New Aspects of the Gold Nanorod Formation Mechanism via Seed-Mediated Methods Revealed by Molecular Dynamics Simulations.

New aspects of the formation and growth mechanism of gold nanorods (AuNRs) during seed-mediated colloidal synthesis are revealed from the results of molecular dynamics simulation. The model systems consist of cetyltrimethylammonium bromide (CTAB) units adsorbed on low-index [Au(110), Au(100), and Au(111)] and high-index [Au(250)] gold surfaces. The CTAB units are adsorbed as adjacent cylindrical micelles when the relative number of adsorbed bromide ions is small. At later AuNR growth stages, the number of bromide ions increases as the [AuBr2]- species pass through the channels between the adsorbed micelles on the gold surface. Thus, the mature AuNRs have a high concentration of bromide ions at their surface, which appears to change the organization of the CTAB units on the particle surface from adsorbed micelles to a compact CTAB bilayer.