Fabrication Of Silica-polymer Based Colloidal Photonic Crystals And Investigation Of Their Applications

Colloidal photonic crystals(CPCs)show potential applications in the fields of display,printing,detection,anti-counterfeiting and so on due to their periodic micro/nano-structures,optical stop bands and structural colors.In general,the traditional methods of preparing CPCs require harsh assembly conditions and time-consuming process with lack of control on the large-area fabrication,which limits the practical applications of CPCs.Developing new methods that can prepare responsive CPCs with new functions in a rapid and efficient way and the extension of their applications remains a big challenge.This article can be divided into five chapters including(1)introduction,(2)preparation of silica-polyethylene glycol methacrylate CPC and its application in detection of solvent,(3)preparation of CPC-based invisible prints and study on the anti-counterfeiting applications,(4)preparation of SiO₂-based amorphous CPC and study on the printing application,and(5)conclusion and prospect.The main research contents are listed as following:(1)We have designed and prepared test paper based on the swellable silica-polyethylene glycol methacrylate(SiO₂-PEGMA)film that can detect solvents precisely.When being swelled by solvent,the reflection wavelength and intensity of the film varied significantly.Therefore,the solvent with specific dynamic swelling reflectance spectra(DSRS)pattern can be obtained by continuously recording its reflection spectra.Using DSRS,40 kinds of homologues(alcohols,esters,aromatic hydrocarbons and organic acids/bases),isomers and other solvents with similar refractive indices and structures can be precisely distinguished.(2)Invisible prints are prepared by selective adsorption of oleylamine on the surface of SiO₂-PEGMA film with masks,which can be used as anti-counterfeiting materials of high security.Under the dry conditions,the reflection peaks and structural colors of the pattern(oleylamine adsorption)and the background remain the same,therefore,the pattern is hidden in the background.When the print is immersed in water,the pattern cannot be swelled and still show the original structural color(blue),while the background is swelled with the structural color turns from blue to red.The pattern was revealed owing to the dissimilar color contrast between the pattern and background.The hiding-showing process between the dry and wetted state of the print is fully reversible.Due to the reversible physical adsorption of oleylamine on the surface,the invisible pattern can be reconfigurabed repeatedly with short time(45 s)and by simply erasing the pattern with ethanol.(3)We report a polymer(polyvinylpyrrolidone,PVP)-induced colloidal assembly method to fabricate amorphous CPCs.It was found that the surface potential of SiO₂ colloidal particle has a significant effect on the assembly behavior of colloids.The SiO₂ colloidal particles with higher and lower charged surfaces can assemble into ordered and amorphous colloidal crystals,respectively.The surface potential of SiO₂ particles can be regulated by the adsorption of PVP on the surface of SiO₂ particles,thus,achieving amorphous CPCs with noniridescent colors.