Abstract

Block copolymers in solution can form vesicles with a preferred size when the degree of polymerisation N_B of the hydrophobic block is significantly greater than that of the hydrophilic block. In an earlier publication, we introduced a mean-field theory that treats the vesicle membrane as a bilayer. Here, a model is presented in which the hydrophobic blocks form a single interdigitated layer. In the model with interdigitation, the vesicles still have a preferred radius, but this increases more slowly as a function of N_B than in the bilayer model, in better agreement with experiment. However, the predictions of the bilayer model for the relationship between N_B and the vesicle membrane thickness T_m are consistent with the experimental result T_m ∝ N_B^0.79 over a wide range of parameters, while the model with interdigitation predicts an exponent of around 2/3. This suggests that the structure of the vesicles may lie between these two cases.