Preparation Of Self-supporting And Solvent-responsive Colloidal Photonic Crystals For Anti-counterfeiting Application

Photonic crystals(PCs)are artificial microstructures formed by periodic arrangement of media with different refractive indices.Their unique photonic forbidden band can selectively reflect visible light and produce bright structural colors.These characteristics make it have broad application prospects in display,printing,anti-counterfeiting and many other fields.The traditional colloidal photonic crystal(colloidal crystal)is an ordered structure formed by close packing of microspheres,but its mechanical stability is poor and does not have functionality,which limits the development and application of colloidal crystals.We prepared a series of colloidal crystalline materials with self-supporting and solvent-responsive properties through selective solvent volatilization combined with a photocuring strategy and used them for anti-counterfeiting.This thesis is divided into five chapters,including the research background of colloidal crystals,the preparation of self-supporting near-infrared colloidal crystals and their encoding-decoding applications,the preparation of acetic acid-responsive colloidal crystals and their anti-counterfeiting applications.and the preparation and anti-counterfeiting application of ethanol-responsive colloidal crystal prints.The main research contents are:(1)Near-infrared colloidal crystals(NIRPCs)films with self-supporting properties of"SiO₂/poly(ethylene glycol)phenylene ether acrylate"were prepared by selective solvent volatilization-driven colloidal assembly combined with a photocuring strategy.By controlling the size of SiO₂ particles,NIRPCs films with different wavelengths were prepared.We arranged NIRPCs with different wavelengths into linear codes.Since human eyes cannot recognize NIRPCs films,they can only be decoded by spatial reflectance spectroscopy(SRS).The method for preparing the code is simple and efficient,and has the advantage that the code can be recycled.With the introduction of multi-layer coding,due to the occlusion of light by the upper-layer coding,the reflection signal of the lower-layer coding becomes weak,and the reflected intensity of the coding reveals the stacking order,further realizing more complex line coding.This newly developed encoding-decoding system expands the application of PCs in anti-counterfeiting,information protection and communication.(2)"SiO₂/polymer poly(ethylene glycol)phenylene ether acrylate(PEGPEA)"acetate-responsive self-supporting colloidal crystals were prepared by colloidal self-assembly strategy.In the acetic acid solution,the self-supporting responsive colloidal crystals swelled,the lattice spacing became larger,and the peak position was red-shifted.The study found that the introduction of poly(ethylene glycol)diacrylate(PEGDA,a cross-linking agent)into the scaffold polymer controlled the degree of cross-linking and the maximum red shift of the peak position;adjusted the ratio of the mixed solution of acetic acid and ethanol to control the reflection peak specific location.Based on the above characteristics,multi-level color-changing photonic prints(CCPPs)were prepared by combining responsive colloidal crystal patterns with different cross-linking degrees through selective polymerization.In a dry environment,the consistent information of the reflection peak positions between the pattern and the background is hidden.When the CCPPs are immersed in the responsive solvent,the red shift of the responsive colloidal crystals with different cross-linking degrees is different,and the color difference information is revealed.After drying,the CCPPs returned to the hidden state,and the hiding and revealing were fully reversible.This method for preparing CCPPs is simple and novel,which promotes the application of CCPPs in high security level and multi-level anti-counterfeiting.(3)A fast ethanol-responsive"SiO₂/poly(propylene glycol)acrylate(PPGA)"photonic paper was prepared by selective solvent volatilization-driven colloidal assembly combined with a photocuring strategy.Using hydroxyethyl methacrylate(HEMA),which is similar in structure to PPGA,as a colorless ink,the photonic paper is partially swollen and subjected to secondary light curing.The lattice spacing of the swollen part becomes larger and red-shifted,forming a pattern with a significant color difference with the background.,thus preparing responsive photonic prints(RPPs).In the pattern part of RPPs,the degree of cross-linking became larger due to secondary swelling and curing,and ethanol could not swell.The background of RPPs is in ethanol solution,the swollen lattice spacing increases and the peak position corresponds to a red shift,and the pattern part does not swell.The volume fraction of the mixed solution of ethanol and water is adjusted,and the color difference is displayed in multiple stages.The color change is reversible between dry and swollen states,and the RPPs can be recycled.This novel multi-color RPPs preparation method is simple,the prepared RPPs respond quickly,have rich color development,and can be recycled,which enriches the application of RPPs in security and anti-counterfeiting.