Tuning the Surface Density of Thiols on Gold Surface via Free-Energy Landscapes to Direct Micelle-Mediated Gold Nanocrystal Growth.

Nanoparticle-surface interactions critically influence nucleation pathways and determine the efficiency of nanomaterial structures and their applicability. In this study, molecular dynamics simulations were employed to elucidate how a hexadecanethiol (HT) layer on a gold surface modifies the free-energy landscape governing the migration of a gold-nucleate-infused cylindrical micelle onto an Au(111) surface. Potential of mean force analysis indicates that the fully thiol-functionalized surface exhibits a desorption energy barrier of 8.8 ± 0.2 kcal/mol, arising from steric and hydrophobic resistance within the densely packed thiol layer. Systematic variation in thiol surface density reveals a nonmonotonic dependence of the free energy change with surface coverage density, with an optimum density of 3.34 × 10-6 mol/m2 corresponding to a free energy of -5.8 kcal/mol. This optimal condition balances interfacial stabilization and steric effects, thereby facilitating efficient nucleation at the functionalized interface. Structural analyses revealed that cetyltrimethylammonium bromide/oleylamine (CTAB/OLA) micelles deform and reorganize near the surface to promote favorable gold-thiol interactions. This study provides molecular-level insights into the influence of thiol surface density on interfacial energetics, thereby offering design guidelines for optimizing functionalized surfaces for energy applications, sensors, and catalysis.