Simulation of CTAB bilayer adsorbed on Au (100), Au (110), and Au (111) surfaces: structure stability and dynamic properties

Abstract

Anisotropic growth of gold nanorods is often attributed to the adsorption of surfactant cetyltrimethyl ammonium bromide (CTAB) bilayer on gold facets. In this work, we performed DFT (density function theory) calculations to investigate possible binding sites of Br ions on Au (100), Au (110), and Au (111) facets. The CTAB bilayers on these facets were then constructed, and the structures of these interdigitated bilayers were studied by using molecular dynamics simulation. In addition, the dynamic properties of CTAB bilayer were investigated, and the results indicate that the outer layer exhibits noticeable lateral diffusion and undergoes fluctuation along surface normal. Both lateral diffusion and surface normal fluctuation of CTAB bilayer on Au (111) facet are more profound. The stability of CTAB bilayers on gold surfaces was estimated in terms of the required energy for dissociation of a CTA+ ion from the outer layer. The stability of CTAB bilayer on Au (111) is considerably weaker than on Au (100) and Au (110). Higher volatility and weaker stability may be due to lower packing density of CTAB bilayer on Au (111) facet, and both of them induce the growth tendency of gold nanoparticles along the (111) direction.