Hydrogel-based direct printing platform and method for realizing security of optical image information

Abstract

The application discloses a kind of based on hydrogel direct printing platform and the method for realizing optical image information security, the hydrogel direct printing platform is composed of metal-polyvinyl alcohol-metal three-layer film, using electron beam exposure technology, can directly print out ladder type hydrogel nanometer microcavity, for the generation of structural color;The polyvinyl alcohol layer as a typical hydrogel, can absorb water molecules and swell behavior;The method for realizing optical image information security includes: one-time optical information transmission and optical image hiding.By electron beam exposure technology on hydrogel nanometer microcavity prints out optical image information, when information transmission is completed, can utilize environmental humidity change and destroy information instantly, reach one-time optical information transmission.Further, using relative humidity brings the structural color change of ladder type nanometer microcavity, can realize optical image hiding and decryption.The application can be applied to optical information security, encryption and anti-counterfeiting and the like field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of thin film optics, in particular to a water gel direct printing platform and a method for realizing optical image information security. BACKGROUND

[0002] The nano microcavity composed of a metal-dielectric-metal three-layer thin film structure can filter the spectrum of incident light based on the Fabry-Perot (FP) interference principle. By adjusting the thickness of the dielectric layer to change the resonant cavity length, the metal-dielectric-metal nano microcavity can realize a rich color structural color (Li Z, Butun S, Aydin K. Large-area, lithography-free super absorbers and color filters at visible frequencies using ultrathin metallic films[J]. ACS Photonics, 2015, 2(2): 183-188.). In addition, by using micro-nano processing technology to manufacture stepped nano microcavities with different cavity lengths and arranging them in space, colorful optical images can be obtained for optical information display. At the same time, the structural color produced by the micro-nano structure has the advantages of not fading and being environmentally friendly compared with pigment coloring.

[0003] However, the nano microcavity based on the metal-dielectric-metal architecture lacks active control capability, that is, once the structure is processed, the structural color produced is fixed and cannot be changed, which limits its further use in the field of optical information security such as one-time optical information transmission and optical image hiding, and new innovations are urgently needed. As a hydrophilic material, water gel can absorb water molecules to swell, which can give FP-type nano microcavities the ability to actively control, and is expected to expand the application of FP-type nano microcavities in structural color display and optical information security. SUMMARY

[0004] In view of the deficiencies in the prior art, the present application provides a method for realizing optical image information security based on a water gel direct printing platform. The water gel direct printing platform uses polyvinyl alcohol hydrogel as the intermediate layer of the FP-type nano microcavity to construct a metal-polyvinyl alcohol-metal three-layer thin film nano microcavity architecture. By using electron beam exposure technology, a stepped nano microcavity can be obtained by directly printing a metal layer-polyvinyl alcohol layer-metal layer three-layer thin film. By using the pattern produced by the structural color to carry the optical image information and the unique water absorption characteristics of polyvinyl alcohol, the transmission of optical image information security is realized.

[0005] Specifically, the present application provides a method for realizing security of optical image information based on a hydrogel direct printing platform to realize one-time optical information transmission and optical image information hiding.

[0006] To achieve the above functions and purposes, the technical solutions of the present application are as follows:

[0007] In the first aspect, the present application provides a hydrogel direct printing platform, characterized in that the printing platform is designed by the following method:

[0008] By electron beam exposure technology, a metal-polyvinyl alcohol-metal three-layer film structure is directly printed, and by using different exposure doses, a stepped hydrogel nanocavity structure can be obtained for generating structural color.

[0009] The stepped hydrogel nanocavity is designed for spatial arrangement to carry optical image information.

[0010] When the environmental humidity increases or is oversaturated, two kinds of optical image information security can be realized according to the design, including one-time optical image transmission and optical image hiding.

[0011] As a preferred solution, the hydrogel direct printing platform is composed of a metal-polyvinyl alcohol-metal three-layer film structure and is sequentially placed on a silicon dioxide substrate to form an FP-type nanocavity.

[0012] The metal-polyvinyl alcohol-metal three-layer film structure is of micro-nano size.

[0013] The thickness of the polyvinyl alcohol layer is customized by electron beam exposure dose.

