Surface Intaglio Nanostructures on Microspheres of Gold-Cored Block Copolymer Spheres

The confined self-assembly of block copolymers (BCPs) can be used to generate hierarchically structured composite microspheres. In this study, microspheres of gold-cored BCP (Au-BCP) spheres were first produced from an evaporative toluene-in-water-emulsion in which polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCPs incorporated with Au precursors (AuCl4-) were dissolved in toluene. Interestingly, the addition of cetyltrimethylammonium bromide (CTAB) into the microspheres resulted in the selective extraction of Au precursors within the Au-BCP spheres near the surface of the microsphere because of the strong electrostatic attraction between the CTAB and Au precursors. Therefore, regular-patterned porous nanostructures on the surface of Au-BCP microspheres were formed, of which the size could be varied by controlling the molecular weight of the PS-b-P4VP polymers. In addition, the depth of the pores could be modulated independently by tuning the amounts of Au precursors that were incorporated into the Au-BCP spheres (lambda). This method was then generalized using other additives (i.e., thiol-terminated molecules) that had a favorable interaction with the Au precursors, producing both controlled inner and surface morphologies of the microspheres. Pores at surface could be used to successfully load various metal nanoparticles, potentially making them useful in optical, catalytic, and drug-delivery or therapeutic applications.