Controlling Shell Thickness in Core−Shell Gold Nanoparticles via\nSurface-Templated Adsorption of Block Copolymer Surfactants

Abstract

When Au nanoparticles are encapsulated within shells of cross-linked, block copolymer\namphiphiles, the structure of the shells is determined by the initial interaction between the amphiphile\nand the nanoparticle surface. In the case of small nanoparticles, for which particle size is comparable to\nthe dimension of the block copolymer (ρ_Au/<i>R</i>_g ≈ 1), particles act like solutes that are dissolved within\npolystyrene-<i>block</i>-poly(acrylic acid) (PS-<i>b</i>-PAA) micelle cores. In the case of larger nanoparticles (ρ_Au/<i>R</i>_g\n> 1), PS-<i>b</i>-PAA adsorption is templated by the particle surface, and a concentric core−shell structure is\nformed. The thickness of this shell can be predicted from theoretical models of polymer adsorption onto\nhighly curved surfaces and controlled by varying the ratio of polymer to available nanoparticle surface\narea. We anticipate that these rules will illustrate how cross-linked copolymer shells with predetermined\nthickness can be used to stabilize and functionalize a variety of nanoparticle materials.