Modeling Stretching-Induced Immiscibility in Nonmonodisperse Polymer Systems

The behavior of polymer chains under stretching is a classical problem in polymer science. However, a fundamental question still in mist is how the stretching affects the interactions between polymer chains, especially when the tensions on the chains are unequal. In this work, we combine statistical theory and molecular simulations to study the influence of this tension disparity on the miscibility of athermal polymer systems. Through a minimal model, we demonstrate that when polymer chains of different lengths are under the same stretching disparate tension states among polymer chains can lead to either macroscopic or microscopic phase separation, depending on whether their ending points are mobile or not. Generally, the immiscibility found here is an entropic effect arising from conformational asymmetry between unequally stretched polymer chains. Our findings provide a new mechanism to explain the flow-induced demixing in polymer blends and indicate that heterogeneous structure can occur during stretching, simply as a result of nonmonodispersity in elastic polymer materials.拉伸状态下高分子链的行为是高分子科学中的经典研究课题。然而，仍有一个基础问题尚未厘清：拉伸作用如何影响高分子链之间的相互作用，尤其是当各高分子链所受张力不均等时。本研究结合统计理论与分子模拟方法，探究了这种张力差异对无热高分子体系相溶性的影响。通过构建极简模型，我们证明：当不同长度的高分子链受到同等拉伸时，链间不均等的张力状态会引发宏观或微观相分离，具体取决于其链末端是否可移动。总体而言，本研究中观测到的不相溶性，源于不等拉伸高分子链之间构象不对称所带来的熵效应。本研究结果为解释高分子共混物中的流动诱导相分离提供了全新机制，同时表明弹性高分子材料仅因多分散性即可在拉伸过程中形成非均相结构。