The cooperative self-assembly of amphiphilic polystyrene-block-poly(acrylic acid) (PS144-b-PAA(22)) and polystyrene-block-poly(4-vinylpyridine) (PS144-b-P4VP(33)) diblock copolymers in DMF/H2O mixtures has been investigated. Both copolymers self assemble into small spherical micelles (SSMs) if used individually. However, the equimolar mixture of these two copolymers cooperatively self-assembles into vesicles. It is found that the formation of vesicles is attributed to the complex interactions between PAA and P4VP chains, including the hydrogen bonds between un-ionized acrylic acid units and pyridine units as well as the electronic attractions between ionized acrylic acid units and protonated pyridine units. Since these interactions between PAA and P4VP chains depend on pH value, the cooperatively self-assembled morphology can be easily tuned by the addition of HCl or NaOH. At high addition of H+ or OH-, the intercorona interaction is repulsive and the copolymer mixture tends to form SSMs (basic condition) or cylindrical micelles (acidic condition), whereas it prefers to aggregate into vesicles at low addition of H+ or OH- because the intercorona interaction is attractive. Interestingly, the same morphology of the self-assembled aggregates can be obtained either at high Er addition or at low OH- addition, which from the nonmonotonic variation of the intercorona interaction along with the addition of HCl or NaOH. The current study implies that it is the intercorona interaction rather than the chemical condition that dominates the cooperatively self-assembled morphology.