Gold nanoparticles are widely used in many areas such as photothermal cancer therapy, biochemical sensing and medical imaging due to their size and shape-dependent optical properties. Directly manipulating and controlling the size and shape of metal nanoparticles is, therefore, a key step for their tailored applications. Gold nanoparticles are normally prepared using seed-mediated growth technique, which require gold seeds, ascorbic acid, reactant HAuCl4 and aqueous cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium chloride (CTAC) surfactant. However, the microscopic origin of the anisotropic growth is still missing. Microscopic mechanism for the role of halides in regulating the anisotropic growth of gold nanoparticles has been investigated through molecular dynamic simulations and experiments. Our simulations revealed that CTAB form a layer of micelles on the gold surface immersed in the growing electrolyte solution where channels among micelles provide direct access of gold ions to the surface of gold nanorod. The Au(111) surface exhibits the lower CTAB packing density and the higher electrostatic potential with respect to Au(110) and Au(100) surfaces. Both elements would favour the growth of the nanorods in the direction of Au(111) facet [1]. On the other hand, CTAC micelles prefer to be in the solution, leaving the gold surfaces unprotected. Only a few CTAC molecules adsorbed on the gold surfaces which would favour a faster isotropic growth. Predictions from our simulations have been confirmed by two sets of experiments where nanoparticle’s growth in different CTAB/CTAC surfactant mixtures show a more isotropic and faster growth as the amount of Cl- increases. Also, the surfactant layer thickness measured on nanorods exposed to CTAB and CTAC quantitatively agrees with the simulation results [2]. [1] S. K. Meena and M. Sulpizi, “Understanding the microscopic origin of gold nanoparticle anisotropic growth from molecular dynamics simulations” Langmuir, 2013, 29 (48), 14954-14961 [2] S. K. Meena, S. Celiksoy, P. Schäfer, A. Henkel, C. Sönnichsen, M. Sulpizi, “The role of halide ions in the anisotropic growth of gold nanoparticles: A microscopic, atomistic perspective” J. Phys. Chem. C., 2015 (submitted)

Insight on growth mechanism of gold nanorods from molecular dynamics simulations

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.