Polymer Brushes Govern Defect‐Selective Oxidative Etching of Penta‐Twinned Gold Nanorods

Oxidative etching of plasmonic nanoparticles provides an effective approach to the variation of their morphology and optical properties, yet polymer ligands are generally treated as passive steric barriers. Here, we show that polymer molecules end-grafted to the surface of penta-twinned gold nanorods (AuNRs) perform as active interfacial regulators controlling defect-selective oxidative metal etching. Through a combination of experiments and simulations, we show that polymer brushes localize etchant ions on the AuNR surface, lowering the energetic barrier for Au atom removal at defect-rich regions. This defect-ligand interplay leads to the emergence of surface corrugations along the AuNR longitudinal facets, in stark contrast to the etching behavior of single-crystal AuNR counterparts. By varying polymer molecular weight and grafting density, we achieve precise control of the plasmonic properties of etched AuNRs. These findings establish polymer brushes as active modulators of nanoscale interfacial reaction pathways, providing a strategy for defect-directed nanoengineering with applications in catalysis, sensing, and photonics.