| With the increasing frequency of information interaction,counterfeit and inferior products defined as a serious security threat always challenge to security communication and authentication of products and brought unbearable losses to many aspects of human society,such as medical care,finance,trade,and the Internet of Things.Therefore,adding anti-counterfeiting labels to products that need to be protected has become an effective technology to prevent counterfeiting.Traditionally,anti-counterfeiting technologies mainly achieve the purpose of protecting products by creating and using labels generated during the determination process.These anti-counterfeiting technologies usually range from simple watermarks,holograms,graphical barcodes,and security inks.However,the current anti-counterfeiting technology still has many shortcomings and challenges,such as easy forgery,lack of relevant technical means to prevent external attacks and high cost.Physical unclonable functions(PUFs),which have received widespread attention in the field of anti-counterfeiting,is considered to be one of the most potential encryption methods to solve these problems.In the previously reported optical PUFs,although anti-counterfeiting labels such as Raman PUF,fluorescent PUF,and laser scattering PUF have the ability to be applied to PUF systems,most optical PUF materials have defects such as high cost,unstable material structure,cumbersome preparation methods,and inconspicuous feature information,which limit their possibilities as anti-counterfeiting labels.Compared with traditional solid-state photonic crystals,the nanospheres in the liquid colloidal crystal structure also exhibit periodic arrangement.The liquid colloidal crystals have unique physicochemical properties,such as fluidity,metastable structure,reversible assembly and disassembly,and high color saturation.Therefore,if we fabricate responsive photonic crystals by combining the structural properties of liquid colloidal crystals with physical unclonability,this will develop a novel optical PUF with high stability and anti-counterfeiting capabilities.To solve the above-mentioned key scientific problems,this work prepared positively/negatively charged polymer nanospheres as assembly units,wherein the nanospheres self-assembled into periodically arranged liquid colloidal crystal layers using an electrostatic field.Then,the polymerized monomer was introduced to prepare the optical PUF anti-counterfeiting label,and its applications in artificial intelligence recognition and digital recognition were elaborated.The main research results are as follows:In order to prepare liquid colloidal crystals,we prepared polymer nanospheres by emulsion polymerization.By reducing the ionic strength,the nanospheres precipitated into liquid colloidal crystal layers in supersaturated colloidal solution.Liquid colloidal crystal layers possessed highly saturated structural colors.The method for preparing liquid colloidal crystals had the characteristics of one-step molding,rapidity,and large-area preparation.The colloidal crystal layers assembled by nanospheres of different sizes had different structural colors.Taking nanospheres with a particle size of 122 nm as the experimental object,the structural color can be regulated by adjusting the mass fraction of nanospheres in the colloidal solution,which cannot be achieved by other colloidal crystals prepared from supersaturated solutions.In the solution system,as the mass fraction of nanospheres in the solution system decreased,the structural color changed from blue to red,and the spacing of the nanospheres increased.Through the above experiments,it could be found that there was a critical mass fraction range of nanospheres in solution.When the mass fraction of nanospheres was within this range,the reversible assembly-disassembly process of liquid colloidal crystals could be observed by reflection spectrometer.When the mass fraction of nanospheres was higher than the critical mass fraction range,the structure of the colloidal crystal layer was extremely stable and would not be disassembled by external disturbances.We introduced acrylamide monomer into the colloidal crystal solution,and then the acrylamide monomer was polymerized by UV light to fix the colloidal crystal structure and finally prepare a solvent-responsive hydrogel film.In photonic crystal hydrogel films,the nanospheres could not only produce structural color but also act as toughening cross-linking points in the hydrogel film,making the hydrogel film had good elongation ratio and tensile strength.The microscopic morphologies of the microcrystalline and amorphous regions on the film surface were characterized by scanning electron microscopy and atomic force microscopy.Since the colloidal crystals randomly formed microphase separation regions during the film preparation process,the randomly distributed colloidal crystals with different colors had the characteristics of “fingerprint”,which made the photonic crystal film highly random and unclonable.To combine PUF and artificial intelligence recognition,we developed a low-cost,convenient,fast,and encoding-capacity-controllable anti-counterfeiting technology based on unclonable properties.First,we prepared negatively charged nanospheres by introducing maleic anhydride onto the surface of the colloid using a simple emulsion polymerization method.The structure of the liquid colloidal crystals was regulated by the electrostatic field formed between the positively charged acrylamide and the negatively charged nanospheres,and the reassembled colloidal crystals formed a large number of light spots with various structural colors in the solution.At the same time,the size of the colloidal crystals could be effectively controlled by the amount of acrylamide added,and the encoding capacity of the PUF label could be regulated.And then the light spot formed in the liquid phase was completely immobilized in the polymer film by photo-induced acrylamide polymerization.Due to the uncertainty in the reassembly process of colloidal crystallites caused by the electrostatic field and the randomness of the colloidal crystal positions and structural colors,the formed polymer films had unique spot distributions and exhibited PUF features.We used the self-developed five-layer convolutional neural network image to extract and learn the light spot shape and color information.In the anti-counterfeiting verification,the software first classified and compared the light spot information in the images,and then verified the images.The results showed that it had extremely high image recognition speed(200 ms)and accuracy(83%).Using viscous fluids(liquid colloidal crystals)to form momentum exchange between laminar flows during the flow process,a striped PUF label composed of responsive colloidal crystals was developed.Since the process of nanospheres forming colloidal crystals in electrostatic and hydrodynamic resistance fields was unpredictable,the source of entropy for anti-counterfeiting labels came from randomly distributed colloidal crystals.Based on the water responsiveness of the polymer film,the PUF properties in the anti-counterfeiting label could be switched between invisible and visible states,improving the security of the label.The structural and morphological changes of the PUF label during water loss were measured by reflectance spectrometer,which proved that the tag has good reversibility and reproducibility.In this work,PUF labels were converted into digital labels by a reflectance spectroscopy system,and the uniformity,uniqueness and randomness of digital labels proved that PUF labels endowed with unclonable properties.The verification experiment results showed that the PUF label had good robustness.In addition,a high-security supply chain mutual authentication system based on digital identification had been developed to effectively verify authenticity at each node of the supply chain.Overall,responsive optical PUF and digital identification provided an effective means to combat counterfeit and shoddy products,which was of great significance in the anti-counterfeiting of confidential documents,jewelry,banknotes,medicines or other expensive commodities. |
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