Collaborative: Viscoelasticity of Nanoparticle Dispersed Polymer Melts: Experiment and Simulation

技术：实验和理论将结合起来描述为什么在聚合物中加入纳米粒子可以改善其机械性能。注意集中在两个方面：(a)颗粒大小的影响：现在人们认为，添加颗粒可以使聚合物熔体的模量增加几个数量级。这种增强对于轮胎或引擎盖下的应用至关重要，因为未填充的聚合物太“软”而无法在这些环境中使用。由于这种增强模量被推测为随着颗粒尺寸（在10纳米尺寸尺度上）的变化而达到最大值，因此显然存在这种性能的最佳纳米颗粒尺寸。证明这个假设最大值的存在，并探索其分子起源，是这项工作的重点。(b)佩恩效应：虽然通过添加纳米颗粒获得的模量增加对材料的某些静态特性至关重要，但这也会使纳米复合材料难以加工。佩恩效应，即材料的机械强度随着应变的增加而下降的数量级，在不影响材料最终使用行为的情况下规避了这个问题。了解佩恩效应的分子基础是这项工作的第二个相互关联的目标。特别是，在这种情况下，结合的聚合物层与颗粒之间的聚合物桥的作用将通过设计这两者的相对比例变化的材料来严格检查。这项工作利用两个pi的独特能力，利用实验和模拟相结合的方法，研究具有完全分散的纳米颗粒的纳米复合材料流变行为的这些相关方面。非技术：塑料现在在许多情况下无处不在，比如包装。不太熟悉的是这些材料在结构应用（例如，建筑材料）或引擎盖下的使用，这些缺陷归因于这些材料相对较软的机械性能。一个正在进行的目标是改进聚合物的这一特殊方面，据推测，添加纳米颗粒是实现这一目标的一种简便方法。这项工作将针对这一问题，系统地、批判性地评估纳米颗粒在塑料力学行为中的作用。研究活动将与针对K-12、本科和研究生水平的学生的广泛教育和推广活动相结合。这些项目的目标是招收/留住代表性不足的少数族裔学生进入研究生及以上的科学/工程学科。特别是，已经与佛罗里达农工大学和格兰布林州立大学（都是HBCUs）建立了互动，目的是招募本科生进入该计划。pi将继续与当地城市高中教师合作，目标是为学生，特别是高年级学生提供“动手”研究经验。

TECHNICAL:Experiments and theory will be combined to delineate why adding nanoparticles to a polymer improves its mechanical properties. Attention is focused on two aspects: (a) Effect of Particle Size: It is now accepted that the modulus of a polymer melt can be increased by several orders of magnitude on the addition of particles. This reinforcement is critical to applications, e.g., tires or under the hood, since unfilled polymers are too "soft" to be used in these contexts. Since this modulus reinforcement is conjectured to go through a maximum as a function of particle size (in the 10 nm size scale), there is apparently an optimum nanoparticle size for this property. Proving the existence of this postulated maximum, and exploring its molecular origins, is a focus of this work. (b) The Payne Effect: While the increase in modulus achieved through the addition of nanoparticles is critical to certain quiescent properties of the material, this can also make the nanocomposites hard to process. The Payne effect, i.e., the orders-of-magnitude decrease of the mechanical strength of a material with increasing strain, circumvents this problem without compromising the materials' end use behavior. Understanding the molecular underpinnings of the Payne effect is then the second, interrelated goal of this work. In particular, the role of the bound polymer layer vs. polymer bridges between particles in this context will be critically examined by devising materials where the relative proportion of these two is varied. This work exploits the unique capabilities of the two PIs to study these interrelated aspects of the rheological behavior of nanocomposites with fully dispersed nanoparticles, using a combination of experiment and simulation. NON-TECHNICAL:Plastics are by now ubiquitous in many contexts, such as in packaging. Less familiar is the use of these materials in structural applications (e.g., building materials) or under the hood, with these deficiencies being attributed to the relative soft mechanical behavior of these materials. An ongoing goal has been to improve this particular aspect of polymers, and it has been conjectured that the addition of nanoparticles is one facile means of achieving this goal. This work will target this issue and systematically and critically evaluate the role of nanoparticles on the mechanical behavior of plastics. The research activities will be coupled to extensive education and outreach activities that target students at the K-12, undergraduate and graduate levels. The PIs will aim to recruit/retain underrepresented minority students into science/engineering disciplines at the graduate level and beyond. In particular, interactions have been developed with Florida A&M University and Grambling State University (both HBCUs) with the goal of recruiting undergraduates into the program. The PIs will continue to work with local city high school teachers with the goal of giving students, especially seniors, "hands-on"research experience.