Composition Conversion-Induced Disassembly of Amphiphilic ABA Triblock Copolymer Vesicles: A Monte Carlo Study

The composition conversion in block copolymer induced by external stimuli such as light and pH is an effective strategy to trigger the disassembly of vesicles experimentally. Based on this strategy, the disassembly behavior of the A₂B₁₂A₂ triblock copolymer vesicle induced by the composition conversion from B block to C block was studied using Monte Carlo simulation. In this study, a part of the B block in the A₂B₁₂A₂ triblock copolymer was converted to the new block C with weaker hydrophobicity, forming the A₂B_12-CA₂ tetrablock copolymer. The composition conversion makes the originally stable vesicle unstable, and after sufficiently long simulation time, the system reached a new equilibrium state. The aggregate morphology of the new equilibrium state was highly dependent on the converted chain length (n). A variety of micelles with novel Janus-type phase-separated microstructures in their hydrophobic parts have been observed in the systems with different n. It should be noticed that those Janus-type micelles cannot be obtained via traditional self-assembly processes from homogeneous states of A₂B_12-CA₂ tetrablock copolymers under the same conditions. The simulation results further indicated that the morphological transformation from ABA vesicle to ABCA micelles induced by the composition conversion is reversible.