling it at room temperature for 48-72h. After the ball milling is completed, filtering it, washing it with 50-75mL of dimethyl sulfoxide for 3-5 times, and then washing it with 50-75mL of ethanol and deionized water for 3-5 times, and drying it at 45-60°C for 12-18h to obtain activated nano titanium dioxide; Step 1.2, take 5-10 g of the activated nano carbon dioxide obtained in step 1.1, add 0.5-1 mL of acrylic acid and 0.1-0.15 g of nitroxyl radical pyridone, raise the temperature to 80-90° C., then add 0.02-0.04 g of phosphoric acid and continue the reaction for 30-45 min to obtain acrylic acid-modified titanium dioxide.

3. The method for reversibly controlling the refractive index of a nano-titanium dioxide film according to claim 2, characterized in that: The specific process of step 2 is as follows: 3.61-7.22 g of 2,7-anthracenedithiol and 2.83-5.66 g of 3,7-dichlorodibenzo[b,d]thiophene 5,5-dioxide are dissolved in 10-20 mL of cyclopentane sulfone solution, 0.2-0.3 g of potassium carbonate is added, and the mixture is reacted at 180-190° C. for 15-20 min under a nitrogen atmosphere. After the reaction, 1-1.2 mol / L acetic acid solution is added to neutralize the reaction, and the precipitate is collected and washed by immersion with 100-150 mL of industrial alcohol, which is repeated three times. The washed product is dried at 45-60° C. for 12-18 h to obtain a structurally reversible polymer.

4. The method for reversibly controlling the refractive index of a nano-titanium dioxide film according to claim 3, characterized in that: The specific process of step 3 is as follows: Take 2-4g of acrylic acid modified titanium dioxide and disperse it in 10-15mL of anhydrous N-methylpyrrolidone solution, then add 0.1-0.15mL of isocyanate ethyl acrylate, 1.5-3g of 2-iodostyrene and 0.02-0.03g of azobisisobutyronitrile in sequence, and react for 12-18h at 65-85℃ under nitrogen conditions; then, reduce the reaction temperature to 45-50℃, add 4-8g of the structurally reversible polymer obtained in step 2, and continue stirring for 3-6h. After the reaction is completed, add anhydrous ethanol to quench the reaction, and colorless solid powder is precipitated. Collect the solid powder and dry it at 45-50℃ for 12-18h to obtain titanium dioxide with reversible refractive index.

5. The method for reversibly controlling the refractive index of a nano-titanium dioxide film according to claim 4, characterized in that: The specific process of step 4 is: taking 100-150 mg of titanium dioxide with reversible refractive index and dispersing it in 20-30 mL of a mixed solution of dichlorotoluene and N-methylpyrrolidone to obtain a mixed solution, and spin-coating the mixed solution on the surface of a single crystal silicon wafer at a rotation speed of 3000-4000 r / min, and the thickness of the spin-coated film is 25-30 um, so as to obtain a refractive index reversible film.

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