Magnetic Assembly And Application Of Photonic Crystals Based On Anisotropic Colloids

Colloidal photonic crystals,which has the periodical structure,can adjust and control the light thus become one of the important materials for new optical devices,information storage components,sensors and so forth.Traditional colloidal photonic crystals assembled by spherical colloids have the disadvantages of limited types of ordered structures and incomplete photonic band gap.Compared with traditional colloidal spheres,non-spherical colloids have the superiority that their physical/chemical properties rely on anisotropic shapes,leading to a highly ordered crystal structure with excellent performance.Therefore,it is necessary to contrast functional ordered structures from nonspherical particles with lower symmetry.However,because the position and orientation of an anisotropic colloid are difficult to be controlled at the same time,it is hard to use these traditional methods for spheres to assemble anisotropic building blocks.The preparation of anisotropic colloids also face challenges in high cost and complex processes,which may affect the shape uniformity and physicochemical properties.Therefore,it is urgent to develop a general method for anisotropic colloids,and use an effective strategy to assemble them into highly ordered structures.Based on the mentioned issues,the purposes of this paper are showing as follows:(1)Considering the difficulty in controlling the position and orientation of non-spherical particles at the same time,we propose here magnetic-field-assisted assembly and manipulation of non-spherical building blocks into highly ordered structures.The anisotropic magnetic interactions exerted on the nonspherical particles allow accurate control over their position and orientation,driving the formation of diverse types of ordered structures.The as-formed photonic crystal structure can also directly used as a photonic ink with fastness,high contrast,high resolution and free of glare.(2)Due to the complicated synthesis process and high cost of anisotropic magnetic colloids,we propose a general porous nanoreactor strategy for converting non-magnetic templates into highly dispersible anisotropic magnetic colloids under mild reaction conditions.Mild phase transition conditions not only help to improve energy efficiency,but also improve the colloidal dispersion of magnetic particles in aqueous solution,making it easier for colloidal particles to assemble into ordered structures.Based on the preparation of such anisotropic magnetic nanoparticles,we also describe the corresponding assembled magnetic photonic crystals for detecting weak magnetic fields.(3)We report the instant and reversible assembly of shape anisotropic colloids into 1D and 2D ordered structures through the application of external magnetic fields.With the use of high quality magnetite-nanocrystal-based ferrofluids,we demonstrate the magnetic assembly of nonmagnetic rods and ellipsoids with sizes ranging from a few hundred nanometers to above one micrometer,which just represents a few examples of assembled shape anisotropic particles.The rapid formation of highly ordered 1D and 2D photonic nanostructures with different structural colors is also demonstrated,for the first time,by using anisotropic nonmagnetic building blocks.Compared with other assembly methods,our instant and reversible assembly strategy features the significantly improved efficiency,simultaneous orientational and positional control,general applicability to non-spherical colloids with various shapes and size ranges,ease for large-area production.