Thermally Driven Assembly of Nanoparticles in Polymer Matrices

Thermally responsive bulk polymer films utilizing reversible Diels−Alder chemistry have been developed. Gold nanoparticles (AuNPs) were passivated with thiol-terminated poly(styrene)-b-poly(ethylene glycol) (PS-b-PEG) copolymer ligand, where the PS and PEG blocks are joined via a Diels−Alder (DA) linkage. The ligand-functionalized nanoparticles were dispersed within a microphase-separated PS-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer. Nanoparticle location was dictated by the compatibility of the external shell with the block copolymer matrix. As cast, the PEG shell compatibilized the nanoparticles with the PMMA domains. Subsequent thermal treatment caused the Diels−Alder linkages between the polymer blocks to dissociate, leaving the AuNPs functionalized by PS ligands. Immiscibility within the PMMA matrix caused AuNP migration to the PS domains. Migration of the Au nanoparticles was determined using morphological characterization via small-angle X-ray scattering (SAXS) and cross-sectional transmission electron microscopy (TEM).