Synthesis of monodisperse zinc sulfide particles grafted with concentrated polystyrene brush by surface-initiated nitroxide-mediated polymerization

Monodisperse zinc sulfide (ZnS) particles of diameters ranging from 120 to 400 nm were prepared and then coated with a thin layer of silica (SiO2). After the surface modification with an alkoxyamine derivative, polystyrene (PS) brushes of chain lengths ranging from 30,000 to 114,000 in Mn with relatively low polydispersities less than 1.5 in Mw/Mn were successfully grafted by surface-initiated nitroxide-mediated polymerization, where the Mn and Mw are the number- and weight-averaged molecular weights, respectively. The graft density reached a value as high as 0.9 chains nm−2. These core–shell hybrid particles (ZnS@SiO2–PS) were highly dispersible, without any aggregation, in various solvents good for PS, also forming a monolayer at the air–water interface by spreading its solution. The transmission electron microscopic observation of the monolayers deposited on a solid support revealed two-dimensionally close-packed arrays of particles. These monolayers exhibited a beautiful structural color dependent on the angle of incident light because of such an ordered array of the ZnS cores with a high refractive index. Hollow spheres constituted of a SiO2 shell with well-defined, high-density PS brushes were first synthesized by selective dissolution of the ZnS core from the ZnS@SiO2–PS hybrid particle.