半刚性链聚合物共混体系相分离的非平衡动力学研究

The studies of dynamics and crystallization of polymer systems have important scientific significance. In the recent years, the semiflexible polymer systems have more and more applications. However, there is less study on their dynamic behavior of phase separation. Even for the flexible polymer the dynamic behaviors obtained from the evolution of free energy and that from the microscopic kinetics are not consistent. Therefore, in this project we propose to study this problem from the followings two approaches. The first approach is to construct the free energy of the semiflexible polymer blends within the theoretical frame of single-chain in mean-field simulation, and develop an efficient numerical method to study the dynamics of phase separation. The second approach is to study the kinetics based on the tube model, in which the stretch and relax of polymer chain will be considered. Comparing these two approaches, one can find what important dynamic factors are missed during the corase graining, and improve our understanding on the phase separation. Besides, we will also study the nucleation in polymer crystallization based on the results obtained before, since before nucleation the polymer chain becomes semiflexible because of the decrease of temperature. In this semiflexible polymer melts, there are fluctuations both in density and conformation, and also their coupling. Thus, the system can be considered as a blends constituted by flexible chains and semiflexible chains. By studying this liquid-liquid phase separation we expect to develop the nucleation in polymer crystallization.

聚合物的动力学和相变研究具有重要的科学意义。近年来半刚性链体系到了广泛应用，而其相分离动力学研究上却基本是空白。即使对于柔性链体系的动力学研究，利用自由能演化所得到动力学行为与从微观链运动出发得到的动力学行为也不一致。为此本项目将从以下两个方面开展这一问题的研究：一、利用单链平均场理论研究半刚性链共混体系的自由能，构建这一体系的单链动态场理论，发展高效的数值求解方案，研究这一体系相分离的动力学行为；二、从分子链运动的管子模型出发，考虑链的拉伸与松弛，从微观上研究相分离的动力学过程，并与第一种研究方案作对比，寻求是否有哪些动力学因素在粗粒化的过程中丢失了，建立对相分离动力学的深刻理解。此外，我们还将从上述研究中获得的结果和启示应用于结晶前熔体中由于降温所导致半刚性链的成核过程，将其视为密度涨落与构象涨落耦合的、半刚性链与柔性链共混体系的液-液相分离加以研究，以期对成核动力学的研究有所帮助。

近年来关于半刚性链的理论研究逐渐成为高分子体系的研究重点。一方面，半刚性链在现实中有越来越多应用，特别是有机共轭高分子体系和生物大分子体系；另一方面，柔性高分子链的理论已趋于完善，而半刚性链的理论还有很多问题亟待解决。此前我们分别研究过相分离成核动力学和半刚性链的自组装问题，我们希望能将在前期研究中发展的方法应用到本项目中来。本项目旨在研究半刚性链共混体系的相分离动力学问题。为此我们先后研究了相界面处的链构象问题和成核动力学问题等。另一方面，高分子链在结晶前也呈现出半刚性，同时分子链也被拉伸，存在着一个沿着分子链上的构象上的分离，它决定了结晶的成核动力学，由此我们也研究了与之相关的问题。作为拓展，我们还研究了高分子网络的力学性质。在原计划中，我们还试图从分子链运动的管子模型出发，考虑链的拉伸与松弛，从微观上研究相分离的动力学过程。但这一过程过于复杂，我们的工作正在进行之中，还没有取得突破性进展，我们将在后续工作中完成这一目标。通过这一项目的开展，我们对于半刚性链共混物体系的相分离问题有了深入的理解，能对实验和实际应用提供参考，并为后续的结晶成核动力学提供帮助。