Block copolymer microspheres with controlled surface nanostructures

Abstract

Using emulsion droplets to confine block copolymer (BCP) solutions in water, BCP colloidal particles can be produced, as the solvent in the emulsion droplets evaporates. The nanostructures of these particles are unique and can be controlled by changing the volume fraction of blocks, the particle size, and the interfacial tension between each of the blocks and the particle interface. In this study, BCP microspheres containing spherical BCP micelles are produced from an evaporative oil-in-water-emulsion. After then, the surface nanostructures of the microspheres are controlled under different external environments. First, Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) micro-spheres in Chapter 2. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloro-form into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UV-Vis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP domains on the microspheres. Our approach for creating Au-NP-hybrid BCP-microspheres...