Preparation Of Patterned Photonic Crystals On Textile Substrate Via Screen Printing And Investigation Into Their Properties

Photonic crystals(PC)are a kind of crystal materials composed of periodic microor nanostructures with different dielectric constants.Patterned PCs with a particular visual effect are attractive for textile printing and dyeing industry.The screen printing has been proven to be highly effective in the field of conventional textile printing.Moreover,high-viscous dye/pigment pastes are preferentially used in conventional screen printing to obtain the patterns with clearly defined outlines.Hence,there is the need in thickeners,which play the role of viscosity adjustment in the printing precursor systems.However,the addition of a thickening agent to the assembly system of colloidal microspheres enable to not only yield high viscosity,but also block the free movement of nanospheres during their assembly.As a result,the PC obtained show a short-range order/long-range quasiorder structure with a non-iridescent structural color.In order to solve the problem that the contour definition and optical properties of patterned PC are difficult to achieve prepared by the screen printing method,this study prepared different styles of patterned PC suitable for industrial production by studying appropriate viscosity regulator,designing and optimizing screen printing process.This work mainly studied the following two aspects:(1)The printing precursor with high viscosity and shear thinning performance was constructed by introducing synthetic thickener into liquid photonic crystal(LPC)system.The influence of screen printing process on patterned PC was studied.The quasi-ordered patterned PC was prepared and its structure and properties were characterized.The structure-activity relationship between different types of thickener and patterned PC was further discussed.(2)Based on the patten with hydrophilic and hydrophobic difference constructed by screen printing,and the angle-dependent patterned PC was prepared via the shear-induced assembly technique.The spreading behavior of the LPC paste on the hydrophilic and hydrophobic boundaries of different contact angle difference values(ΔCA)was studied.The relationships between the LPC color paste system and the patterned PC were investaged.The assembly process and mechanism of the color paste on the surface of the substrate were studied.The protective layer was prepared on the patterned PC to achieve the unification of its structure stability and color saturation.The technology of double anticounterfeiting patterned PC was developed based on the above method.The main research results are as follows:(1)The best block-area uniformity and line fineness of the pattern after screen printing could be achieved by using the synthetic thickener content of 2.5 wt% and the120-mesh hydrophobic modified screen.Since the synthetic thickener has strong thickening ability and accounts for a small proportion in the printing precursor,and the "temporary" network structure formed in the thickened system had the property of reversible reconstruction.The regularity of the micro arrangement structure evolution of the PC assembled from the nanospheres with a certain space range of free movement was in quasi-order arrangement that is short-range order/long-range quasi-order.Besides,the photochromic pattern of such PC structure exhibited a specific visual "flicker" effect with a certain angular dependence(iridescence effect).(2)Based on the idea of resist printing,a patten with hydrophilic and hydrophobic difference was constructed by screen printing.Once the contact angle difference(ΔCA)between the hydrophilic and hydrophobic areas exceeded 80,the LPC paste spread and assembled in the hydrophilic pattern but resisted in the hydrophobic areas,and the assembled PCs pattern showed good contour sharpness and high-saturation iridescence effect.The double anti-counterfeiting patterned PC was prepared by combining the technique with conventional responsive substances.(3)The application of the bearing-layer onto the textile substrate endowed the printed pattern with improved structural stability and high-fastness structural colors.Moreover,the preparation of the protective layer on the PC surface by spraying or limited scraping can be effectively improved the structural stability of the patterned PCs while retaining the optical properties of the PC pattern.The application of LPCs as the main body of printing printing paste is conducive to the rapid assembly of the nanospheres into ordered photonic crystal structure on the surface of the fabric.The brightness and saturation of the photonic crystal structural color are high.The multi-color pattern on the fabric can be realized by adjusting the size of the nanospheres and the multi-step screen printing process.