Structural development of gold and silver nanoparticles within hexagonally ordered spherical micellar diblock copolymer thin films

Abstract

The spatial arrangement of metal nanoparticle (NP) arrays in block copolymers has many potential applications in OFET-type memory devices. In this study, we adopted a trapping approach in which we used a monolayer thin film of polystyrene-block-poly(4-vinylpyridine) (PS_56k-b-P4VP_8k)—a highly asymmetric diblock copolymer having a spherical micelle morphology—to incorporate various amounts of one-phase-synthesized dodecanethiol-passivated silver (DT–Ag) NPs and a fixed amount of ligand-exchanged pyridine-coated gold (Py–Au) NPs into the polystyrene (PS) and poly(4-vinylpyridine) (P4VP) blocks, respectively. We characterized the packing of these metal NPs in the two blocks of the nanostructured diblock copolymer using reciprocal-space synchrotron grazing incidence small-angle X-ray scattering (GISAXS) as well as atomic force microscopy (AFM) and transmission electron microscopy (TEM) in the real space. The packing of the Ag NPs in the PS block was dependent on their content, which we tuned by varying the concentrations in the composite solution at a constant rate of spin-coating. The two-dimensional hierarchical arrangement of Ag and Au NPs within the BCP thin films was enhanced after addition of the Py–Au NPs into the P4VP block and after spin-coating a thinner film from a low concentration solution (0.1 wt%), due to the DT–Ag NPs accumulating around the Py–Au/P4VP cores; this two-dimensional hierarchical arrangement decreased at a critical DT–Ag NP weight ratio (c) of 0.8 when incorporating the Py–Au NPs into the P4VP domains through spin-coating at higher solution concentration (0.5 wt%), where the DT–Ag NPs realigned by rotating 20° along the z axis in the real space, due to oversaturation of the DT–Ag NPs within the PS domains.