标题： 通过非均匀Rouse模型定量连接聚合物在玻璃化转变附近的实验时间-温度-叠加失效与动态异质性的关系 显示英文标题

标题： Quantitatively Connecting Experimental Time-Temperature-Superposition-Breakdown of Polymers near the Glass Transition to Dynamic Heterogeneity via the Heterogeneous Rouse Model

摘要： 聚合物在玻璃转变温度Tg附近通常表现出时间-温度叠加（TTS）的失效，其中链段弛豫时间和粘度的温度依赖性比基元弛豫时间弱。这种热力学复杂性的出现原因一直存在争议。在这里，我们扩展了异质Rouse模型（HRM），该模型将Rouse模型推广以考虑动态异质性，从而预测无缠绕聚合物在Tg附近的弛豫模量G(t)和复数模量G*($\omega$)。HRM预测，在存在动态异质性的情况下，G(t)和G*($\omega$)在Rouse区域内表现出增强的有效标度指数，随着系统在冷却过程中变得更具动态异质性，从玻璃态平台的快速衰减现象出现。这种行为被预测来源于链动力学所探测的基元移动分布的矩与链段长度的依赖关系。我们表明，HRM的预测与聚苯乙烯、聚甲基丙烯酸甲酯和聚(2-乙烯基吡啶)的实验复数模量数据相符。HRM还预测了在我们的实验系统中，链尺度量如终端弛豫时间和粘度之间出现不同的温度依赖性，似乎解决了关于TTS失效异质性起源的一个最重要的持续异议。因此，HRM提供了一个广义理论，用于描述无缠绕聚合物在Tg附近的链尺度线性流变响应，从分子机制层面解释了TTS失效的起源。它还指出了基于Rouse区域内修改标度的温度演化来推断玻璃形成聚合物系统动态异质性的新策略。 显示英文摘要

摘要： Polymers near the glass transition temperature Tg often exhibit a breakdown of time-temperature-superposition (TTS), with chain relaxation times and viscosity exhibiting a weaker temperature dependence than segmental relaxation times. The origin of this onset of thermorheological complexity has remained unsettled and a matter of debate. Here we extend the Heterogeneous Rouse Model (HRM), which generalizes the Rouse model to account for dynamic heterogeneity, to make predictions for the relaxation modulus G(t) and complex modulus G*($\omega$) of unentangled polymers near Tg. The HRM predicts that G(t) and G*($\omega$) exhibit enhanced effective scaling exponents in the Rouse regime in the presence of dynamic heterogeneity, with a more rapid decay from the glassy plateau emerging as the system becomes more dynamically heterogeneous on cooling. This behavior is predicted to emerge from a strand-length dependence of the moment of the segmental mobility distribution probed by chain dynamics. We show that the HRM predictions are in good accord with experimental complex modulus data for polystyrene, poly(methyl methacrylate), and poly(2-vinyl pyridine). The HRM also predicts the onset of distinct temperature dependences among chain scale quantities such as terminal relaxation time and viscosity in our experimental systems, apparently resolving one of the most significant standing objections to a heterogeneity-based origin of TTS-breakdown. The HRM thus provides a generalized theory of the chain-scale linear rheological response of unentangled polymers near Tg, accounting for the origin of TTS-breakdown at a molecular mechanistic level. It also points towards a new strategy of inferring the dynamic heterogeneity of glass-forming polymeric systems based on the temperature-evolution of modified scaling in the Rouse regime.