Estimation of the energy barrier for a co-surfactant-driven gold nanocrystal nucleation and its growth on a surface: A molecular dynamics investigation

Abstract

Understanding nanocrystal nucleation and growth within micellar environments is critical for optimizing nanomaterial synthesis across various applications, including catalysis, electronics, and biomedical technologies. Molecular dynamics simulations were carried out to investigate the self-assembled structures of mixed surfactants—oleylamine (OLA) and cetyltrimethylammonium bromide (CTAB) — at various molar ratios. Notably, the OLA to CTAB molar ratio of 1:2 resulted in the formation of a well-structured and stable cylindrical micelle, whereas deviations from this ratio led to partial aggregation of OLA molecules outside the micellar structure, even after significantly long simulations. In this study, we investigated the role of a co-surfactant system, elucidating its structural aspects, in controlling the growth of gold nanocrystals and its influence on the energy landscape of nanocrystal nucleation while depositing on a gold surface. Using the potential of mean force (PMF) approach, we quantify the energy barrier for gold nucleation and release, showing a reduction from 10.36 ± 0.3 kcal/mol (for CTAB-only micelles) to 8.42 ± 0.3 kcal/mol with incorporation of OLA molecules. This decrease is attributed to increased micelle flexibility, which facilitates nucleate release and surface attachment. The attachment of OLA and CTAB molecules onto the gold surface further refines the energy landscape, emphasizing their role in controlling nanocrystal growth. These findings provide deeper insights into the molecular mechanisms governing micelle-mediated nucleation and offer strategies for designing tailored surfactant systems to enhance nanoparticle synthesis, drug delivery, and advanced material fabrication.