Modelling aggregates of cetyltrimethylammonium bromide on gold surfaces using dissipative particle dynamics simulations

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ABSTRACT In this study, we developed a coarse-grained model based on the dissipative particle dynamics (DPD) method to investigate the aggregates of the cetyltrimethylammonium bromide (CTAB) molecules on gold surfaces including nanoparticles. We adopted the DPD model for CTAB solutions developed by Mao et al. [Modeling aggregation of ionic surfactants using a smeared charge approximation in dissipative particle dynamics simulations. J Phys Chem B. 2015;119:11673–11683] and introduced an attractive interaction between gold (Au) particles and bromide (Br) ions (i.e. Au-Br attraction) to bind CTAB molecules onto the gold surface via the electrostatic interactions between their cationic head groups and Br ions adsorbed on the gold surface. The proposed model with a proper Au-Br attraction can semi-quantitatively describe the structures of CTAB aggregates on a flat gold surface and around gold nanorods (AuNRs). As the Au-Br attraction and the CTAB concentration increase, the CTAB aggregates on the gold surface can change from micelles to a compact bilayer structure. In particular, our model predicts that in the CTAB layer, the inner sub-layer may have a higher ligand density than the outer sub-layer. The anisotropic distribution of CTAB molecules around AuNRs is also captured in our model.