A thermochromic polymer photonic film with color-changeable path programmability and application thereof

Abstract

The application discloses a thermochromic polymer photonic film with programmable color change path and application thereof. The photonic film is formed by self-assembly of bottlebrush block copolymer. The bottlebrush block copolymer comprises a main chain and a side chain grafted on the main chain. The side chain comprises a flexible first block and a rigid second block. When the rigid second block is a non-crystalline block, the photonic film is color stable during the heating and cooling processes. When the rigid second block is a crystalline block and the polymerization degree of the flexible first block is 40-80, the photonic film presents a monotone red shift and a monotone blue shift color evolution path during the heating and cooling processes respectively. When the rigid second block is a crystalline block and the polymerization degree of the flexible first block is not more than 40, the photonic film presents a color evolution path of red shift first and then blue shift during the heating and cooling processes. The application can be used for designing a complex thermochromic path and has application prospects in dynamic display, anti-fake identification and the like.

Description

Technical Field

[0001] This application relates to the field of dynamic response structural color technology, specifically to a thermochromic polymer photonic thin film with a programmable color-changing path and its applications. Background Technology

[0002] Thermochromic materials change color with temperature, enabling direct optical reading of temperature variations and finding wide applications in thermal sensing, display technology, and adaptive devices. Beyond the magnitude of color change, controlling the thermochromic evolution path is equally important. However, the color evolution paths of existing thermochromic materials are largely determined by their structural or intrinsic chemical properties, typically exhibiting a single and fixed pattern, making multi-path programmable control difficult. Thermochromic materials based on physical structural color mechanisms, such as systems relying on liquid crystal phase transitions, polymer swelling behavior, or changes in colloidal crystal assembly structures, typically exhibit color changes determined by collective nanostructure rearrangement, presenting only a single and fixed color evolution path and lacking the ability to control the evolution pattern. Systems based on chemical color-emitting mechanisms, such as thermochromic dyes or pigments, typically trigger color changes through chemical reactions at specific temperatures, and their color evolution processes are often monotonous. Although these systems can achieve significant and reversible color changes, their color-changing paths are usually determined by the intrinsic properties of their molecular structure, making reprogramming or control difficult. Therefore, realizing multiple programmable color evolution paths in a single thermochromic system remains a challenging technical problem.

[0003] Polymers, composed of monomers, possess tunable chain topology and nanoscale structures, making them ideal materials for constructing thermoresponsive systems. Bottle brush block copolymers (BBCPs) are a class of macromolecules with high-density side-chain branching structures, capable of self-assembling into ordered nanostructures and producing structural colors. Their molecular configuration effectively suppresses chain entanglement, enabling the system to rapidly achieve microphase separation and form ordered nanostructures at the photon scale. The length, chemical composition, and crystallinity of the side chains play a crucial role in regulating the microphase separation process, thereby determining the periodic size of the nanostructures and the macroscopic structural color. In particular, bottle brush block copolymers containing crystalline side chains exhibit a change in the refractive index of their crystalline regions during heating, which can induce a significant and reversible structural color transition. Therefore, based on their multiple tunable parameters, including molecular structure, side-chain crystallinity, and inter-block interactions, bottle brush block copolymers have potential advantages in constructing material systems with different thermochromic pathways. Summary of the Invention

[0004] The purpose of this application is to provide a thermochromic polymer photonic thin film with a programmable color-changing path and its applications. This application utilizes a side-chain engineering strategy to control the structural parameters and crystallinity of bottle-brush block copolymers, thereby achieving programmable design of the thermochromic path.

[0005] On the one hand, this application provides a thermochromic polymer photonic film with a programmable color-changing path, which is formed by the self-assembly of a bottle brush block copolymer. The bottle brush block copolymer includes a main chain and side chains grafted onto the main chain. The side chains include a flexible first block and a rigid second block. When the rigid second block is an amorphous block, the corresponding photonic film is designated as a type I photonic film. The type I photonic film has stable color during both heating and cooling processes. When the rigid second block is a crystalline block and the degree of polymerization of the flexible first block is 40~80, the corresponding photonic film is denoted as a type II photonic film. The type II photonic film exhibits a monotonically red-shifted color evolution path during the heating process and a monotonically blue-shifted color evolution path during the cooling process. When the rigid second block is a crystalline block and the degree of polymerization of the flexible first block does not exceed 40, the corresponding photonic film is designated as a type III photonic film. The type III photonic film exhibits a color evolution path of first red shift and then blue shift during the heating and cooling process.

