Cooperative Intramolecular Dynamics Control the Chain-Length-Dependent Glass Transition in Polymers
Cooperative Intramolecular Dynamics Control the Chain-Length-Dependent Glass Transition in Polymers
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DOI：
10.1103/physrevx.12.021047
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发表时间：
2022-05-27
影响因子：
12.5
通讯作者：
Mattsson, Johan
中科院分区：
文献类型：
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作者：
Baker, Daniel L.;Reynolds, Matthew;Mattsson, Johan
玻璃化转变是材料科学中一个长期未解决的问题。对于聚合物，由于链连接和灵活性的复杂性，我们对玻璃形成的理解特别差；因此，聚合物的结构松弛涉及分子内和分子间协同性之间的复杂相互作用。在这里，我们研究了不同聚合物化学性质和链柔韧性下玻璃化转变温度T-g随分子量M的变化。我们发现T-g(M)由每个构象自由度的平均质量（或体积）控制，并且“局部”分子弛豫（涉及几个构象）控制负责T-g的更大规模合作α弛豫。我们提出动态简化，其中局部松弛促进相邻松弛，导致分层动力学，可以解释我们的观察结果，包括对数T-g(M)依赖性。我们的研究为聚合物中的分子弛豫和玻璃化转变提供了新的认识，为基于单体尺度指标的聚合物预测设计铺平了道路。
The glass transition is a long-standing unsolved problem in materials science. For polymers, our understanding of glass formation is particularly poor because of the added complexity of chain connectivity and flexibility; structural relaxation of polymers thus involves a complex interplay between intramolecular and intermolecular cooperativity. Here, we study how the glass-transition temperature T-g varies with molecular weight M for different polymer chemistries and chain flexibilities. We find that T-g(M) is controlled by the average mass (or volume) per conformational degree of freedom and that a "local" molecular relaxation (involving a few conformers) controls the larger-scale cooperative alpha relaxation responsible for T-g. We propose that dynamic facilitation where a local relaxation facilitates adjacent relaxations, leading to hierarchical dynamics, can explain our observations, including logarithmic T-g(M) dependences. Our study provides a new understanding of molecular relaxations and the glass transition in polymers, which paves the way for predictive design of polymers based on monomer-scale metrics.