Self-assembly of colloidal particles into crystalline arrays is becoming one of themost intriguing fields because it is a relatively simple, cost-efficient strategy to fabricate novel materials with advanced functionality for some important potential applications such as photonic crystals biosensors, templates, and even paints, photonic papers, and cosmetics. Recently, fabrication of spherical assemblies (crystal balls or supraballs) of colloidal particles is of particular interest because these crystal balls possess photonic band gaps for normal incident light independent of position on the crystal surface, which is different from the anisotropies of the band gaps on crystal films and can be used as building units for more complex colloidal assemblies or even new types of photonic crystals, as pigments in paints, or as light diffusers for various light sources, including light bulbs and display screens.
In this article, they report a novel and facile approach to fabricate robust crystal balls directly through the self-assembly of â€œsoftâ€ polymer spheres by the aid of colloidal silica using the electrospraying technique. In this approach, â€œsoftâ€ colloidal polymer spheres are synthesized by emulsion polymerization and then blended with colloidal silica to obtain nanocomposite latex. When this dispersion is loaded into an injector and forced to flow through the nozzle under direct electric field, the detached droplets are collected by an oil solvent in which the colloidal polymer spheres and silica beads directly self-assemble into ordered crystal balls as water and solvent evaporate.
Different particle size, resulting in different colors
Compared to other techniques for fabrication of crystal balls, this approach is very simple, highly efficient, and can be used for mass of production of crystal balls. The obtained robust crystal balls have excellent mechanical properties towithstand external forces such as cutting, puckering, bending, and reversible deformation. Different color crystal balls can be tuned by the sizes of polymer spheres.The size and shape of crystal balls can be easily controlled by electric field strength solvent, container substrate, and surface charge density of polymer spheres. The excellent mechanical property and reversible deformation behavior of this crystal ball combined with its inherent isotropic optical property could open up a wider range of applications of crystal balls such as color pigments in reflection mode displays, e-papers, printing, and chemical and biological sensors.
Shen et al. Fabrication of Robust Crystal Balls from the Electrospray of Soft Polymer Spheres/Silica Dispersion. Langmuirpp. 6604-6609.