Self-assembly of paint-on colloidal crystals using poly(styrene-co-N-isopropylacrylamide) spheres

We report on the synthesis of monodispersed, spherical colloidal particles composed of poly(styrene-co-N-isopropylacrylamide) (pS-co-NIPAm) that rapidly self-assemble via simple solvent evaporation to form 3-D colloidal crystals that are both robust and uniformly diffractive. As a suspension of the pS-co-NIPAm particles dries, the interactions of their soft, flexible peripheries assist in particle self-assembly to form a close-packed ordered structure. Interparticle adhesion occurs at these contacts as the final amount of solvent evaporates, enhancing the durability of the assembly. The dense core provides stability of the ordered structure subsequent to drying. These dried, crystalline films exhibit Bragg diffraction, which can be modified by changing the particle size through varying the monomer feed concentrations. The facile drying process used for crystalline assembly presents a unique approach to photonic inks that can be used as paint-on (i.e., processable) dispersions, which are advantageous for the fabrication of materials for optical applications.