[0006] In this application, the thermochromic path of the bottle brush block copolymer photonic film can be controlled by adjusting the degree of polymerization (i.e., chain length) of the flexible first block and / or the crystallinity of the rigid second block of the bottle brush block copolymer.

[0007] During the process of heating from 0°C to 90°C and cooling from 90°C to 0°C, the Type I photonic thin film only undergoes slight color changes. For example, the redshift during the heating process from 0°C to 90°C does not exceed 2.5%, and it is considered to be color stable.

[0008] During the process of heating from 0°C to 90°C, the type II photonic thin film exhibits a monotonic redshift with an amplitude of 5% to 7%.

[0009] During the process of heating from 0°C to 90°C, the Type III photonic thin film first exhibits a red shift of 1% to 2.5%, followed by a blue shift of 8% to 9%.

[0010] Optionally, the volume of the rigid second segment accounts for 30% to 40%.

[0011] Optionally, the flexible first block is a polydimethylsiloxane block.

[0012] Optionally, the rigid second block is a polylactic acid block (PLA block), or a poly(lactic acid) block. ε - Caprolactone block (PCL block) or polyethylene oxide block (PEO block).

[0013] Bottle brush block copolymers can be represented as - ,in, These represent the flexible first segment and the rigid second segment, for example. It can be PDMS. It can be a PLA, PCL, or PEO block; x , y Main chain aggregation degree, a , b The degree of polymerization of the side chain. f %for Volume fraction.

[0014] In some embodiments, x The range is 110~210. y The value is 52~153.

[0015] On the other hand, this application also provides the application of the above-mentioned thermochromic polymer photonic thin film in dynamic information display, anti-counterfeiting mark or multi-threshold temperature sensor.

[0016] Specifically, the aforementioned Type II or Type III photonic thin films can be applied to dynamic information displays.

[0017] One specific application of the aforementioned thermochromic polymer photonic film in anti-counterfeiting labels is as follows: using type I photonic film as a non-responsive reference element and type II or type III photonic film as a temperature-responsive decoding element to construct two-dimensional encrypted information.

[0018] Specifically, the aforementioned Type III photonic thin film can be applied to multi-threshold temperature sensors. For example, by utilizing the characteristic of Type III photonic thin films to first red-shift and then blue-shift, a red-shift signal is output in the first temperature range and a blue-shift signal is output in the second temperature range during the heating process. The first temperature range is the temperature range in which the Type III photonic thin film red-shifts, and the second temperature range is the temperature range in which the Type III photonic thin film blue-shifts.

[0019] For example, a certain type III photonic thin film exhibits a redshift during the heating process from 0°C to 40°C and a blueshift during the heating process from 40°C to 90°C. In the operation of a multi-threshold temperature sensor, a redshift signal is output during the heating process from 0°C to 40°C and a blueshift signal is output during the heating process from 40°C to 90°C.

[0020] This application can be used to design structural color materials with complex thermal response paths, and has promising applications in fields such as dynamic display and anti-counterfeiting. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 The diagram shows the molecular structures of the three types of BBCPs prepared in the examples. Figure 2 Optical microscope images of the three types of BBCP photonic thin films prepared for this example, varying with temperature. Scale bar is 100. m; Figure 3 The reflection spectra of the three types of BBCP photonic thin films prepared for the example during the heating process; Figure 4 The curves showing the change in the relative displacement of the reflection peaks of the three types of BBCP photonic thin films prepared for the example during the heating process; Figure 5 The reflection spectra of a type III photonic thin film after being heated at 90 °C for 1 hour and 2 hours; Figure 6 The changes in the position of the reflection peak of type II and type III photonic thin films during heating and cooling cycles; Figure 7 The curves show the evolution of the reflection peak shift ratio, POM intensity, and normalized heat flux as a function of temperature for type II photonic thin films. Figure 8 The curves show the evolution of the reflection peak shift ratio, POM intensity, and normalized heat flux as a function of temperature for type III photonic thin films. Figure 9 The reflection spectra of PEO-based type II and type III photonic thin films at different temperatures; Figure 10 The sixth power of the reflection peak wavelength of a PLC-based Type III photonic thin film during heating. λ 6 With temperature change; Figure 11 Applications of Type III photonic thin films in information displays; Figure 12 This relates to the application of photonic thin films in two-dimensional information encryption. Detailed Implementation

