Fabrication And Properties Study Of Structural Color Coatings Based On Single Particle Size Nano SiO₂ Microspheres

Unlike traditional dyes or pigments that are prone to aging and fading,and the preparation process is prone to environmental pollution by sewage and wastewater,structural colors have the advantages of never fading,environmental friendliness,and biocompatibility because they are produced by periodic nanostructures.These properties make structural colors expected to replace traditional dyes or pigments in the fields of decoration,packaging,anti-counterfeiting,and sensing.At present,low-angle-dependent structural color coatings are prepared by building amorphous photonic crystal structures,but traditional amorphous photonic crystals have weak interactions between colloidal microspheres,and the mechanical properties of the prepared structural color coatings are poor,making it difficult to achieve practical applications.The color of the structural color coating is usually adjusted by changing the particle size of colloidal microspheres,which requires precise control of the particle size of the colloidal microspheres,and the process is complicated to produce on a large scale.In addition,when the liquid infiltrates the structural color coating,the structural color will disappear due to the change in refractive index,which limits the application of structural color coating.Based on the above problems,this paper investigates the color adjustment,mechanical properties,and hydrophobic properties of photonic structural color coatings.First,monodisperse SiO₂ microspheres with a particle size of 187 nm were prepared as assembly units by the St（?）ber method,and then a polyurethane（PU）colloid with a particle size of 52.6 nm was prepared as a polymer matrix.The particle size,monodispersity,surface morphology,and phase structure of SiO₂ microspheres and PU were analyzed by zeta potential,particle size analysis,field emission scanning electron microscopy,and XRD.The color-tunable high-strength photonic structural color coatings were prepared by the co-assembly of SiO₂ microspheres and PU colloids on various substrates（slide,black PVC cardboard,and black aluminum plate）.The properties of the photonic structural color coatings were characterized by field emission scanning electron microscopy,reflection spectroscopy,optical photographs,and mechanical property tests.The effect of PU mass fraction on the photonic structural color coatings was investigated,and it was found that with the increase of PU mass fraction,the maximum reflection peak of the photonic structural color coatings was redshifted and its corresponding color was changed,which realized a variety of structural color adjustment of single-size SiO₂microspheres.The mechanical properties of the photonic structural color coatings also increased with the increase of PU mass fraction,and the peel adhesion force of the coatings reached 406.06 N/m when the PU mass fraction increased to 36wt%,which was 8 times higher than that without PU addition.By examining the effect of the polymer matrix on the photonic structural color coatings,it was found that the addition of PU not only increased the crystalline spacing of the amorphous photonic crystal,but also increased the actual refractive index of the coatings,and the two together increased the maximum reflection peak of the photonic structural color coatings.Hydrophobic encapsulation of the above coatings by polydimethylsiloxane（PDMS）was used to prepare photonic structural color coatings with good hydrophobic properties.The properties of the hydrophobic photonic structural color coatings were characterized using field emission scanning electron microscopy,reflection spectroscopy,optical photographs,and contact angle tests.The effect of the difference in PDMS concentration on the optical and hydrophobic properties of the photonic structural color coatings was investigated to determine the optimal PDMS concentration.The contact angles of the 3 wt%PDMS-encapsulated photonic structural color coatings were 123°,137°,139°,142°,143°,and 148°with increasing the PU mass fraction from 0 wt%to 36 wt%,respectively,all showing good hydrophobicity.When the liquid infiltrates the structural color coatings,the liquid cannot penetrate the coating due to the good encapsulation,so the structural color remains stable and does not disappear.