Gold nanorods 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 [1]. Directly manipulating and controlling the size and shape of metal nanoparticles is therefore a key step for their tailored application. Gold nanorods are normally prepared using seed-mediated growth technique, which require gold seeds, ascorbic acid and aqueous cetyltrimethylammonium bromide (CTAB) solution of HAuCL4. Isotropic morphology breaking of the seeds by crystal twinning results into formation of pentatetrahedral nanorod structure with different facets. Although possible mechamism have been proposed, the microscopic understanding of the anisotropic growth is still missing.We use molecular dynamics simulations in order to understand the microscopic origin of the asymmetric growth mechanism in gold nanorods. We provide the first atomistic model of adsorption of CTAB on different surfaces, namely (111), (110) and (100) in growing electrolyte solution. We find that on all the investigated surfaces, the CTAB form a layer of distorted cylindrical micelles where channels among micelles would provide direct ions access to the surface. In particular, we show how AuCl2� ions, can freely diffuse from the bulk solution to the gold surface. We also find that the (111) surface exhibits the higher CTAB packing density and the higher electrostatic potential. Both elements would favor the growth of the nanorod in the direction of (111) facet [2].Furthermore, we investigate the effect of halide ions (X= Cl- , Br- and I-) on adsorption of CTAX on the (111) surface and we provide a rational for the influence of halide ions on anisotropy of gold nanoparticles.[1] A. M. Alkilany, L. B. Thompson, S. P. Boulos, P. N. Sisco, C. J. Murphy, Advanced Drug Delivery Review, 2012  , 64,190-199[2] S. K. Meena, M. Sulpizi, Langmuir 2013 , DOI: 10.1021/la403843n

Insights on the microscopic mechanisms of anisotropic growth of gold nanorods from molecular dynamics simulations

248th National Meeting (2014)

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