[0014] The thickness of the polyvinyl alcohol layer responds to environmental humidity, and within a relative humidity range, the polyvinyl alcohol layer expands, causing the structural color generated by the nanocavity to change; when the environmental humidity is saturated and excessively humid, the polyvinyl alcohol layer absorbs excess water and undergoes irreversible dissolution, which can destroy the nanocavity structure.

[0015] The metal material of the metal-polyvinyl alcohol-metal three-layer film structure is silver, and the thickness of the silver material is set to 20 nm; the thickness of the polyvinyl alcohol layer is 450-550 nm.

[0016] In the second aspect, the present application provides a method for realizing optical image information security using the above-mentioned hydrogel direct printing platform, characterized in that the method is used for one-time optical image transmission.

[0017] By using two different electron beam exposure doses, a stepped hydrogel nanocavity distribution with a required optical pattern is printed for optical image information transmission.

[0018] When the delivered information is received, the structural color generated by the nanocavity is destroyed by making the ambient humidity of the image surface supersaturated, dissolving the polyvinyl alcohol layer, and ultimately causing the delivered optical image information to be destroyed; that is, the one-time optical image delivery is achieved.

[0019] In a third aspect, the present application also provides a method for realizing optical image information security by using the hydrogel direct printing platform as described above, characterized in that the method is used for optical information hiding.

[0020] By using two similar exposure doses, two hydrogel nanocavities with similar cavity lengths are directly printed to construct the required optical image; because the cavity lengths of the two nanocavities are similar, the same color can be generated in the indoor humidity environment, and the printed optical image cannot be observed, realizing the hiding of optical information.

[0021] When the ambient humidity increases, the thickness of the polyvinyl alcohol layer expands, making the cavity lengths of the two nanocavities change from similar to different, resulting in different colors generated, and ultimately decrypting the hidden optical image information.

[0022] In combination with the mechanism of the application, it is specifically expanded as follows:

[0023] The hydrogel direct printing platform is composed of a metal-polyvinyl alcohol-metal three-layer film structure and is placed on a silica substrate in sequence to form an FP-type nanocavity. The metal-polyvinyl alcohol-metal three-layer film structure is of micro-nano size; the thickness of the polyvinyl alcohol layer can be customized by electron beam exposure; the thickness of the polyvinyl alcohol layer responds to the ambient humidity, and when the ambient humidity is saturated and too humid, the polyvinyl alcohol layer is irreversibly dissolved; the metal layer is silver material, and the thickness is set to 20 nm; the thickness of the polyvinyl alcohol layer is 450-550 nm.

[0024] For one-time optical information delivery in optical image information security, the present application directly prints the optical image information to be delivered onto the metal-polyvinyl alcohol-metal nanocavity by using electron beam gray exposure technology, and uses the structural color generated by the nanocavity to deliver the optical image information. At the same time, by using the characteristic that polyvinyl alcohol can be dissolved in water, when the ambient humidity is too humid, the polyvinyl alcohol layer is dissolved due to the absorption of excessive water molecules, making the nanocavity structure for displaying optical information irreversibly destroyed, thereby destroying the delivered optical image information, and achieving the purpose of one-time optical information delivery of optical image information security.

[0025] For realizing optical image hiding in optical image information security, the application utilizes the water absorption and expansion behavior of a polyvinyl alcohol layer under a certain environmental humidity, and the color change of the nano microcavity transmission brought by the water absorption and expansion behavior. The color of the optical image generated by the designed directly printed ladder nano microcavity is used to achieve that the color generated by the ladder nano microcavity pattern cannot be distinguished under the condition of relative humidity 1, so that the carried optical image information is hidden; under the condition of relative humidity 2, the color difference of the ladder nano microcavity generated due to the expansion of the polyvinyl alcohol layer causes the hidden optical image to appear, so that the optical image hiding optical information security is realized.

[0026] The advantages and beneficial effects of the application are as follows:

[0027] (1) The optical image information security realization method provided by the application is based on a hydrogel direct printing platform, and can destroy or decrypt the carried optical image information through environmental humidity. The control means is simple, easy to obtain, and green and environmentally friendly. For example, after the transmitted optical information is received, the humidity around the hydrogel platform is oversaturated by simply taking a deep breath by a person, so that the carried optical image information can be destroyed and is irreversible, and therefore has high practicability and security.

