Molecular Dynamics Simulation of Phase Behavior in a Bolaamphiphilic Solution

The phase behavior of bolaamphiphilic solutions is studied by coarse-grained molecular dynamics simulations of semiflexible bolaamphiphilic molecules with explicit solvent molecules. Our simulations show that six kinds of self-assembled structures (spherical micelles, worm-like micelles, bicontinuous structure, hexagonal structure, plate-like micelles, and lamellar structure) are obtained. It is established that, at low concentrations, a plate-like micelle changes to worm-like micelles, and then to spherical micelles as the hydrophilic interaction increases. Conversely, at intermediate concentrations, a lamellar structure changes to a bicontinuous structure; it then changes to worm-like micelles or a hexagonal structure as the hydrophilic interaction increases. It is also observed that the global orientational order parameter for the end bonds of bolaamphiphilic molecules can be used to clearly distinguish between the randomly-oriented structures (the spherical micelles, the worm-like micelles, and the bicontinuous structure), the lamellar structure, the hexagonal structure, and the plate-like micelles.