Determining the Relation Between Molecular Structure and Macroscopic Heat Transport in Oriented and Stressed Polymers.

TECHNICAL SUMMARY: An experimental study into the origins of anisotropic thermal conductivity of solid polymers is proposed. In particular, a relationship between the molecular structure of the polymer and the resulting macroscopic properties is sought. It has already been established that (1) deformed, cross-linked elastomers exhibit an anisotropic thermal conductivity tensor, k (2) the tensor k is linearly related to the extra stress tensor, for the polymer in the same state, and (3) the constant of relation for these two quantities exhibits a universal value of 0.03, independent of chemistry for the few systems studied, when properly made dimensionless. In this work a set of experiments has been designed that will distinguish between competing theories to describe these observations. A non-invasive optical technique called Forced Rayleigh Light Scattering to examine novel material states is used. Results will necessarily distinguish between competing theories on the origins of the effect. The results of the study will have broad impact on the transport modeling of advanced materials containing plastic. While previous work showed how non-isothermal modeling of liquids requires an additional complexity because of anisotropy, it also suggested that this complexity could be easily modeled through use of a phenomenological relation to stress. The current work, if successful, should determine if similar principles apply to the solid polymer during cooling. NON-TECHNICAL SUMMARY: An experimental study into the origins of how heat flows differently in different directions for solid polymers, such as plastic, is proposed. In particular, a relationship between how the molecules are behaving and the resulting heat-flow properties is sought. In this work a set of experiments has been designed that will distinguish between competing theories to describe these observations using a non-invasive optical technique called Forced Rayleigh Light Scattering. Results will necessarily distinguish between competing theories on the origins of the effect. The results of the study will have broad impact on the modeling of advanced materials containing plastic. While previous work showed how temperature modeling of these liquids requires an additional complexity, it also suggested that this complexity could be easily modeled through use of a simple relation to stress which is typically calculated already. The current work, if successful, should determine if similar principles apply to the solid polymer during cooling. Secondly, as part of the project, a display explaining the key optical technique employed will be provided to the Holography Museum in Chicago. Visitors will learn that holography is used to study material properties, and how the technique is employed.