[0023] To further illustrate this application, a detailed description is provided below with reference to embodiments and comparative examples. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of this application and are not intended to limit the scope of the claims of this application. Example 1

[0024] In this embodiment, bottle brush block polymer (BBCP) was synthesized using sequential ring-opening metathesis polymerization (ROMP) under anhydrous conditions inside the glove box. The specific steps are as follows: (1) Preparation of NBI-COOH: In a 500 mL single-necked round-bottom flask, add cis-5-norbornene-ex-2,3-dicarboxylic anhydride (6.0 g, 36.6 mmol, manufacturer: Aladdin Chemical, CAS: 2746-19-2), 6-aminohexanoic acid (4.8 g, 36.6 mmol, manufacturer: Aladdin Chemical, CAS: 60-32-2), and triethylamine (514.3 mg, 3.7 mmol, manufacturer: Aladdin Chemical, CAS: 121-44-8), and dissolve in 150 mL of toluene.

[0025] The flask was equipped with a magnetic stirrer, a Dean-Stark apparatus (water separator), and a reflux condenser. The reaction was carried out at 130°C with stirring for 16 hours. After the reaction was completed, the mixture was cooled to room temperature, and the crude product was washed with 1 mol / L hydrochloric acid aqueous solution. The organic phase was dried and rinsed with anhydrous water. After removing residual moisture, the solution was concentrated under reduced pressure to obtain a brown solid. The brown solid was recrystallized in ethyl acetate to give a white powdery 5-norbornene-2-carboxylic acid, denoted as NBI-COOH.

[0026] This step uses a dehydration imidization reaction to prepare NBI-COOH. Specifically, the target product 5-norbornen-2-carboxylic acid is obtained through a condensation ring-closing reaction between cis-5-norbornen-ex-2,3-dicarboxylic anhydride and 6-aminohexanoic acid.

[0027] (2) Preparation of long-side-chain macromonomer NBI-PDMS: In a 250 mL reaction flask, NBI-COOH (0.7 g, 2.5 mmol) and 4-dimethylaminopyridine (DMAP, 61.1 mg, 0.5 mmol, manufacturer: Adamas, CAS: 1122-58-7) were added and dissolved in 25 mL of anhydrous dichloromethane. At 0°C, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl, 668.3 mg, 3.5 mmol, manufacturer: Aladdin Chemicals, CAS: 25952-53-8) was slowly added, and the reaction was stirred for 15 minutes. Subsequently, monohydroxy-terminated polydimethylsiloxane (PDMS) was added. 68 -OH, 4.67 g, 1.0 mmol, manufacturer: Sigma-480355), continue stirring at room temperature for 48 hours.

[0028] After the reaction was complete, the mixture was diluted with dichloromethane and extracted successively with 1 mol / L hydrochloric acid aqueous solution and water. The collected organic phase was then treated with anhydrous water. The sample was dried to remove residual moisture. It was then purified by alkaline alumina column chromatography, concentrated under reduced pressure, and vacuum dried at 45°C for 24 hours to obtain norbornene-terminated polydimethylsiloxane macromonomers. It is a colorless liquid.

[0029] This step involves a condensation esterification reaction to prepare the product. Using EDC·HCl as a condensing agent and DMAP as a catalyst, NBI-COOH reacts with PDMS. 68 -OH undergoes dehydration condensation to form an ester bond, yielding the target product. The synthesis route is shown in equation (Ⅰ).

[0030] (I) (3) Preparation of short-side-chain macromonomer NBI-PDMS: In a 250 mL dry round-bottom flask, add exo-norborneol anhydride (2.8 g, 16.9 mmol, manufacturer: Aladdin Chemical, CAS: 2746-19-2) and monoaminopropyl-terminated polydimethylsiloxane (…). 34.9 g (17.50 mmol, manufacturer: Gelest MCR-A12) and triethylamine (303.6 mg (3.0 mmol, manufacturer: Aladdin Chemical, CAS: 121-44-8) were dissolved in 300 mL of toluene. The flask was equipped with a Dean-Stark apparatus, and the reaction was carried out under reflux at 130°C for 16 hours. After the reaction was complete, the solvent was removed under reduced pressure, and the crude product was purified by silica gel column chromatography to obtain norbornene-terminated polydimethylsiloxane macromonomers. It is a colorless liquid.

