Spontaneous formation of vesicles from mixed amphiphiles with dispersed molecular weight: Monte Carlo simulation

The spontaneous formation of vesicles from amphiphiles with dispersed molecular weight (MW) as well as with mono-MW has been studied by a lattice Monte Carlo simulation. Both pure and mixed amphiphiles were self-assembled into vesicles under appropriate conditions. When mixed amphiphiles were examined, the amphiphiles with longer hydrophilic blocks preferred to segregate into the outer monolayer of the resultant vesicles, which is consistent with the experimental observations in recent literature. The kinetic study reveals that the increase of vesicle size is mainly caused by the mechanism of vesicle fusion at the early stage, and the evaporation-condensation mechanism cannot be neglected at the late stage. The fusion of vesicles is accompanied by translocation of chains from the outer monolayer to the inner monolayer. For mixed amphiphiles, the degree of segregation exhibits a size dependence of the vesicle. Compared to the chains with shorter hydrophilic blocks, those with longer hydrophilic blocks exhibit stronger trends to translocate from the outer monolayer to the inner one in vesicle self-adjustment, which leads to the quasi-equilibrium asymmetric distribution of the hydrophilic blocks in the post-fused vesicles.