表面活性剂与高分子链混合体系的模拟

Monte Carlo Simulation on Surfactant-Polymer Mixed System

计算机模拟了高分子链对表面活性剂胶束形成过程的影响,以及高分子链构象性质随胶束化过程的变化.结果表明,当高分子链与表面活性剂之间的相互作用强度超过临界值后,高分子链的存在有利于表面活性剂胶束的形成.临界聚集浓度(CAC)与临界胶束浓度(CMC)的比值CAC/CMC随高分子链长的增大和相互吸引作用的增强而减小.在CAC之前,高分子链与表面活性剂分子只有动态的聚集;但在CAC之后,表面活性剂胶束随表面活性剂浓度X的增加而增大,并静态地吸附在高分子链上,形成表面活性剂/高分子聚集体.随着表面活性剂分子的加入,高分子链的均方末端距<R2>和平均非球形因子<A>先保持恒定;从X略小于CAC开始,<R2>和<A>快速减小,至极小值后又逐渐增大.模拟结果支持高分子链包裹在胶束表面的实验模型.

The effect of polymer chain on the formation of surfactant micelles and the variation of polymer configurational properties are simulated. Results show that polymer chain helps the formation of surfactant micelles if the strength of the interaction between the polymer chain and surfactant exceeds a critical value, which decreases with the increase of the chain length. The value CAC/CMC, ratio of the critical aggregation concentration (CAC) to the critical micelle concentration (CMC), decreases with the increase of the chain length and the interaction strength between the polymer chain and surfactant. There is only dynamic adsorption between the chain and surfactant when surfactant concentration X < CAC; after CAC, however, the size of the surfactant micelle increases and the static adsorption between polymer chain and micelles brings about. The mean-square end-to-end distance <R-2> and mean asphericity <A> are almost constants at very small X, but they drop steeply when X reaches CAC, and finally they increase when the micelles are large enough. Simulation results show that the polymer chain always wraps outside of the surfactant micelles, which supports the experimental model of polymer chain wrapping micelles.