[0031] This step involves a dehydration imidization reaction to prepare... Specifically, to make extrin-norbornenoic anhydride and A condensation and ring-closure reaction occurs to obtain the target product. The synthesis route is shown in equation (II) below.

[0032] (II) (4) Preparation of macromonomer NB-PCL: In a 250 mL dry Schlenk flask, add 5-norbornene-2-methanol (0.83 g, 6.5 mmol, manufacturer: Adamas, CAS: 95-12-5), ε-caprolactone (ε-CL, 20 g, 175.4 mmol, manufacturer: Adamas, CAS: 502-44-3), and stannous octoate (… 0.1g (manufacturer: Adamas) was used to degas the mixture through three cycles of freezing, vacuuming, and nitrogen purging. Then, under nitrogen protection, the mixture was stirred at 120°C for 8 hours. After the reaction, the mixture was cooled to room temperature, dissolved in 25 mL of tetrahydrofuran, and precipitated in cold methanol at 0°C. After centrifugation to remove the supernatant, the resulting solid was vacuum dried at 45°C for 24 hours to obtain norbornene-terminated poly(ε-caprolactone) macromonomer NB-PCL. 33 .

[0033] This step uses 5-norbornene-2-methanol as an initiator and stannous octoate as a catalyst to achieve the ring-opening polymerization of ε-CL. The synthetic route is shown in equation (Ⅲ) below.

[0034] (III) (5) Preparation of macromonomer NB-PLA: In a 250 mL dry Schlenk flask, 5-norbornene-2-methanol (539 mg, 4.3 mmol, manufacturer: Adamas, CAS: 95-12-5), racemic D,L-lactide (D,L-LA, 10 g, 68.8 mmol, manufacturer: Jinan Daigang Biotechnology Co., Ltd., CAS: 95-96-5), and 1,8-diazabicycloundec-7-ene (DBU, 0.1 g, manufacturer: Adamas, CAS: 6674-22-2) were added and dissolved in 64 mL dichloromethane. The reaction was stirred at room temperature for 2 hours. After the reaction was completed, the resulting polymer precipitated in cold methanol and dried under vacuum at 45°C for 24 hours to obtain the norbornene-terminated polylactic acid macromonomer NB-PLA. 32 .

[0035] This step uses 5-norbornene-2-methanol as an initiator and DBU as a catalyst to achieve the ring-opening polymerization of D,L-LA, yielding the target product NB-PLA. 32 The synthesis route is shown in equation (Ⅳ).

[0036] (IV) (6) Preparation of the macromonomer NBI-PEO: In a 250 mL reaction flask, NBI-COOH (2.1 g, 7.5 mmol), 4-(dimethylamino)pyridine (DMAP, 183.3 mg, 1.5 mmol, manufacturer: Adamas, CAS: 1122-58-3), and anhydrous dichloromethane (75 mL) were added sequentially. 1-Ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl, 2.0 g, 10.5 mmol, manufacturer: Adamas, CAS: 25952-53-8) was slowly added at 0 °C. After stirring for 15 min, polyethylene glycol monomethyl ether (6.0 g, 3.0 mmol, manufacturer: Adamas, CAS: 9004-74-4) was added, and the mixture was stirred at room temperature for 48 h. The reaction mixture was diluted with dichloromethane and washed three times with 1M hydrochloric acid solution, saturated sodium bicarbonate, and deionized water, respectively. The organic phase was dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated under reduced pressure and precipitated in 0 °C ice-cold ether. The white solid obtained by centrifugation was dried under vacuum at 45 °C for 24 h to obtain norbornene-terminated polyethylene glycol macromonomer NBI-PEO. 43 Its synthesis route is shown in equation (V).

[0037] (V) (7) Synthesis of bottle brush block polymer (BBCP) using sequential ring-opening metathesis polymerization (ROMP): PDMS- b -PCL ( a The synthesis method of (=33) is as follows: In a 10mL vial, 100mg of the macromonomer NBI-PDMS is added. 33 Dissolve in 2 mL of anhydrous tetrahydrofuran; prepare a 2.0 mg / mL tetrahydrofuran solution (the catalyst solution) using the third-generation Grubbs catalyst (G3, manufacturer: Aladdin Chemicals); calculate the required volume based on the target degree of polymerization and quickly add it to the reaction system while stirring rapidly; the volume of catalyst solution added here is 128 μL. After reacting at room temperature for 15 minutes, add the macromonomer NB-PCL. 33 The solution was added and the reaction continued for 4 hours; then vinyl ether was added to terminate the reaction. After the reaction was complete, the resulting polymer was purified by precipitation in cold methanol to give a white solid product PDMS- b -PCL. PDMS- b The synthetic route for -PCL is shown in equation (VI) below, and the synthesized product is denoted as... - .

