Chiral circularly polarized fluorescent composite film and preparation and application thereof

Abstract

The application discloses a kind of for anti-fake, convertible chiral circular polarized fluorescence composite film, the method adopts physical doping method and evaporation induced self-assembly technology is combined, through 2,6-pyridine dicarboxylic acid coordination rare earth metal, again with polyethylene glycol hybrid as precursor, be added to cellulose nanocrystal solution, self-assembly is obtained after drying chiral circular polarized fluorescence composite film;Specific steps include: step 1, 2,6-pyridine dicarboxylic acid coordination rare earth metal preparation;Step 2, the preparation of polyethylene glycol wrapped 2,6-pyridine dicarboxylic acid coordination rare earth metal precursor;Step 3, the preparation of self-assembly composite film of cellulose nanocrystal and precursor.The application uses green sustainable cellulose nanocrystal as matrix;2,6-pyridine dicarboxylic acid coordination rare earth metal is fluorescent light source;Excellent multilevel optical nature and anti-fake ability.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation technology, specifically relating to a counterfeit-proof, convertible chiral circularly polarized fluorescent composite film, specifically a composite film of cellulose nanocrystals and rare earth metals coordinated with 2,6-pyridine dicarboxylic acid and polyethylene glycol solution. A representative cellulose composite film was prepared, exhibiting humidity-responsive structural color variation, tunable fluorescence, convertible chiral optics, and selective chiral circularly polarized light. It also has excellent mechanical flexibility and adhesion. Background Technology

[0002] The fierce competition between counterfeit and protective products is a long-standing and complex issue. As early as ancient China, numerous anti-counterfeiting (AC) labels, including graphic, watermark, fingerprint, and handwriting recognition, were extensively intertwined with culture, economy, and military affairs. In general, innovative anti-counterfeiting technologies are crucial for market stability, healthcare, and social sustainability. For example, an increasing number of pharmaceutical preparations are incorporating micro-AC labels into their packaging to combat counterfeit drugs. Despite this, counterfeit goods remain prevalent worldwide. By 2025, the AC market is projected to reach $72.2 billion. Today, the latest generation of AC labels focuses on using sophisticated and stimulus-responsive luminescence modes to convey covert information, such as multimode perovskite nanocrystals, time-dependent phosphorescent materials, full-color quantum dots, and stable lanthanide luminescence. More profoundly, some luminescent materials are endowed with reflective colors to display an integration of dual optical states. However, only after professional training with improved commercial printers and systems can these fluorescent nanocrystals and particles (such as high-viscosity inks) be used in commercial printing to achieve full loading and long-term stability of the AC materials. Furthermore, it is impractical to require untrained consumers to activate AC tags using invasive stimuli (such as acids, alkalis, or other chemicals). In addition to the reasons mentioned above, the following problems exist regarding these complex communication patterns at the molecular (organic) or energy level structure (inorganic) level: 1) Expensive monomer materials and cumbersome synthesis increase production costs; 2) Modifying the reflective color of luminescent materials by altering their inherent chemical structure (typical examples are compounds of azobenzene or ropyran) inevitably changes the fluorescence properties; 3) Secret encoding is limited to two-dimensional optical information, and high-dimensional AC patterns are rarely explored. Therefore, designing an ideal anti-counterfeiting technology that is low-cost, non-destructive, multi-level complex, easy to operate, and easy to authenticate has become the most challenging task.

[0003] Here, we address the aforementioned challenges by incorporating rare-earth metal complexes into chiral nematic nanocrystals (CNCs)-polyethylene glycol (PEG). Within the confines of the soft PEG matrix, the rare-earth metal complexes can adhere to each CNC, ensuring uniform emission of the chiral light-emitting film. More significantly, the PEG polymer provides mechanical flexibility and adhesion, enabling the use of various AC products on diverse substrates. This research opens a new field for AC products and novel, high-performance circularly polarized light (CPL) materials, which will play a crucial role in next-generation photonic devices such as polarized light-based security encryption, low-threshold distributed feedback lasers, chiral optically active structural materials, and intelligent nanosystems, offering advantages related to lower cost and sustainability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention discloses a convertible chiral circularly polarized fluorescent composite film for anti-counterfeiting. This method combines physical doping with evaporation-induced self-assembly technology. Rare earth metals coordinated with 2,6-pyridinedicarboxylic acid and polyethylene glycol are used as precursors added to cellulose nanocrystals to obtain the cellulose composite film. The specific steps are as follows:

[0005] Step 1, 2,6-pyridinedicarboxylic acid-coordinated rare earth metals;

[0006] Step 2: Preparation of rare earth metal precursors coordinated with 2,6-pyridinedicarboxylic acid and encapsulated in polyethylene glycol;

[0007] Step 3: Preparation of self-assembled composite membrane of cellulose nanocrystals and precursors.

