环形嵌段共聚物的胶束化行为模拟简

利用Monte Carlo模拟，对比了相同组成下环形二嵌段共聚物AB和线形三嵌段共聚物ABA在选择性溶剂中的胶束化行为. 结果发现，相同链组成的环形和线形嵌段共聚物的临界胶束浓度(cmc)的差别与A嵌段的比例(fA)及B嵌段间的吸引强度(ε)密切相关. 在fA较小、ε较大的情况下，相应环形嵌段共聚物的cmc值更小；而在fA较大、ε较小的情况下，线形嵌段共聚物的cmc值更小. 为了进一步理解胶束化行为同fA及ε的关系，计算了胶束化过程中熵和势能部分对自由能的贡献. 结果表明，在所研究的fA和ε范围内，环形嵌段共聚物形成胶束时的熵损失更小，因而从熵贡献角度来看，环形嵌段共聚物更易发生胶束化. 而从势能贡献角度来看，当fA较小、ε较大时，环形嵌段共聚物形成胶束时势能有较大程度的降低，对自由能的贡献更大，因而此时环形嵌段共聚物更易发生胶束化. 而当fA较大、ε较小时，线形嵌段共聚物形成胶束时势能有较大程度的降低，对自由能的贡献更大，因而此时线形嵌段共聚物更易发生胶束化. 由此可见，对体系的胶束化自由能进行系统分析，有助于更好地理解环形和线形嵌段共聚物的胶束化行为.

Computer Simulation of Micellization for Ring-like Block Copolymers

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, fA, and the strength of attractive interaction between B monomers, ε. When fA is relatively small and ε 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 ε 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 ε 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 ε, 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 ε 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 fA is big and ε 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.