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

技术：实验和理论将结合起来，以说明为什么添加纳米粒子到聚合物提高其机械性能。注意力集中在两个方面：（a）颗粒尺寸的影响：现在公认的是，聚合物熔体的模量可以在添加颗粒时增加几个数量级。这种增强对于应用是至关重要的，例如，轮胎或引擎盖下，因为未填充的聚合物太“软”而不能用于这些情况。由于该模量增强被限制为经历作为粒度（在10 nm尺寸尺度中）的函数的最大值，因此对于该性质显然存在最佳的纳米颗粒尺寸。证明这个假设的最大值的存在，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实现的模量增加对材料的某些静态性能至关重要，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降低数量级，避免了这个问题，而不损害材料的最终使用性能。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材料来严格检查，其中这两者的相对比例是变化的。这项工作利用了两个PI的独特能力，使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的流变行为的这些相互关联的方面。非技术性：到目前为止，塑料在许多情况下都是无处不在的，例如包装。不太熟悉的是这些材料在结构应用中的使用（例如，建筑材料）或引擎盖下，这些缺陷归因于这些材料的相对软的机械性能。一个正在进行的目标是改善聚合物的这一特定方面，并且已经证实，添加纳米颗粒是实现这一目标的一种容易的手段。这项工作将针对这一问题，系统地、批判性地评估纳米颗粒对塑料力学行为的作用。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。PI的目标是招募/留住代表性不足的少数民族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A M大学和格兰布林州立大学（均为HBCU）开展了互动，目的是招募本科生参加该计划。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.