[0008] This invention combines physical doping and evaporation-induced self-assembly techniques to prepare a convertible chiral circularly polarized fluorescent composite film for anti-counterfeiting purposes.

[0009] The technical solution adopted in this invention is:

[0010] A convertible chiral circularly polarized fluorescent composite film for anti-counterfeiting is produced according to the following steps:

[0011] Step 1, Preparation of rare earth metals coordinated with 2,6-pyridinedicarboxylic acid:

[0012] 220 mg of europium trichloride hexahydrate (EuCl3·6H2O) was added to 60 mL of an aqueous solution containing 300 mg of 2,6-pyridinedicarboxylic acid (DPA). The mixture was refluxed at 60 °C for 24 hours. After freeze-drying, a white europium tri(2,6-pyridinedicarboxylic acid) complex (Eu(DPA)3) was obtained. Similarly, several other rare earth (La, Ce, Sm, Gd, Tb, and Dy) complexes could also be obtained.

[0013] Step 2: Preparation of rare earth metal precursors coordinated with 2,6-pyridinedicarboxylic acid and encapsulated in polyethylene glycol:

[0014] The 60 mg of Eu(DPA)3 was added to 20 mL of an aqueous solution containing 2 g of polyethylene glycol (PEG), and stirred in a 60 °C water bath for 12 h. Finally, the homogeneous solution of PEG-coated Eu(DPA)3 (PEG-Eu(DPA)3) was purified by ultrapure water dialysis (molecular weight cutoff of 2 kDa) for 12 h and then diluted to 8 wt%.

[0015] Step 3: Preparation of self-assembled composite membrane of cellulose nanocrystals and precursor;

[0016] A 3.0 wt% CNC aqueous suspension was sonicated in cold water for 10 min, then stirred with 3 mL of PEG-Eu(DPA)3 precursor solution at room temperature for 2 h. The homogeneous mixture was transferred to a 50 mm polystyrene Petri dish. After drying under ambient conditions for 48 h, a red CNC / PEG-Eu(DPA)3 composite film was obtained. To prepare full-color composite films, yellow, green, and blue films with the same composition as the red film were synthesized by adding three different concentrations (1 mM, 2 mM, and 3 mM) of NaCl(aq) to the suspension before casting.

[0017] Step 4: Photoluminescence test of the composite film:

[0018] The CNC / PEG-Eu(DPA)3 from step 3 was cut into 50mm×10mm pieces. The thickness of the film was 30μm. The film was tested with a UV spectrophotometer under 30% humidity conditions.

[0019] In step 1, the amount of EuCl3·6H2O was 0.6 mmol; the concentration of DPA was 0.03 mol / L; the molar ratio of EuCl3·6H2O to DPA was 1:3; the mixture was refluxed at 60 °C for 24 hours. Eu(DPA)3 was obtained after freeze-drying.

[0020] In step 2, 60 mg of Eu(DPA)3 was added to a 20 mL aqueous solution containing 2 g of polyethylene glycol (PEG), and stirred in a 60 °C water bath for 12 h. After PEG-Eu(DPA)3 was purified by ultrapure water dialysis (molecular weight cutoff value of 2 kDa) for 12 h, it was diluted to 8 wt%.

[0021] In step 3, CNC and PEG-Eu solutions with a mass ratio of 64:36 (w:w) are mixed to prepare a co-assembled membrane;

[0022] In step 4, the membrane obtained in step 3 is placed at 30% and 80% humidity, respectively. It turns blue at 30% humidity and red at 80% humidity.

[0023] This invention uses physical doping and self-assembly techniques to prepare cellulose composite membranes, which exhibit high anti-counterfeiting and convertible chiral capabilities.