[0028] (2) The ladder hydrogel nano microcavity generated by the directly printed metal-polyvinyl alcohol-metal three-layer film structure has rich structural color, and has the advantages of controllability, non-fading, environmental protection, etc. At the same time, the encrypted or hidden optical image information is more abundant, and can assist high-end industries in anti-counterfeiting.

[0029] (3) The pixel size of the hydrogel platform based on electron beam direct printing carrying optical image information is micro-nano scale, so it has high image resolution, and can realize high-density and large-capacity optical information security encryption and storage. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a processing flow diagram of the hydrogel direct printing platform in the application;

[0031] Figure 2 is an experimental effect diagram of realizing one-time optical information transmission in the embodiment of the application (part of the two-dimensional code is shielded);

[0032] Figure 3 is a schematic diagram of realizing optical information hiding principle design of the hydrogel nano microcavity in the embodiment of the application;

[0033] Figure 4 is an experimental effect diagram of spectral changes of two kinds of different dose printed hydrogel nano microcavities under different humidity conditions in the embodiment of the application;

[0034] Figure 5is a schematic diagram of a nano-cavity structure used for fingerprint optical image hiding in embodiments of the present application;

[0035] Figure 6 is an experimental effect diagram for realizing fingerprint optical image hiding in embodiments of the present application;

[0036] In the figure: h Initial thickness of the polyvinyl alcohol layer; Δ h Thickness of the polyvinyl alcohol layer after electron beam exposure; Δ H 1 is the height difference of the stepped hydrogel nano-cavity printed by two exposure doses under relative humidity 1; Δ H 2 is the height difference of the stepped hydrogel nano-cavity printed by two exposure doses under relative humidity 2. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the embodiments of the present application and the functions realized thereby, the present application will be further described below in conjunction with the accompanying drawings.

[0038] Embodiment 1

[0039] This embodiment is a method for realizing optical image information security based on a hydrogel direct printing platform. Specifically, by using electron beam exposure technology, a hydrogel nano-cavity structure composed of a metal-polyvinyl alcohol-metal three-layer film is directly printed. Since the polyvinyl alcohol will collapse under electron beam exposure, the thickness of the hydrogel nano-cavity can be customized according to the exposure dose, thereby obtaining a stepped nano-cavity array, as shown in Figure 1 Because the hydrogel nano-cavity is based on the FP cavity architecture, nano-cavities with different cavity lengths will exhibit different colors, and by designing and arranging the stepped nano-cavity arrangement, the direct printing hydrogel platform can carry color optical image information.

[0040] For the hydrogel platform using direct printing, the optical information security of one-time optical information transmission is realized. Figure 2 It is shown that the two-dimensional code pattern obtained by directly printing the hydrogel nano-cavity with two exposure doses can be clearly observed under indoor humidity. The ruler in the figure is 100 μm. However, when the two-dimensional code pattern is successfully acquired by the information receiver during information transmission. The receiver only needs to take a deep breath on the surface of the hydrogel nano-cavity, so that the surrounding air humidity is supersaturated, the polyvinyl alcohol layer will absorb excess water and dissolve, causing the nano-cavity structure to be destroyed, and finally the two-dimensional code pattern is destroyed instantly, as shown in Figure 2The destroyed optical image does not carry any valid information and cannot be reconstructed, so the hydrogel direct printing platform can be used for optical image information security for one-time optical information transmission, and the information destruction has the advantages of simple and easy way, instant response, and irreversibility, which can improve the security of information transmission.

