Investigation of Molecular Mechanisms for Anisotropic Thermal Transport in Polymers

CBET-1336442 Venerus聚合物材料的加工涉及机械和热传输过程的复杂相互作用。 尽管它的重要性，在流动聚合物的热传输知之甚少。 然而，已经确定的是，聚合物链段的流动诱导的各向异性导致应力对应变率的非线性依赖性，并且导致热导率的各向异性。完整的热导率张量的定量测量进行了几种类型的聚合物材料进行定义明确，拉伸变形。这些测量是在熔融，玻璃态和交联状态的聚合物上进行的，使用基于强迫瑞利散射的灵敏和非侵入性光学技术。从以前的研究，热导率张量和应力张量之间的线性关系，或应力-热规则，已被观察到的几个聚合物系统。这一观察具有相当深远的意义，伴随着两个意想不到的结果。首先，应力-热规则似乎是有效的应力水平的应力-光学规则，它给出了一个线性依赖于应力的方向，失败。 第二，当通过聚合物模量归一化时，应力-热规则中的前置因子对聚合物化学相对不敏感。这些观察结果与目前试图将热导率与聚合物中分子取向联系起来的模型不一致。热导率测量是由应力，双折射和声速的测量补充，以阐明聚合物材料中各向异性热传输的基本分子机制。聚合物材料是现代社会不可或缺的组成部分，具有许多不同的应用。聚合物材料的底层微观结构及其在加工过程中发生的变形对材料行为具有深远的影响，这在加工过程中和最终产品中都表现出来。流动聚合物中各向异性热导率的定量测量揭示了取向和应力的相对重要性，大大扩展了加工方法的知识基础，并且对于推进宏观性质与分子结构相关的理论模型至关重要。在芝加哥科学与工业博物馆展出的一个展览展示了强迫瑞利散射背后的原理，使大量不同的观众了解到光学和热传输在材料加工中的有趣应用。

CBET- 1336442Venerus The processing of polymeric materials involves a complex interaction of mechanical and thermal transport processes. Despite its importance, thermal transport in flowing polymers is poorly understood. It is well established, however, that flow-induced anisotropy of polymer chain segments leads to a non-linear dependence of stress on strain rate, and to anisotropy in thermal conductivity. Quantitative measurements of the complete thermal conductivity tensor are made on a several types of polymeric materials subjected to well-defined, elongational deformations. These measurements are made on polymers in molten, glassy and cross-linked states using a sensitive and non-invasive optical technique based on forced Rayleigh scattering. From previous studies a linear relationship between the thermal conductivity tensor and stress tensor, or the stress-thermal rule, has been observed for several polymeric systems. This observation, which has rather profound implications, is accompanied by two unexpected results. First, the stress-thermal rule appears to be valid at stress levels where the stress-optic rule, which gives a linear dependence of orientation on stress, fails. Second, the pre-factor in the stress-thermal rule, when normalized by the polymer modulus, is relatively insensitive to polymer chemistry. These observations are not consistent with current models that attempt to relate thermal conductivity to molecular orientation in polymers. Thermal conductivity measurements are complemented by measurements of stress, birefringence, and speed of sound, to elucidate the underlying molecular mechanisms for anisotropic thermal transport in polymeric materials. Polymeric materials are an integral component of modern society with numerous and diverse applications. The underlying micro-structure of polymeric materials and its orientation by deformations that occur during processing have profound effects on material behavior, which are manifested both during processing and in final products. Quantitative measurements of anisotropic thermal conductivity in flowing polymers that reveal the relative importance of orientation and stress significantly expand the knowledge base for processing methods, and are crucial for advancing theoretical models relating macroscopic properties to molecular structure. An exhibit displayed at the Museum of Science and Industry in Chicago demonstrating the principles behind forced Rayleigh scattering exposes a large and diverse audience to interesting applications of optics and thermal transport in materials processing.