[0024] A CNC / Eu(DPA)3 composite film with optical response was constructed using physical doping. However, this composite film is prone to cracking upon bending, and these luminescent complexes exhibit an uneven optical distribution on the film under 254 nm UV light. To address these issues, polyethylene glycol (PEG) was introduced into a rigid environment composed of a CNC matrix. On one hand, PEG acts as a plasticizer, enhancing mechanical flexibility and facilitating the manufacture of various products; on the other hand, PEG can act as a binder to restrict the disordered movement of Eu(DPA)3 particles, which further follow the co-assembly of PEG and CNC to achieve homogeneous hybridization. Ultimately, a cellulose composite film with good mechanical properties was obtained, and this cellulose optical film can also be used for anti-counterfeiting. Here, the luminescent material derived from cellulose nanocrystals can simultaneously exhibit a unique combination of structural color, chiral light switching, and circularly polarized luminescence, enabling higher-level communication applications. Bright photoluminescence and multimodal integrated coding facilitate the co-assembly of CNC with lanthanide complexes encapsulated in a polyethylene glycol matrix. A representative blue thin-film humidity-responsive thin-film switch was prepared using a convenient method, in which full-color reflection and flexibility were achieved by adjusting ionic strength and soft polymer. This method is superior to the preparation of other anti-counterfeiting materials, which suffer from secondary pollution, high cost, and are not conducive to large-scale application.

[0025] Technical advantages of the present invention:

[0026] A cellulose composite film was prepared using physical doping and self-assembly techniques; a highly anti-counterfeiting and convertible chiral circularly polarized fluorescent composite film was also prepared; the preparation process of this material is easy to operate and low in cost; this optical structure color film is an intelligent nano-microsystem with advantages of low cost and sustainability.

[0027] Using sustainable cellulose as a matrix, optical structured color films are constructed using physical doping and self-assembly techniques; the plasticizing effect of polyethylene glycol enables the mechanical flexibility and homogeneous hybridization capability of the optical films; and convertible chiral optics are achieved.

[0028] This invention uses green and sustainable cellulose nanocrystals as the matrix; rare earth metals coordinated with 2,6-pyridine dicarboxylic acid as the fluorescent light source; the composite film has high strength, excellent multi-layer optical properties and anti-counterfeiting capabilities. Attached Figure Description

[0029] Figure 1The image shows the fluorescence spectrum of Eu(DPA)3 in Example 1. The excitation wavelength was set to 285 nm and the emission wavelength was measured to be 614 nm. At the highest point of the image, the concentration ratio of Eu:DPA was 1:3.

[0030] Figure 2 The rare earth metals La, Ce, Sm, Gd, Tb and Dy in Example 1 exhibit different fluorescent colors after being physically doped with DPA. Eu shows red after being doped with DPA, Tb shows green after being doped with DPA, La shows brownish-red, Ce shows dark red, Sm shows deep red, Gd shows blue-violet and Dy shows blue-black.

[0031] Figure 3 The image shows an atomic force microscopy (AFM) characterization of the CNC / PEG-Au film from Example 3. The AFM image reveals that the width and length of the CNC / PEG-Au film are significantly larger than those of the CNC film. This is consistent with the average size of the CNC / PEG–Eu film (204 nm), indicating that the PEG is wound within the CNC film, providing it with mechanical flexibility and adhesion.

[0032] Figure 4 The image shows the UV spectrum of the CNC / PEG-Au film in Example 3 at different salt concentrations. At 0 mmol, the wavelength of its emission peak is 680 nm; at 1 mmol, the wavelength of its emission peak is 575 nm; at 2 mmol, the wavelength of its emission peak is 500 nm; and at 3 mmol, the wavelength of its emission peak is 438 nm. It can be seen that the wavelength gradually blue shifts with the increase of salt concentration.

[0033] Figure 5 This is an actual image of the CNC / PEG-Au membrane from Example 3 after immersion in water for 24 hours. It can be seen that the membrane structure remains stable and unchanged in water.

[0034] Figure 6 : SEM images of the CNC / PEG-Au blue and red films of Example 4. It can be seen that they both have a periodic layered structure, but the interlayer distances are different, at 318 and 656 nm respectively.