[0041] For the hydrogel platform using direct printing, optical image hiding is achieved for optical information security. When the two similar doses are used to expose the hydrogel nanocavity, the obtained stepped nanocavity has little difference in the collapse degree of the polyvinyl alcohol layer, and can exhibit the same transmission color at relative humidity (RH) 1, as shown in Figure 3 When the environmental humidity increases to relative humidity 2, the difference in cavity length of the two hydrogel nanocavities increases due to the expansion of the polyvinyl alcohol layer, resulting in a difference in the transmission color of the two nanocavities. This change in transmission color from the same to different can be used to encrypt and hide the image. Figure 4 The transmission spectra of two nanocavities with different cavity lengths printed by two different exposure doses are experimentally demonstrated. It can be observed that at relative humidity ~ 40%, the transmission spectra of the two nanocavities are basically the same, so they will exhibit the same transmission color; at relative humidity ~ 80%, the two nanocavities have different spectra due to the expansion of the polyvinyl alcohol layer, so they will exhibit different transmission colors. Further, by using the transmission color change caused by the humidity response, a fingerprint pattern is printed on the surface of the hydrogel nanocavity by using two similar doses, as shown in Figure 5 Due to the similar doses, at relative humidity 1 (RH1 ~ 45%-65%), the height difference of the two nanocavities with different cavity lengths is small. When white light is incident on the fingerprint pattern, the areas printed by dose 1 and dose 2 will exhibit the same color, so that the fingerprint pattern cannot be observed; at relative humidity 2 (RH2 ~ 80%-90%), the height difference of the two nanocavities with different cavity lengths is amplified. Under white light illumination, due to the inconsistency of the colors of the two nanocavities, the hidden fingerprint pattern information can be obtained. Figure 6 The experimental results of the above design method are shown. Since the relative humidity 1 is basically in the indoor humidity range, the fingerprint pattern cannot be observed under indoor humidity. To increase the environmental humidity to relative humidity 2, the polyvinyl alcohol layer can be expanded but not dissolved by simply exhaling. Finally, the encrypted fingerprint pattern is observed under relative humidity 2.

[0042] In this embodiment, two exposure doses are used to realize one-time optical information transmission and optical image hiding based on the direct printing hydrogel platform. For those skilled in the art, without creative labor, more exposure doses can be used to increase the number of optical image information channels carried by the direct printing hydrogel platform, and other drawings can be obtained.

Claims

1. A hydrogel-based direct printing platform, characterized in that: The printing platform was designed using the following method: Electron beam lithography was used to directly print a metal-polyvinyl alcohol-metal three-layer thin film structure. By using different exposure doses, a stepped hydrogel nanocavity structure could be obtained for the generation of structural colors. A spatial arrangement design was implemented for the stepped hydrogel nanocavities to carry optical image information. When the ambient humidity increases or becomes supersaturated, the design enables two types of optical image information security, including one-time optical image transmission and optical image concealment. The hydrogel direct printing platform consists of a metal-polyvinyl alcohol-metal three-layer thin film structure, which is placed sequentially on a silica substrate to form an FP-type nanocavity. The metal-polyvinyl alcohol-metal three-layer thin film structure is all micro-nano sized; The thickness of the polyvinyl alcohol layer is determined by the electron beam exposure dose; The thickness of the polyvinyl alcohol layer responds to the ambient humidity. Within the relative humidity range, the polyvinyl alcohol layer expands, causing a change in the structural color of the nanocavities. When the ambient humidity is saturated and too humid, the polyvinyl alcohol layer absorbs excessive water and undergoes irreversible dissolution, which can destroy the nanocavity structure. The metal material of the metal-polyvinyl alcohol-metal three-layer thin film structure is silver, and the thickness of the silver material is set to 20 nm; the thickness of the polyvinyl alcohol layer is 450-550 nm.

2. A method for achieving optical image information security using the hydrogel-based direct printing platform as described in claim 1, characterized in that: This method is used for one-time optical image transfer; By using two different electron beam exposure doses, a stepped hydrogel nanocavity distribution with the desired optical pattern was printed for use in optical image information transmission. Once the transmitted information is received, the polyvinyl alcohol layer is dissolved by making the ambient humidity on the image surface supersaturate, which destroys the structural color generated by the nanocavity and ultimately destroys the transmitted optical image information; that is, one-time optical image transmission is achieved.

3. A method for achieving optical image information security using the hydrogel-based direct printing platform as described in claim 1, characterized in that: This method is used for optical information hiding; By using two similar exposure doses, two hydrogel nanocavities with similar cavity lengths were directly printed to construct the required optical images. Since the cavity lengths of the two nanocavities are similar, they can produce the same color in an indoor humidity environment, and the printed optical images cannot be observed, thus achieving the concealment of optical information. As ambient humidity increases, the polyvinyl alcohol layer expands, causing the cavity lengths of the two nanocavities to become different from similar, resulting in different colors and ultimately revealing the hidden optical image information.

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