Phase Behaviors of Dialkyldimethylammonium Bromide Bilayers

Dialkyldimethylammonium bromide (2CBr) surfactants in bilayer exhibit polymorphic phases and rich self-assembly behaviors. However, the effects of alkyl chain length on the phase behavior of the 2CBr bilayer are still not completely understood. Herein, we investigate the 2CBr bilayers by performing all-atom molecular dynamics simulations, taking into consideration the influence of temperature and initial interdigitated degree. Our findings indicate that DOAB (2C₈Br) is challenging to remain in a bilayer structure, while DDAB (2C₁₂Br) and DPAB (2C₁₆Br) 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 2CBr 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.