[0035] Figure 7 The image shows the CNC / PEG-Au blue film of Example 4 under illumination with 285nm left-handed circularly polarized light (285nm L-CPL) and 285nm right-handed circularly polarized light (285nm R-CPL). That is, using light with a wavelength of 285 nm, the light is first incident on a quarter-wave plate, and a polarizer parallel or perpendicular to the optical axis of the quarter-wave plate is placed behind the plate. Looking towards the light, the light vibration that rotates counterclockwise is left-handed polarized light. At a wavelength of 614 nm, the intensity of left-handed polarized light is lower than that of right-handed polarized light.

[0036] Figure 8 The CNC / PEG-Au film of Example 4 can be coated on a glass film and made into a DICP pattern. After wetting and drying, different colors can be observed on a linear polarizer at different angles. Detailed Implementation

[0037] The invention will be further explained below with reference to specific implementation examples.

[0038] Example 1:

[0039] (1) Preparation of rare earth metal Eu and DPA complex: 220 mg of europium trichloride hexahydrate (EuCl3·6H2O) was added to 60 mL of an aqueous solution containing 300 mg of 2,6-pyridinedicarboxylic acid (DPA). The mixture was refluxed at 60 °C for 24 hours. After freeze-drying, a white europium tri(2,6-pyridinedicarboxylic acid) complex (Eu(DPA)3) was obtained.

[0040] The fluorescence spectrum of Eu(DPA)3 is as follows: Figure 1 As shown in the figure, at the highest point, the concentration ratio of Eu:DPA is 1:3. Figure 2 EuCl3·6H2O was doped with DPA at molar concentrations of 0:10-10:0 (0:10, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, 10:0), and fluorescence tests were performed. The results showed that the fluorescence intensity was strongest when the Eu to DPA ratio was 1:3, therefore this ratio is the optimal ratio.

[0041] Similarly, other rare earth element (La, Ce, Sm, Gd, Tb, and Dy) complexes can also be obtained, such as Figure 2 As shown. The process and conditions are the same as above, except that: using the same molar amounts of La, Ce, Sm, Gd, Tb or Dy chlorides, complexes of rare earth metals La, Ce, Sm, Gd, Tb or Dy with DPA are prepared respectively. The results are as follows: Eu shows red after doping with DPA, Tb shows green after doping with DPA, La shows brownish-red, Ce shows dark red, Sm shows deep red, Gd shows blue-violet, and Dy shows blue-black.

[0042] (2) Preparation of rare earth metal precursors encapsulated in polyethylene glycol and coordinated with 2,6-pyridinedicarboxylic acid:

[0043] The 60 mg of Eu(DPA)3 was added to 20 mL of an aqueous solution containing 2 g of polyethylene glycol (PEG), and stirred in a 60 °C water bath for 12 h. Finally, the homogeneous solution of PEG-coated Eu(DPA)3 (PEG-Eu(DPA)3) was purified by ultrapure water dialysis (molecular weight cutoff of 2 kDa) for 12 h and then diluted with water to 8 wt%.

[0044] (3) Preparation of self-assembled composite membrane of cellulose nanocrystals and precursor: 3.0 wt% of CNC rod-shaped particles (172±25 nm long and 22±3 nm wide) in aqueous suspension were ultrasonically treated in water at 12 °C for 10 min, and then stirred with 3 mL of PEG-Eu(DPA)3 precursor solution at room temperature for 2 h. The homogeneous mixture was transferred to a polystyrene Petri dish with an inner diameter of 50 mm. After drying under ambient conditions for 48 h, a red CNC / PEG-Eu(DPA)3 composite membrane with a thickness of approximately 10 μM was obtained.

[0045] To prepare a full-color composite film, a yellow film was synthesized by adding 1 mM NaCl(aq) to the suspension (the homogeneous mixture) before transferring it to a 50 mm inner diameter polystyrene Petri dish. The process and conditions were the same as above, except that the mass of sodium chloride added was different.

[0046] Example 2:

[0047] (1) To prepare a rare earth metal Eu complex with DPA, 220 mg of europium trichloride hexahydrate (EuCl3·6H2O) was added to a 60 mL aqueous solution containing 300 mg of 2,6-pyridinedicarboxylic acid (DPA). The mixture was refluxed at 60 °C for 24 hours. After freeze-drying, a white europium tri(2,6-pyridinedicarboxylic acid) complex (Eu(DPA)3) was obtained.

