Monodisperse, high refractive index, highly charged ZnS colloids self assemble into crystalline colloidal arrays.

We developed an efficient synthesis of monodisperse, highly surface charged, high refractive index ZnS spherical particles by using a gel-sol method. Concentrated solutions of zinc-ammonia-NTA (nitrilotriacetic acid) were reacted with thioacetamide in the presence of gelatin which stabilized the growing particles. We dramatically increased the particle surface charge density by condensing silica and silylated phosphonate groups on the particle surface. These monodisperse highly charged ZnS particles are somewhat porous and have a refractive index of 1.868. These are the highest refractive index, monodisperse, highly charged spherical particles to self assemble into non-close-packed crystalline colloidal arrays which Bragg diffract light.