[0038] (VI) The synthesized polymer PDMS- b-PCL represents - ,in, x , y Main chain aggregation degree, a , b The degree of polymerization of the side chain. f % represents the PCL volume fraction.

[0039] In addition, four other PDMS with different target degrees of polymerization were synthesized using the aforementioned method. b -PCL, the only difference being the volume of the catalyst solution added. These other four PDMS-... b - The catalyst solution volume corresponding to PCL is 148 L, 113 L, 101 L, 92 L. The four synthesized products are denoted as follows: - , - , - , - .

[0040] PDMS- b -PCL ( a =68) Synthesis method and the aforementioned PDMS- b -PCL ( a =33) Same, the only difference is that the large monomer uses NBI-PDMS. 68 The PDMS synthesized in this embodiment- b -PCL ( a =68) is denoted as - .

[0041] PDMS- b -PLA ( a The synthesis method of (=33) is as follows: In a 10mL vial, 100mg of the macromonomer NBI-PDMS is added. 33Dissolved in 2 mL of anhydrous tetrahydrofuran; a 2.0 mg / mL tetrahydrofuran solution was prepared from the third-generation Grubbs catalyst (G3, manufacturer: Aladdin Chemicals), which served as the catalyst solution; the required volume, calculated based on the target degree of polymerization, was rapidly added to the reaction system with constant stirring; the volume of catalyst solution added here was 128 μL. After reacting at room temperature for 15 minutes, the macromonomer NB-PLA solution was added, and the reaction continued for 4 hours; subsequently, vinyl ether was added to terminate the reaction. After the reaction was complete, the resulting polymer was purified by precipitation in cold methanol to obtain a white solid product, PDMS- b -PLA. PDMS- b The synthetic route for PLA is shown in equation (VII) below, and the synthesized product is denoted as... - .

[0042] The synthesized polymer PDMS- b -PLA indicates that - ,in, x , y Main chain aggregation degree, a , b The degree of polymerization of the side chain. f % represents the PCL volume fraction.

[0043] (VII) PDMS- b -PEO ( a The synthesis method of (=33) is as follows: In a 10mL vial, 100mg of the macromonomer NBI-PDMS is added. 33 Dissolve in 2 mL of anhydrous tetrahydrofuran; prepare a 2.0 mg / mL tetrahydrofuran solution (the catalyst solution) using the third-generation Grubbs catalyst (G3, manufacturer: Aladdin Chemicals); calculate the required volume based on the target degree of polymerization and quickly add it to the reaction system while stirring rapidly; the volume of catalyst solution added here is 175 mL. L. After reacting at room temperature for 15 minutes, the macromonomer NBI-PEO was added. 43 The solution was added and the reaction continued for 4 hours; then vinyl ether was added to terminate the reaction. After the reaction was complete, the resulting polymer was purified by precipitation in cold methanol to give a white solid product PDMS- b -PEO ( a =33). PDMS- b The synthetic route for -PEO is shown in equation (VIII) below, and the synthesized product is denoted as... - .

[0044] (VIII) PDMS- b -PEO ( a =68) Synthesis method and PDMS- b -PEO ( a =33) Same, the only difference is that the large monomer uses NBI-PDMS. 68 .

[0045] The synthesis in this embodiment - , - , - See the molecular structure. Figure 1 .

[0046] Example 2 The bottle brush block polymers obtained in Example 1 were self-assembled into photonic thin films using a solution casting method. The specific process is as follows: The bottle brush block polymer was completely dissolved in toluene at 60°C, followed by solution casting at room temperature in a toluene vapor atmosphere. After the solvent evaporated, the photonic thin film was thermally annealed in a vacuum.

[0047] Among them, PDMS -b -PCL photonic thin films and PDMS -b -PEO photonic thin films were thermally annealed at 90°C for 12 hours, and PDMS- b The PLA photonic thin film was annealed at 120°C for 12 hours. The purpose of thermal annealing is to remove residual solvent from the photonic thin film and reduce its structural defects.

