Disassembly of Amphiphilic AB Block Copolymer Vesicles in Selective Solvents: A Molecular Dynamics Simulation Study

The disassembly of amphiphilic AB block copolymers in selective solvents by molecular dynamic simulation is investigated in this study. The disassembly from one initial assembly into different aggregates is controlled by thermodynamic processes that depend on the instability of the system. Based on this strategy, Bx can be converted to Ax in A2BxB18-x diblock copolymers (where x is a variable integer) by external stimuli such as light and pH. The A2BxB18-x copolymer vesicle in a stable state becomes unstable when A2BxB18-x copolymers are converted to A2AxB18-x copolymers. The simulation results show that the instability of the system induced by Bx conversion is a function of x, and the larger x, the higher the instability. The assembly can thereby disassemble from the initial vesical into a ring, rod, sphere, disorder aggregate, as well as completely dispersed polymer chains by increasing x. Notably, some of those structures cannot be obtained by self-assembly from the initial homogeneous state. Taking x = 5 as an example, toroid micelles are obtained by converting A2B5B13 into A7B13, whereas they are not obtained by self-assembly from a homogeneous state for the A7B13 block copolymer under the same conditions. Moreover, in addition to the x value, the Bx conversion rate and the conversed amount of polymer chains can also affect the disassembly. Toroid micelles are impossible to form under a slow Bx conversion rate and when the conversion amount is less than 75% of the total copolymer chains.