Phase Behaviors of Dialkyldimethylammonium Bromide Bilayers.

Dialkyldimethylammonium bromide (2C n Br) surfactants in bilayer exhibit polymorphic phases and rich self-assembly behaviors. However, the effects of alkyl chain length on the phase behavior of the 2C n Br bilayer are still not completely understood. Herein, we investigate the 2C n Br bilayers by performing all-atom molecular dynamics simulations, taking into consideration the influence of temperature and initial interdigitated degree. Our findings indicate that DOAB (2C 8 Br) is challenging to remain in a bilayer structure, while DDAB (2C 12 Br) and DPAB (2C 16 Br) maintain bilayers in different phases. DDAB bilayers exhibit an interdigitated gel phase, and this phase structure enhances the stability and rigidity of the bilayer membrane. In contrast, DPAB bilayers show a ripple gel phase, which has better softness and ductility. The differences in phase behaviors can be attributed to a competition between the rigidity of the 2C n Br surfactants and the hydrophobic interaction of the alkyl tails. The results reveal the crucial role of the bilayer phase in determining the rigidity of bilayer membranes.