[0048] The prepared BBCP photonic thin film was characterized and its performance was tested as follows: (1) The changes of BBCP photonic thin films with temperature in the temperature range of 0 ~ 90 °C were observed using an optical microscope. The optical microscope images are shown in [reference]. Figure 2 ,from Figure 2 It can be seen that: During the process of heating from 0°C to 90°C - The photonic thin film exhibits only a slight color change, which is why the PDMS- b -PLA photonic thin films are designated as Type I.

[0049] During the heating process from 0°C to 90°C, the PDMS segments with longer lengths... - The photonic thin film exhibits a structural color shift from pale yellow to red; and its color reverts to its initial state during cooling from 90°C to 0°C. This PDMS... -b -PCL photonic thin film (a =68) is denoted as type II.

[0050] During the heating process from 0°C to 90°C, the PDMS segments with shorter lengths... - Photonic film ( a =33), which exhibits non-monotonic thermochromic behavior. During heating, its structural color shifts from pale yellow to red to brown; upon further heating to 90°C, its structural color undergoes a significant blue shift, changing from brown to green. During cooling from 90°C to 0°C, within the temperature range of 90°C to 20°C, it shifts from green to red to brown; subsequently, during further cooling to 0°C, it shifts back to pale yellow. These phenomena indicate that this PDMS- b -PCL photonic thin film ( a =33) There is an asymmetric color transition temperature. This PDMS- b -PCL film ( a =33) is denoted as type III.

[0051] (2) The change of the reflection peak of the BBCP photonic thin film with temperature was determined by in-situ reflectance spectroscopy: Please see Figure 3 The image shows the in-situ reflection spectra of three types of BBCP photonic thin films during the heating process from 0°C to 90°C; please refer to [link to relevant documentation]. Figure 4 The figure shows the curves illustrating the relative shift of the reflection peaks of three types of BBCP photonic thin films as the temperature increases from 0°C to 90°C. The relative shift of the reflection peaks refers to the relative shift of the reflection peak of the photonic thin film at 0°C as a reference reflection peak. The three types of BBCP photonic thin films are as follows: - photonic film, - photonic film, - Photonic film.

[0052] from Figures 3-4 It can be seen that: Type I photonic thin films exhibit only a slight red shift of about 2.2% during the heating process from 0°C to 90°C; Type II photonic thin films gradually exhibit a red shift of about 2.3% during the heating process from 0°C to 40°C, followed by a significant red shift of about 3.8% during the heating process from 40°C to 45°C, and remain basically stable during the heating process from 45°C to 90°C; In contrast, Type III photonic thin films exhibit non-monotonic thermochromic behavior, with a red shift of about 2.1% during the heating process from 0°C to 40°C, and a significant blue shift of about 8.1% during the heating process from 40°C to 90°C.

[0053] (3) The thermal stability and cyclic reversibility of BBCP photonic thin films were tested using in-situ reflectance spectroscopy: Please see Figure 5 The image shows a type III photonic thin film (i.e., - The reflection spectra of the photonic thin film after being kept at 90°C for 1 hour and 2 hours are shown in the upper right inset. The inset at the top right of the figure is an optical microscope image of the III photonic thin film at the corresponding temperature. The scale bar is 50. m. From Figure 5 It can be seen that Type III photonic thin films have excellent thermal stability.

[0054] For type II and type III photonic thin films (i.e. - photonic film, - The photonic thin film underwent 25 cycles of heating and cooling, including heating from 0°C to 90°C and cooling from 90°C to 0°C, with the position of the reflection peak of the photonic thin film measured at 0°C and 90°C during each cycle. See [link to relevant documentation]. Figure 6 The figure shows the changes in the reflection peak positions of Type II and Type III photonic thin films during heating and cooling cycles. Here, the change in reflection peak position refers to the change in the reflection peak position of the photonic thin film relative to 0°C. Hollow dots represent the relative change in the reflection peak position of the photonic thin film at 0°C, and solid dots represent the relative change in the reflection peak position of the photonic thin film at 90°C. Figure 6 It can be seen that, during 25 cycles of heating and cooling, the reflection peak positions of Type II and Type III photonic thin films can be reversibly changed within the temperature range of 0°C to 90°C.

