Preparation And Response Study Of Inverse Opal Hydrogel Photonic Crystals

Photonic crystals (PCs) are materials patterned with a periodicity in dielectric constant, which can create a range of 'forbidden' frequencies called a photonic bandgap. PCs have the characteristics of photonic bandgap and photonic localization, which makes PCs control and enhance the spontaneous emission of excited atoms.Responsive photonic crystals are materials with photonic bandgap responding to external environments. Combined responsive polymers with photonic crystals, responsive photonic crystals happen to change on volume or phase transition due to certain responsive mechanism, which cause the photonic bandgap changes. Much attention has been paid to functional photonic crystals with controllable photonic bandgap recently. In this dissertation, inverse opal hydrogels have been prepared by colloid crystal templating and capillary attraction induced methods. The structural color and the response to external environments of inverse opal hydrogels have been investigated.Firstly, the monodispersed polystyrene (PS) spheres with different diameters have been synthesized by emulsion polymerization.Secondly, the PS opal structural colloidal crystals were formed by self-assembly process, during which temperature and humidity were the major factors that affect the quality of the colloidal crystals. Single crystalline and long-range ordered opal templates with face centered cubic(FCC) structure can be obtained by controlling temperature and humidity. Because of Bragg diffraction, the colloidal crystal templates follow the law of Bragg diffraction and show fresh iridescent colors.Thirdly, inverse opal hydrogels have been prepared by the colloid crystal templating method, during which the opal templates firstly are infiltrated by the precursor solutions, and then polymerized and in the end the polymerized composites are immersed in organic solvents for the removal of opal templates. By the analysis of SEM and reflectance spectra, single crystalline inverse opal structure with well-ordered, three dimensionally long range order can be observed. Although the size of the pores shrinks about 20%, compared to the opal template, the long-range order structure is still preserved. The brilliant structural colors of inverse opal hydrogels are controlled greatly by the crosslinking density and the content of AA in aqueous solutions.In the end, according to the law of Bragg diffraction, the brilliant structure colors can be adjusted by the refractive index, crystal lattice and the angle we observed. Inverse opal hydrogels we have prepared can greatly respond to various external enironments such as solvents, pH, ion strength and mechanical press etc due to its chemical structure.