Controllable Preparation Of SiO₂@Ag Core-Shell Structure And Structural Color Enhancement

At present,low-carbon development has become a global consensus.Structural color is an environment-friendly material which can avoid color fading and contaminant degradation of dyes and pigments.Structural color contains photonic crystal structural color(PC)and amorphous photonic crystal structural color(APC).High-quality crystal structure is the key to the color rendering effect,which is of great importance for the optimization of the structural color assembly.Disordered structure will cause incoherent scattering in most APCs,which leads to a decrease in structural color saturation.Generally,it is necessary to add light-absorbing materials such as Ag nanoparticles to improve the color saturation.However,the Ag NPs easily agglomerates,which limits the practical application.Based on the above background,the following research is conducted.Firstly,the structural color construction process is optimized based on the mechanism of different assembly technologies.Then,in order to enhance the structural color saturation and visibility of the assembled SiO2@Ag/SiO2 APC structure,the Ag NPs were loaded onto the surface of SiO2 by reduction method.Furthermore,a fluorescent substance is introduced onto the surface.A dual optical response of visible light and fluorescence can be achieved,since the LSPR of Ag NPs enhances the luminescent intensity.The main results are obtained as follows:(1)The mass fraction of microspheres and the assembly temperature were controlled to optimize the vertical self-assembly process of SiO2 PC.The mass fraction of microspheres,solvent ratio and rotation speed were regulated to optimize the spin coating of SiO2 APC.The results show that the PC microstructure is most ordered and iridescent structural color with angular heterochromia is demonstrated,while assembling at 60℃ with 0.5 wt%SiO2.As to the spin coating process,the optimized condition is as follows:the dispersant is a mixture of ethanol and glycol in a mass ratio of 8.5:1.5,2 wt%SiO2,with spin coating speed of 3000 rpm.The PC structure is disordered in the long-range and shows non-iridescent structural color independent of angle.(2)SiO2@Ag core-shell structure was prepared to improve the agglomeration of Ag nanoparticles.The hydroxyl groups on the surface of SiO2 microspheres were modified with 3-aminopropyl triethoxysilane(APTES)to form amino groups that can chelate Ag+.Then a large number of Ag NPs were reduced and a uniform and dense coating of Ag was formed.When glutaraldehyde was used as the reducing agent,reacting at 85℃ for 60 mins,the best morphology of SiO2@Ag microspheres was obtained.Uniform and dense coating of silver nanoparticles is shown,and better light absorption capacity in the visible light range is resulted.(3)SiO2@Ag/SiO2 APC were prepared through layer-by-layer assembly of SiO2@Ag and SiO2 of different particle sizes.As a light absorbent,SiO2@Ag can effectively absorb non-coherent scattering to make the structural color exhibit higher color saturation and visualization.The structural color saturation of SiO2 with different particle sizes increases by 2-3 times when the mass ratio of SiO2@Ag:SiO2 is 0.5:1.The luminescence intensity of rhodamine B(RhB)coating was enhanced by 2.8 times by the surface plasmon resonance effect(SPR)of SiO2@Ag,showing a bright yellow fluorescent color.Thus,dual optical responses of structural color and fluorescent color for the SiO2@Ag/SiO2 APC were realized,which will expand its application in the fields of anticounterfeiting labels and information encryption,et al.