[0055] Combination Figures 5-6 It is known that photonic thin films possess thermal stability and cyclic reversibility, thus ensuring the reliability and repeatability of the color response of photonic thin films, making them particularly suitable for applications requiring long-term stable operation.

[0056] (4) Characterizing the thermal response behavior of type II and type III photonic thin films: Optical spectroscopy, polarizing microscopy (POM), and differential scanning calorimetry (DSC) were used to study type II and type III photonic thin films (i.e., - photonic film, - The thermal response behavior of the photonic thin film was characterized. Please refer to [link to relevant documentation]. Figures 7-8Figure 1 shows the thermal response behavior characterization data of type II and type III photonic thin films, respectively. Figure 2 shows the curve of the peak value of the reflection spectrum of the photonic thin film as a function of temperature during the heating and cooling process. Figure 3 shows the curve of the POM intensity as a function of temperature during the heating and cooling process. Figure 4 shows the curve of the normalized heat flux as a function of temperature during the heating and cooling process. The red and blue curves correspond to the heating and cooling processes, respectively.

[0057] from Figures 7-8 It can be seen that both Type II and Type III photonic thin films exhibit significant spectral abrupt changes at approximately 15°C during the cooling process from 90°C to 0°C; and during the heating process from 0°C to 90°C, they both exhibit significant spectral abrupt changes at approximately 43°C.

[0058] Polarizing microscopy data showed that the POM intensity change curve with temperature exhibited significant transitions at approximately 43°C and 15°C, highly consistent with the color transition temperature. In contrast, Type I photonic thin films only showed a glass transition at approximately 54°C and had extremely low crystallinity, approximately 2%.

[0059] Differential scanning calorimetry data showed that both Type II and Type III photonic thin films exhibited high crystallinity, ranging from 38% to 43%; crystallization temperature T approximately 9°C, melting temperature Approximately 46°C.

[0060] The above results indicate that the color change of Type II and Type III photonic thin films towards longer wavelengths during heating is mainly due to the phase transition behavior of crystalline PCL blocks.

[0061] (5) Determination of PDMS- b -Reflectance spectra of PEO photonic thin films at different temperatures: Please see Figure 9 The figure shows the reflection spectra of PEO-based type II and type III photonic thin films at different temperatures. The inset in the upper right corner is an optical microscope image of the corresponding temperature. Scale bar: 50 μm. PEO and PCL have similar crystallinity and glass transition temperatures. Figure 9 It can be seen that type II photonic thin films based on PEO (i.e. - Photonic thin films also exhibit monotonic redshift behavior during the heating process from 0°C to 90°C; Type III photonic thin films based on PEO (i.e. - The photonic thin film exhibits a non-monotonic color change as it heats from 0°C to 90°C; a redshift of approximately 7 nm (1.1%) occurs as it heats from 0°C to 30°C, while a significant blueshift of approximately 43 nm (8.4%) occurs as it heats from 30°C to 90°C. This color change pattern is consistent with that of PCL-based Type II and Type III photonic thin films.

[0062] (6) Determination of the thermochromic pathway of type III photonic thin films with different molecular weights: Please see Figure 10 The figure shows the sixth power of the reflection peak wavelength of five different molecular weight type III photonic thin films during the process of heating from 0°C to 90°C. λ 6 Changes with temperature. From Figure 10 It can be seen that there are two temperature ranges with opposite trends: in temperature range I (0~50°C). λ 6 Increases with increasing temperature; in temperature range II (50°C~90°C). λ 6 It decreases with increasing temperature and conforms to a scaling relationship. λ 6 ~- T . Figure 10 The data is divided into two temperature ranges: range I is marked with hollow dots, and range II is marked with solid dots. A relational expression is used for the data in range II. λ 6 = A · T+B Perform fitting.

[0063] Theoretically, the Flory–Huggins interaction parameter χ With temperature χ ∝ T -1 Relationship, and combined with self-consistent field theory (SCFT) regarding interlayer spacing. d ~ N 2 / 3 χ -1 / 6 From this, we can deduce d ~ N 2 / 3 T 1 / 6 There is no phase transition in the temperature range of 50°C to 90°C, and the change in refractive index is negligible. Therefore, the observed blue shift is mainly attributed to... χ The periodicity of layered structures caused by temperature changes d The decrease.

