Polymer Chain Length and Branching Effects on the Viscolestic Bulk Modulus and Structural Recovery at High Pressure

本项目的目标是扩展化学结构对时间依赖性体积模量的影响的基础研究，以包括链长和支化对高压下时间依赖性体积模量和结构恢复的影响。 特别是，在窄分子量分布的聚苯乙烯的链长的影响和使用星形支化聚苯乙烯的支化的效果将进行研究。 在这些测量过程中，将检查脆性的概念，其在聚苯乙烯中作为分子量的函数而变化。 测量作为温度和压力（或体积）的函数的体积变形响应还将允许提供关于在平衡密度下体积弛豫时间如何随温度和体积变化的基本新信息。 在玻璃态在高压下的响应也将被调查，并将被用来测试库巴特的建议，即体积模量是直接相关的比dh/dv在非线性结构恢复实验。 除了提供新的基础知识的分子结构上的时间依赖性的体积模量和结构恢复在高压下的影响，工作也具有实际意义，特别是在复合材料系统中，因为体积模量是负责各向同性残余应力的大小。 理解玻璃中的弛豫时间如何取决于结构对于结构恢复和伴随的机械性能变化的预测建模也是至关重要的。拟议工作的更广泛影响或外在价值包括培训一名研究生、一名本科生研究员和一名博士后研究员，并将作出巨大努力，让少数民族学生和女学生参加这一项目。 这项工作还将以各种方式传播，包括纳入PI教授的本科和研究生课程; PI，博士后研究员和学生在国家和地方论坛上的演讲;以及在会议记录和档案期刊上发表。非技术概述体积模量是一个重要的性质，因为例如它与复合材料中残余应力的发展有关，残余应力会对复合部件的完整性产生不利影响。 类似地，聚合物玻璃的物理老化和结构恢复，包括在复合材料中使用的那些，导致脆化，这再次对部件寿命产生负面影响。 在这个项目中，无论是体积模量和结构恢复研究在高压下，并作为聚合物分子结构的函数，以获得必要的建模和预测这些属性的理解。 将使用一种能够进行这些困难测量的新型可加压压力计。 除了通过这项工作产生新的知识，一名研究生，一名本科生研究员和一名博士后研究员将接受高分子物理，压力效应和仪器设计领域的前沿研究培训;将努力将少数民族和女性学生纳入该项目。 这项工作也将以各种方式传播，包括纳入PI教授的本科生和研究生课程。

Technical SummaryThe goal of this project is to extend fundamental studies of the effect of chemical structure on the time-dependent bulk modulus to include the effects of chain length and branching on the time-dependent bulk modulus and structural recovery at high pressure. In particular, the influence of chain length in narrow molecular weight distribution polystyrenes and the effect of branching using star-branched polystyrenes will be investigated. In the course of these measurements, the concept of fragility, which varies in polystyrene as a function of molecular weight, will be examined. Measuring the bulk deformation response as a function of temperature and pressure (or volume) will also allow provide fundamental new information on how the bulk relaxation time varies with temperature and volume at equilibrium density. The response in the glassy state at high pressure will also be investigated and will be used to test Kubat's suggestion that the bulk modulus is directly related to the ratio of dh/dv in nonlinear structural recovery experiments. In addition to providing new fundamental knowledge on the impact of molecular structure on the time-dependent bulk modulus and on structural recovery at high pressure, the work is also of practical importance, particularly in composite systems, since the bulk modulus is responsible for the magnitude of isotropic residual stresses. An understanding of how the relaxation time in the glass depends on structure is also critical for predictive modeling of structural recovery and concomitant changes in mechanical properties. The broader impact or extrinsic merit of the proposed work includes the training of a graduate student, an undergraduate researcher, and a post-doctoral researcher, and strong efforts will be made to include minority and female students in this project. The work will also be disseminated in a variety of ways, including incorporation into undergraduate and graduate courses taught by the PI; presentations by the PI, post-doctoral researcher, and students at national and local forums; and publication in both conference proceedings and archival journals. Non-Technical SummaryThe bulk modulus is an important property because, for example, it is related to the development of residual stresses in composite materials, which can adversely impact the integrity of composite components. Similarly, physical aging and structural recovery of polymeric glasses, including those used in composites, result in embrittlement, which again, has negative consequences for component lifetime. In this project, both the bulk modulus and structural recovery are studied at high pressure and as a function of polymer molecular structure in order to gain the understanding necessary to model and predict these properties. A novel pressurizable dilatometer capable of making these difficult measurements will be used. In addition to producing new knowledge through this work, a graduate student, an undergraduate researcher, and a post-doctoral researcher will be trained in cutting edge research in the areas of polymer physics, pressure effects, and instrument design; strong efforts will be made to include minority and female students in this project. The work will also be disseminated in a variety of ways, including incorporation into undergraduate and graduate courses taught by the PI.