[0048] (2) To prepare a polyethylene glycol-encapsulated rare earth metal precursor coordinated with 2,6-pyridinedicarboxylic acid, 60 mg of the above-mentioned Eu(DPA)3 was added to 20 mL of an aqueous solution containing 2 g of polyethylene glycol (PEG), and stirred in a water bath at 60 °C for 12 h. Finally, the homogeneous solution of PEG-encapsulated Eu(DPA)3 (PEG-Eu(DPA)3) was purified by ultrapure water dialysis (molecular weight cutoff value of 2 kDa) for 12 h and then diluted to 8 wt%.

[0049] (3) Preparation of self-assembled composite membranes of cellulose nanocrystals and precursors: A 3.0 wt% CNC aqueous suspension was ultrasonically treated in cold water for 10 min, and then stirred with 3 mL of PEG-Eu(DPA)3 precursor solution at room temperature for 2 h. The homogeneous mixture was transferred to a polystyrene Petri dish with an inner diameter of 50 mm. After drying under ambient conditions for 48 h, a red CNC / PEG-Eu(DPA)3 composite membrane was obtained. To prepare full-color composite membranes, the same method was used to synthesize green membranes before casting these membranes by adding NaCl(aq) to a homogeneous mixture (the addition should be done before placing the membranes into the Petri dish) to a final concentration of 2 mM.

[0050] (4) Atomic force microscopy characterization of the CNC / PEG-Au film, showing that the PEG polymer provides mechanical flexibility and adhesion, such as Figure 3 The results, obtained from AFM images, show that the width of CNC / PEG-Au is significantly larger than that of CNC; specifically, the width of CNC is 17 nm, while the width of CNC / PEG-Au is 22.4 nm. This is consistent with the average size of CNC / PEG–Eu (204 nm), indicating that PEG is wound within the CNC, providing it with mechanical flexibility and adhesion.

[0051] Example 3:

[0052] (1) To prepare a complex of rare earth metal Eu and DPA, 220 mg of europium trichloride hexahydrate (EuCl3·6H2O) was added to a 60 mL aqueous solution containing 300 mg of 2,6-pyridinedicarboxylic acid ((DPA)). The mixture was refluxed at 60 °C for 24 hours. After freeze-drying, a white europium tri(2,6-pyridinedicarboxylic acid) complex (Eu(DPA)3) was obtained.

[0053] (2) To prepare a polyethylene glycol-encapsulated rare earth metal precursor coordinated with 2,6-pyridinedicarboxylic acid, 60 mg of Eu(DPA)3 was added to 20 mL of an aqueous solution containing 2 g of polyethylene glycol (PEG), and the mixture was stirred in a water bath at 60 °C for 12 h. Finally, the homogeneous solution of PEG-encapsulated Eu(DPA)3 (PEG-Eu(DPA)3) was purified by ultrapure water dialysis (molecular weight cutoff value of 2 kDa) for 12 h and then diluted to 8 wt%.

[0054] (3) Preparation of self-assembled composite membranes of cellulose nanocrystals and precursors: A 3.0 wt% CNC aqueous suspension was ultrasonically treated in cold water for 10 min, and then stirred with 3 mL of PEG-Eu(DPA)3 precursor solution at room temperature for 2 h. The homogeneous mixture was transferred to a polystyrene Petri dish with an inner diameter of 50 mm. After drying under ambient conditions for 48 h, a red CNC / PEG-Eu(DPA)3 composite membrane was obtained. To prepare a full-color composite membrane, a blue membrane was synthesized by adding NaCl(aq) to the homogeneous mixture (the addition should always be done before placing the mixture into the Petri dish) to a final concentration of 3 mM before placing the mixture into the Petri dish.

[0055] (4) Fluorescence spectra of CNC / PEG-Au films at different salt concentrations. As the salt concentration increases, the wavelength gradually blue shifts, such as... Figure 4 The results showed that the emission peak wavelength was 680 nm at 0 mmol; 575 nm at 1 mmol NaCl in Example 1; 500 nm at 2 mmol NaCl in Example 2; and 438 nm at 3 mmol NaCl in Example 3. This demonstrates that the wavelength gradually blue-shifts with increasing salt concentration.

[0056] (5) A real image of the CNC / PEG-Au membrane after immersion in water for 24 hours. The structural color of the membrane remains unchanged, as shown. Figure 5 The results show that the structure of CNC / PEG-Au in Example 3 remained stable and unchanged after being heated and then soaked in water for 24 hours.