[0064] χ ( T PCBP plays a crucial role in determining photonic-scale structural changes and color responses. Within the heating range of 50°C to 90°C, no interlayer shrinkage was observed in Type II photonic films based on PCL. This is likely due to the stronger crowding effect generated by the longer PDMS side chains, which enhances the stretchability and rigidity of the PCBP chains, thereby increasing the threshold for thermally driven structural rearrangement. Therefore, the color of Type II photonic films remains almost unchanged after the melting temperature, making it difficult for them to exhibit bidirectional thermochromic behavior.

[0065] Therefore, the blue shift of Type III photonic films with short PDMS side chains in the high-temperature range is due to the interlayer spacing shrinkage caused by temperature changes, while the color of Type II photonic films with long PDMS side chains remains almost unchanged in the high-temperature range because the longer PDMS side chains generate a stronger crowding effect and no interlayer spacing shrinkage occurs with temperature changes.

[0066] As described above, different thermochromic pathways can be achieved by controlling the side chains of the bottle-brush block polymer BBCP. Different types of photonic thin films correspond to different thermochromic pathways, leading to the following applications.

[0067] Type III photonic thin films exhibit a reversible, bidirectional thermochromic pathway, which can be applied to information displays. For example, floral patterns fabricated using Type III photonic thin films based on PCL can display non-monotonic color evolution during heating, visually demonstrating the encoding effect of the reversible bidirectional thermochromic pathway in spatial pattern structures. See [link to documentation] for details. Figure 11 .

[0068] By utilizing the different thermochromic paths of different types of photonic thin films, thermochromic photonic thin films can be used as decoding elements for two-dimensional information encryption. Using PLA-based Type I photonic thin films as non-responsive reference elements and PCL-based Type II or Type III photonic thin films as temperature-responsive decoding elements, two-dimensional encrypted information can be constructed. (See [link to relevant documentation]). Figure 12 Due to the flexible sidechain length effect, the color of the Type II photonic thin film shifts from orange-yellow to red during heating, thus encrypting the two-dimensional information of the Type I photonic thin film combined with the Type II photonic thin film, which is decrypted upon heating. Similarly, the color of the Type III photonic thin film shifts from yellow to red during cooling, thus encrypting the two-dimensional information of the Type I photonic thin film combined with the Type III photonic thin film, which is decrypted upon cooling. The same optical output can be decoded through the opposite thermal processing, providing an additional dimension for information encryption based on the color-changing path. These results demonstrate that programmable thermochromism achieved through sidechain engineering surpasses traditional color-changing methods, enabling controllable optical encoding and decoding.

[0069] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A thermochromic polymer photonic thin film with a programmable color-changing path, characterized in that: The photonic thin film is formed by self-assembly of a bottle brush block copolymer, which includes a main chain and side chains grafted onto the main chain. The side chains include a flexible first block and a rigid second block. When the rigid second block is an amorphous block, the corresponding photonic film is designated as a type I photonic film. The type I photonic film has stable color during both heating and cooling processes. When the rigid second block is a crystalline block and the degree of polymerization of the flexible first block is 40~80, the corresponding photonic film is denoted as a type II photonic film. The type II photonic film exhibits a monotonically red-shifted color evolution path during the heating process and a monotonically blue-shifted color evolution path during the cooling process. When the rigid second block is a crystalline block and the degree of polymerization of the flexible first block does not exceed 40, the corresponding photonic film is designated as a type III photonic film. The type III photonic film exhibits a color evolution path of first red shift and then blue shift during the heating and cooling process.

2. The thermochromic polymer photonic thin film as described in claim 1, characterized in that: The volume of the rigid second segment accounts for 30% to 40%.

3. The thermochromic polymer photonic thin film as described in claim 1, characterized in that: The flexible first block is a polydimethylsiloxane block.

4. The thermochromic polymer photonic thin film as described in claim 1, characterized in that: The rigid second block is a polylactic acid block, or a poly... ε - Caprolactone block or polyethylene oxide block.

5. The application of the thermochromic polymer photonic film according to any one of claims 1 to 4 in dynamic information display.

6. The application of the thermochromic polymer photonic film according to any one of claims 1 to 4 in anti-counterfeiting labels.

7. The application as described in claim 6, characterized in that: Two-dimensional encrypted information is constructed by using type I photonic thin films as non-responsive reference elements and type II or type III photonic thin films as temperature-responsive decoding elements.

8. The application of the thermochromic polymer photonic thin film according to any one of claims 1 to 4 in a multi-threshold temperature sensor.

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