Wu Yung-Hsu, Wang Da-Ming, Lai Juin-Yi
Department of Chemical Engineering, Institute of Polymer Science and Engineering, National Taiwan University, Taipei, Taiwan 10617.
J Phys Chem B. 2008 Apr 17;112(15):4604-12. doi: 10.1021/jp074403y. Epub 2008 Mar 27.
Three-dimensional dissipative particle dynamics (DPD) simulations were performed to investigate the phase separation dynamics of semidilute polymer solutions with different polymer chain length and stiffness. For the polymer solution composed of shorter and more flexible chains, a crossover of the domain growth exponent from 1/3 to 2/3 was observed during the course of phase separation, indicating that the growth mechanism altered from diffusion to interfacial-tension driven flow. When the chain flexibility was kept the same but the chain was lengthened to allow for the chain entanglement to occur, the growth exponent changed to 1/4 in the diffusion-dominating coarsening regime while the growth exponent remained 2/3 in the flow-dominating regime. When the chain length was kept short but the stiffness was increased, the growth exponent became 1/6 in the diffusion-dominating regime and little effect was observed in the flow-dominating coarsening regime. The slow down of the phase separation dynamics in the diffusion-dominating coarsening could be explained by that the polymer chains could only perform wormlike movement when chain entanglements occurred or when the chain motion was limited by chain stiffness during phase separation. Moreover, when both the effects of chain length and stiffness were enhanced, polymer networks composed of longer and stiffer chains appeared and imposed an energy barrier for phase separation to occur. As a result, the polymer solution with stiffer and longer chains required a larger quench depth to initiate the phase separation and caused the delay in crossover of the coarsening mechanism from diffusion to flow.
进行了三维耗散粒子动力学（DPD）模拟，以研究具有不同聚合物链长度和刚度的半稀聚合物溶液的相分离动力学。对于由较短且更灵活的链组成的聚合物溶液，在相分离过程中观察到畴生长指数从1/3交叉到2/3，这表明生长机制从扩散驱动转变为界面张力驱动的流动。当链的柔韧性保持不变但链被加长以允许链缠结发生时，在扩散主导的粗化 regime 中生长指数变为1/4，而在流动主导 regime 中生长指数保持为2/3。当链长度保持较短但刚度增加时，在扩散主导 regime 中生长指数变为1/6，而在流动主导的粗化 regime 中观察到的影响很小。扩散主导的粗化过程中相分离动力学的减慢可以解释为，在相分离过程中，当链缠结发生或链运动受到链刚度限制时，聚合物链只能进行蠕虫状运动。此外，当链长度和刚度的影响都增强时，由更长且更硬的链组成的聚合物网络出现，并对相分离的发生施加了能量屏障。结果，具有更硬且更长链的聚合物溶液需要更大的淬火深度来引发相分离，并导致粗化机制从扩散到流动的交叉延迟。
