Spontaneous onion shape vesicle formation and fusion of comb-like block copolymers studied by dissipative particle dynamics

A dissipative particle dynamics (DPD) simulation is performed to investigate the spontaneous onion shape vesicle formation and fusion of A6(B2)3 type comb-like block copolymers with a semiflexible hydrophobic backbone. Our results show that comb-like block copolymers of A6(B2)3 type may be a good candidate for onion shape vesicle formation. The spontaneous fusion dynamics between the onion shape vesicles is studied, and the fusion process can be characterized as having two parts: outer and inner membrane fusion. However, both parts have similar fusion dynamics which coincide with that observed in vesicles formed of linear diblock copolymers. In addition, the mixed systems containing amphipathic linear and comb-like block copolymers are investigated in dilute solution. By systemically varying the amount of linear block copolymers and the bond angle potential of the hydrophobic blocks, we construct a diagram to indicate the thermodynamically stable region, in which irregular vesicles, tubular vesicles, spherical vesicles, rod-like and toroidal micelles are observed. Nevertheless, no difference in the vesicle fusion dynamics is found. The main reason may be attributed to the molecular structures which possess the same hydrophobic but different hydrophilic block.