Computer Simulation of Micellization for Ring-like Block Copolymers

Abstract

The micellization behaviour of ring-like AB diblock copolymers in a selective solvent was compared with the corresponding linear ABA triblock copolymers via Monte Carlo simulation. The simulation results show that the difference in the critical micellization concentration (cmc) values between ring-like copolymers and linear copolymers with same compositions is closely related to the content of A blocks, f(A), and the strength of attractive interaction between B monomers, epsilon. When fA is relatively small and e is big, the cmc values of ring-like block copolymers are smaller than those of the corresponding linear ones; whereas when fA is big and e is small, the cmc values of triblock copolymers are smaller than those of the corresponding ring-like ones. To further understand the effect of fA and e on the micellization behavior, we calculated the entropy and the potential energy contributions to the micellization free energy, respectively. The results show that in the studied range of fA and 8, the entropy loss in micellization for ring-like block copolymers is always smaller than that for triblock copolymers, so it seems that the micellization of ring-like block copolymers is always easier than that of the linear ones if we only consider the entropy contributions to the free energy. But if we calculate the potential energy contributions to the free energy, it can be found when fA is relatively small and 8 is big, the potential energy decreases greatly during the micellization of ring-like block copolymers. Considering the less unfavorable contribution of entropy part to the free energy for ring-like block copolymers, the micellization of ring-like block copolymers should be much easier than that of the linear ones. When f(A), is big and e is small, the potential energy decreases greatly when the micelles form for linear block copolymers. Although the entropic contribution to the free energy is unfavorable for linear ones, the potential energy still shows the dominative contribution to the free energy and therefore the micellization of linear block copolymers is much easier than the ring-like ones. The above analysis of the free energy will help us understand the micellization behavior of ring-like block copolymers and linear block copolymers.