Construction Of Colloidal Photonic Crystal And Their Applications In Anti-counterfeiting Materials,Printing And Chemical Analysis

After more than ten years of development,traditional solid colloidal photonic crystals and their derived structures have become increasingly mature and can be fabricated on a large scale.The literature reported so far has also proposed several response systems and application based on solid colloidal crystals,but the applications are relatively scarce and lack of innovation.The response performance has not been significantly improved and the progress in this area is relatively slow.In order to solve this,this thesis develops a variety of colloidal photonic crystal films with unique response characteristics based on the construction of new response mechanisms and the unique properties of the building blocks.It has been successfully applied to the photonic crystal structural color printing,anti-counterfeiting labels and analysis and detection,which further expands the application of photonic crystal films and improves the response speed of photonic crystal films.The specific research contents are as follows:In the second chapter,a thermally responsive double layered SiO₂-PC/PEG film was prepared through the lamination of photonic crystals and thermal phase change materials,and applied it to photonic crystal thermal printing.Under appropriate heating temperature,PEG will melt rapidly and fill into the interparticle voids of colloidal particles and lead to an increased refractive index and color changes on the photonic crystal film.Compared with the previously reported thermochromic photonic crystal films,the thermal response speed is greatly improved,which can be directly compatible with the existing thermal printing technology and used for fast,high-resolution and grayscale thermal printing under program control.In addition,compared with ordinary dye-based thermal paper,SiO₂-PC/PEG thermal paper does not contain toxic bisphenol A,and has more environmentally friendly components and excellent light stability,showing broad application prospects.In the third chapter,we designed a multi-layered composite photonic crystal film based on paraffin/hydrophobic SiO₂/polyurethane（Para/HPO-SiO₂-PC/PU）with further improved structural stability,solvent stability and practicality.Para/HPO-SiO₂-PC/PU film is prepared by sequentially blade coating paraffin wax,assembling hydrophobic colloidal photonic crystals,and spraying PU film on the PET film,paper or other substrates.Compared with previously reported thermally responsive photonic crystals,the thermally responsive material is located below the photonic crystal layer,the thermal response speed of the thin film is faster.And fast,high-resolution and grayscale thermal printing was achieved on such multi-layered films under program control.The color stability in humid environments was improved owning to the use of hydrophobic thermal phase change material and hydrophobic SiO₂ colloidal particles,and the fading of traditional thermal paper in moisture was completely solved.In the fourth chapter,hollow silica（h-SiO₂）with different shell thicknesses and corresponding photonic crystal films were prepared by a templating method.We find that the solvent response behavior was significantly related to the shell thickness of h-SiO₂ particle through solvent wetting experiments,water and ethanol exhibiting asymmetric solvent response in h-SiO₂.Based on this,PU we infiltrated into the h-SiO₂ photonic crystal film to improve the structure stability,and two different photonic crystal structure was introduced into the h-SiO₂/PU film by HF acid etching.The prepared photonic crystal patterns are invisible because the difference of thickness layer does not lead to a large color difference in the h-SiO₂/PU film in the dry state;however,when the film was soaked in water and ethanol,it exhibits different solvent responses.Finally,the triple response including invisible when drying,appearing in water,and invisible in ethanol can be realized,and those three states can be switched arbitrarily,with good reversibility.When such an invisible pattern was applied to the photonic crystal anti-counterfeiting patterns,its switching effect is more difficult to imitate,and it has higher security when used in anti-counterfeiting labels.In the fifth chapter,amorphous photonic crystal（APC）film was prepared by using mesoporous SiO₂ as assembly unit,when the APC film was used as stationary phase in thin-layer chromatographic,efficient separation of similar chemicals and visual detection of sample position was realized simultaneously.APC film with relatively low volume ratio of colloidal particles and increased micro-scale pores were beneficial to the enhanced capillary force and developing speed.Simultaneously,mesoporous colloidal particles with larger specific surface area are beneficial to the adsorption-desorption effect and chemicals with similar property could be quickly separated on the film.In addition,the increased refractive index and color change in the spotting position after chemical loading and separation could be directly identified by the naked eyes,visual detection and efficiently separating were achieves simultaneously on this film.Compared with traditional silica gel chromatographic,complex post-processing are not required for various chemical substances that are colorless,non-fluorescent or non-strong ultraviolet absorption since the sample points can be directly identified by color changes on the APC film,and the thin-layer chromatography.analysis process was significantly simplified.