Faceted Shapes of Cooled Emulsion Droplets of CTAB and Hexadecane

Recent experiments [Denkov et al., Nature 528 (2015) 392] have shown that the emulsion droplets resulting from the spontaneous self-assembly of cetyltrimethylammonium bromide (CTAB) surfactants with alkanes of similar carbon chain length such as Hexadecane in water “self- shape” into regular polyhedral, platelets, and rods on cooling. To understand the mechanism of the faceting of those emulsion droplets, we performed the coarse-grained (CG) molecular dynamics simulation of aqueous solutions of CTAB and Hexadecane using the Martini force field in GROMACS. In 1 (CTAB): 1(Hexadecane) solutions, we find that the average droplet size scales as~C^0.4 with the concentration of Hexadecane (C). A variety of polyhedral shapes of the emulsion droplets observed at low temperatures in simulations will be compared with those of the experiments. The mechanism for faceting of the droplets will be discussed.