Fabrication of closed-cell inverse opal photonic crystal pigments with angle-independent and stable structural colors†

Brilliant and non-photobleaching structural colors make photonic crystal (PC) pigments an appealing replacement for traditional chemical pigments. However, pigments with angle-independent structural colors are usually fabricated through amorphous arrays, PC balls or PC powders with an opal or inverse opal structure, which suffer from problems such as pale colors, inefficient and tedious fabrication processes as well as unstable indefinite colors during usage. Herein, PS@SiO₂ core–shell spheres were first synthesized and assembled into an opal template with SiO₂ sol infiltrated into interstices between the spheres. Subsequent calcination transformed PS cores into pores enclosing in situ formed carbon black. Thus, bulk closed-cell inverse opal PCs (IOPCs) were obtained with ordered and isolated pores embedded into a continuous SiO₂ matrix. After being ground into fine powders, PC pigments with three vivid and angle-independent primary structural colors were obtained with 268 nm, 305 nm and 352 nm PS@SiO₂ spheres as building blocks. The closed cells protect the pores from infiltration of the solvent inside and maintain the necessary refractive index between the pores and SiO₂ matrix for bright structural colors. Thus, PC pigments with stable colors can be mixed with linseed oil and painting medium to prepare painting pigments, which can be used for painting a delicate pattern with multiple colors. The stable, vivid and angle-independent structural colors and the abundant colors from the color mixing effect endow the PC pigments with great value in broad potential applications, including art, aesthetics and displays.