Unraveling the Role of Surfactants in Micelle‐Templated Growth of Chiral Plasmonic Nanoparticles

Micelle template‐directed growth, pioneered by Luis Liz‐Marzán's group, offers precise control over the chiroptical properties of gold nanorods (AuNRs). Using chiral micelles formed from hexadecyltrimethylammonium chloride (CTAC) to direct asymmetric growth, this approach enables tunable circular dichroism (CD) responses across the UV–vis–NIR range. Despite its potential, the fundamental mechanisms governing this process remain poorly understood. To address this, we investigated the role of surfactant hydrophobicity by comparing CTAC with two analogues differing in aliphatic tail length. Combined CD and electron microscopy analyses revealed two unexpected effects of increasing tail length: enhanced inclination of surface grooves relative to the AuNRs axis and reduced groove density. Leveraging these insights, growth conditions are optimized for the longer‐tail surfactant, yielding chiral AuNRs with a slightly higher g ‐factor than those obtained with the standard CTAC surfactant. These findings establish a straightforward and effective strategy for fine‐tuning the chiral morphology of plasmonic nanoparticles.