Micelle-mediated growth of gold nanocrystals on a surface

Abstract

Understanding nanocrystal growth is crucial for several reasons, as it plays a significant role in various scientific, technological, and industrial applications. Knowledge of nanocrystal growth allows scientists and engineers to control the size, shape, and composition of nanocrystals. This control is essential for tailoring the properties of nanomaterials for specific applications, such as electronics, catalysis, sensing and medicine. Nanocrystals are used in various biomedical applications, such as drug delivery, imaging, etc. Understanding their growth is essential for designing nanomaterials with specific functionalities for targeted drug delivery and imaging modalities. A molecular dynamics simulation study has been carried out to investigate the growth of nanocrystals in aqueous solutions in the presence of surfactants. In this study, we investigated the structural and thermodynamic properties of a micelle formed by cetyltrimethylammonium bromide (CTAB) in the aqueous solution and used that to quantify its role in the nucleation process when gold nucleates are in close proximity to another gold nanoparticle or surface. The path through which the nucleate gets fused with other entities, such as gold nanoparticles or surfaces, in the presence of a micelle in solution needs an explanation. We have shown the path and quantified energy required for the gold nucleate to get infused into the gold surface. Well-dispersed sets of gold atoms in solution were subjected to a series of steered molecular dynamics simulations, and it revealed that gold atoms, individually, must overcome an energy barrier of 10.52 ± 0.3 kcal/mol to start nucleating on the substrate. Due to this energy barrier, atoms form aggregate or nucleate inside the micelle. To control the release of the engulfed nucleate into the micelle onto the substrate, one needs to understand the mechanism of its release and quantify the energy requirement for the process. Here, we have used an enhanced sampling technique (umbrella sampling) to calculate the free energy required for the process mentioned above. A gold nucleate would require an additional energy of ∼10.36 kcal/mol to break the strong layering of micelle and water on the substrate. The radius of gyration and order parameter calculations show the extent of deformation of the micelle while releasing the engulfed nucleate on the substrate, and it gives us a recipe to alter the shape of the micelle and easier release of the nucleate on the surface. This study summarizes the path of nucleation of nucleates in the micellar solution and the recipe for the easier release of nucleates on the substrate.