[0057] (6) SEM images of the CNC / PEG-Au blue film in Example 3 and the red film in Example 1. The diameters of the cellulose nanocrystals are different, such as... Figure 6 The results showed that they all possessed a periodic layered structure, but the interlayer distances differed, being 318 nm and 656 nm, respectively. Images of the CNC / PEG-Au blue film in Example 3 under illumination with 285 nm left-handed circularly polarized light (285 nm L-CPL) and 285 nm right-handed circularly polarized light (285 nm R-CPL) are shown below. Figure 7 The results show that at a wavelength of 614 nm, the intensity of left-handed polarized light is lower than that of right-handed polarized light, which explains why left-handed and right-handed polarized light produce different colors.

[0058] (7) The CNC / PEG-Au blue film from Example 3 can be coated onto a glass plate or mold to create a DICP pattern. After wetting with water and drying, different colors are observed on a linear polarizing microscope at different angles (0 degrees and 90 degrees), such as... Figure 8The results showed that under dry conditions, it could turn red, khaki, and blue, corresponding to 254 nm ultraviolet light radiation, 90°RA, and 0°RA, respectively. In contrast, when the wet coating was exposed to the same stimulus, it turned non-fluorescent, scarlet, and green.

[0059] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a chiral circularly polarized fluorescent composite film, characterized in that: Including rare earth metals coordinated with 2,6-pyridinedicarboxylic acid, polyethylene glycol and cellulose nanocrystals; The molar ratio of rare earth metals to 2,6-pyridinedicarboxylic acid is 1:3; The mass ratio of PEG to rare earth metals coordinated with 2,6-pyridinedicarboxylic acid is 100:3-200:

3. The mass ratio of CNC and PEG to the sum of rare earth metals coordinated with 2,6-pyridinedicarboxylic acid is 9:20-10:

3. The specific steps are as follows: 1) In an aqueous solution, a rare earth metal precursor coordinated with 2,6-pyridinedicarboxylic acid is encapsulated in polyethylene glycol to obtain a precursor; 2) After uniformly mixing cellulose nanocrystals and precursors in an aqueous solution, the aqueous solvent is evaporated on a plate to self-assemble into a composite membrane. The specific process is as follows: A cellulose nanocrystal (CNC) suspension with a final mass concentration of 3.0-5.0 wt% is ultrasonically treated in water at 10-15℃ for 8-12 min. Then, 12-16 mL of the CNC suspension and 3-8 mL of the precursor solution are stirred at 15-20℃ for 2-3 h. The homogeneous mixture is transferred or cast onto a plate and dried at 15-20℃ for 48-56 hours to obtain a red composite membrane. The thickness of the composite membrane is 10-30 micrometers; The rare earth element is Eu or Tb.

2. The preparation method according to claim 1, characterized in that: The drying time in step 2) is 48-50 hours.

3. The method for preparing the composite membrane according to claim 1, characterized in that: The preparation process of the rare earth metal coordinated with 2,6-pyridinedicarboxylic acid is as follows: 200-250 mg of a soluble rare earth compound was added to 55-65 mL of an aqueous solution containing 290-310 mg of 2,6-pyridinedicarboxylic acid (DPA). The mixture was refluxed at 58-62 °C for 24-27 hours. After freeze-drying, the rare earth metal complex coordinated with 2,6-pyridinedicarboxylic acid was obtained.

4. A chiral circularly polarized fluorescent composite film prepared by the method described in claim 1.

5. The application of the chiral circularly polarized fluorescent composite film of claim 4 in the use of or preparation of anti-counterfeiting labels.

6. The application according to claim 4, characterized in that: When a linear polarizer is placed above the composite film, different colors of light are reflected by rotating it at different angles, or the degree of wetting of the film can be controlled to observe different colors of light, thus making it suitable for use as an anti-counterfeiting label. Alternatively, the application process involves attaching the cellulose composite membrane to the product or forming a coating on the product, or adding the film made from it or the material used to make the film to a transparent matrix and then attaching it to the product or forming a coating on the product. Alternatively, the application process involves further processing the material used to prepare the thin film into a coating pattern. Different intensities of reflected light are detected using a linear polarizer, fluorescence, or ultraviolet light. Alternatively, different colors are observed based on the different water contents of the thin film, which are used for product material identification and anti-counterfeiting label verification.

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