Study On Preparation And Properties Of Structural Color Films By Ultrasonic Spraying

Structural color,also known as physical color is caused by scattering,diffraction and interference of light when passing through very thin structures.Compared to pigment color,structural color has the advantages of high brightness,high saturation and good colorfastness.Moreover,the structural color materials have simple structures,a wide selection of materials,and have wide application prospects in the fields of display,functional coating,and anti-counterfeiting.There are many methods for preparing structural color materials.The traditional precision processing method is expensive and the manufacturing cost is high;while the self-assembly method based on the solution system is simple and efficient,such as dip coating,spin coating and pressure spray coating.This paper introduces the concept of micro-spraying to achieve accurate control of the assembly process,and ultrasonic spraying technology,which has been applied in some fields of film preparation in recent years,is employed for investigation.In this work,we perform a research of the influence of material properties and operating modes on ultrasonic spray coating of colloidal particle film,aiming at producing colloidal particle film of uniform thickness?less than 200 nm?.Silicon dioxide?SiO2?and titanium dioxide?TiO2?are selected as stacking materials and the substrates used are silicon wafer and glass.In order to reduce the surface tension of the colloidal solution,polyvinylpyrrolidone?PVP?is used as the surfactant.Firstly,the average hydration particle size and solution PDI of TiO2 nanoparticles and SiO₂nanoparticles in the water dispersion solution are measured.The average particle size of TiO2nanoparticles is 36.75 nm and the PDI is 0.186.SiO2 nanoparticles have an average diameter of 52.57 nm and a PDI of 0.228.Before and after the addition of PVP,the PDI of TiO2nanoparticles dispersion solution are 0.186 and 0.197,respectively,with an increase of 5.9%.while the average hydration particle diameter of the particles are 36.75 nm and 41.05 nm,respectively,with an increase of 11.7%.It can be seen that the addition of PVP have only a little impact on the particle size and dispersion of the system.Secondly,the pure solution of PVP is used as the raw material for film assembly,and the ultrasonic spraying parameters were preliminarily determined.0.1 wt.%PVP and 0.1 wt.%nanoparticle dispersions are mixed for assembly,and PVP is removed after calcination.The results shows that SiO2 and PVP in the S/P system contributed to the film thickness by 1:1,and TiO2 and PVP in the T/P system contribute to the film thickness by 6:4.Studies have shown that the thickness of the film will be halved if the number of spraying times or the concentration of the material is halved.The EDS spectrum test of the calcined TiO2 nanoparticle coating shows that the coating had good coverage on the substrate surface.Thirdly,reducing the concentration of material,so as to decrease the thickness of the film,making it easy to fall into the thickness range of the film interference,and then the color is modulated by adjusting the operating parameters.The concentrations of the nanoparticle is 0.05wt.%and the PVP is 0.01 wt.%which are selected as the mixture system.The influence of the bottom temperature on the drying process of the film is investigated.Finally,60?is selected as the dry film assembly temperature,40?is selected as the wet film assembly temperature and the carrier gas pressure is controlled within 20 kPa.The coating assembled without PVP does not produce structural color,optical microscope images show that its microstructure is pebble shaped.As the number of spraying times increases,the color of the SiO2 nanoparticle coating gradually becomes redshift,which conforms to the interference law of the thin film.Because as the number of spraying times increases,the quality of the thin film increases,resulting in an increase in the thickness of the thin film.For the SiO2 nanoparticle coating obtained by dry film spraying,the calcined sample is tested by profilometry,and the surface roughness RMS is 130 nm,and the coating surface shows a porous structure.The study of ultrasonic spray coating of TiO2 nanoparticles shows that the number of spraying increases,then the thickness of the coating increases;the phenomenon of the sample obtained without the addition of PVP is consistent with the SiO2 coating;the thickness of the sample does not change significantly before and after calcination,and the coating refractive index decreases 0.22,this is because after calcination,air occupies the position of the previous PVP.Finally,the SiO2 nanoparticle coating can reduce the water contact angle of the silicon wafer from 43.0°to 5.5°,showing a significant wetting effect.Subsequently,the SiO2nanoparticle coating is assembled on the glass substrate,the light transmittance of the resulting product is above 85%,the water contact angle of the glass drops from 57.0°to 8.0°,therefore,it have excellent anti-fog properties.