Self-assembly of gold nanoparticles grafted with amphiphilic supramolecular block copolymers

Design of polymer grafted plasmonic metal nanoparticles (PGNPs) has received continuous interest due to polymer-driven self-assembly of plasmonic nanoparticles (NPs) as a means to control interparticle plasmon coupling in ensembles. We report the use of supramolecular "V-shaped " block copolymers (VBCPs) as surface ligands of PGNPs to study their hydrophobicity-driven self-assembly. The amphiphilic VBCPs are prepared from two homopolymers, namely dipicolyamine (DPA)terminated polystyrene (PS) and pyridine (Py)-terminated poly(N,N-dimethylacrylamide) (PDMA) where the two polymers are bridged with Cu2+ ions. Those supramolecular VBCPs formed spherical micelles in the range of 100-300 nm, much larger than those of linear BCPs with similar chemical composition as a result of Cu2+ ions at the hydrophobic/hydrophilic interface. Thioester-containing supramolecular polymers can modify plasmonic AuNPs through ligand exchange even in the presence of Cu2+ ions. Those supramolecular polymers can drive PGNPs to form giant vesicles and two-dimensional (2-D) layered nanosheets. Using in situ light scattering, the supramolecular dynamics is found to allow maximum chain reconformation of polymer ligands where the interparticle distance of PGNPs grafted with VBCPs is smaller compared to that of PGNPs with linear BCPs. The assembled nanostructures with VBCPs also showed similar stimuli-responsive properties where the dissociation of DPA-Cu2+-Py coordination results in the disruption of assembled nanostructures. The supramolecular approaches potentially provide a new toolbox to design PGNP assemblies with tunable nanostructures and interesting dynamic properties enabled by non-covalent interaction.